diff --git a/package.json b/package.json
index 4d840540db75..91b01831c72a 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,19 @@
     "recast": "^0.11.18"
   },
   "devDependencies": {
-    "glob": "^7.1.1"
+    "glob": "^7.1.1",
+    "jest": "^18.0.0",
+    "flow-parser": "^0.37.0"
+  },
+  "scripts": {
+    "test": "jest"
+  },
+  "jest": {
+    "setupFiles": [
+      "<rootDir>/tests_config/run_spec.js"
+    ],
+    "testRegex": [
+      "jsfmt\\.spec\\.js$"
+    ]
   }
 }
diff --git a/tests/abnormal/__snapshots__/jsfmt.spec.js.snap b/tests/abnormal/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3963bef56d30
--- /dev/null
+++ b/tests/abnormal/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,127 @@
+exports[`test break-continue.js 1`] = `
+"function foo() {
+    while(true) { break; }
+}
+
+function bar() {
+    L: do { continue L; } while(false)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:925
+      if (endsWithBrace(doBody))
+          ^
+
+ReferenceError: endsWithBrace is not defined
+    at genericPrintNoParens (/src/printer.js:925:11)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:963:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test return.js 1`] = `
+"function bar(x:number) { }
+function foo() {
+    var x = null;
+    if (x == null) return;
+    bar(x);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function bar(x: number) {
+  
+}
+function foo() {
+  var x = null;
+  if (x == null)
+    return;
+  bar(x);
+}
+
+"
+`;
+
+exports[`test toplevel_break.js 1`] = `
+"// @flow
+
+break; // error, illegal
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unsyntactic break (3:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$1.parseBreakContinueStatement (/node_modules/babylon/lib/index.js:1843:44)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1703:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+    at Object.parse (/index.js:34:26)
+    at Object.parse (/node_modules/recast/lib/parser.js:26:34)
+"
+`;
+
+exports[`test toplevel_continue.js 1`] = `
+"// @flow
+
+continue; // error, illegal
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unsyntactic continue (3:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$1.parseBreakContinueStatement (/node_modules/babylon/lib/index.js:1843:44)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1703:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+    at Object.parse (/index.js:34:26)
+    at Object.parse (/node_modules/recast/lib/parser.js:26:34)
+"
+`;
+
+exports[`test toplevel_return.js 1`] = `
+"// @flow
+
+return; // error, illegal
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: \'return\' outside of function (3:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$1.parseReturnStatement (/node_modules/babylon/lib/index.js:1939:10)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1722:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+    at Object.parse (/index.js:34:26)
+    at Object.parse (/node_modules/recast/lib/parser.js:26:34)
+"
+`;
+
+exports[`test toplevel_throw.js 1`] = `
+"// @flow
+
+throw new Error(\'foo\'); // no error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+throw new Error(\"foo\");// no error
+
+"
+`;
diff --git a/tests/abnormal/break-continue.js b/tests/abnormal/break-continue.js
new file mode 100644
index 000000000000..1f10210ca25b
--- /dev/null
+++ b/tests/abnormal/break-continue.js
@@ -0,0 +1,7 @@
+function foo() {
+    while(true) { break; }
+}
+
+function bar() {
+    L: do { continue L; } while(false)
+}
diff --git a/tests/abnormal/jsfmt.spec.js b/tests/abnormal/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/abnormal/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/abnormal/return.js b/tests/abnormal/return.js
new file mode 100644
index 000000000000..c2c32814d414
--- /dev/null
+++ b/tests/abnormal/return.js
@@ -0,0 +1,6 @@
+function bar(x:number) { }
+function foo() {
+    var x = null;
+    if (x == null) return;
+    bar(x);
+}
diff --git a/tests/abnormal/toplevel_break.js b/tests/abnormal/toplevel_break.js
new file mode 100644
index 000000000000..15dd4120aefd
--- /dev/null
+++ b/tests/abnormal/toplevel_break.js
@@ -0,0 +1,3 @@
+// @flow
+
+break; // error, illegal
diff --git a/tests/abnormal/toplevel_continue.js b/tests/abnormal/toplevel_continue.js
new file mode 100644
index 000000000000..63ecd26c0a9e
--- /dev/null
+++ b/tests/abnormal/toplevel_continue.js
@@ -0,0 +1,3 @@
+// @flow
+
+continue; // error, illegal
diff --git a/tests/abnormal/toplevel_return.js b/tests/abnormal/toplevel_return.js
new file mode 100644
index 000000000000..64233d781de2
--- /dev/null
+++ b/tests/abnormal/toplevel_return.js
@@ -0,0 +1,3 @@
+// @flow
+
+return; // error, illegal
diff --git a/tests/abnormal/toplevel_throw.js b/tests/abnormal/toplevel_throw.js
new file mode 100644
index 000000000000..91f0b353915d
--- /dev/null
+++ b/tests/abnormal/toplevel_throw.js
@@ -0,0 +1,3 @@
+// @flow
+
+throw new Error('foo'); // no error
diff --git a/tests/annot/__snapshots__/jsfmt.spec.js.snap b/tests/annot/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b4924ebb8612
--- /dev/null
+++ b/tests/annot/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,234 @@
+exports[`test annot.js 1`] = `
+"function foo(str:string, i:number):string {
+  return str;
+}
+var bar: (str:number, i:number)=> string = foo;
+
+var qux = function(str:string, i:number):number { return foo(str,i); }
+
+var obj: {str:string; i:number; j:boolean} = {str: \"...\", i: \"...\", k: false};
+
+var arr: Array<number> = [1,2,\"...\"];
+
+// array sugar
+var array: number[] = [1,2,\"...\"];
+
+var matrix: number[][] = [[1,2],[3,4]];
+var matrix_parens: (number[])[] = matrix;
+
+var nullable_array: ?number[] = null;
+var nullable_array_parens: ?(number[]) = nullable_array;
+
+var array_of_nullable: (?number)[] = [null, 3];
+
+var array_of_tuple: [number, string][] = [[0, \"foo\"], [1, \"bar\"]];
+var array_of_tuple_parens: ([number, string])[] = array_of_tuple;
+
+type ObjType = { \'bar-foo\': string; \'foo-bar\': number; };
+var test_obj: ObjType = { \'bar-foo\': \'23\' };
+
+// param type annos are strict UBs like var type annos
+function param_anno(n:number):void {
+  n = \"hey\"; // error
+}
+
+// another error on param UB, more typical of www (mis)use-cases
+// this one cribbed from API.atlas.js
+function param_anno2(
+    batchRequests: Array<{method: string; path: string; params: ?Object}>,
+  ): void {
+
+    // error below, since we\'re assigning elements to batchRequests
+    // which lack a path property.
+    // just assign result to new var instead of reassigning to param.
+
+    // Transform the requests to the format the Graph API expects.
+    batchRequests = batchRequests.map((request) => {
+      return {
+        method: request.method,
+        params: request.params,
+        relative_url: request.path,
+      };
+    });
+    // ...
+  }
+
+var toz : null = 3;
+
+var zer : null = null;
+
+function foobar(n : ?number) : number | null | void { return n; }
+function barfoo(n : number | null | void) : ?number { return n; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test forward_ref.js 1`] = `
+"let myClassInstance: MyClass = null; // forward ref ok, null ~> class error
+
+function bar(): MyClass {
+  return null; // forward ref ok, null ~> class error
+}
+
+class MyClass { } // looked up above
+
+function foo() {
+  let myClassInstance: MyClass = mk(); // ok (no confusion across scopes)
+  function mk() { return new MyClass(); }
+
+  class MyClass { } // looked up above
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let myClassInstance: MyClass = null;// forward ref ok, null ~> class error
+function bar(): MyClass {
+  return null;// forward ref ok, null ~> class error
+}
+class MyClass {}// looked up above
+function foo() {
+  let myClassInstance: MyClass = mk();// ok (no confusion across scopes)
+  function mk() {
+    return new MyClass();
+  }
+  class MyClass {}// looked up above
+}
+
+"
+`;
+
+exports[`test issue-530.js 1`] = `
+"function foo(...args: any) { }
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(...args) {
+  
+}
+module.exports = foo;
+
+"
+`;
+
+exports[`test leak.js 1`] = `
+"/** @flow */
+
+/* This test documents an example we ran into of a type annotation leaking.
+ *
+ * When foo() calls bar(), we should make sure the type of x matches the type
+ * annotation for y and stop. We should type the body of bar() with the type
+ * annotation of y.
+ *
+ * However, the leaky type annotation meant that we were flowing x\'s type to y
+ * and type checking the body of bar() using the stricter dictionary type,
+ * leading to an error.
+ */
+
+type MyObj = Object;
+
+function foo(x: {[key: string]: mixed}) {
+  bar(x);
+}
+
+function bar(y: MyObj): string {
+  return y.foo;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/** @flow */
+/* This test documents an example we ran into of a type annotation leaking.
+ *
+ * When foo() calls bar(), we should make sure the type of x matches the type
+ * annotation for y and stop. We should type the body of bar() with the type
+ * annotation of y.
+ *
+ * However, the leaky type annotation meant that we were flowing x\'s type to y
+ * and type checking the body of bar() using the stricter dictionary type,
+ * leading to an error.
+ */
+type MyObj = Object;
+function foo(x: { [key: string]: mixed }) {
+  bar(x);
+}
+function bar(y: MyObj): string {
+  return y.foo;
+}
+
+"
+`;
+
+exports[`test other.js 1`] = `
+"class C { }
+module.exports = (C: any);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {}
+module.exports = (C: any);
+
+"
+`;
+
+exports[`test scope.js 1`] = `
+"type Merge<T> = (a: T, b: T) => T;
+
+// hypothetical immutable map
+declare class Map<K,V> {
+  (): Map<K,V>;
+  insertWith(fn: Merge<V>, k: K, v: V): Map<K,V>;
+}
+
+declare function foldr<A,B>(fn: (a: A, b: B) => B, b: B, as: A[]): B;
+
+function insertMany<K,V>(merge: Merge<V>, vs: [K,V][], m: Map<K,V>): Map<K,V> {
+  function f([k,v]: [K,V], m: Map<K,V>): Map<K,V> {
+    return m.insertWith(merge, k, v)
+  }
+  return foldr(f, m, vs)
+}
+
+class Foo<A> {
+  bar<B>() {
+    return function<C>(a: A, b: B, c: C): void {
+      ([a,b,c] : [A,B,C]);
+    }
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"var C = require(\'./other\');
+((0: C): string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var C = require(\"./other\");
+((0: C): string);
+
+"
+`;
diff --git a/tests/annot/annot.js b/tests/annot/annot.js
new file mode 100644
index 000000000000..4d1b25a5ad64
--- /dev/null
+++ b/tests/annot/annot.js
@@ -0,0 +1,60 @@
+function foo(str:string, i:number):string {
+  return str;
+}
+var bar: (str:number, i:number)=> string = foo;
+
+var qux = function(str:string, i:number):number { return foo(str,i); }
+
+var obj: {str:string; i:number; j:boolean} = {str: "...", i: "...", k: false};
+
+var arr: Array<number> = [1,2,"..."];
+
+// array sugar
+var array: number[] = [1,2,"..."];
+
+var matrix: number[][] = [[1,2],[3,4]];
+var matrix_parens: (number[])[] = matrix;
+
+var nullable_array: ?number[] = null;
+var nullable_array_parens: ?(number[]) = nullable_array;
+
+var array_of_nullable: (?number)[] = [null, 3];
+
+var array_of_tuple: [number, string][] = [[0, "foo"], [1, "bar"]];
+var array_of_tuple_parens: ([number, string])[] = array_of_tuple;
+
+type ObjType = { 'bar-foo': string; 'foo-bar': number; };
+var test_obj: ObjType = { 'bar-foo': '23' };
+
+// param type annos are strict UBs like var type annos
+function param_anno(n:number):void {
+  n = "hey"; // error
+}
+
+// another error on param UB, more typical of www (mis)use-cases
+// this one cribbed from API.atlas.js
+function param_anno2(
+    batchRequests: Array<{method: string; path: string; params: ?Object}>,
+  ): void {
+
+    // error below, since we're assigning elements to batchRequests
+    // which lack a path property.
+    // just assign result to new var instead of reassigning to param.
+
+    // Transform the requests to the format the Graph API expects.
+    batchRequests = batchRequests.map((request) => {
+      return {
+        method: request.method,
+        params: request.params,
+        relative_url: request.path,
+      };
+    });
+    // ...
+  }
+
+var toz : null = 3;
+
+var zer : null = null;
+
+function foobar(n : ?number) : number | null | void { return n; }
+function barfoo(n : number | null | void) : ?number { return n; }
diff --git a/tests/annot/any/A.js b/tests/annot/any/A.js
new file mode 100644
index 000000000000..093d2d63a2ce
--- /dev/null
+++ b/tests/annot/any/A.js
@@ -0,0 +1,9 @@
+type T = any;
+
+export default class {
+  p: T;
+
+  constructor() {
+    this.p = 0;
+  }
+}
diff --git a/tests/annot/any/B.js b/tests/annot/any/B.js
new file mode 100644
index 000000000000..1e0776d87a61
--- /dev/null
+++ b/tests/annot/any/B.js
@@ -0,0 +1,5 @@
+import A from "./A"
+
+class B extends A {
+  p: string; // OK, string ~> any
+}
diff --git a/tests/annot/any/__snapshots__/jsfmt.spec.js.snap b/tests/annot/any/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a65f786d3a96
--- /dev/null
+++ b/tests/annot/any/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,36 @@
+exports[`test A.js 1`] = `
+"type T = any;
+
+export default class {
+  p: T;
+
+  constructor() {
+    this.p = 0;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+type T = any;
+export default class {
+  p: T;
+  constructor() {
+    this.p = 0;
+  }
+}
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"import A from "./A"
+
+class B extends A {
+  p: string; // OK, string ~> any
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+import A from "./A";
+class B extends A {
+  p: string;// OK, string ~> any
+}
+
+"
+`;
diff --git a/tests/annot/any/jsfmt.spec.js b/tests/annot/any/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/annot/any/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/annot/forward_ref.js b/tests/annot/forward_ref.js
new file mode 100644
index 000000000000..8061d65a3aad
--- /dev/null
+++ b/tests/annot/forward_ref.js
@@ -0,0 +1,14 @@
+let myClassInstance: MyClass = null; // forward ref ok, null ~> class error
+
+function bar(): MyClass {
+  return null; // forward ref ok, null ~> class error
+}
+
+class MyClass { } // looked up above
+
+function foo() {
+  let myClassInstance: MyClass = mk(); // ok (no confusion across scopes)
+  function mk() { return new MyClass(); }
+
+  class MyClass { } // looked up above
+}
diff --git a/tests/annot/issue-530.js b/tests/annot/issue-530.js
new file mode 100644
index 000000000000..bd8d893e516d
--- /dev/null
+++ b/tests/annot/issue-530.js
@@ -0,0 +1,3 @@
+function foo(...args: any) { }
+
+module.exports = foo;
diff --git a/tests/annot/jsfmt.spec.js b/tests/annot/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/annot/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/annot/leak.js b/tests/annot/leak.js
new file mode 100644
index 000000000000..bfc8254c74be
--- /dev/null
+++ b/tests/annot/leak.js
@@ -0,0 +1,22 @@
+/** @flow */
+
+/* This test documents an example we ran into of a type annotation leaking.
+ *
+ * When foo() calls bar(), we should make sure the type of x matches the type
+ * annotation for y and stop. We should type the body of bar() with the type
+ * annotation of y.
+ *
+ * However, the leaky type annotation meant that we were flowing x's type to y
+ * and type checking the body of bar() using the stricter dictionary type,
+ * leading to an error.
+ */
+
+type MyObj = Object;
+
+function foo(x: {[key: string]: mixed}) {
+  bar(x);
+}
+
+function bar(y: MyObj): string {
+  return y.foo;
+}
diff --git a/tests/annot/other.js b/tests/annot/other.js
new file mode 100644
index 000000000000..0407c8397d80
--- /dev/null
+++ b/tests/annot/other.js
@@ -0,0 +1,2 @@
+class C { }
+module.exports = (C: any);
diff --git a/tests/annot/scope.js b/tests/annot/scope.js
new file mode 100644
index 000000000000..3f0b7ec6c5c8
--- /dev/null
+++ b/tests/annot/scope.js
@@ -0,0 +1,24 @@
+type Merge<T> = (a: T, b: T) => T;
+
+// hypothetical immutable map
+declare class Map<K,V> {
+  (): Map<K,V>;
+  insertWith(fn: Merge<V>, k: K, v: V): Map<K,V>;
+}
+
+declare function foldr<A,B>(fn: (a: A, b: B) => B, b: B, as: A[]): B;
+
+function insertMany<K,V>(merge: Merge<V>, vs: [K,V][], m: Map<K,V>): Map<K,V> {
+  function f([k,v]: [K,V], m: Map<K,V>): Map<K,V> {
+    return m.insertWith(merge, k, v)
+  }
+  return foldr(f, m, vs)
+}
+
+class Foo<A> {
+  bar<B>() {
+    return function<C>(a: A, b: B, c: C): void {
+      ([a,b,c] : [A,B,C]);
+    }
+  }
+}
diff --git a/tests/annot/test.js b/tests/annot/test.js
new file mode 100644
index 000000000000..94f65159e8d0
--- /dev/null
+++ b/tests/annot/test.js
@@ -0,0 +1,2 @@
+var C = require('./other');
+((0: C): string);
diff --git a/tests/annot2/A.js b/tests/annot2/A.js
new file mode 100644
index 000000000000..06abcbf1ddd4
--- /dev/null
+++ b/tests/annot2/A.js
@@ -0,0 +1,14 @@
+/**
+ * @providesModule A
+ * @flow
+ */
+
+import type T from "T";
+
+export default class {
+  p: T;
+
+  constructor() {
+    this.p = 0;
+  }
+}
diff --git a/tests/annot2/B.js b/tests/annot2/B.js
new file mode 100644
index 000000000000..823a7e8935ff
--- /dev/null
+++ b/tests/annot2/B.js
@@ -0,0 +1,9 @@
+/**
+ * @flow
+ */
+
+import A from "A"
+
+class B extends A {
+  p: string; // OK, string ~> any
+}
diff --git a/tests/annot2/T.js b/tests/annot2/T.js
new file mode 100644
index 000000000000..d90bf5a54587
--- /dev/null
+++ b/tests/annot2/T.js
@@ -0,0 +1,3 @@
+/**
+ * @providesModule T
+ */
diff --git a/tests/annot2/__snapshots__/jsfmt.spec.js.snap b/tests/annot2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..dbc3d4a41a3c
--- /dev/null
+++ b/tests/annot2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,62 @@
+exports[`test A.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+
+import type T from "T";
+
+export default class {
+  p: T;
+
+  constructor() {
+    this.p = 0;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule A
+ * @flow
+ */
+import type T from "T";
+export default class {
+  p: T;
+  constructor() {
+    this.p = 0;
+  }
+}
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"/**
+ * @flow
+ */
+
+import A from "A"
+
+class B extends A {
+  p: string; // OK, string ~> any
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+import A from "A";
+class B extends A {
+  p: string;// OK, string ~> any
+}
+
+"
+`;
+
+exports[`test T.js 1`] = `
+"/**
+ * @providesModule T
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/annot2/jsfmt.spec.js b/tests/annot2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/annot2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/any/__snapshots__/jsfmt.spec.js.snap b/tests/any/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c15d72b9755c
--- /dev/null
+++ b/tests/any/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,202 @@
+exports[`test any.js 1`] = `
+"// @flow
+
+function foo(x:any):any { return x; }
+function bar(x:any):mixed { return x; }
+function qux(x:mixed):any { return x; }
+
+var x:string = foo(0);
+var y:string = bar(0);
+var z:string = qux(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function foo(x: any): any {
+  return x;
+}
+function bar(x: any): mixed {
+  return x;
+}
+function qux(x: mixed): any {
+  return x;
+}
+var x: string = foo(0);
+var y: string = bar(0);
+var z: string = qux(0);
+
+"
+`;
+
+exports[`test anyexportflowfile.js 1`] = `
+"// @flow
+
+module.exports = ((x: any) => x: any);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+module.exports = ((x: any) => x: any);
+
+"
+`;
+
+exports[`test flowfixme.js 1`] = `
+"/*
+  FlowFixMe is a synonym for any, used by the Flow team to
+  signal a needed mod to JS devs.
+
+  @flow
+ */
+
+// no param
+function foo(x:$FlowFixMe):$FlowFixMe { return x; }
+function bar(x:$FlowFixMe):mixed { return x; }
+// param (info only)
+function qux(x:$FlowFixMe<number>):$FlowFixMe<number> { return x; }
+// ...params are still checked. unknown type
+function baz(x:$FlowFixMe<nnumber>): $FlowFixMe<number> { return x; }
+
+var x:string = foo(0);
+var y:string = bar(0);
+var z:string = qux(0);
+var w:string = baz(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test flowissue.js 1`] = `
+"/*
+  $FlowIssue is a synonym for any, used by JS devs to signal
+  a potential typechecker bug to the Flow team.
+
+  @flow
+ */
+
+// no param
+function foo(x:$FlowIssue):$FlowIssue { return x; }
+function bar(x:$FlowIssue):mixed { return x; }
+// param (info only)
+function qux(x:$FlowIssue<number>):$FlowIssue<number> { return x; }
+// ...params are still checked. unknown type
+function baz(x:$FlowIssue<nnumber>): $FlowIssue<number> { return x; }
+
+var x:string = foo(0);
+var y:string = bar(0);
+var z:string = qux(0);
+var w:string = baz(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test nonflowfile.js 1`] = `
+"// @noflow
+
+module.exports = (x) => x;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @noflow
+module.exports = x => x;
+
+"
+`;
+
+exports[`test propagate.js 1`] = `
+"// @flow
+
+declare class C {
+  bar(n1: number, n2: number): number;
+  bar(s1: string, s2: string): string;
+}
+
+function foo(c: C, x: any): string {
+  let y = x.y;
+  return c.bar(0, y); // should be able to select first case and error
+}
+
+var any_fun1 = require(\'./nonflowfile\');
+function bar1(x: mixed) {
+  if (any_fun1(x)) {
+    (x: boolean);
+  }
+}
+
+var any_fun2 = require(\'./anyexportflowfile\');
+function bar2(x: mixed) {
+  if (any_fun2(x)) {
+    (x: boolean);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test reach.js 1`] = `
+"/**
+ * like class and function values, any-typed values may be used in
+ * type annotations. Here we test propagation of any through the
+ * annotation - without it, the body of the if will be unreachable 
+ */
+
+type AsyncRequest = any;
+
+function foo(o: ?AsyncRequest) {
+  if (o) {
+    var n: number = o;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * like class and function values, any-typed values may be used in
+ * type annotations. Here we test propagation of any through the
+ * annotation - without it, the body of the if will be unreachable 
+ */
+type AsyncRequest = any;
+function foo(o: ?AsyncRequest) {
+  if (o) {
+    var n: number = o;
+  }
+}
+
+"
+`;
diff --git a/tests/any/any.js b/tests/any/any.js
new file mode 100644
index 000000000000..6f5bf81494d7
--- /dev/null
+++ b/tests/any/any.js
@@ -0,0 +1,9 @@
+// @flow
+
+function foo(x:any):any { return x; }
+function bar(x:any):mixed { return x; }
+function qux(x:mixed):any { return x; }
+
+var x:string = foo(0);
+var y:string = bar(0);
+var z:string = qux(0);
diff --git a/tests/any/anyexportflowfile.js b/tests/any/anyexportflowfile.js
new file mode 100644
index 000000000000..61671d18a14e
--- /dev/null
+++ b/tests/any/anyexportflowfile.js
@@ -0,0 +1,3 @@
+// @flow
+
+module.exports = ((x: any) => x: any);
diff --git a/tests/any/flowfixme.js b/tests/any/flowfixme.js
new file mode 100644
index 000000000000..bb3886027a77
--- /dev/null
+++ b/tests/any/flowfixme.js
@@ -0,0 +1,19 @@
+/*
+  FlowFixMe is a synonym for any, used by the Flow team to
+  signal a needed mod to JS devs.
+
+  @flow
+ */
+
+// no param
+function foo(x:$FlowFixMe):$FlowFixMe { return x; }
+function bar(x:$FlowFixMe):mixed { return x; }
+// param (info only)
+function qux(x:$FlowFixMe<number>):$FlowFixMe<number> { return x; }
+// ...params are still checked. unknown type
+function baz(x:$FlowFixMe<nnumber>): $FlowFixMe<number> { return x; }
+
+var x:string = foo(0);
+var y:string = bar(0);
+var z:string = qux(0);
+var w:string = baz(0);
diff --git a/tests/any/flowissue.js b/tests/any/flowissue.js
new file mode 100644
index 000000000000..2fbd2f280369
--- /dev/null
+++ b/tests/any/flowissue.js
@@ -0,0 +1,19 @@
+/*
+  $FlowIssue is a synonym for any, used by JS devs to signal
+  a potential typechecker bug to the Flow team.
+
+  @flow
+ */
+
+// no param
+function foo(x:$FlowIssue):$FlowIssue { return x; }
+function bar(x:$FlowIssue):mixed { return x; }
+// param (info only)
+function qux(x:$FlowIssue<number>):$FlowIssue<number> { return x; }
+// ...params are still checked. unknown type
+function baz(x:$FlowIssue<nnumber>): $FlowIssue<number> { return x; }
+
+var x:string = foo(0);
+var y:string = bar(0);
+var z:string = qux(0);
+var w:string = baz(0);
diff --git a/tests/any/jsfmt.spec.js b/tests/any/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/any/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/any/nonflowfile.js b/tests/any/nonflowfile.js
new file mode 100644
index 000000000000..f03c2cd668ba
--- /dev/null
+++ b/tests/any/nonflowfile.js
@@ -0,0 +1,3 @@
+// @noflow
+
+module.exports = (x) => x;
diff --git a/tests/any/propagate.js b/tests/any/propagate.js
new file mode 100644
index 000000000000..1e073c54d2cf
--- /dev/null
+++ b/tests/any/propagate.js
@@ -0,0 +1,25 @@
+// @flow
+
+declare class C {
+  bar(n1: number, n2: number): number;
+  bar(s1: string, s2: string): string;
+}
+
+function foo(c: C, x: any): string {
+  let y = x.y;
+  return c.bar(0, y); // should be able to select first case and error
+}
+
+var any_fun1 = require('./nonflowfile');
+function bar1(x: mixed) {
+  if (any_fun1(x)) {
+    (x: boolean);
+  }
+}
+
+var any_fun2 = require('./anyexportflowfile');
+function bar2(x: mixed) {
+  if (any_fun2(x)) {
+    (x: boolean);
+  }
+}
diff --git a/tests/any/reach.js b/tests/any/reach.js
new file mode 100644
index 000000000000..ec1232f6b989
--- /dev/null
+++ b/tests/any/reach.js
@@ -0,0 +1,13 @@
+/**
+ * like class and function values, any-typed values may be used in
+ * type annotations. Here we test propagation of any through the
+ * annotation - without it, the body of the if will be unreachable 
+ */
+
+type AsyncRequest = any;
+
+function foo(o: ?AsyncRequest) {
+  if (o) {
+    var n: number = o;
+  }
+}
diff --git a/tests/arith/Arith.js b/tests/arith/Arith.js
new file mode 100644
index 000000000000..818619d805bd
--- /dev/null
+++ b/tests/arith/Arith.js
@@ -0,0 +1,91 @@
+
+/* @providesModule Arith */
+
+function num(x:number) { }
+
+function str(x:string) { }
+
+function foo() {
+  var x = 0;
+  var y = "...";
+  var z = {};
+  num(x+x);
+  num(x+y); // error
+  str(x+y);
+  str(x+x); // error
+  str(z+y); // error
+}
+
+// test MaybeT(NumT)
+function bar0(x: ?number, y: number) {
+  num(x + y);
+}
+function bar1(x: number, y: ?number) {
+  num(x + y);
+}
+
+// test OptionalT(NumT)
+function bar2(x?: number, y: number) {
+  num(x + y);
+}
+function bar3(x: number, y?: number) {
+  num(x + y);
+}
+
+// test OptionalT(MaybeT(NumT))
+function bar4(x?: ?number, y: number) {
+  num(x + y);
+}
+function bar5(x: number, y?: ?number) {
+  num(x + y);
+}
+
+num(null + null); // === 0
+num(undefined + undefined); // === NaN
+
+num(null + 1); // === 1
+num(1 + null); // === 1
+num(undefined + 1); // === NaN
+num(1 + undefined); // === NaN
+
+num(null + true); // === 1
+num(true + null); // === 1
+num(undefined + true); // === NaN
+num(true + undefined); // === NaN
+
+str("foo" + true); // error
+str(true + "foo"); // error
+str("foo" + null); // error
+str(null + "foo"); // error
+str("foo" + undefined); // error
+str(undefined + "foo"); // error
+
+let tests = [
+  function(x: mixed, y: mixed) {
+    (x + y); // error
+    (x + 0); // error
+    (0 + x); // error
+    (x + ""); // error
+    ("" + x); // error
+    (x + {}); // error
+    ({} + x); // error
+  },
+
+  // when one side is a string or number and the other is invalid, we
+  // assume you are expecting a string or number (respectively), rather than
+  // erroring twice saying number !~> string and obj !~> string.
+  function() {
+    ((1 + {}): number); // error: object !~> number
+    (({} + 1): number); // error: object !~> number
+    (("1" + {}): string); // error: object !~> string
+    (({} + "1"): string); // error: object !~> string
+  },
+
+  function(x: any, y: number, z: string) {
+    (x + y: string); // ok
+    (y + x: string); // ok
+
+    (x + z: empty); // error, string ~> empty
+    (z + x: empty); // error, string ~> empty
+  },
+];
diff --git a/tests/arith/__snapshots__/jsfmt.spec.js.snap b/tests/arith/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..22d3fa7b2599
--- /dev/null
+++ b/tests/arith/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,318 @@
+exports[`test Arith.js 1`] = `
+"
+/* @providesModule Arith */
+
+function num(x:number) { }
+
+function str(x:string) { }
+
+function foo() {
+  var x = 0;
+  var y = \"...\";
+  var z = {};
+  num(x+x);
+  num(x+y); // error
+  str(x+y);
+  str(x+x); // error
+  str(z+y); // error
+}
+
+// test MaybeT(NumT)
+function bar0(x: ?number, y: number) {
+  num(x + y);
+}
+function bar1(x: number, y: ?number) {
+  num(x + y);
+}
+
+// test OptionalT(NumT)
+function bar2(x?: number, y: number) {
+  num(x + y);
+}
+function bar3(x: number, y?: number) {
+  num(x + y);
+}
+
+// test OptionalT(MaybeT(NumT))
+function bar4(x?: ?number, y: number) {
+  num(x + y);
+}
+function bar5(x: number, y?: ?number) {
+  num(x + y);
+}
+
+num(null + null); // === 0
+num(undefined + undefined); // === NaN
+
+num(null + 1); // === 1
+num(1 + null); // === 1
+num(undefined + 1); // === NaN
+num(1 + undefined); // === NaN
+
+num(null + true); // === 1
+num(true + null); // === 1
+num(undefined + true); // === NaN
+num(true + undefined); // === NaN
+
+str(\"foo\" + true); // error
+str(true + \"foo\"); // error
+str(\"foo\" + null); // error
+str(null + \"foo\"); // error
+str(\"foo\" + undefined); // error
+str(undefined + \"foo\"); // error
+
+let tests = [
+  function(x: mixed, y: mixed) {
+    (x + y); // error
+    (x + 0); // error
+    (0 + x); // error
+    (x + \"\"); // error
+    (\"\" + x); // error
+    (x + {}); // error
+    ({} + x); // error
+  },
+
+  // when one side is a string or number and the other is invalid, we
+  // assume you are expecting a string or number (respectively), rather than
+  // erroring twice saying number !~> string and obj !~> string.
+  function() {
+    ((1 + {}): number); // error: object !~> number
+    (({} + 1): number); // error: object !~> number
+    ((\"1\" + {}): string); // error: object !~> string
+    (({} + \"1\"): string); // error: object !~> string
+  },
+
+  function(x: any, y: number, z: string) {
+    (x + y: string); // ok
+    (y + x: string); // ok
+
+    (x + z: empty); // error, string ~> empty
+    (z + x: empty); // error, string ~> empty
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Arith */
+function num(x: number) {
+  
+}
+function str(x: string) {
+  
+}
+function foo() {
+  var x = 0;
+  var y = \"...\";
+  var z = {};
+  num(x + x);
+  num(x + y);// error
+  str(x + y);
+  str(x + x);// error
+  str(z + y);// error
+}
+// test MaybeT(NumT)
+function bar0(x: ?number, y: number) {
+  num(x + y);
+}
+function bar1(x: number, y: ?number) {
+  num(x + y);
+}
+// test OptionalT(NumT)
+function bar2(x: number, y: number) {
+  num(x + y);
+}
+function bar3(x: number, y: number) {
+  num(x + y);
+}
+// test OptionalT(MaybeT(NumT))
+function bar4(x: ?number, y: number) {
+  num(x + y);
+}
+function bar5(x: number, y: ?number) {
+  num(x + y);
+}
+num(null + null);// === 0
+num(undefined + undefined);// === NaN
+num(null + 1);// === 1
+num(1 + null);// === 1
+num(undefined + 1);// === NaN
+num(1 + undefined);// === NaN
+num(null + true);// === 1
+num(true + null);// === 1
+num(undefined + true);// === NaN
+num(true + undefined);// === NaN
+str(\"foo\" + true);// error
+str(true + \"foo\");// error
+str(\"foo\" + null);// error
+str(null + \"foo\");// error
+str(\"foo\" + undefined);// error
+str(undefined + \"foo\");// error
+let tests = [
+  function(x: mixed, y: mixed) {
+    x + y;// error
+    x + 0;// error
+    0 + x;// error
+    x + \"\";// error
+    \"\" + x;// error
+    x + {};// error
+    ({}) + x;// error
+  },
+  // when one side is a string or number and the other is invalid, we
+  // assume you are expecting a string or number (respectively), rather than
+  // erroring twice saying number !~> string and obj !~> string.
+  function() {
+    (1 + {}: number);// error: object !~> number
+    ({} + 1: number);// error: object !~> number
+    (\"1\" + {}: string);// error: object !~> string
+    ({} + \"1\": string);// error: object !~> string
+  },
+  function(x: any, y: number, z: string) {
+    (x + y: string);// ok
+    (y + x: string);// ok
+    (x + z: empty);// error, string ~> empty
+    (z + x: empty);// error, string ~> empty
+  }
+];
+
+"
+`;
+
+exports[`test exponent.js 1`] = `
+"/* @flow */
+
+let x: number = 2 ** 3;
+x **= 4;
+
+let y: string = \"123\";
+y **= 2; // error
+
+1 + 2 ** 3 + 4;
+2 ** 2;
+(-2) ** 2;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+let x: number = 2 ** 3;
+x **= 4;
+let y: string = \"123\";
+y **= 2;// error
+1 + 2 ** 3 + 4;
+2 ** 2;
+-2 ** 2;
+
+"
+`;
+
+exports[`test generic.js 1`] = `
+"/* @flow */
+
+function f<A>(a: A): A { return a + a; } // error
+function f<A,B>(a: A, b: B): A {return a + b; } // error
+function f<A,B>(a: A, b: B): A {return b + a; } // error
+function f<A,B>(a: A, b: B): B {return a + b; } // error
+function f<A,B>(a: A, b: B): B {return b + a; } // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test mult.js 1`] = `
+"/* @flow */
+
+function num(x:number) { }
+
+num(null * 1);
+num(1 * null);
+
+let x: number = 2 * 3;
+x *= 4;
+
+let y: string = \"123\";
+y *= 2; // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function num(x: number) {
+  
+}
+num(null * 1);
+num(1 * null);
+let x: number = 2 * 3;
+x *= 4;
+let y: string = \"123\";
+y *= 2;// error
+
+"
+`;
+
+exports[`test relational.js 1`] = `
+"/* @flow */
+
+(1 < 2);
+(1 < \"foo\"); // error
+(\"foo\" < 1); // error
+(\"foo\" < \"bar\");
+(1 < {foo: 1}); // error
+({foo: 1} < 1); // error
+({foo: 1} < {foo: 1}); // error
+(\"foo\" < {foo: 1}); // error
+({foo: 1} < \"foo\"); // error
+
+var x = (null : ?number);
+(1 < x); // 2 errors: null !~> number; undefined !~> number
+(x < 1); // 2 errors: null !~> number; undefined !~> number
+
+(null < null); // error
+(undefined < null); // error
+(null < undefined); // error
+(undefined < undefined); // error
+(NaN < 1);
+(1 < NaN);
+(NaN < NaN);
+
+let tests = [
+  function(x: any, y: number, z: string) {
+    (x > y);
+    (x > z);
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+1 < 2;
+1 < \"foo\";// error
+\"foo\" < 1;// error
+\"foo\" < \"bar\";
+1 < { foo: 1 };// error
+({ foo: 1 }) < 1;// error
+({ foo: 1 }) < { foo: 1 };// error
+\"foo\" < { foo: 1 };// error
+({ foo: 1 }) < \"foo\";// error
+var x = (null: ?number);
+1 < x;// 2 errors: null !~> number; undefined !~> number
+x < 1;// 2 errors: null !~> number; undefined !~> number
+null < null;// error
+undefined < null;// error
+null < undefined;// error
+undefined < undefined;// error
+NaN < 1;
+1 < NaN;
+NaN < NaN;
+let tests = [
+  function(x: any, y: number, z: string) {
+    x > y;
+    x > z;
+  }
+];
+
+"
+`;
diff --git a/tests/arith/exponent.js b/tests/arith/exponent.js
new file mode 100644
index 000000000000..2bac6484428a
--- /dev/null
+++ b/tests/arith/exponent.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+let x: number = 2 ** 3;
+x **= 4;
+
+let y: string = "123";
+y **= 2; // error
+
+1 + 2 ** 3 + 4;
+2 ** 2;
+(-2) ** 2;
diff --git a/tests/arith/generic.js b/tests/arith/generic.js
new file mode 100644
index 000000000000..217c990ecb2e
--- /dev/null
+++ b/tests/arith/generic.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+function f<A>(a: A): A { return a + a; } // error
+function f<A,B>(a: A, b: B): A {return a + b; } // error
+function f<A,B>(a: A, b: B): A {return b + a; } // error
+function f<A,B>(a: A, b: B): B {return a + b; } // error
+function f<A,B>(a: A, b: B): B {return b + a; } // error
diff --git a/tests/arith/jsfmt.spec.js b/tests/arith/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/arith/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/arith/mult.js b/tests/arith/mult.js
new file mode 100644
index 000000000000..43620ffbc80c
--- /dev/null
+++ b/tests/arith/mult.js
@@ -0,0 +1,12 @@
+/* @flow */
+
+function num(x:number) { }
+
+num(null * 1);
+num(1 * null);
+
+let x: number = 2 * 3;
+x *= 4;
+
+let y: string = "123";
+y *= 2; // error
diff --git a/tests/arith/relational.js b/tests/arith/relational.js
new file mode 100644
index 000000000000..f86edee6953e
--- /dev/null
+++ b/tests/arith/relational.js
@@ -0,0 +1,30 @@
+/* @flow */
+
+(1 < 2);
+(1 < "foo"); // error
+("foo" < 1); // error
+("foo" < "bar");
+(1 < {foo: 1}); // error
+({foo: 1} < 1); // error
+({foo: 1} < {foo: 1}); // error
+("foo" < {foo: 1}); // error
+({foo: 1} < "foo"); // error
+
+var x = (null : ?number);
+(1 < x); // 2 errors: null !~> number; undefined !~> number
+(x < 1); // 2 errors: null !~> number; undefined !~> number
+
+(null < null); // error
+(undefined < null); // error
+(null < undefined); // error
+(undefined < undefined); // error
+(NaN < 1);
+(1 < NaN);
+(NaN < NaN);
+
+let tests = [
+  function(x: any, y: number, z: string) {
+    (x > y);
+    (x > z);
+  },
+];
diff --git a/tests/array-filter/__snapshots__/jsfmt.spec.js.snap b/tests/array-filter/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bd957a9257f6
--- /dev/null
+++ b/tests/array-filter/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,63 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+function filterOutVoids<T> (arr: Array<?T>): Array<T> {
+  return arr.filter(Boolean)
+}
+
+function filterOutSmall (arr: Array<?number>): Array<?number> {
+  return arr.filter(num => num && num > 10)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"/* @flow */
+
+function filterItems(items: Array<string|number>): Array<string|number> {
+  return items.map(item => {
+    if (typeof item === \'string\') {
+      return item.length > 2 ? item : null;
+    } else {
+      return item*10;
+    }
+  }).filter(Boolean);
+}
+
+const filteredItems = filterItems([\'foo\', \'b\', 1, 2]);
+
+console.log(filteredItems);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/array-filter/jsfmt.spec.js b/tests/array-filter/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/array-filter/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/array-filter/test.js b/tests/array-filter/test.js
new file mode 100644
index 000000000000..9dc5b1096fd7
--- /dev/null
+++ b/tests/array-filter/test.js
@@ -0,0 +1,9 @@
+/* @flow */
+
+function filterOutVoids<T> (arr: Array<?T>): Array<T> {
+  return arr.filter(Boolean)
+}
+
+function filterOutSmall (arr: Array<?number>): Array<?number> {
+  return arr.filter(num => num && num > 10)
+}
diff --git a/tests/array-filter/test2.js b/tests/array-filter/test2.js
new file mode 100644
index 000000000000..a51043419dfd
--- /dev/null
+++ b/tests/array-filter/test2.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+function filterItems(items: Array<string|number>): Array<string|number> {
+  return items.map(item => {
+    if (typeof item === 'string') {
+      return item.length > 2 ? item : null;
+    } else {
+      return item*10;
+    }
+  }).filter(Boolean);
+}
+
+const filteredItems = filterItems(['foo', 'b', 1, 2]);
+
+console.log(filteredItems);
diff --git a/tests/array_spread/__snapshots__/jsfmt.spec.js.snap b/tests/array_spread/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d761c1fb2b0e
--- /dev/null
+++ b/tests/array_spread/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test test.js 1`] = `
+"var A = [1,2,3];
+var B = [...A];
+var C = [1,2,3];
+B.sort((a, b) => a - b);
+C.sort((a, b) => a - b);
+
+var x: Array<string> = [\'1\', \'2\'];
+var y: Array<string> = [\'3\', ...x];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/array_spread/jsfmt.spec.js b/tests/array_spread/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/array_spread/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/array_spread/test.js b/tests/array_spread/test.js
new file mode 100644
index 000000000000..73789d89ad35
--- /dev/null
+++ b/tests/array_spread/test.js
@@ -0,0 +1,8 @@
+var A = [1,2,3];
+var B = [...A];
+var C = [1,2,3];
+B.sort((a, b) => a - b);
+C.sort((a, b) => a - b);
+
+var x: Array<string> = ['1', '2'];
+var y: Array<string> = ['3', ...x];
diff --git a/tests/arraylib/__snapshots__/jsfmt.spec.js.snap b/tests/arraylib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..22c7fb2420eb
--- /dev/null
+++ b/tests/arraylib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,76 @@
+exports[`test array_lib.js 1`] = `
+"/* @flow */
+function foo(x:string) { }
+
+var a = [0];
+var b = a.map(function (x) { foo(x); return \"\" + x; });
+
+var c: number = a[0];
+var d: number = b[0];
+
+var e:Array<string> = a.reverse();
+
+var f = [\"\"];
+var g:number = f.map(function () { return 0; })[0];
+
+var h: Array<number> = [1,2,3];
+var i: Array<string> = [\'a\', \'b\', \'c\'];
+var j: Array<number | string> = h.concat(i);
+var k: Array<number> = h.concat(h);
+var l: Array<number> = h.concat(1,2,3);
+var m: Array<number | string> = h.concat(\'a\', \'b\', \'c\');
+var n: Array<number> = h.concat(\'a\', \'b\', \'c\'); // Error
+
+function reduce_test() {
+  /* Adapted from the following source:
+   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
+   */
+  [0, 1, 2, 3, 4].reduce(function(previousValue, currentValue, index, array) {
+    return previousValue + currentValue + array[index];
+  });
+
+  [0, 1, 2, 3, 4].reduce(function(previousValue, currentValue, index, array) {
+    return previousValue + currentValue + array[index];
+  }, 10);
+
+  var total = [0, 1, 2, 3].reduce(function(a, b) {
+    return a + b;
+  });
+
+  var flattened = [[0, 1], [2, 3], [4, 5]].reduce(function(a, b) {
+    return a.concat(b);
+  });
+
+  /* Added later, because the above is insufficient */
+
+  // acc is element type of array when no init is provided
+  [\"\"].reduce((acc, str) => acc * str.length); // error, string ~> number
+  [\"\"].reduceRight((acc, str) => acc * str.length); // error, string ~> number
+}
+
+function from_test() {
+  var a: Array<string> = Array.from([1, 2, 3], function(val, index) {
+    return index % 2 ? \"foo\" : String(val);
+  });
+  var b: Array<string> = Array.from([1, 2, 3], function(val) {
+    return String(val);
+  });
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/arraylib/array_lib.js b/tests/arraylib/array_lib.js
new file mode 100644
index 000000000000..6db0cbc2d025
--- /dev/null
+++ b/tests/arraylib/array_lib.js
@@ -0,0 +1,57 @@
+/* @flow */
+function foo(x:string) { }
+
+var a = [0];
+var b = a.map(function (x) { foo(x); return "" + x; });
+
+var c: number = a[0];
+var d: number = b[0];
+
+var e:Array<string> = a.reverse();
+
+var f = [""];
+var g:number = f.map(function () { return 0; })[0];
+
+var h: Array<number> = [1,2,3];
+var i: Array<string> = ['a', 'b', 'c'];
+var j: Array<number | string> = h.concat(i);
+var k: Array<number> = h.concat(h);
+var l: Array<number> = h.concat(1,2,3);
+var m: Array<number | string> = h.concat('a', 'b', 'c');
+var n: Array<number> = h.concat('a', 'b', 'c'); // Error
+
+function reduce_test() {
+  /* Adapted from the following source:
+   * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/Reduce
+   */
+  [0, 1, 2, 3, 4].reduce(function(previousValue, currentValue, index, array) {
+    return previousValue + currentValue + array[index];
+  });
+
+  [0, 1, 2, 3, 4].reduce(function(previousValue, currentValue, index, array) {
+    return previousValue + currentValue + array[index];
+  }, 10);
+
+  var total = [0, 1, 2, 3].reduce(function(a, b) {
+    return a + b;
+  });
+
+  var flattened = [[0, 1], [2, 3], [4, 5]].reduce(function(a, b) {
+    return a.concat(b);
+  });
+
+  /* Added later, because the above is insufficient */
+
+  // acc is element type of array when no init is provided
+  [""].reduce((acc, str) => acc * str.length); // error, string ~> number
+  [""].reduceRight((acc, str) => acc * str.length); // error, string ~> number
+}
+
+function from_test() {
+  var a: Array<string> = Array.from([1, 2, 3], function(val, index) {
+    return index % 2 ? "foo" : String(val);
+  });
+  var b: Array<string> = Array.from([1, 2, 3], function(val) {
+    return String(val);
+  });
+}
diff --git a/tests/arraylib/jsfmt.spec.js b/tests/arraylib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/arraylib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/arrays/Arrays.js b/tests/arrays/Arrays.js
new file mode 100644
index 000000000000..cc3cd2f6956d
--- /dev/null
+++ b/tests/arrays/Arrays.js
@@ -0,0 +1,39 @@
+
+/* @providesModule Arrays */
+
+function foo(x:string) { }
+
+var a = [];
+a[0] = 1;
+a[1] = "...";
+
+foo(a[1]);
+var y;
+a.forEach(x => y=x);
+
+// for literals, composite element type is union of individuals
+// note: test both tuple and non-tuple inferred literals
+var alittle: Array<?number> = [0, 1, 2, 3, null];
+var abig: Array<?number> = [0, 1, 2, 3, 4, 5, 6, 8, null];
+
+var abig2: Array<{x:number; y:number}> = [
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0, a:true},
+  {x:0, y:0, b:"hey"},
+  {x:0, y:0, c:1},
+  {x:0, y:0, c:"hey"}
+];
+
+module.exports = "arrays";
diff --git a/tests/arrays/__snapshots__/jsfmt.spec.js.snap b/tests/arrays/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e2440d0d381c
--- /dev/null
+++ b/tests/arrays/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,77 @@
+exports[`test Arrays.js 1`] = `
+"
+/* @providesModule Arrays */
+
+function foo(x:string) { }
+
+var a = [];
+a[0] = 1;
+a[1] = \"...\";
+
+foo(a[1]);
+var y;
+a.forEach(x => y=x);
+
+// for literals, composite element type is union of individuals
+// note: test both tuple and non-tuple inferred literals
+var alittle: Array<?number> = [0, 1, 2, 3, null];
+var abig: Array<?number> = [0, 1, 2, 3, 4, 5, 6, 8, null];
+
+var abig2: Array<{x:number; y:number}> = [
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0},
+  {x:0, y:0, a:true},
+  {x:0, y:0, b:\"hey\"},
+  {x:0, y:0, c:1},
+  {x:0, y:0, c:\"hey\"}
+];
+
+module.exports = \"arrays\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test numeric_elem.js 1`] = `
+"var arr = [];
+var day = new Date;
+
+// Date instances are numeric (see Flow_js.numeric) and thus can index into
+// arrays.
+arr[day] = 0;
+(arr[day]: string); // error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var arr = [  ];
+var day = new Date();
+// Date instances are numeric (see Flow_js.numeric) and thus can index into
+// arrays.
+arr[day] = 0;
+(arr[day]: string);// error: number ~> string
+
+"
+`;
diff --git a/tests/arrays/jsfmt.spec.js b/tests/arrays/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/arrays/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/arrays/numeric_elem.js b/tests/arrays/numeric_elem.js
new file mode 100644
index 000000000000..afdffa392b14
--- /dev/null
+++ b/tests/arrays/numeric_elem.js
@@ -0,0 +1,7 @@
+var arr = [];
+var day = new Date;
+
+// Date instances are numeric (see Flow_js.numeric) and thus can index into
+// arrays.
+arr[day] = 0;
+(arr[day]: string); // error: number ~> string
diff --git a/tests/arrows/__snapshots__/jsfmt.spec.js.snap b/tests/arrows/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c62df90c14c6
--- /dev/null
+++ b/tests/arrows/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,60 @@
+exports[`test advanced_arrows.js 1`] = `
+"/**
+ * @flow
+ */
+
+var add = (x: number, y: number): number => x + y;
+
+var bad = (x: number): string => x; // Error!
+
+var ident = <T>(x: T): T => x;
+(ident(1): number);
+(ident(\"hi\"): number); // Error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:367:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test arrows.js 1`] = `
+"function selectBestEffortImageForWidth(
+    maxWidth: number,
+    images: Array<Image>
+): Image {
+    var maxPixelWidth = maxWidth;
+    //images = images.sort(function (a, b) { return a.width - b.width });
+    images = images.sort((a, b) => (a.width - b.width) + \"\");
+    return images.find(image => image.width >= maxPixelWidth) ||
+        images[images.length - 1];
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/arrows/advanced_arrows.js b/tests/arrows/advanced_arrows.js
new file mode 100644
index 000000000000..010ca4c71a77
--- /dev/null
+++ b/tests/arrows/advanced_arrows.js
@@ -0,0 +1,11 @@
+/**
+ * @flow
+ */
+
+var add = (x: number, y: number): number => x + y;
+
+var bad = (x: number): string => x; // Error!
+
+var ident = <T>(x: T): T => x;
+(ident(1): number);
+(ident("hi"): number); // Error
diff --git a/tests/arrows/arrows.js b/tests/arrows/arrows.js
new file mode 100644
index 000000000000..f25cc0fb3c40
--- /dev/null
+++ b/tests/arrows/arrows.js
@@ -0,0 +1,10 @@
+function selectBestEffortImageForWidth(
+    maxWidth: number,
+    images: Array<Image>
+): Image {
+    var maxPixelWidth = maxWidth;
+    //images = images.sort(function (a, b) { return a.width - b.width });
+    images = images.sort((a, b) => (a.width - b.width) + "");
+    return images.find(image => image.width >= maxPixelWidth) ||
+        images[images.length - 1];
+}
diff --git a/tests/arrows/jsfmt.spec.js b/tests/arrows/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/arrows/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/ast_tokens/__snapshots__/jsfmt.spec.js.snap b/tests/ast_tokens/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a4b93d5aafe9
--- /dev/null
+++ b/tests/ast_tokens/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,34 @@
+exports[`test foo.js 1`] = `
+"// Regex literals require a lexer mode change
+/asdf/g;
+
+// JSX also requires a lexer mode change
+<div attr1=\'42\' attr2={\'asdf\'} >asdf</div>;
+
+// Async arrow functions require backtracking
+var a = async () => 42;
+
+// Type annotations have a special lex mode
+var a: number = 42;
+
+// Token stream should continue even with parse errors
+var var
+a;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (14:4)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$2.parseBindingAtom (/node_modules/babylon/lib/index.js:2929:12)
+    at Parser.pp$1.parseVarHead (/node_modules/babylon/lib/index.js:2226:18)
+    at Parser.parseVarHead (/node_modules/babylon/lib/index.js:5611:13)
+    at Parser.pp$1.parseVar (/node_modules/babylon/lib/index.js:2209:10)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2042:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+"
+`;
diff --git a/tests/ast_tokens/foo.js b/tests/ast_tokens/foo.js
new file mode 100644
index 000000000000..cca10855f7a7
--- /dev/null
+++ b/tests/ast_tokens/foo.js
@@ -0,0 +1,15 @@
+// Regex literals require a lexer mode change
+/asdf/g;
+
+// JSX also requires a lexer mode change
+<div attr1='42' attr2={'asdf'} >asdf</div>;
+
+// Async arrow functions require backtracking
+var a = async () => 42;
+
+// Type annotations have a special lex mode
+var a: number = 42;
+
+// Token stream should continue even with parse errors
+var var
+a;
diff --git a/tests/ast_tokens/jsfmt.spec.js b/tests/ast_tokens/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/ast_tokens/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/async/__snapshots__/jsfmt.spec.js.snap b/tests/async/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a3c8cadc6de3
--- /dev/null
+++ b/tests/async/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,471 @@
+exports[`test async.js 1`] = `
+"// @flow
+
+// \"For async functions, a Promise<T> is returned,
+// and the type of return expressions must be T.\"
+//
+
+async function f0(): Promise<number> {
+  return 1;
+}
+
+async function f1(): Promise<bool> {
+  return 1;  // error, number != bool
+}
+
+// await: (p: Promise<T> | T) => T
+//
+
+async function f2(p: Promise<number>): Promise<number> {
+  var x: number = await p;
+  var y: number = await 1;
+  return x + y;
+}
+
+async function f3(p: Promise<number>): Promise<number> {
+  return await p;
+}
+
+// TODO: this is one of those bad generic errors, currently:
+// \"inconsistent use of library definitions\" with two core.js locs
+async function f4(p: Promise<number>): Promise<bool> {
+  return await p; // error, number != bool
+}
+
+// async arrow functions
+//
+
+var f5: () => Promise<number> = async () => await 1;
+
+// async methods
+//
+
+class C {
+  async m() { return 1; }
+  async mt<T>(a: T): Promise<T> { return a; }
+  static async m(a): void { await a; } // error, void != Promise<void>
+  static async mt<T>(a: T): Promise<T> { return a; }
+}
+
+// async function props
+
+var obj = { f: async () => await 1 };
+var objf : () => Promise<number> = obj.f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test async_base_class.js 1`] = `
+"// This is kind of weird, but it should parse. This works in babel without the
+// parens around (await promise). From the es6 and async/await specs I (nmote)
+// am not clear on whether it should. In any case it\'s a strange corner case
+// that is probably not important to support.
+class C {};
+
+var P: Promise<Class<C>> = new Promise(function (resolve, reject) {
+  resolve(C);
+});
+
+async function foo() {
+  class Bar extends (await P) { }
+  return Bar;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test async_parse.js 1`] = `
+"async function f() {}
+async function ft<T>(a: T) {}
+
+class C {
+  async m() {}
+  async mt<T>(a: T) {}
+  static async m(a) {}
+  static async mt<T>(a: T) {}
+}
+
+var e = async function () {};
+var et = async function<T> (a: T) {};
+
+var n = new async function() {};
+
+var o = { async m() {} };
+var ot = { async m<T>(a: T) {} };
+var oz = { async async() {} };
+
+var x = { async : 5 };
+console.log(x.async);
+
+var async = 3;
+var y = { async };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test async_promise.js 1`] = `
+"async function f(): Promise<number> {
+  return Promise.resolve(1);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test async_return_void.js 1`] = `
+"// @flow
+
+async function foo1(): Promise<string> {
+  return;
+}
+
+async function foo2(): Promise<string> {
+  return undefined;
+}
+
+async function foo3(): Promise<string> {
+  function bar() { }
+  return bar();
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test async2.js 1`] = `
+"// @flow
+
+// misc basic
+
+function test1() {
+  async function foo() {
+    return 42;
+  }
+
+  async function bar() {
+    var a = await foo();
+    var b: number = a; // valid
+    var c: string = a; // Error: number ~> string
+  }
+}
+
+//
+// void returns:
+//
+
+// inference should produce return type Promise<void>
+// in the absence of an explicit return
+//
+
+function test2() {
+  async function voidoid1() {
+    console.log(\"HEY\");
+  }
+
+  var voidoid2: () => Promise<void> = voidoid1; // ok
+
+  var voidoid3: () => void = voidoid1; // error, void != Promise<void>
+}
+
+// annotated return type of Promise<void> should work
+//
+
+function test3() {
+  async function voidoid4(): Promise<void> { // ok
+    console.log(\"HEY\");
+  }
+}
+
+// other annotated return types should fail
+// (note: misannotated return types with explicit
+// return statements are covered in async.js)
+//
+
+function test4() {
+  async function voidoid5(): void { // error, void != Promise<void>
+    console.log(\"HEY\");
+  }
+}
+
+function test5() {
+  async function voidoid6()
+  : Promise<number> { // error, number != void
+    console.log(\"HEY\");
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test async3.js 1`] = `
+"// @flow
+
+/**
+ * test nested-promise unwrapping.
+ * Note: currently we don\'t do this properly in the underlying
+ * type of the Promise class, which causes spurious errors to
+ * be raised here. Once that\'s fixed, the errors here will go
+ * away.
+ */
+
+async function foo() {
+  return 42;
+}
+
+async function bar() {
+  return foo();
+}
+
+async function baz() {
+
+  // a should now be typed as number, but is in fact
+  // Promise<number> until nested-promise unwrap is fixed
+  var a = await bar();
+
+  // TODO this is valid code, but currently gives Promise ~> number error
+  // due to lack of transitive Promise unwrap.
+  var b: number = a;
+
+  // should be number ~> string error, but currently gives
+  // Promise ~> string error for the same reason
+  var c: string = a;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+/**
+ * test nested-promise unwrapping.
+ * Note: currently we don\'t do this properly in the underlying
+ * type of the Promise class, which causes spurious errors to
+ * be raised here. Once that\'s fixed, the errors here will go
+ * away.
+ */
+async function foo() {
+  return 42;
+}
+async function bar() {
+  return foo();
+}
+async function baz() {
+  // a should now be typed as number, but is in fact
+  // Promise<number> until nested-promise unwrap is fixed
+  var a = await bar();
+  // TODO this is valid code, but currently gives Promise ~> number error
+  // due to lack of transitive Promise unwrap.
+  var b: number = a;
+  // should be number ~> string error, but currently gives
+  // Promise ~> string error for the same reason
+  var c: string = a;
+}
+
+"
+`;
+
+exports[`test await_not_in_async.js 1`] = `
+"// note: currently, await-within-async enforcement is a
+// done by the parser, which bails after a single error.
+
+function f() {
+  await 1;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: await is a reserved word (5:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$3.checkReservedWord (/node_modules/babylon/lib/index.js:4143:10)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4121:12)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3490:21)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+"
+`;
+
+exports[`test await_not_in_async2.js 1`] = `
+"// note: currently, await-within-async enforcement is a
+// done by the parser, which bails after a single error.
+
+function f(x) { return x; }
+
+f(await 1);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: await is a reserved word (6:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$3.checkReservedWord (/node_modules/babylon/lib/index.js:4143:10)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4121:12)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3490:21)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+"
+`;
+
+exports[`test await_not_in_async3.js 1`] = `
+"// note: currently, await-within-async enforcement is a
+// done by the parser, which bails after a single error.
+
+async function f(x) { return x; }
+
+f(await 1);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: await is a reserved word (6:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$3.checkReservedWord (/node_modules/babylon/lib/index.js:4143:10)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4121:12)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3490:21)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+"
+`;
+
+exports[`test await_parse.js 1`] = `
+"async function f() { await 1; }
+async function ft<T>(a: T) { await 1; }
+
+class C {
+  async m() { await 1; }
+  async mt<T>(a: T) { await 1; }
+  static async m(a) { await 1; }
+  static async mt<T>(a: T) { await 1; }
+}
+
+var e = async function () { await 1; };
+var et = async function<T> (a: T) { await 1; };
+
+var n = new async function() { await 1; };
+
+var o = { async m() { await 1; } };
+var ot = { async m<T>(a: T) { await 1; } };
+var oz = { async async(async) { await async; } };
+
+var x = { await : 5 };
+console.log(x.await);
+
+var await = 3;
+var y = { await };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: await is a reserved word (23:4)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$3.checkReservedWord (/node_modules/babylon/lib/index.js:4143:10)
+    at Parser.pp$2.checkLVal (/node_modules/babylon/lib/index.js:2990:12)
+    at Parser.checkLVal (/node_modules/babylon/lib/index.js:5446:22)
+    at Parser.pp$1.parseVarHead (/node_modules/babylon/lib/index.js:2227:8)
+    at Parser.parseVarHead (/node_modules/babylon/lib/index.js:5611:13)
+    at Parser.pp$1.parseVar (/node_modules/babylon/lib/index.js:2209:10)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2042:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+"
+`;
diff --git a/tests/async/async.js b/tests/async/async.js
new file mode 100644
index 000000000000..85d27b27b3a9
--- /dev/null
+++ b/tests/async/async.js
@@ -0,0 +1,52 @@
+// @flow
+
+// "For async functions, a Promise<T> is returned,
+// and the type of return expressions must be T."
+//
+
+async function f0(): Promise<number> {
+  return 1;
+}
+
+async function f1(): Promise<bool> {
+  return 1;  // error, number != bool
+}
+
+// await: (p: Promise<T> | T) => T
+//
+
+async function f2(p: Promise<number>): Promise<number> {
+  var x: number = await p;
+  var y: number = await 1;
+  return x + y;
+}
+
+async function f3(p: Promise<number>): Promise<number> {
+  return await p;
+}
+
+// TODO: this is one of those bad generic errors, currently:
+// "inconsistent use of library definitions" with two core.js locs
+async function f4(p: Promise<number>): Promise<bool> {
+  return await p; // error, number != bool
+}
+
+// async arrow functions
+//
+
+var f5: () => Promise<number> = async () => await 1;
+
+// async methods
+//
+
+class C {
+  async m() { return 1; }
+  async mt<T>(a: T): Promise<T> { return a; }
+  static async m(a): void { await a; } // error, void != Promise<void>
+  static async mt<T>(a: T): Promise<T> { return a; }
+}
+
+// async function props
+
+var obj = { f: async () => await 1 };
+var objf : () => Promise<number> = obj.f;
diff --git a/tests/async/async2.js b/tests/async/async2.js
new file mode 100644
index 000000000000..79e69a7c1070
--- /dev/null
+++ b/tests/async/async2.js
@@ -0,0 +1,60 @@
+// @flow
+
+// misc basic
+
+function test1() {
+  async function foo() {
+    return 42;
+  }
+
+  async function bar() {
+    var a = await foo();
+    var b: number = a; // valid
+    var c: string = a; // Error: number ~> string
+  }
+}
+
+//
+// void returns:
+//
+
+// inference should produce return type Promise<void>
+// in the absence of an explicit return
+//
+
+function test2() {
+  async function voidoid1() {
+    console.log("HEY");
+  }
+
+  var voidoid2: () => Promise<void> = voidoid1; // ok
+
+  var voidoid3: () => void = voidoid1; // error, void != Promise<void>
+}
+
+// annotated return type of Promise<void> should work
+//
+
+function test3() {
+  async function voidoid4(): Promise<void> { // ok
+    console.log("HEY");
+  }
+}
+
+// other annotated return types should fail
+// (note: misannotated return types with explicit
+// return statements are covered in async.js)
+//
+
+function test4() {
+  async function voidoid5(): void { // error, void != Promise<void>
+    console.log("HEY");
+  }
+}
+
+function test5() {
+  async function voidoid6()
+  : Promise<number> { // error, number != void
+    console.log("HEY");
+  }
+}
diff --git a/tests/async/async3.js b/tests/async/async3.js
new file mode 100644
index 000000000000..d0062d5f21a7
--- /dev/null
+++ b/tests/async/async3.js
@@ -0,0 +1,32 @@
+// @flow
+
+/**
+ * test nested-promise unwrapping.
+ * Note: currently we don't do this properly in the underlying
+ * type of the Promise class, which causes spurious errors to
+ * be raised here. Once that's fixed, the errors here will go
+ * away.
+ */
+
+async function foo() {
+  return 42;
+}
+
+async function bar() {
+  return foo();
+}
+
+async function baz() {
+
+  // a should now be typed as number, but is in fact
+  // Promise<number> until nested-promise unwrap is fixed
+  var a = await bar();
+
+  // TODO this is valid code, but currently gives Promise ~> number error
+  // due to lack of transitive Promise unwrap.
+  var b: number = a;
+
+  // should be number ~> string error, but currently gives
+  // Promise ~> string error for the same reason
+  var c: string = a;
+}
diff --git a/tests/async/async_base_class.js b/tests/async/async_base_class.js
new file mode 100644
index 000000000000..de7afc58ec61
--- /dev/null
+++ b/tests/async/async_base_class.js
@@ -0,0 +1,14 @@
+// This is kind of weird, but it should parse. This works in babel without the
+// parens around (await promise). From the es6 and async/await specs I (nmote)
+// am not clear on whether it should. In any case it's a strange corner case
+// that is probably not important to support.
+class C {};
+
+var P: Promise<Class<C>> = new Promise(function (resolve, reject) {
+  resolve(C);
+});
+
+async function foo() {
+  class Bar extends (await P) { }
+  return Bar;
+}
diff --git a/tests/async/async_parse.js b/tests/async/async_parse.js
new file mode 100644
index 000000000000..e633ae4efc65
--- /dev/null
+++ b/tests/async/async_parse.js
@@ -0,0 +1,24 @@
+async function f() {}
+async function ft<T>(a: T) {}
+
+class C {
+  async m() {}
+  async mt<T>(a: T) {}
+  static async m(a) {}
+  static async mt<T>(a: T) {}
+}
+
+var e = async function () {};
+var et = async function<T> (a: T) {};
+
+var n = new async function() {};
+
+var o = { async m() {} };
+var ot = { async m<T>(a: T) {} };
+var oz = { async async() {} };
+
+var x = { async : 5 };
+console.log(x.async);
+
+var async = 3;
+var y = { async };
diff --git a/tests/async/async_promise.js b/tests/async/async_promise.js
new file mode 100644
index 000000000000..8c2ce87dbd42
--- /dev/null
+++ b/tests/async/async_promise.js
@@ -0,0 +1,3 @@
+async function f(): Promise<number> {
+  return Promise.resolve(1);
+}
diff --git a/tests/async/async_return_void.js b/tests/async/async_return_void.js
new file mode 100644
index 000000000000..1e312f63386e
--- /dev/null
+++ b/tests/async/async_return_void.js
@@ -0,0 +1,14 @@
+// @flow
+
+async function foo1(): Promise<string> {
+  return;
+}
+
+async function foo2(): Promise<string> {
+  return undefined;
+}
+
+async function foo3(): Promise<string> {
+  function bar() { }
+  return bar();
+}
diff --git a/tests/async/await_not_in_async.js b/tests/async/await_not_in_async.js
new file mode 100644
index 000000000000..cbcc4191ac41
--- /dev/null
+++ b/tests/async/await_not_in_async.js
@@ -0,0 +1,6 @@
+// note: currently, await-within-async enforcement is a
+// done by the parser, which bails after a single error.
+
+function f() {
+  await 1;
+}
diff --git a/tests/async/await_not_in_async2.js b/tests/async/await_not_in_async2.js
new file mode 100644
index 000000000000..0037d0905eb3
--- /dev/null
+++ b/tests/async/await_not_in_async2.js
@@ -0,0 +1,6 @@
+// note: currently, await-within-async enforcement is a
+// done by the parser, which bails after a single error.
+
+function f(x) { return x; }
+
+f(await 1);
diff --git a/tests/async/await_not_in_async3.js b/tests/async/await_not_in_async3.js
new file mode 100644
index 000000000000..cacb5dc6749a
--- /dev/null
+++ b/tests/async/await_not_in_async3.js
@@ -0,0 +1,6 @@
+// note: currently, await-within-async enforcement is a
+// done by the parser, which bails after a single error.
+
+async function f(x) { return x; }
+
+f(await 1);
diff --git a/tests/async/await_parse.js b/tests/async/await_parse.js
new file mode 100644
index 000000000000..10149204ecd7
--- /dev/null
+++ b/tests/async/await_parse.js
@@ -0,0 +1,24 @@
+async function f() { await 1; }
+async function ft<T>(a: T) { await 1; }
+
+class C {
+  async m() { await 1; }
+  async mt<T>(a: T) { await 1; }
+  static async m(a) { await 1; }
+  static async mt<T>(a: T) { await 1; }
+}
+
+var e = async function () { await 1; };
+var et = async function<T> (a: T) { await 1; };
+
+var n = new async function() { await 1; };
+
+var o = { async m() { await 1; } };
+var ot = { async m<T>(a: T) { await 1; } };
+var oz = { async async(async) { await async; } };
+
+var x = { await : 5 };
+console.log(x.await);
+
+var await = 3;
+var y = { await };
diff --git a/tests/async/jsfmt.spec.js b/tests/async/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/async/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/async_iteration/__snapshots__/jsfmt.spec.js.snap b/tests/async_iteration/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a9bab4ede39d
--- /dev/null
+++ b/tests/async_iteration/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,213 @@
+exports[`test delegate_yield.js 1`] = `
+"async function *delegate_next() {
+  async function *inner() {
+    var x: void = yield; // error: number ~> void
+  }
+  yield *inner();
+}
+delegate_next().next(0);
+
+async function *delegate_yield() {
+  async function *inner() {
+    yield 0;
+  }
+  yield *inner();
+}
+(async () => {
+  for await (const x of delegate_yield()) {
+    (x: void); // error: number ~> void
+  }
+});
+
+async function *delegate_return() {
+  async function *inner() {
+    return 0;
+  }
+  var x: void = yield *inner(); // error: number ~> void
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+async function* delegate_next() {
+  async function* inner() {
+    var x: void = yield;// error: number ~> void
+  }
+  yield* inner();
+}
+delegate_next().next(0);
+async function* delegate_yield() {
+  async function* inner() {
+    yield 0;
+  }
+  yield* inner();
+}
+async () => {
+  for await (const x of delegate_yield()) {
+    (x: void);// error: number ~> void
+  }
+};
+async function* delegate_return() {
+  async function* inner() {
+    return 0;
+  }
+  var x: void = yield* inner();// error: number ~> void
+}
+
+"
+`;
+
+exports[`test generator.js 1`] = `
+"declare interface File {
+  readLine(): Promise<string>;
+  close(): void;
+  EOF: boolean;
+}
+
+declare function fileOpen(path: string): Promise<File>;
+
+async function* readLines(path) {
+  let file: File = await fileOpen(path);
+
+  try {
+    while (!file.EOF) {
+      yield await file.readLine();
+    }
+  } finally {
+    file.close();
+  }
+}
+
+async function f() {
+  for await (const line of readLines(\"/path/to/file\")) {
+    (line: void); // error: string ~> void
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test return.js 1`] = `
+"declare var gen: AsyncGenerator<void,string,void>;
+
+// You can pass whatever you like to return, it doesn\'t need to be related to
+// the AsyncGenerator\'s return type
+gen.return(0).then(result => {
+  (result.value: void); // error: string | number ~> void
+});
+
+// However, a generator can \"refuse\" the return by catching an exception and
+// yielding or returning internally.
+async function *refuse_return() {
+  try {
+    yield 1;
+  } finally {
+    return 0;
+  }
+}
+refuse_return().return(\"string\").then(result => {
+  if (result.done) {
+    (result.value: string); // error: number | void ~> string
+  }
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test throw.js 1`] = `
+"async function *catch_return() {
+  try {
+    yield 0;
+  } catch (e) {
+    return e;
+  }
+}
+
+(async () => {
+  catch_return().throw(\"\").then(({value}) => {
+    if (value !== undefined) {
+      (value: void); // error: number ~> void
+    }
+  });
+});
+
+async function *yield_return() {
+  try {
+    yield 0;
+    return;
+  } catch (e) {
+    yield e;
+  }
+}
+
+(async () => {
+  yield_return().throw(\"\").then(({value}) => {
+    if (value !== undefined) {
+      (value: void); // error: number ~> void
+    }
+  });
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+async function* catch_return() {
+  try {
+    yield 0;
+  } catch (e) {
+    return e;
+  }
+}
+async () => {
+  catch_return().throw(\"\").then(
+    ({ value }) => {
+      if (value !== undefined) {
+        (value: void);// error: number ~> void
+      }
+    }
+  );
+};
+async function* yield_return() {
+  try {
+    yield 0;
+    return;
+  } catch (e) {
+    yield e;
+  }
+}
+async () => {
+  yield_return().throw(\"\").then(
+    ({ value }) => {
+      if (value !== undefined) {
+        (value: void);// error: number ~> void
+      }
+    }
+  );
+};
+
+"
+`;
diff --git a/tests/async_iteration/delegate_yield.js b/tests/async_iteration/delegate_yield.js
new file mode 100644
index 000000000000..965cfadfaea7
--- /dev/null
+++ b/tests/async_iteration/delegate_yield.js
@@ -0,0 +1,26 @@
+async function *delegate_next() {
+  async function *inner() {
+    var x: void = yield; // error: number ~> void
+  }
+  yield *inner();
+}
+delegate_next().next(0);
+
+async function *delegate_yield() {
+  async function *inner() {
+    yield 0;
+  }
+  yield *inner();
+}
+(async () => {
+  for await (const x of delegate_yield()) {
+    (x: void); // error: number ~> void
+  }
+});
+
+async function *delegate_return() {
+  async function *inner() {
+    return 0;
+  }
+  var x: void = yield *inner(); // error: number ~> void
+}
diff --git a/tests/async_iteration/generator.js b/tests/async_iteration/generator.js
new file mode 100644
index 000000000000..76213a59f63d
--- /dev/null
+++ b/tests/async_iteration/generator.js
@@ -0,0 +1,25 @@
+declare interface File {
+  readLine(): Promise<string>;
+  close(): void;
+  EOF: boolean;
+}
+
+declare function fileOpen(path: string): Promise<File>;
+
+async function* readLines(path) {
+  let file: File = await fileOpen(path);
+
+  try {
+    while (!file.EOF) {
+      yield await file.readLine();
+    }
+  } finally {
+    file.close();
+  }
+}
+
+async function f() {
+  for await (const line of readLines("/path/to/file")) {
+    (line: void); // error: string ~> void
+  }
+}
diff --git a/tests/async_iteration/jsfmt.spec.js b/tests/async_iteration/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/async_iteration/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/async_iteration/return.js b/tests/async_iteration/return.js
new file mode 100644
index 000000000000..28cbc3deb4c1
--- /dev/null
+++ b/tests/async_iteration/return.js
@@ -0,0 +1,22 @@
+declare var gen: AsyncGenerator<void,string,void>;
+
+// You can pass whatever you like to return, it doesn't need to be related to
+// the AsyncGenerator's return type
+gen.return(0).then(result => {
+  (result.value: void); // error: string | number ~> void
+});
+
+// However, a generator can "refuse" the return by catching an exception and
+// yielding or returning internally.
+async function *refuse_return() {
+  try {
+    yield 1;
+  } finally {
+    return 0;
+  }
+}
+refuse_return().return("string").then(result => {
+  if (result.done) {
+    (result.value: string); // error: number | void ~> string
+  }
+});
diff --git a/tests/async_iteration/throw.js b/tests/async_iteration/throw.js
new file mode 100644
index 000000000000..ae6c629bbfa5
--- /dev/null
+++ b/tests/async_iteration/throw.js
@@ -0,0 +1,32 @@
+async function *catch_return() {
+  try {
+    yield 0;
+  } catch (e) {
+    return e;
+  }
+}
+
+(async () => {
+  catch_return().throw("").then(({value}) => {
+    if (value !== undefined) {
+      (value: void); // error: number ~> void
+    }
+  });
+});
+
+async function *yield_return() {
+  try {
+    yield 0;
+    return;
+  } catch (e) {
+    yield e;
+  }
+}
+
+(async () => {
+  yield_return().throw("").then(({value}) => {
+    if (value !== undefined) {
+      (value: void); // error: number ~> void
+    }
+  });
+});
diff --git a/tests/autocomplete/__snapshots__/jsfmt.spec.js.snap b/tests/autocomplete/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8c4dbb8e1566
--- /dev/null
+++ b/tests/autocomplete/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,582 @@
+exports[`test bar.js 1`] = `
+"// @flow
+
+var o = require(\'./unknown\');
+o.x.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test bool.js 1`] = `
+"// @flow
+
+true.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (4:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test customfun.js 1`] = `
+"// @flow
+
+declare var idx: $Facebookism$Idx;
+declare var merge: $Facebookism$Merge;
+declare var mergeDeepInto: $Facebookism$MergeDeepInto;
+declare var mergeInto: $Facebookism$MergeInto;
+declare var mixin: $Facebookism$Mixin;
+declare var objectGetPrototypeOf: Object$GetPrototypeOf
+declare var objectAssign: Object$Assign
+
+m
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+declare var idx: $Facebookism$Idx;
+declare var merge: $Facebookism$Merge;
+declare var mergeDeepInto: $Facebookism$MergeDeepInto;
+declare var mergeInto: $Facebookism$MergeInto;
+declare var mixin: $Facebookism$Mixin;
+declare var objectGetPrototypeOf: Object$GetPrototypeOf;
+declare var objectAssign: Object$Assign;
+m;
+
+"
+`;
+
+exports[`test foo.js 1`] = `
+"/**
+ * @flow
+ */
+
+var obj = {
+  num: 123,
+  str: \'hello\',
+};
+
+obj.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (11:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test foo_parse_fail.js 1`] = `
+"/**
+ * @flow
+ */
+
+var obj = {
+  num: 123,
+  str: \'hello\',
+};
+
+console.log(obj.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (11:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test fun.js 1`] = `
+"/* @flow */
+
+function foo(f: () => number) {
+  f.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test function_builtins.js 1`] = `
+"/* @flow */
+
+function foo(f: Function) {
+  f.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test generics.js 1`] = `
+"// @flow
+
+class C<X> { }
+
+function foo(o: { cn: C<number> }) {
+  o.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (7:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test if.js 1`] = `
+"// @flow
+const x = \'\';
+if (x.)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (3:6)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test issue-1368.js 1`] = `
+"/* @flow */
+class Test {
+  prop: number;
+
+  constructor(prop: number) {
+    this.prop = prop;
+  }
+}
+
+class ExtendTest extends Test {
+  extended: string;
+
+  constructor(extended: string) {
+    super(10);
+    this.extended = extended;
+  }
+
+  method() {
+    this.prop = 12;
+    this./* here */
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (21:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test jsx1.js 1`] = `
+"// @flow
+
+var React = require(\'react\');
+
+class C extends React.Component {
+  props: { x: number };
+}
+<C 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:5687
+          throw jsxError || err;
+          ^
+
+SyntaxError: Unexpected token (9:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$8.jsxParseIdentifier (/node_modules/babylon/lib/index.js:6199:10)
+    at Parser.pp$8.jsxParseNamespacedName (/node_modules/babylon/lib/index.js:6210:19)
+    at Parser.pp$8.jsxParseAttribute (/node_modules/babylon/lib/index.js:6305:20)
+    at Parser.pp$8.jsxParseOpeningElementAt (/node_modules/babylon/lib/index.js:6317:31)
+    at Parser.pp$8.jsxParseElementAt (/node_modules/babylon/lib/index.js:6339:29)
+    at Parser.pp$8.jsxParseElement (/node_modules/babylon/lib/index.js:6394:15)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6406:21)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+"
+`;
+
+exports[`test jsx2.js 1`] = `
+"// @flow
+
+var React = require(\'react\');
+
+class C extends React.Component {
+  props: { x: number, y: string };
+}
+<C x = 0, 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:5687
+          throw jsxError || err;
+          ^
+
+SyntaxError: JSX value should be either an expression or a quoted JSX text (8:7)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$8.jsxParseAttributeValue (/node_modules/babylon/lib/index.js:6255:12)
+    at Parser.pp$8.jsxParseAttribute (/node_modules/babylon/lib/index.js:6306:42)
+    at Parser.pp$8.jsxParseOpeningElementAt (/node_modules/babylon/lib/index.js:6317:31)
+    at Parser.pp$8.jsxParseElementAt (/node_modules/babylon/lib/index.js:6339:29)
+    at Parser.pp$8.jsxParseElement (/node_modules/babylon/lib/index.js:6394:15)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6406:21)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+"
+`;
+
+exports[`test num.js 1`] = `
+"// @flow
+
+var num = 123;
+num.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test object_builtins.js 1`] = `
+"/* @flow */
+
+function foo(o: Object) {
+  o.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test optional.js 1`] = `
+"// @flow
+
+function foo(obj: { x?: string, f: (x?: string) => void, o: { x?: string } }) {
+  return obj.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test override.js 1`] = `
+"// @flow
+
+class C {
+  override(): number | string { return 0; }
+}
+
+class D extends C {
+  foo() { return this.override() }
+  override(): string { return \"\"; }
+  bar() { this.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (11:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test qux.js 1`] = `
+"// @flow
+
+class C { x: number; }
+
+var c: C = new C;
+c.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (7:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test str.js 1`] = `
+"// @flow
+
+\"hello\".
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (4:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test this.js 1`] = `
+"/* @flow */
+
+// issue #1197
+class Foo {
+  baz: string;
+  bar() {}
+  hello() {
+    this.
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (9:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test typeparams.js 1`] = `
+"// @flow
+
+class Bounds<N: number, F: () => N> {
+  foo: F;
+  bar() {
+    this.foo().
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (7:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test union.js 1`] = `
+"/* @flow */
+
+function foo(a: boolean, x: { bar: string }, y: Object) {
+  var z;
+  if (a) {
+    z = x;
+  } else {
+    z = y;
+  }
+  z.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (11:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseSubscripts (/node_modules/babylon/lib/index.js:3360:30)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3347:15)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test unknown.js 1`] = `
+"// @noflow
+module.exports = { x: { y: \"\" } };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @noflow
+module.exports = { x: { y: \"\" } };
+
+"
+`;
diff --git a/tests/autocomplete/bar.js b/tests/autocomplete/bar.js
new file mode 100644
index 000000000000..00c2758f28f5
--- /dev/null
+++ b/tests/autocomplete/bar.js
@@ -0,0 +1,4 @@
+// @flow
+
+var o = require('./unknown');
+o.x.
diff --git a/tests/autocomplete/bool.js b/tests/autocomplete/bool.js
new file mode 100644
index 000000000000..31e0aa0530b1
--- /dev/null
+++ b/tests/autocomplete/bool.js
@@ -0,0 +1,3 @@
+// @flow
+
+true.
diff --git a/tests/autocomplete/customfun.js b/tests/autocomplete/customfun.js
new file mode 100644
index 000000000000..17a57049c5d4
--- /dev/null
+++ b/tests/autocomplete/customfun.js
@@ -0,0 +1,11 @@
+// @flow
+
+declare var idx: $Facebookism$Idx;
+declare var merge: $Facebookism$Merge;
+declare var mergeDeepInto: $Facebookism$MergeDeepInto;
+declare var mergeInto: $Facebookism$MergeInto;
+declare var mixin: $Facebookism$Mixin;
+declare var objectGetPrototypeOf: Object$GetPrototypeOf
+declare var objectAssign: Object$Assign
+
+m
diff --git a/tests/autocomplete/foo.js b/tests/autocomplete/foo.js
new file mode 100644
index 000000000000..fb47a498b239
--- /dev/null
+++ b/tests/autocomplete/foo.js
@@ -0,0 +1,10 @@
+/**
+ * @flow
+ */
+
+var obj = {
+  num: 123,
+  str: 'hello',
+};
+
+obj.
diff --git a/tests/autocomplete/foo_parse_fail.js b/tests/autocomplete/foo_parse_fail.js
new file mode 100644
index 000000000000..ad60a989911a
--- /dev/null
+++ b/tests/autocomplete/foo_parse_fail.js
@@ -0,0 +1,10 @@
+/**
+ * @flow
+ */
+
+var obj = {
+  num: 123,
+  str: 'hello',
+};
+
+console.log(obj.
diff --git a/tests/autocomplete/fun.js b/tests/autocomplete/fun.js
new file mode 100644
index 000000000000..dda5e9788c36
--- /dev/null
+++ b/tests/autocomplete/fun.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+function foo(f: () => number) {
+  f.
+}
diff --git a/tests/autocomplete/function_builtins.js b/tests/autocomplete/function_builtins.js
new file mode 100644
index 000000000000..9ab9ee978fd2
--- /dev/null
+++ b/tests/autocomplete/function_builtins.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+function foo(f: Function) {
+  f.
+}
diff --git a/tests/autocomplete/generics.js b/tests/autocomplete/generics.js
new file mode 100644
index 000000000000..284ca1a8bed5
--- /dev/null
+++ b/tests/autocomplete/generics.js
@@ -0,0 +1,7 @@
+// @flow
+
+class C<X> { }
+
+function foo(o: { cn: C<number> }) {
+  o.
+}
diff --git a/tests/autocomplete/if.js b/tests/autocomplete/if.js
new file mode 100644
index 000000000000..78fb463ed9cd
--- /dev/null
+++ b/tests/autocomplete/if.js
@@ -0,0 +1,3 @@
+// @flow
+const x = '';
+if (x.)
diff --git a/tests/autocomplete/issue-1368.js b/tests/autocomplete/issue-1368.js
new file mode 100644
index 000000000000..fc346f45a1d8
--- /dev/null
+++ b/tests/autocomplete/issue-1368.js
@@ -0,0 +1,22 @@
+/* @flow */
+class Test {
+  prop: number;
+
+  constructor(prop: number) {
+    this.prop = prop;
+  }
+}
+
+class ExtendTest extends Test {
+  extended: string;
+
+  constructor(extended: string) {
+    super(10);
+    this.extended = extended;
+  }
+
+  method() {
+    this.prop = 12;
+    this./* here */
+  }
+}
diff --git a/tests/autocomplete/jsfmt.spec.js b/tests/autocomplete/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/autocomplete/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/autocomplete/jsx1.js b/tests/autocomplete/jsx1.js
new file mode 100644
index 000000000000..4552fc4f0173
--- /dev/null
+++ b/tests/autocomplete/jsx1.js
@@ -0,0 +1,8 @@
+// @flow
+
+var React = require('react');
+
+class C extends React.Component {
+  props: { x: number };
+}
+<C 
diff --git a/tests/autocomplete/jsx2.js b/tests/autocomplete/jsx2.js
new file mode 100644
index 000000000000..d0f39e42ba31
--- /dev/null
+++ b/tests/autocomplete/jsx2.js
@@ -0,0 +1,8 @@
+// @flow
+
+var React = require('react');
+
+class C extends React.Component {
+  props: { x: number, y: string };
+}
+<C x = 0, 
diff --git a/tests/autocomplete/num.js b/tests/autocomplete/num.js
new file mode 100644
index 000000000000..6a4a4f8cbe54
--- /dev/null
+++ b/tests/autocomplete/num.js
@@ -0,0 +1,4 @@
+// @flow
+
+var num = 123;
+num.
diff --git a/tests/autocomplete/object_builtins.js b/tests/autocomplete/object_builtins.js
new file mode 100644
index 000000000000..8d4d728635ef
--- /dev/null
+++ b/tests/autocomplete/object_builtins.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+function foo(o: Object) {
+  o.
+}
diff --git a/tests/autocomplete/optional.js b/tests/autocomplete/optional.js
new file mode 100644
index 000000000000..2fb8c3ce284f
--- /dev/null
+++ b/tests/autocomplete/optional.js
@@ -0,0 +1,5 @@
+// @flow
+
+function foo(obj: { x?: string, f: (x?: string) => void, o: { x?: string } }) {
+  return obj.
+}
diff --git a/tests/autocomplete/override.js b/tests/autocomplete/override.js
new file mode 100644
index 000000000000..6b2e3dae5f46
--- /dev/null
+++ b/tests/autocomplete/override.js
@@ -0,0 +1,10 @@
+// @flow
+
+class C {
+  override(): number | string { return 0; }
+}
+
+class D extends C {
+  foo() { return this.override() }
+  override(): string { return ""; }
+  bar() { this.
diff --git a/tests/autocomplete/qux.js b/tests/autocomplete/qux.js
new file mode 100644
index 000000000000..e25242a8acfb
--- /dev/null
+++ b/tests/autocomplete/qux.js
@@ -0,0 +1,6 @@
+// @flow
+
+class C { x: number; }
+
+var c: C = new C;
+c.
diff --git a/tests/autocomplete/str.js b/tests/autocomplete/str.js
new file mode 100644
index 000000000000..66e25873dc3c
--- /dev/null
+++ b/tests/autocomplete/str.js
@@ -0,0 +1,3 @@
+// @flow
+
+"hello".
diff --git a/tests/autocomplete/this.js b/tests/autocomplete/this.js
new file mode 100644
index 000000000000..8fb80158b295
--- /dev/null
+++ b/tests/autocomplete/this.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+// issue #1197
+class Foo {
+  baz: string;
+  bar() {}
+  hello() {
+    this.
+  }
+}
diff --git a/tests/autocomplete/typeparams.js b/tests/autocomplete/typeparams.js
new file mode 100644
index 000000000000..7231f4c719bb
--- /dev/null
+++ b/tests/autocomplete/typeparams.js
@@ -0,0 +1,8 @@
+// @flow
+
+class Bounds<N: number, F: () => N> {
+  foo: F;
+  bar() {
+    this.foo().
+  }
+}
diff --git a/tests/autocomplete/union.js b/tests/autocomplete/union.js
new file mode 100644
index 000000000000..ddf493f96c32
--- /dev/null
+++ b/tests/autocomplete/union.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+function foo(a: boolean, x: { bar: string }, y: Object) {
+  var z;
+  if (a) {
+    z = x;
+  } else {
+    z = y;
+  }
+  z.
+}
diff --git a/tests/autocomplete/unknown.js b/tests/autocomplete/unknown.js
new file mode 100644
index 000000000000..22090345cfd7
--- /dev/null
+++ b/tests/autocomplete/unknown.js
@@ -0,0 +1,2 @@
+// @noflow
+module.exports = { x: { y: "" } };
diff --git a/tests/auxiliary/__snapshots__/jsfmt.spec.js.snap b/tests/auxiliary/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1aed9affa598
--- /dev/null
+++ b/tests/auxiliary/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test client.js 1`] = `
+"var y:number = x;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var y: number = x;
+
+"
+`;
diff --git a/tests/auxiliary/client.js b/tests/auxiliary/client.js
new file mode 100644
index 000000000000..e3540c1251b2
--- /dev/null
+++ b/tests/auxiliary/client.js
@@ -0,0 +1 @@
+var y:number = x;
diff --git a/tests/auxiliary/jsfmt.spec.js b/tests/auxiliary/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/auxiliary/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/auxiliary/lib/__snapshots__/jsfmt.spec.js.snap b/tests/auxiliary/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..15f3efcda83f
--- /dev/null
+++ b/tests/auxiliary/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test lib.js 1`] = `
+"declare var x: string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare var x: string;
+
+"
+`;
diff --git a/tests/auxiliary/lib/jsfmt.spec.js b/tests/auxiliary/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/auxiliary/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/auxiliary/lib/lib.js b/tests/auxiliary/lib/lib.js
new file mode 100644
index 000000000000..e7640e569efc
--- /dev/null
+++ b/tests/auxiliary/lib/lib.js
@@ -0,0 +1 @@
+declare var x: string;
diff --git a/tests/binary/__snapshots__/jsfmt.spec.js.snap b/tests/binary/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d53527910e3c
--- /dev/null
+++ b/tests/binary/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,112 @@
+exports[`test in.js 1`] = `
+"// @flow
+
+let tests = [
+  // objects on RHS
+  function() {
+    ('foo' in {});
+    ('foo' in { foo: null });
+    (0 in {});
+    (0 in { "0": null });
+  },
+
+  // arrays on RHS
+  function() {
+    ('foo' in []);
+    (0 in []);
+    ('length' in []);
+  },
+
+  // primitive classes on RHS
+  function() {
+    ('foo' in new String('bar'));
+    ('foo' in new Number(123));
+  },
+
+  // primitives on RHS
+  function() {
+    ('foo' in 123); // error
+    ('foo' in 'bar'); // error
+    ('foo' in void 0); // error
+    ('foo' in null); // error
+  },
+
+  // bogus stuff on LHS
+  function() {
+    (null in {}); // error
+    (void 0 in {}); // error
+    ({} in {}); // error
+    ([] in {}); // error
+    (false in []); // error
+  },
+
+  // in predicates
+  function() {
+    if ('foo' in 123) {} // error
+    if (!'foo' in {}) {} // error, !'foo' is a boolean
+    if (!('foo' in {})) {}
+  },
+
+  // annotations on RHS
+  function(x: Object, y: mixed) {
+    ('foo' in x); // ok
+    ('foo' in y); // error
+  },
+]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // objects on RHS
+  function() {
+    "foo" in {};
+    "foo" in { foo: null };
+    0 in {};
+    0 in { "0": null };
+  },
+  // arrays on RHS
+  function() {
+    "foo" in [  ];
+    0 in [  ];
+    "length" in [  ];
+  },
+  // primitive classes on RHS
+  function() {
+    "foo" in new String("bar");
+    "foo" in new Number(123);
+  },
+  // primitives on RHS
+  function() {
+    "foo" in 123;// error
+    "foo" in "bar";// error
+    "foo" in void 0;// error
+    "foo" in null;// error
+  },
+  // bogus stuff on LHS
+  function() {
+    null in {};// error
+    void 0 in {};// error
+    ({}) in {};// error
+    [  ] in {};// error
+    false in [  ];// error
+  },
+  // in predicates
+  function() {
+    if ("foo" in 123) {
+      
+    }// error
+    if (!"foo" in {}) {
+      
+    }// error, !'foo' is a boolean
+    if (!("foo" in {})) {
+      
+    }
+  },
+  // annotations on RHS
+  function(x: Object, y: mixed) {
+    "foo" in x;// ok
+    "foo" in y;// error
+  }
+];
+
+"
+`;
diff --git a/tests/binary/in.js b/tests/binary/in.js
new file mode 100644
index 000000000000..a66b1d84f69b
--- /dev/null
+++ b/tests/binary/in.js
@@ -0,0 +1,54 @@
+// @flow
+
+let tests = [
+  // objects on RHS
+  function() {
+    ('foo' in {});
+    ('foo' in { foo: null });
+    (0 in {});
+    (0 in { "0": null });
+  },
+
+  // arrays on RHS
+  function() {
+    ('foo' in []);
+    (0 in []);
+    ('length' in []);
+  },
+
+  // primitive classes on RHS
+  function() {
+    ('foo' in new String('bar'));
+    ('foo' in new Number(123));
+  },
+
+  // primitives on RHS
+  function() {
+    ('foo' in 123); // error
+    ('foo' in 'bar'); // error
+    ('foo' in void 0); // error
+    ('foo' in null); // error
+  },
+
+  // bogus stuff on LHS
+  function() {
+    (null in {}); // error
+    (void 0 in {}); // error
+    ({} in {}); // error
+    ([] in {}); // error
+    (false in []); // error
+  },
+
+  // in predicates
+  function() {
+    if ('foo' in 123) {} // error
+    if (!'foo' in {}) {} // error, !'foo' is a boolean
+    if (!('foo' in {})) {}
+  },
+
+  // annotations on RHS
+  function(x: Object, y: mixed) {
+    ('foo' in x); // ok
+    ('foo' in y); // error
+  },
+]
diff --git a/tests/binary/jsfmt.spec.js b/tests/binary/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/binary/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/binding/__snapshots__/jsfmt.spec.js.snap b/tests/binding/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ba9f6c6fc639
--- /dev/null
+++ b/tests/binding/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,594 @@
+exports[`test const.js 1`] = `
+"const x = 0;
+
+// errors: const cannot be reassigned
+x++;
+x--;
+x += 0;
+x -= 0;
+x /= 0;
+x %= 0;
+x <<= 0
+x >>= 0;
+x >>>= 0;
+x |= 0;
+x ^= 0;
+x &= 0;
+
+// regression tests -- OK to assign consts like this:
+
+const { foo } = { foo: \"foo\" }
+const [ bar ] = [\"bar\"];
+(foo: number); // error: string ~> number
+(bar: number); // error: string ~> number
+
+declare var bazzes: { baz: string }[];
+for (const { baz } of bazzes) {
+  (baz: number); // error: string ~> number
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+const x = 0;
+// errors: const cannot be reassigned
+x++;
+x--;
+x += 0;
+x -= 0;
+x /= 0;
+x %= 0;
+x <<= 0;
+x >>= 0;
+x >>>= 0;
+x |= 0;
+x ^= 0;
+x &= 0;
+// regression tests -- OK to assign consts like this:
+const { foo } = { foo: \"foo\" };
+const [ bar ] = [ \"bar\" ];
+(foo: number);// error: string ~> number
+(bar: number);// error: string ~> number
+declare var bazzes: { baz: string }[];
+for (const { baz } of bazzes) {
+  (baz: number);// error: string ~> number
+}
+
+"
+`;
+
+exports[`test rebinding.js 1`] = `
+"/* @flow
+ * test errors on illegal rebinding/reassignment
+ *
+ *       type class let const var (reassign)
+ * type  x    x      x   x     x   x
+ * class x    x      x   x     x
+ * let   x    x      x   x     x
+ * const x    x      x   x     x   x
+ * var   x    x      x   x
+ */
+
+// type x *
+
+function type_type() {
+  type A = number;
+  type A = number;  // error: name already bound
+}
+
+function type_class() {
+  type A = number;
+  class A {}        // error: name already bound
+}
+
+function type_let() {
+  type A = number;
+  let A = 0;        // error: name already bound
+}
+
+function type_const() {
+  type A = number;
+  const A = 0;     // error: name already bound
+}
+
+function type_var() {
+  type A = number;
+  var A = 0;        // error: name already bound
+}
+
+function type_reassign() {
+  type A = number;
+  A = 42;           // error: type alias ref\'d from value pos
+}
+
+// class x *
+
+function class_type() {
+  class A {}
+  type A = number;  // error: name already bound
+}
+
+function class_class() {
+  class A {}
+  class A {}        // error: name already bound
+}
+
+function class_let() {
+  class A {}
+  let A = 0;        // error: name already bound
+}
+
+function class_const() {
+  class A {}
+  const A = 0;     // error: name already bound
+}
+
+function class_var() {
+  class A {}
+  var A = 0;        // error: name already bound
+}
+
+// let x *
+
+function let_type() {
+  let A = 0;
+  type A = number;  // error: name already bound
+}
+
+function let_class() {
+  let A = 0;
+  class A {}        // error: name already bound
+}
+
+function let_let() {
+  let A = 0;
+  let A = 0;        // error: name already bound
+}
+
+function let_const() {
+  let A = 0;
+  const A = 0;     // error: name already bound
+}
+
+function let_var() {
+  let A = 0;
+  var A = 0;        // error: name already bound
+}
+
+// const x *
+
+function const_type() {
+  const A = 0;
+  type A = number;  // error: name already bound
+}
+
+function const_class() {
+  const A = 0;
+  class A {}        // error: name already bound
+}
+
+function const_let() {
+  const A = 0;
+  let A = 0;        // error: name already bound
+}
+
+function const_const() {
+  const A = 0;
+  const A = 0;     // error: name already bound
+}
+
+function const_var() {
+  const A = 0;
+  var A = 0;        // error: name already bound
+}
+
+function const_reassign() {
+  const A = 0;
+  A = 42;           // error: cannot be reassigned
+}
+
+// var x *
+
+function var_type() {
+  var A = 0;
+  type A = number;  // error: name already bound
+}
+
+function var_class() {
+  var A = 0;
+  class A {}        // error: name already bound
+}
+
+function var_let() {
+  var A = 0;
+  let A = 0;        // error: name already bound
+}
+
+function var_const() {
+  var A = 0;
+  const A = 0;      // error: name already bound
+}
+
+function var_var() {
+  var A = 0;
+  var A = 0;       // OK
+}
+
+// function x *
+
+function function_toplevel() {
+  function a() {};
+  function a() {}; // OK
+}
+
+function function_block() {
+  {
+    function a() {};
+    function a() {}; // error: name already bound
+  }
+}
+
+// corner cases
+
+function var_shadow_nested_scope() {
+  {
+    let x = 0;
+    {
+      var x = 0; // error: name already bound
+    }
+  }
+}
+
+function type_shadow_nested_scope() {
+  {
+    let x = 0;
+    {
+      type x = string; // error: name already bound
+    }
+  }
+}
+
+// fn params name clash
+
+function fn_params_name_clash(x, x /* error: x already bound */) {}
+function fn_params_clash_fn_binding(x,y) {
+  let x = 0; // error: x already bound
+  var y = 0; // OK
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Argument name clash in strict mode (193:33)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$2.checkLVal (/node_modules/babylon/lib/index.js:3007:16)
+    at Parser.checkLVal (/node_modules/babylon/lib/index.js:5446:22)
+    at Parser.pp$3.parseFunctionBody (/node_modules/babylon/lib/index.js:4072:12)
+    at Parser.parseFunctionBody (/node_modules/babylon/lib/index.js:5211:20)
+    at Parser.pp$1.parseFunction (/node_modules/babylon/lib/index.js:2257:8)
+    at Parser.pp$1.parseFunctionStatement (/node_modules/babylon/lib/index.js:1926:15)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1712:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+"
+`;
+
+exports[`test scope.js 1`] = `
+"function block_scope() {
+  let a: number = 0;
+  var b: number = 0;
+  {
+    let a = \"\"; // ok: local to block
+    var b = \"\"; // error: string ~> number
+  }
+}
+
+function switch_scope(x: string) {
+  let a: number = 0;
+  var b: number = 0;
+  switch (x) {
+    case \"foo\":
+      let a = \"\"; // ok: local to switch
+      var b = \"\"; // error: string ~> number
+      break;
+    case \"bar\":
+      let a = \"\"; // error: a already bound in switch
+      break;
+  }
+}
+
+// a switch is a single lexical scope, so lets and non-disjoint
+// cases can mix in odd ways. our support for edge cases is not
+// yet perfect.
+function switch_scope2(x: number) {
+  switch (x) {
+    case 0:
+     a = \"\";     // error: assign before declaration
+     break;
+    case 1:
+     var b = a;  // error: use before declaration
+     break;
+    case 2:
+      let a = \"\";
+      break;
+    case 3:
+      a = \"\";     // error: skipped initializer
+      break;
+    case 4:
+      var c:string = a;  // error: skipped initializer
+      break;
+  }
+  a = \"\"; // error: a no longer in scope
+}
+
+function try_scope() {
+  let a: number = 0;
+  try {
+    let a = \"\"; // ok
+  } catch (e) {
+    let a = \"\"; // ok
+  } finally {
+    let a = \"\"; // ok
+  }
+}
+
+function for_scope_let() {
+  let a: number = 0;
+  for (let a = \"\" /* ok: local to init */;;) {}
+}
+
+function for_scope_var() {
+  var a: number = 0;
+  for (var a = \"\" /* error: string ~> number */;;) {}
+}
+
+function for_in_scope_let(o: Object) {
+  let a: number = 0;
+  for (let a /* ok: local to init */ in o) {}
+}
+
+function for_in_scope_var(o: Object) {
+  var a: number = 0;
+  for (var a /* error: string ~> number */ in o) {}
+}
+
+function for_of_scope_let(xs: string[]) {
+  let a: number = 0;
+  for (let a /* ok: local to init */ of xs) {}
+}
+
+function for_of_scope_var(xs: string[]) {
+  var a: number = 0;
+  for (var a /* error: string ~> number */ of xs) {}
+}
+
+function default_param_1() {
+  // function binding in scope in default expr
+  function f(
+    x: () => string = f // error: number ~> string
+  ): number {
+    return 0;
+  }
+}
+
+function default_param_2() {
+  // fn body bindings not visible from param scope
+  let a = \"\";
+  function f0(x = () => a): number {
+    let a = 0;
+    return x(); // error: string ~> number
+  }
+  function f1(x = b /* error: cannot resolve b */): number {
+    let b = 0;
+    return x;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test tdz.js 1`] = `
+"/** @flow */
+
+// -- types ---
+
+// type aliases are hoisted and always available
+
+type T1 = T2;   // ok
+type T2 = number;
+
+// --- lets ---
+
+// to be correct, we would
+// - not allow forward refs to lets from value positions,
+// while let is in TDZ.
+// - allow forward refs to lets from type positions.
+//
+// currently we\'re too lenient about TDZ in closures -
+// from value positions, we currently enforce TDZ only in-scope.
+// this is unsound - a let or const may remain uninitialized when
+// a lambda runs. But a simple conservative approach would prohibit
+// forward references to let/consts from within lambdas entirely,
+// which would be annoying. TODO
+
+function f0() {
+  var v = x * c;  // errors, let + const referenced before decl
+  let x = 0;
+  const c = 0;
+}
+
+function f1(b) {
+  x = 10;         // error, attempt to write to let before decl
+  let x = 0;
+  if (b) {
+    y = 10;       // error, attempt to write to let before decl
+    let y = 0;
+  }
+}
+
+function f2() {
+  {
+    var v = x * c; // errors, let + const referenced before decl
+  }
+  let x = 0;
+  const c = 0;
+}
+
+// functions are let-scoped and hoisted
+function f3() {
+  var s: string = foo();          // ok, finds hoisted outer
+  {
+    var n: number = foo();        // ok, finds hoisted inner
+    function foo() { return 0; }
+  }
+  var s2: string = foo();         // ok, hoisted outer not clobbered
+  function foo() { return \"\"; }
+}
+
+// out-of-scope TDZ not enforced. sometimes right...
+function f4() {
+  function g() { return x + c; }  // ok, g doesn\'t run in TDZ
+  let x = 0;
+  const c = 0;
+}
+
+// ...sometimes wrong
+function f5() {
+  function g() { return x; }
+  g();          // should error, but doesn\'t currently
+  let x = 0;
+  const c = 0;
+}
+
+// - from type positions, we currently error on forward refs to any
+// value (i.e., class or function). this is a basic flaw in our
+// phasing of AST traversal, and will be fixed.
+//
+
+var x: C;       // ok
+
+var y = new C(); // error: let ref before decl from value position
+
+class C {}
+
+var z: C = new C(); // ok
+
+// --- vars ---
+
+// it\'s possible to annotate a var with a non-maybe type,
+// but leave it uninitialized until later (as long as it\'s
+// initialized before use)
+
+var a: number;  // not an error per se - only if used before init
+
+function f(n: number) { return n; }
+
+f(a); // error: undefined ~/> number
+
+a = 10;
+
+f(a); // ok, a: number (not ?number)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/** @flow */
+// -- types ---
+// type aliases are hoisted and always available
+type T1 = T2;// ok
+type T2 = number;
+// --- lets ---
+// to be correct, we would
+// - not allow forward refs to lets from value positions,
+// while let is in TDZ.
+// - allow forward refs to lets from type positions.
+//
+// currently we\'re too lenient about TDZ in closures -
+// from value positions, we currently enforce TDZ only in-scope.
+// this is unsound - a let or const may remain uninitialized when
+// a lambda runs. But a simple conservative approach would prohibit
+// forward references to let/consts from within lambdas entirely,
+// which would be annoying. TODO
+function f0() {
+  var v = x * c;// errors, let + const referenced before decl
+  let x = 0;
+  const c = 0;
+}
+function f1(b) {
+  x = 10;// error, attempt to write to let before decl
+  let x = 0;
+  if (b) {
+    y = 10;// error, attempt to write to let before decl
+    let y = 0;
+  }
+}
+function f2() {
+  {
+    var v = x * c;// errors, let + const referenced before decl
+  }
+  let x = 0;
+  const c = 0;
+}
+// functions are let-scoped and hoisted
+function f3() {
+  var s: string = foo();// ok, finds hoisted outer
+  {
+    var n: number = foo();// ok, finds hoisted inner
+    function foo() {
+      return 0;
+    }
+  }
+  var s2: string = foo();// ok, hoisted outer not clobbered
+  function foo() {
+    return \"\";
+  }
+}
+// out-of-scope TDZ not enforced. sometimes right...
+function f4() {
+  function g() {
+    return x + c;
+  }// ok, g doesn\'t run in TDZ
+  let x = 0;
+  const c = 0;
+}
+// ...sometimes wrong
+function f5() {
+  function g() {
+    return x;
+  }
+  g();// should error, but doesn\'t currently
+  let x = 0;
+  const c = 0;
+}
+// - from type positions, we currently error on forward refs to any
+// value (i.e., class or function). this is a basic flaw in our
+// phasing of AST traversal, and will be fixed.
+//
+var x: C;// ok
+var y = new C();// error: let ref before decl from value position
+class C {}
+var z: C = new C();// ok
+// --- vars ---
+// it\'s possible to annotate a var with a non-maybe type,
+// but leave it uninitialized until later (as long as it\'s
+// initialized before use)
+var a: number;// not an error per se - only if used before init
+function f(n: number) {
+  return n;
+}
+f(a);// error: undefined ~/> number
+a = 10;
+f(a);// ok, a: number (not ?number)
+
+"
+`;
diff --git a/tests/binding/const.js b/tests/binding/const.js
new file mode 100644
index 000000000000..387e96cb0fa2
--- /dev/null
+++ b/tests/binding/const.js
@@ -0,0 +1,27 @@
+const x = 0;
+
+// errors: const cannot be reassigned
+x++;
+x--;
+x += 0;
+x -= 0;
+x /= 0;
+x %= 0;
+x <<= 0
+x >>= 0;
+x >>>= 0;
+x |= 0;
+x ^= 0;
+x &= 0;
+
+// regression tests -- OK to assign consts like this:
+
+const { foo } = { foo: "foo" }
+const [ bar ] = ["bar"];
+(foo: number); // error: string ~> number
+(bar: number); // error: string ~> number
+
+declare var bazzes: { baz: string }[];
+for (const { baz } of bazzes) {
+  (baz: number); // error: string ~> number
+}
diff --git a/tests/binding/jsfmt.spec.js b/tests/binding/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/binding/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/binding/rebinding.js b/tests/binding/rebinding.js
new file mode 100644
index 000000000000..195f096b3f54
--- /dev/null
+++ b/tests/binding/rebinding.js
@@ -0,0 +1,197 @@
+/* @flow
+ * test errors on illegal rebinding/reassignment
+ *
+ *       type class let const var (reassign)
+ * type  x    x      x   x     x   x
+ * class x    x      x   x     x
+ * let   x    x      x   x     x
+ * const x    x      x   x     x   x
+ * var   x    x      x   x
+ */
+
+// type x *
+
+function type_type() {
+  type A = number;
+  type A = number;  // error: name already bound
+}
+
+function type_class() {
+  type A = number;
+  class A {}        // error: name already bound
+}
+
+function type_let() {
+  type A = number;
+  let A = 0;        // error: name already bound
+}
+
+function type_const() {
+  type A = number;
+  const A = 0;     // error: name already bound
+}
+
+function type_var() {
+  type A = number;
+  var A = 0;        // error: name already bound
+}
+
+function type_reassign() {
+  type A = number;
+  A = 42;           // error: type alias ref'd from value pos
+}
+
+// class x *
+
+function class_type() {
+  class A {}
+  type A = number;  // error: name already bound
+}
+
+function class_class() {
+  class A {}
+  class A {}        // error: name already bound
+}
+
+function class_let() {
+  class A {}
+  let A = 0;        // error: name already bound
+}
+
+function class_const() {
+  class A {}
+  const A = 0;     // error: name already bound
+}
+
+function class_var() {
+  class A {}
+  var A = 0;        // error: name already bound
+}
+
+// let x *
+
+function let_type() {
+  let A = 0;
+  type A = number;  // error: name already bound
+}
+
+function let_class() {
+  let A = 0;
+  class A {}        // error: name already bound
+}
+
+function let_let() {
+  let A = 0;
+  let A = 0;        // error: name already bound
+}
+
+function let_const() {
+  let A = 0;
+  const A = 0;     // error: name already bound
+}
+
+function let_var() {
+  let A = 0;
+  var A = 0;        // error: name already bound
+}
+
+// const x *
+
+function const_type() {
+  const A = 0;
+  type A = number;  // error: name already bound
+}
+
+function const_class() {
+  const A = 0;
+  class A {}        // error: name already bound
+}
+
+function const_let() {
+  const A = 0;
+  let A = 0;        // error: name already bound
+}
+
+function const_const() {
+  const A = 0;
+  const A = 0;     // error: name already bound
+}
+
+function const_var() {
+  const A = 0;
+  var A = 0;        // error: name already bound
+}
+
+function const_reassign() {
+  const A = 0;
+  A = 42;           // error: cannot be reassigned
+}
+
+// var x *
+
+function var_type() {
+  var A = 0;
+  type A = number;  // error: name already bound
+}
+
+function var_class() {
+  var A = 0;
+  class A {}        // error: name already bound
+}
+
+function var_let() {
+  var A = 0;
+  let A = 0;        // error: name already bound
+}
+
+function var_const() {
+  var A = 0;
+  const A = 0;      // error: name already bound
+}
+
+function var_var() {
+  var A = 0;
+  var A = 0;       // OK
+}
+
+// function x *
+
+function function_toplevel() {
+  function a() {};
+  function a() {}; // OK
+}
+
+function function_block() {
+  {
+    function a() {};
+    function a() {}; // error: name already bound
+  }
+}
+
+// corner cases
+
+function var_shadow_nested_scope() {
+  {
+    let x = 0;
+    {
+      var x = 0; // error: name already bound
+    }
+  }
+}
+
+function type_shadow_nested_scope() {
+  {
+    let x = 0;
+    {
+      type x = string; // error: name already bound
+    }
+  }
+}
+
+// fn params name clash
+
+function fn_params_name_clash(x, x /* error: x already bound */) {}
+function fn_params_clash_fn_binding(x,y) {
+  let x = 0; // error: x already bound
+  var y = 0; // OK
+}
diff --git a/tests/binding/scope.js b/tests/binding/scope.js
new file mode 100644
index 000000000000..8aa169fad3e8
--- /dev/null
+++ b/tests/binding/scope.js
@@ -0,0 +1,109 @@
+function block_scope() {
+  let a: number = 0;
+  var b: number = 0;
+  {
+    let a = ""; // ok: local to block
+    var b = ""; // error: string ~> number
+  }
+}
+
+function switch_scope(x: string) {
+  let a: number = 0;
+  var b: number = 0;
+  switch (x) {
+    case "foo":
+      let a = ""; // ok: local to switch
+      var b = ""; // error: string ~> number
+      break;
+    case "bar":
+      let a = ""; // error: a already bound in switch
+      break;
+  }
+}
+
+// a switch is a single lexical scope, so lets and non-disjoint
+// cases can mix in odd ways. our support for edge cases is not
+// yet perfect.
+function switch_scope2(x: number) {
+  switch (x) {
+    case 0:
+     a = "";     // error: assign before declaration
+     break;
+    case 1:
+     var b = a;  // error: use before declaration
+     break;
+    case 2:
+      let a = "";
+      break;
+    case 3:
+      a = "";     // error: skipped initializer
+      break;
+    case 4:
+      var c:string = a;  // error: skipped initializer
+      break;
+  }
+  a = ""; // error: a no longer in scope
+}
+
+function try_scope() {
+  let a: number = 0;
+  try {
+    let a = ""; // ok
+  } catch (e) {
+    let a = ""; // ok
+  } finally {
+    let a = ""; // ok
+  }
+}
+
+function for_scope_let() {
+  let a: number = 0;
+  for (let a = "" /* ok: local to init */;;) {}
+}
+
+function for_scope_var() {
+  var a: number = 0;
+  for (var a = "" /* error: string ~> number */;;) {}
+}
+
+function for_in_scope_let(o: Object) {
+  let a: number = 0;
+  for (let a /* ok: local to init */ in o) {}
+}
+
+function for_in_scope_var(o: Object) {
+  var a: number = 0;
+  for (var a /* error: string ~> number */ in o) {}
+}
+
+function for_of_scope_let(xs: string[]) {
+  let a: number = 0;
+  for (let a /* ok: local to init */ of xs) {}
+}
+
+function for_of_scope_var(xs: string[]) {
+  var a: number = 0;
+  for (var a /* error: string ~> number */ of xs) {}
+}
+
+function default_param_1() {
+  // function binding in scope in default expr
+  function f(
+    x: () => string = f // error: number ~> string
+  ): number {
+    return 0;
+  }
+}
+
+function default_param_2() {
+  // fn body bindings not visible from param scope
+  let a = "";
+  function f0(x = () => a): number {
+    let a = 0;
+    return x(); // error: string ~> number
+  }
+  function f1(x = b /* error: cannot resolve b */): number {
+    let b = 0;
+    return x;
+  }
+}
diff --git a/tests/binding/tdz.js b/tests/binding/tdz.js
new file mode 100644
index 000000000000..da081b0999c1
--- /dev/null
+++ b/tests/binding/tdz.js
@@ -0,0 +1,100 @@
+/** @flow */
+
+// -- types ---
+
+// type aliases are hoisted and always available
+
+type T1 = T2;   // ok
+type T2 = number;
+
+// --- lets ---
+
+// to be correct, we would
+// - not allow forward refs to lets from value positions,
+// while let is in TDZ.
+// - allow forward refs to lets from type positions.
+//
+// currently we're too lenient about TDZ in closures -
+// from value positions, we currently enforce TDZ only in-scope.
+// this is unsound - a let or const may remain uninitialized when
+// a lambda runs. But a simple conservative approach would prohibit
+// forward references to let/consts from within lambdas entirely,
+// which would be annoying. TODO
+
+function f0() {
+  var v = x * c;  // errors, let + const referenced before decl
+  let x = 0;
+  const c = 0;
+}
+
+function f1(b) {
+  x = 10;         // error, attempt to write to let before decl
+  let x = 0;
+  if (b) {
+    y = 10;       // error, attempt to write to let before decl
+    let y = 0;
+  }
+}
+
+function f2() {
+  {
+    var v = x * c; // errors, let + const referenced before decl
+  }
+  let x = 0;
+  const c = 0;
+}
+
+// functions are let-scoped and hoisted
+function f3() {
+  var s: string = foo();          // ok, finds hoisted outer
+  {
+    var n: number = foo();        // ok, finds hoisted inner
+    function foo() { return 0; }
+  }
+  var s2: string = foo();         // ok, hoisted outer not clobbered
+  function foo() { return ""; }
+}
+
+// out-of-scope TDZ not enforced. sometimes right...
+function f4() {
+  function g() { return x + c; }  // ok, g doesn't run in TDZ
+  let x = 0;
+  const c = 0;
+}
+
+// ...sometimes wrong
+function f5() {
+  function g() { return x; }
+  g();          // should error, but doesn't currently
+  let x = 0;
+  const c = 0;
+}
+
+// - from type positions, we currently error on forward refs to any
+// value (i.e., class or function). this is a basic flaw in our
+// phasing of AST traversal, and will be fixed.
+//
+
+var x: C;       // ok
+
+var y = new C(); // error: let ref before decl from value position
+
+class C {}
+
+var z: C = new C(); // ok
+
+// --- vars ---
+
+// it's possible to annotate a var with a non-maybe type,
+// but leave it uninitialized until later (as long as it's
+// initialized before use)
+
+var a: number;  // not an error per se - only if used before init
+
+function f(n: number) { return n; }
+
+f(a); // error: undefined ~/> number
+
+a = 10;
+
+f(a); // ok, a: number (not ?number)
diff --git a/tests/bom/FormData.js b/tests/bom/FormData.js
new file mode 100644
index 000000000000..79db76483ad1
--- /dev/null
+++ b/tests/bom/FormData.js
@@ -0,0 +1,67 @@
+/* @flow */
+
+// constructor
+const a: FormData = new FormData(); // correct
+new FormData(''); // incorrect
+new FormData(document.createElement('input')); // incorrect
+new FormData(document.createElement('form')); // correct
+
+// has
+const b: boolean = a.has('foo'); // correct
+
+// get
+const c: ?(string | File) = a.get('foo'); // correct
+const d: string = a.get('foo'); // incorrect
+const e: Blob = a.get('foo'); // incorrect
+const f: ?(string | File | Blob) = a.get('foo'); // incorrect
+a.get(2); // incorrect
+
+// getAll
+const a1: Array<string | File> = a.getAll('foo'); // correct
+const a2: Array<string | File | number> = a.getAll('foo'); // incorrect
+const a3: Array<string | Blob | File> = a.getAll('foo'); // incorrect
+a.getAll(23); // incorrect
+
+// set
+a.set('foo', 'bar'); // correct
+a.set('foo', {}); // incorrect
+a.set(2, 'bar'); // incorrect
+a.set('foo', 'bar', 'baz'); // incorrect
+a.set('bar', new File([], 'q')) // correct
+a.set('bar', new File([], 'q'), 'x') // correct
+a.set('bar', new File([], 'q'), 2) // incorrect
+a.set('bar', new Blob) // correct
+a.set('bar', new Blob, 'x') // correct
+a.set('bar', new Blob, 2) // incorrect
+
+// append
+a.append('foo', 'bar'); // correct
+a.append('foo', {}); // incorrect
+a.append(2, 'bar'); // incorrect
+a.append('foo', 'bar', 'baz'); // incorrect
+a.append('foo', 'bar'); // incorrect
+a.append('bar', new File([], 'q')) // correct
+a.append('bar', new File([], 'q'), 'x') // correct
+a.append('bar', new File([], 'q'), 2) // incorrect
+a.append('bar', new Blob) // correct
+a.append('bar', new Blob, 'x') // correct
+a.append('bar', new Blob, 2) // incorrect
+
+// delete
+a.delete('xx'); // correct
+a.delete(3); // incorrect
+
+// keys
+for (let x: string of a.keys()) {} // correct
+for (let x: number of a.keys()) {} // incorrect
+
+// values
+for (let x: string | File of a.values()) {} // correct
+for (let x: string | File | Blob of a.values()) {} // incorrect
+
+// entries
+for (let [x, y]: [string, string | File] of a.entries()) {} // correct
+for (let [x, y]: [string, string | File | Blob] of a.entries()) {} // incorrect
+for (let [x, y]: [number, string] of a.entries()) {} // incorrect
+for (let [x, y]: [string, number] of a.entries()) {} // incorrect
+for (let [x, y]: [number, number] of a.entries()) {} // incorrect
diff --git a/tests/bom/MutationObserver.js b/tests/bom/MutationObserver.js
new file mode 100644
index 000000000000..e1d588b5f7a8
--- /dev/null
+++ b/tests/bom/MutationObserver.js
@@ -0,0 +1,29 @@
+/* @flow */
+
+// constructor
+function callback(arr: Array<MutationRecord>, observer: MutationObserver): void {
+  return;
+}
+const o: MutationObserver = new MutationObserver(callback); // correct
+new MutationObserver((arr: Array<MutationRecord>) => true); // correct
+new MutationObserver(() => {}); // correct
+new MutationObserver(); // incorrect
+new MutationObserver(42); // incorrect
+new MutationObserver((n: number) => {}); // incorrect
+
+// observe
+const div = document.createElement('div');
+o.observe(div, { attributes: true, attributeFilter: ['style'] }); // correct
+o.observe(div, { characterData: true, invalid: true }); // correct
+o.observe(); // incorrect
+o.observe('invalid'); // incorrect
+o.observe(div); // incorrect
+o.observe(div, {}); // incorrect
+o.observe(div, { subtree: true }); // incorrect
+o.observe(div, { attributes: true, attributeFilter: true }); // incorrect
+
+// takeRecords
+o.takeRecords(); // correct
+
+// disconnect
+o.disconnect(); // correct
diff --git a/tests/bom/__snapshots__/jsfmt.spec.js.snap b/tests/bom/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6483f642c78d
--- /dev/null
+++ b/tests/bom/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,135 @@
+exports[`test FormData.js 1`] = `
+"/* @flow */
+
+// constructor
+const a: FormData = new FormData(); // correct
+new FormData(\'\'); // incorrect
+new FormData(document.createElement(\'input\')); // incorrect
+new FormData(document.createElement(\'form\')); // correct
+
+// has
+const b: boolean = a.has(\'foo\'); // correct
+
+// get
+const c: ?(string | File) = a.get(\'foo\'); // correct
+const d: string = a.get(\'foo\'); // incorrect
+const e: Blob = a.get(\'foo\'); // incorrect
+const f: ?(string | File | Blob) = a.get(\'foo\'); // incorrect
+a.get(2); // incorrect
+
+// getAll
+const a1: Array<string | File> = a.getAll(\'foo\'); // correct
+const a2: Array<string | File | number> = a.getAll(\'foo\'); // incorrect
+const a3: Array<string | Blob | File> = a.getAll(\'foo\'); // incorrect
+a.getAll(23); // incorrect
+
+// set
+a.set(\'foo\', \'bar\'); // correct
+a.set(\'foo\', {}); // incorrect
+a.set(2, \'bar\'); // incorrect
+a.set(\'foo\', \'bar\', \'baz\'); // incorrect
+a.set(\'bar\', new File([], \'q\')) // correct
+a.set(\'bar\', new File([], \'q\'), \'x\') // correct
+a.set(\'bar\', new File([], \'q\'), 2) // incorrect
+a.set(\'bar\', new Blob) // correct
+a.set(\'bar\', new Blob, \'x\') // correct
+a.set(\'bar\', new Blob, 2) // incorrect
+
+// append
+a.append(\'foo\', \'bar\'); // correct
+a.append(\'foo\', {}); // incorrect
+a.append(2, \'bar\'); // incorrect
+a.append(\'foo\', \'bar\', \'baz\'); // incorrect
+a.append(\'foo\', \'bar\'); // incorrect
+a.append(\'bar\', new File([], \'q\')) // correct
+a.append(\'bar\', new File([], \'q\'), \'x\') // correct
+a.append(\'bar\', new File([], \'q\'), 2) // incorrect
+a.append(\'bar\', new Blob) // correct
+a.append(\'bar\', new Blob, \'x\') // correct
+a.append(\'bar\', new Blob, 2) // incorrect
+
+// delete
+a.delete(\'xx\'); // correct
+a.delete(3); // incorrect
+
+// keys
+for (let x: string of a.keys()) {} // correct
+for (let x: number of a.keys()) {} // incorrect
+
+// values
+for (let x: string | File of a.values()) {} // correct
+for (let x: string | File | Blob of a.values()) {} // incorrect
+
+// entries
+for (let [x, y]: [string, string | File] of a.entries()) {} // correct
+for (let [x, y]: [string, string | File | Blob] of a.entries()) {} // incorrect
+for (let [x, y]: [number, string] of a.entries()) {} // incorrect
+for (let [x, y]: [string, number] of a.entries()) {} // incorrect
+for (let [x, y]: [number, number] of a.entries()) {} // incorrect
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1412:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test MutationObserver.js 1`] = `
+"/* @flow */
+
+// constructor
+function callback(arr: Array<MutationRecord>, observer: MutationObserver): void {
+  return;
+}
+const o: MutationObserver = new MutationObserver(callback); // correct
+new MutationObserver((arr: Array<MutationRecord>) => true); // correct
+new MutationObserver(() => {}); // correct
+new MutationObserver(); // incorrect
+new MutationObserver(42); // incorrect
+new MutationObserver((n: number) => {}); // incorrect
+
+// observe
+const div = document.createElement(\'div\');
+o.observe(div, { attributes: true, attributeFilter: [\'style\'] }); // correct
+o.observe(div, { characterData: true, invalid: true }); // correct
+o.observe(); // incorrect
+o.observe(\'invalid\'); // incorrect
+o.observe(div); // incorrect
+o.observe(div, {}); // incorrect
+o.observe(div, { subtree: true }); // incorrect
+o.observe(div, { attributes: true, attributeFilter: true }); // incorrect
+
+// takeRecords
+o.takeRecords(); // correct
+
+// disconnect
+o.disconnect(); // correct
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/bom/jsfmt.spec.js b/tests/bom/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/bom/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/bounded_poly/__snapshots__/jsfmt.spec.js.snap b/tests/bounded_poly/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..609f1e49a3b5
--- /dev/null
+++ b/tests/bounded_poly/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,68 @@
+exports[`test scope.js 1`] = `
+"function foo<X, Y:X>(x:X, y:Y):void { }
+foo(0, \"\");
+
+function bar<X:number, Y:X>(x:X, y:Y): number { return y*0; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"function foo<T: number>(x: T): T {
+    var _ = x * 1; // OK
+    var y: string = x; // error
+    return x; // OK
+}
+
+class C<T: number> {
+    bar<U: number>(x: U): T {
+        return x; // error, since T: number and U: number does not imply U: T
+    }
+    qux<U: T>(x: U): T {
+        var _ = x * 1; // OK, since T: number and U: T implies U: number
+        var y: string = x; // error
+        return x; // OK, since U: T
+    }
+}
+
+function example<T: {x: number}>(o: T): T { o.x = 0; return o; }
+var obj1: {x: number; y: string} = example({x: 0, y: \"\"});
+var obj2: {x: number} = example({x: 0});
+
+var c: C<string> = new C; // error, since T = string is incompatible with number
+var q: number = c.qux(0);
+/* 2 more errors, since argument U = number is incompatible with T = string, and
+ * result T = string is incompatible with number */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/bounded_poly/jsfmt.spec.js b/tests/bounded_poly/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/bounded_poly/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/bounded_poly/scope.js b/tests/bounded_poly/scope.js
new file mode 100644
index 000000000000..0bade54aae3c
--- /dev/null
+++ b/tests/bounded_poly/scope.js
@@ -0,0 +1,4 @@
+function foo<X, Y:X>(x:X, y:Y):void { }
+foo(0, "");
+
+function bar<X:number, Y:X>(x:X, y:Y): number { return y*0; }
diff --git a/tests/bounded_poly/test.js b/tests/bounded_poly/test.js
new file mode 100644
index 000000000000..cddb17861a72
--- /dev/null
+++ b/tests/bounded_poly/test.js
@@ -0,0 +1,25 @@
+function foo<T: number>(x: T): T {
+    var _ = x * 1; // OK
+    var y: string = x; // error
+    return x; // OK
+}
+
+class C<T: number> {
+    bar<U: number>(x: U): T {
+        return x; // error, since T: number and U: number does not imply U: T
+    }
+    qux<U: T>(x: U): T {
+        var _ = x * 1; // OK, since T: number and U: T implies U: number
+        var y: string = x; // error
+        return x; // OK, since U: T
+    }
+}
+
+function example<T: {x: number}>(o: T): T { o.x = 0; return o; }
+var obj1: {x: number; y: string} = example({x: 0, y: ""});
+var obj2: {x: number} = example({x: 0});
+
+var c: C<string> = new C; // error, since T = string is incompatible with number
+var q: number = c.qux(0);
+/* 2 more errors, since argument U = number is incompatible with T = string, and
+ * result T = string is incompatible with number */
diff --git a/tests/break/__snapshots__/jsfmt.spec.js.snap b/tests/break/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..03752e1fb8e3
--- /dev/null
+++ b/tests/break/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,87 @@
+exports[`test break.js 1`] = `
+"function foo(b) {
+    var x = b ? null: false;
+    var z;
+    while(b) {
+        if (x == null) { z = \"\"; break; }
+        var y:number = x; // error: boolean !~> number
+    }
+    var w:number = z; // 2 errors: ?string !~> number
+}
+
+function bar(b) {
+    var x = b ? null: false;
+    if (x == null) return;
+    switch (\"\") {
+    case 0:
+        var y:number = x; // error: boolean !~> number
+        x = \"\";
+    case 1:
+        var z:number = x; // 2 errors: (boolean | string) !~> number
+        break;
+    case 2:
+    }
+    var w:number = x; // 2 errors: (boolean | string) !~> number
+}
+
+function bar2(b) {
+    var x = b ? null: false;
+    if (x == null) return;
+    switch (\"\") {
+    case 0: {
+      let y:number = x; // error: boolean !~> number
+      x = \"\";
+    }
+    case 1: {
+      let z:number = x; // 2 errors: (boolean | string) !~> number
+      break;
+    }
+    case 2:
+    }
+    var w:number = x; // 2 errors: (boolean | string) !~> number
+}
+
+function qux(b) {
+    var z = 0;
+    while(b) {
+        var y:number = z;
+        if (b) { z = \"\"; continue; } // error: string !~> number
+        z = 0;
+    }
+    var w:number = z; // error: string !~> number
+}
+
+// same basic test as foo(), but with const. probes the
+// logic that still uses havoc to do env resets.
+function test_const() {
+  let st: string = \'abc\';
+
+  for (let i = 1; i < 100; i++) {
+    const fooRes: ?string = \"HEY\";
+    if (!fooRes) {
+      break;
+    }
+
+    st = fooRes; // no error
+  }
+
+  return st;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/break/break.js b/tests/break/break.js
new file mode 100644
index 000000000000..67986714a41d
--- /dev/null
+++ b/tests/break/break.js
@@ -0,0 +1,68 @@
+function foo(b) {
+    var x = b ? null: false;
+    var z;
+    while(b) {
+        if (x == null) { z = ""; break; }
+        var y:number = x; // error: boolean !~> number
+    }
+    var w:number = z; // 2 errors: ?string !~> number
+}
+
+function bar(b) {
+    var x = b ? null: false;
+    if (x == null) return;
+    switch ("") {
+    case 0:
+        var y:number = x; // error: boolean !~> number
+        x = "";
+    case 1:
+        var z:number = x; // 2 errors: (boolean | string) !~> number
+        break;
+    case 2:
+    }
+    var w:number = x; // 2 errors: (boolean | string) !~> number
+}
+
+function bar2(b) {
+    var x = b ? null: false;
+    if (x == null) return;
+    switch ("") {
+    case 0: {
+      let y:number = x; // error: boolean !~> number
+      x = "";
+    }
+    case 1: {
+      let z:number = x; // 2 errors: (boolean | string) !~> number
+      break;
+    }
+    case 2:
+    }
+    var w:number = x; // 2 errors: (boolean | string) !~> number
+}
+
+function qux(b) {
+    var z = 0;
+    while(b) {
+        var y:number = z;
+        if (b) { z = ""; continue; } // error: string !~> number
+        z = 0;
+    }
+    var w:number = z; // error: string !~> number
+}
+
+// same basic test as foo(), but with const. probes the
+// logic that still uses havoc to do env resets.
+function test_const() {
+  let st: string = 'abc';
+
+  for (let i = 1; i < 100; i++) {
+    const fooRes: ?string = "HEY";
+    if (!fooRes) {
+      break;
+    }
+
+    st = fooRes; // no error
+  }
+
+  return st;
+}
diff --git a/tests/break/jsfmt.spec.js b/tests/break/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/break/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/builtin_uses/__snapshots__/jsfmt.spec.js.snap b/tests/builtin_uses/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a833f9c2987d
--- /dev/null
+++ b/tests/builtin_uses/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,21 @@
+exports[`test test.js 1`] = `
+"var o = Object.freeze({ foo: 0 });
+(o.foo: string);
+module.exports = o;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = Object.freeze({ foo: 0 });
+(o.foo: string);
+module.exports = o;
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"var o = require('./test');
+(o.foo: string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = require("./test");
+(o.foo: string);
+
+"
+`;
diff --git a/tests/builtin_uses/jsfmt.spec.js b/tests/builtin_uses/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/builtin_uses/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/builtin_uses/test.js b/tests/builtin_uses/test.js
new file mode 100644
index 000000000000..3adc7cba9b8b
--- /dev/null
+++ b/tests/builtin_uses/test.js
@@ -0,0 +1,3 @@
+var o = Object.freeze({ foo: 0 });
+(o.foo: string);
+module.exports = o;
diff --git a/tests/builtin_uses/test2.js b/tests/builtin_uses/test2.js
new file mode 100644
index 000000000000..678f4c9af730
--- /dev/null
+++ b/tests/builtin_uses/test2.js
@@ -0,0 +1,2 @@
+var o = require('./test');
+(o.foo: string);
diff --git a/tests/builtins/__snapshots__/jsfmt.spec.js.snap b/tests/builtins/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3be55c8e21da
--- /dev/null
+++ b/tests/builtins/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,78 @@
+exports[`test array.js 1`] = `
+"var a = [\"...\"];
+var b = a.map (function (x) { return 0; });
+var c: string = b[0]; // error: number !~> string
+
+var array = [];
+function f() {
+    array = array.map (function () { return \"...\"; });
+    var x:number = array[0]; // error: string !~> number
+}
+
+var Foo = require(\'./genericfoo\');
+var foo = new Foo();
+function g() {
+    var foo1 = foo.map (function() { return \"...\"; });
+    var x:number = foo1.get(); // error: string !~> number
+    foo = foo1;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var a = [ \"...\" ];
+var b = a.map(
+  function(x) {
+    return 0;
+  }
+);
+var c: string = b[0];// error: number !~> string
+var array = [  ];
+function f() {
+  array = array.map(
+    function() {
+      return \"...\";
+    }
+  );
+  var x: number = array[0];// error: string !~> number
+}
+var Foo = require(\"./genericfoo\");
+var foo = new Foo();
+function g() {
+  var foo1 = foo.map(
+    function() {
+      return \"...\";
+    }
+  );
+  var x: number = foo1.get();// error: string !~> number
+  foo = foo1;
+}
+
+"
+`;
+
+exports[`test genericfoo.js 1`] = `
+"class Foo<T> {
+    x:T;
+    self():Foo<T> { return this; }
+    map<U>(callbackfn: () => U): Foo<U> { return new Foo(); }
+    set(x:T): void { }
+    get(): T { return this.x; }
+}
+
+module.exports = Foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/builtins/array.js b/tests/builtins/array.js
new file mode 100644
index 000000000000..c84ddcb02bee
--- /dev/null
+++ b/tests/builtins/array.js
@@ -0,0 +1,17 @@
+var a = ["..."];
+var b = a.map (function (x) { return 0; });
+var c: string = b[0]; // error: number !~> string
+
+var array = [];
+function f() {
+    array = array.map (function () { return "..."; });
+    var x:number = array[0]; // error: string !~> number
+}
+
+var Foo = require('./genericfoo');
+var foo = new Foo();
+function g() {
+    var foo1 = foo.map (function() { return "..."; });
+    var x:number = foo1.get(); // error: string !~> number
+    foo = foo1;
+}
diff --git a/tests/builtins/genericfoo.js b/tests/builtins/genericfoo.js
new file mode 100644
index 000000000000..53d5feb2438f
--- /dev/null
+++ b/tests/builtins/genericfoo.js
@@ -0,0 +1,9 @@
+class Foo<T> {
+    x:T;
+    self():Foo<T> { return this; }
+    map<U>(callbackfn: () => U): Foo<U> { return new Foo(); }
+    set(x:T): void { }
+    get(): T { return this.x; }
+}
+
+module.exports = Foo;
diff --git a/tests/builtins/jsfmt.spec.js b/tests/builtins/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/builtins/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/call_properties/A.js b/tests/call_properties/A.js
new file mode 100644
index 000000000000..8f5e02ce82a0
--- /dev/null
+++ b/tests/call_properties/A.js
@@ -0,0 +1,30 @@
+// You should be able to call objects with call properties
+function a(f: { (): string }, g: { (x: number): string } ): string {
+  return f() + g(123);
+}
+
+// ...and get an error if the return type is wrong
+function b(f: { (): string }): number {
+  return f();
+}
+
+// ...or if the param type is wrong
+function c(f: { (x: number): number }): number {
+  return f("hello");
+}
+
+// ...or if the arity is wrong
+function d(f: { (x: number): number }): number {
+  return f();
+}
+
+// ...or if there is no call property
+function e(f: {}): number {
+  return f();
+}
+
+// Make sure we complain even if the object literal is unsealed.
+function f(): number {
+  var x = {};
+  return x();
+}
diff --git a/tests/call_properties/B.js b/tests/call_properties/B.js
new file mode 100644
index 000000000000..5441f2f7e235
--- /dev/null
+++ b/tests/call_properties/B.js
@@ -0,0 +1,20 @@
+// You should be able to use a function as an object with a call property
+var a: { (x: number): string } = function (x: number): string { return "hi"; };
+
+// ...and it should notice when the return type is wrong
+var b: { (x: number): number } = function (x: number): string { return "hi"; };
+
+// ...or if the param type is wrong
+var c: { (x: string): string } = function (x: number): string { return "hi"; };
+
+// ...or if the arity is wrong
+var d: { (): string } = function (x: number): string { return "hi"; };
+
+// ...but subtyping rules still apply
+var e: { (x: any): void } = function() { } // arity
+var f: { (): mixed } = function(): string { return "hi" } // return type
+var g: { (x: string): void } = function(x: mixed) { } // param type
+
+// A function can be an object
+var y : {} = function (x: number): string { return "hi"; };
+var z : Object = function (x: number): string { return "hi"; };
diff --git a/tests/call_properties/C.js b/tests/call_properties/C.js
new file mode 100644
index 000000000000..75576e3a16b0
--- /dev/null
+++ b/tests/call_properties/C.js
@@ -0,0 +1,34 @@
+// You should be able to use an object as a function
+function a(x: { (z: number): string }): (z: number) => string {
+  return x;
+}
+
+// ...and it should notice when the return type is wrong
+function b(x: { (z: number): string }): (z: number) => number {
+  return x;
+}
+
+// ...or if the param type is wrong
+function c(x: { (z: number): string }): (z: string) => string {
+  return x;
+}
+
+// ...or if the arity is wrong
+function d(x: { (z: number): string }): () => string {
+  return x;
+}
+
+// ...or if it doesn't have a call property
+function e(x: {}): () => string {
+  return x;
+}
+
+// AnyFunT should also be allowed
+function f(x: { (z: number): string }): Function {
+  return x;
+}
+
+// ... but only if the object is callable
+function g(x: {}): Function {
+  return x; // error
+}
diff --git a/tests/call_properties/D.js b/tests/call_properties/D.js
new file mode 100644
index 000000000000..38a1874289e5
--- /dev/null
+++ b/tests/call_properties/D.js
@@ -0,0 +1,22 @@
+// Multiple call properties should also be supported
+function a(f: { (): string; (x: number): string }): string {
+  return f() + f(123);
+}
+
+// It should be fine when a function satisfies them all
+var b: { (): string; (x: number): string } =
+  function (x?: number): string { return "hi"; };
+
+// ...but should notice when a function doesn't satisfy them all
+var c: { (): string; (x: number): string } =
+  function (x: number): string { return "hi"; };
+
+// Only one call property needs to match the function
+function d(x: { (): string; (x: number): string }): () => string {
+  return x;
+}
+
+// ...but you need at least one
+function e(x: { (): string; (x: number): string }): () => number {
+  return x;
+}
diff --git a/tests/call_properties/E.js b/tests/call_properties/E.js
new file mode 100644
index 000000000000..873d9eccc4cb
--- /dev/null
+++ b/tests/call_properties/E.js
@@ -0,0 +1,10 @@
+// Expecting properties that don't exist should be an error
+var a : { someProp: number } = function () {};
+
+// Expecting properties that do exist should be fine
+var b : { apply: Function } = function () {};
+
+// Expecting properties in the functions statics should be fine
+var f = function () {};
+f.myProp = 123;
+var c : { myProp: number } = f;
diff --git a/tests/call_properties/F.js b/tests/call_properties/F.js
new file mode 100644
index 000000000000..c3e37bfd3f68
--- /dev/null
+++ b/tests/call_properties/F.js
@@ -0,0 +1,21 @@
+// You should be able to use an arrow function as an object with a call property
+
+var a: { (x: number): string } = (x) => x.toString()
+
+// ...and it should notice when the return type is wrong
+var b: { (x: number): number } = (x) => "hi"
+
+// ...or if the param type is wrong
+var c: { (x: string): string } = (x) => x.toFixed()
+
+// ...or if the arity is wrong
+var d: { (): string } = (x) => "hi"
+
+// ...but subtyping rules still apply
+var e: { (x: any): void } = () => { } // arity
+var f: { (): mixed } = () => "hi" // return type
+var g: { (x: Date): void } = (x) => { x * 2 } // param type (date < number)
+
+// A function can be an object
+var y : {} = (x) => "hi"
+var z : Object = (x) => "hi"
diff --git a/tests/call_properties/__snapshots__/jsfmt.spec.js.snap b/tests/call_properties/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e18cbd0809a3
--- /dev/null
+++ b/tests/call_properties/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,256 @@
+exports[`test A.js 1`] = `
+"// You should be able to call objects with call properties
+function a(f: { (): string }, g: { (x: number): string } ): string {
+  return f() + g(123);
+}
+
+// ...and get an error if the return type is wrong
+function b(f: { (): string }): number {
+  return f();
+}
+
+// ...or if the param type is wrong
+function c(f: { (x: number): number }): number {
+  return f(\"hello\");
+}
+
+// ...or if the arity is wrong
+function d(f: { (x: number): number }): number {
+  return f();
+}
+
+// ...or if there is no call property
+function e(f: {}): number {
+  return f();
+}
+
+// Make sure we complain even if the object literal is unsealed.
+function f(): number {
+  var x = {};
+  return x();
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1425:19)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test B.js 1`] = `
+"// You should be able to use a function as an object with a call property
+var a: { (x: number): string } = function (x: number): string { return \"hi\"; };
+
+// ...and it should notice when the return type is wrong
+var b: { (x: number): number } = function (x: number): string { return \"hi\"; };
+
+// ...or if the param type is wrong
+var c: { (x: string): string } = function (x: number): string { return \"hi\"; };
+
+// ...or if the arity is wrong
+var d: { (): string } = function (x: number): string { return \"hi\"; };
+
+// ...but subtyping rules still apply
+var e: { (x: any): void } = function() { } // arity
+var f: { (): mixed } = function(): string { return \"hi\" } // return type
+var g: { (x: string): void } = function(x: mixed) { } // param type
+
+// A function can be an object
+var y : {} = function (x: number): string { return \"hi\"; };
+var z : Object = function (x: number): string { return \"hi\"; };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1425:19)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test C.js 1`] = `
+"// You should be able to use an object as a function
+function a(x: { (z: number): string }): (z: number) => string {
+  return x;
+}
+
+// ...and it should notice when the return type is wrong
+function b(x: { (z: number): string }): (z: number) => number {
+  return x;
+}
+
+// ...or if the param type is wrong
+function c(x: { (z: number): string }): (z: string) => string {
+  return x;
+}
+
+// ...or if the arity is wrong
+function d(x: { (z: number): string }): () => string {
+  return x;
+}
+
+// ...or if it doesn\'t have a call property
+function e(x: {}): () => string {
+  return x;
+}
+
+// AnyFunT should also be allowed
+function f(x: { (z: number): string }): Function {
+  return x;
+}
+
+// ... but only if the object is callable
+function g(x: {}): Function {
+  return x; // error
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1425:19)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test D.js 1`] = `
+"// Multiple call properties should also be supported
+function a(f: { (): string; (x: number): string }): string {
+  return f() + f(123);
+}
+
+// It should be fine when a function satisfies them all
+var b: { (): string; (x: number): string } =
+  function (x?: number): string { return \"hi\"; };
+
+// ...but should notice when a function doesn\'t satisfy them all
+var c: { (): string; (x: number): string } =
+  function (x: number): string { return \"hi\"; };
+
+// Only one call property needs to match the function
+function d(x: { (): string; (x: number): string }): () => string {
+  return x;
+}
+
+// ...but you need at least one
+function e(x: { (): string; (x: number): string }): () => number {
+  return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1425:19)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test E.js 1`] = `
+"// Expecting properties that don\'t exist should be an error
+var a : { someProp: number } = function () {};
+
+// Expecting properties that do exist should be fine
+var b : { apply: Function } = function () {};
+
+// Expecting properties in the functions statics should be fine
+var f = function () {};
+f.myProp = 123;
+var c : { myProp: number } = f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// Expecting properties that don\'t exist should be an error
+var a: { someProp: number } = function() {
+  
+};
+// Expecting properties that do exist should be fine
+var b: { apply: Function } = function() {
+  
+};
+// Expecting properties in the functions statics should be fine
+var f = function() {
+  
+};
+f.myProp = 123;
+var c: { myProp: number } = f;
+
+"
+`;
+
+exports[`test F.js 1`] = `
+"// You should be able to use an arrow function as an object with a call property
+
+var a: { (x: number): string } = (x) => x.toString()
+
+// ...and it should notice when the return type is wrong
+var b: { (x: number): number } = (x) => \"hi\"
+
+// ...or if the param type is wrong
+var c: { (x: string): string } = (x) => x.toFixed()
+
+// ...or if the arity is wrong
+var d: { (): string } = (x) => \"hi\"
+
+// ...but subtyping rules still apply
+var e: { (x: any): void } = () => { } // arity
+var f: { (): mixed } = () => \"hi\" // return type
+var g: { (x: Date): void } = (x) => { x * 2 } // param type (date < number)
+
+// A function can be an object
+var y : {} = (x) => \"hi\"
+var z : Object = (x) => \"hi\"
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1425:19)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/call_properties/jsfmt.spec.js b/tests/call_properties/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/call_properties/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/callable/__snapshots__/jsfmt.spec.js.snap b/tests/callable/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f699cf940cc0
--- /dev/null
+++ b/tests/callable/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,70 @@
+exports[`test optional.js 1`] = `
+"type F = {
+  (x: string): number;
+  p?: string;
+}
+
+function f(x) {
+  return x.length;
+}
+
+(f: F);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1425:19)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test primitives.js 1`] = `
+"var x = Boolean(4);
+function foo(fn:(value:any)=>boolean) { }
+foo(Boolean);
+
+var dict: { [k: string]: any } = {};
+dict(); // error, callable signature not found
+
+interface ICall {
+  (x: string): void;
+}
+declare var icall: ICall;
+icall(0); // error, number ~> string
+icall.call(null, 0); // error, number ~> string
+
+type Callable = {
+  (x: string): void;
+}
+
+declare var callable: Callable;
+callable(0); // error, number ~> string
+callable.call(null, 0); // error, number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/callable/jsfmt.spec.js b/tests/callable/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/callable/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/callable/optional.js b/tests/callable/optional.js
new file mode 100644
index 000000000000..6d16aeec66c7
--- /dev/null
+++ b/tests/callable/optional.js
@@ -0,0 +1,10 @@
+type F = {
+  (x: string): number;
+  p?: string;
+}
+
+function f(x) {
+  return x.length;
+}
+
+(f: F);
diff --git a/tests/callable/primitives.js b/tests/callable/primitives.js
new file mode 100644
index 000000000000..2fa4c16f0ea5
--- /dev/null
+++ b/tests/callable/primitives.js
@@ -0,0 +1,21 @@
+var x = Boolean(4);
+function foo(fn:(value:any)=>boolean) { }
+foo(Boolean);
+
+var dict: { [k: string]: any } = {};
+dict(); // error, callable signature not found
+
+interface ICall {
+  (x: string): void;
+}
+declare var icall: ICall;
+icall(0); // error, number ~> string
+icall.call(null, 0); // error, number ~> string
+
+type Callable = {
+  (x: string): void;
+}
+
+declare var callable: Callable;
+callable(0); // error, number ~> string
+callable.call(null, 0); // error, number ~> string
diff --git a/tests/check-contents/__snapshots__/jsfmt.spec.js.snap b/tests/check-contents/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..202940e64222
--- /dev/null
+++ b/tests/check-contents/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,30 @@
+exports[`test not_flow.js 1`] = `
+"1 * \'foo\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+1 * \"foo\";
+
+"
+`;
+
+exports[`test syntax_error.js 1`] = `
+"/* @flow */
+
+(
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (4:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3592:12)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
diff --git a/tests/check-contents/jsfmt.spec.js b/tests/check-contents/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/check-contents/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/check-contents/not_flow.js b/tests/check-contents/not_flow.js
new file mode 100644
index 000000000000..f2562df539af
--- /dev/null
+++ b/tests/check-contents/not_flow.js
@@ -0,0 +1 @@
+1 * 'foo';
diff --git a/tests/check-contents/syntax_error.js b/tests/check-contents/syntax_error.js
new file mode 100644
index 000000000000..6ac6aff468a8
--- /dev/null
+++ b/tests/check-contents/syntax_error.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+(
diff --git a/tests/class_fields/__snapshots__/jsfmt.spec.js.snap b/tests/class_fields/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ec8cdbd64a47
--- /dev/null
+++ b/tests/class_fields/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,523 @@
+exports[`test base_class.js 1`] = `
+"// @flow
+
+class Base {
+  unannotatedField;
+  annotatedField: number;
+  initializedField = 42;
+  initializedFieldWithThis = this.initializedField;
+  annotatedInitializedFieldValid: ?number = 42;
+  annotatedInitializedFieldInvalid: number = \'asdf\'; // Error: string ~> number
+
+  static unannotatedField;
+  static annotatedField: number;
+  static initializedField = \'asdf\';
+  static initializedFieldWithThis = this.initializedField;
+  static annotatedInitializedFieldValid: ?number = 42;
+  static annotatedInitializedFieldInvalid: number = \'asdf\'; // Error: string ~> number
+}
+
+var o = new Base();
+
+/**
+ * Unannotated fields are open.
+ */
+(o.unannotatedField: string);
+(o.unannotatedField: number);
+(Base.unannotatedField: string);
+(Base.unannotatedField: number);
+
+/**
+ * Annotated (but uninitialized) fields still have a type.
+ */
+(o.annotatedField: number);
+(o.annotatedField: string); // Error: number ~> string
+(Base.annotatedField: number);
+(Base.annotatedField: string); // Error: number ~> string
+
+/**
+ * Initialized (but unannotated) fields assume the type of their initializer.
+ */
+(o.initializedField: number);
+(o.initializedField: string); // Error: number ~> string
+(Base.initializedField: string);
+(Base.initializedField: number); // Error: string ~> number
+
+/**
+ * Initialized fields can reference \`this\`.
+ */
+(o.initializedFieldWithThis: number);
+(o.initializedFieldWithThis: string); // Error: number ~> string
+(Base.initializedFieldWithThis: string);
+(Base.initializedFieldWithThis: number); // Error: string ~> number
+
+/**
+ * Initialized + annotated fields take the type of the annotation.
+ * (Note that this matters when the annotation is more general than the type of
+ *  the initializer)
+ */
+(o.annotatedInitializedFieldValid: ?number);
+(o.annotatedInitializedFieldValid: number); // Error: ?number ~> number
+(Base.annotatedInitializedFieldValid: ?number);
+(Base.annotatedInitializedFieldValid: number); // Error: ?number ~> number
+
+/**
+ * Initialized + annotated fields where the init/annot combo is a mismatch
+ * should assume the type of the annotation.
+ *
+ * (This happens in addition to erroring at the site of initialization)
+ */
+(o.annotatedInitializedFieldInvalid: number);
+(o.annotatedInitializedFieldInvalid: string); // Error: number ~> string
+(Base.annotatedInitializedFieldInvalid: number);
+(Base.annotatedInitializedFieldInvalid: string); // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class Base {
+  unannotatedField;
+  annotatedField: number;
+  initializedField = 42;
+  initializedFieldWithThis = this.initializedField;
+  annotatedInitializedFieldValid: ?number = 42;
+  annotatedInitializedFieldInvalid: number = \"asdf\";// Error: string ~> number
+  static unannotatedField;
+  static annotatedField: number;
+  static initializedField = \"asdf\";
+  static initializedFieldWithThis = this.initializedField;
+  static annotatedInitializedFieldValid: ?number = 42;
+  static annotatedInitializedFieldInvalid: number = \"asdf\";// Error: string ~> number
+}
+var o = new Base();
+/**
+ * Unannotated fields are open.
+ */
+(o.unannotatedField: string);
+(o.unannotatedField: number);
+(Base.unannotatedField: string);
+(Base.unannotatedField: number);
+/**
+ * Annotated (but uninitialized) fields still have a type.
+ */
+(o.annotatedField: number);
+(o.annotatedField: string);// Error: number ~> string
+(Base.annotatedField: number);
+(Base.annotatedField: string);// Error: number ~> string
+/**
+ * Initialized (but unannotated) fields assume the type of their initializer.
+ */
+(o.initializedField: number);
+(o.initializedField: string);// Error: number ~> string
+(Base.initializedField: string);
+(Base.initializedField: number);// Error: string ~> number
+/**
+ * Initialized fields can reference \`this\`.
+ */
+(o.initializedFieldWithThis: number);
+(o.initializedFieldWithThis: string);// Error: number ~> string
+(Base.initializedFieldWithThis: string);
+(Base.initializedFieldWithThis: number);// Error: string ~> number
+/**
+ * Initialized + annotated fields take the type of the annotation.
+ * (Note that this matters when the annotation is more general than the type of
+ *  the initializer)
+ */
+(o.annotatedInitializedFieldValid: ?number);
+(o.annotatedInitializedFieldValid: number);// Error: ?number ~> number
+(Base.annotatedInitializedFieldValid: ?number);
+(Base.annotatedInitializedFieldValid: number);// Error: ?number ~> number
+/**
+ * Initialized + annotated fields where the init/annot combo is a mismatch
+ * should assume the type of the annotation.
+ *
+ * (This happens in addition to erroring at the site of initialization)
+ */
+(o.annotatedInitializedFieldInvalid: number);
+(o.annotatedInitializedFieldInvalid: string);// Error: number ~> string
+(Base.annotatedInitializedFieldInvalid: number);
+(Base.annotatedInitializedFieldInvalid: string);// Error: number ~> string
+
+"
+`;
+
+exports[`test derived_class.js 1`] = `
+"// @flow
+
+class Base {
+  base_unannotatedField;
+  base_annotatedField: number;
+  base_initializedField = 42;
+  base_initializedFieldWithThis = this.base_initializedField;
+  base_annotatedInitializedFieldValid: ?number = 42;
+  base_annotatedInitializedFieldInvalid: number = \'asdf\'; // Error: string ~> number
+
+  static base_unannotatedField;
+  static base_annotatedField: number;
+  static base_initializedField = \'asdf\';
+  static base_initializedFieldWithThis = this.base_initializedField;
+  static base_annotatedInitializedFieldValid: ?number = 42;
+  static base_annotatedInitializedFieldInvalid: number = \'asdf\'; // Error: string ~> number
+
+  inherited_initializer = 42;
+  static inherited_initializer = 42;
+}
+
+class Child extends Base {
+  child_unannotatedField;
+  child_annotatedField: number;
+  child_initializedField = 42;
+  child_initializedFieldWithThis = this.child_initializedField;
+  child_annotatedInitializedFieldValid: ?number = 42;
+  child_annotatedInitializedFieldInvalid: number = \'asdf\'; // Error: string ~> number
+
+  static child_unannotatedField;
+  static child_annotatedField: number;
+  static child_initializedField = \'asdf\';
+  static child_initializedFieldWithThis = this.child_initializedField;
+  static child_annotatedInitializedFieldValid: ?number = 42;
+  static child_annotatedInitializedFieldInvalid: number = \'asdf\'; // Error: string ~> number
+
+  inherited_initializer;
+  static inherited_initializer;
+}
+
+var o = new Child();
+
+/**
+ * Unannotated fields are open.
+ */
+(o.base_unannotatedField: string);
+(o.base_unannotatedField: number);
+(Child.base_unannotatedField: string);
+(Child.base_unannotatedField: number);
+
+(o.child_unannotatedField: string);
+(o.child_unannotatedField: number);
+(Child.child_unannotatedField: string);
+(Child.child_unannotatedField: number);
+
+
+/**
+ * Annotated (but uninitialized) fields still have a type.
+ */
+(o.base_annotatedField: number);
+(o.base_annotatedField: string); // Error: number ~> string
+(Child.base_annotatedField: number);
+(Child.base_annotatedField: string); // Error: number ~> string
+
+(o.child_annotatedField: number);
+(o.child_annotatedField: string); // Error: number ~> string
+(Child.child_annotatedField: number);
+(Child.child_annotatedField: string); // Error: number ~> string
+
+/**
+ * Initialized (but unannotated) fields assume the type of their initializer.
+ */
+(o.base_initializedField: number);
+(o.base_initializedField: string); // Error: number ~> string
+(Child.base_initializedField: string);
+(Child.base_initializedField: number); // Error: string ~> number
+
+(o.child_initializedField: number);
+(o.child_initializedField: string); // Error: number ~> string
+(Child.child_initializedField: string);
+(Child.child_initializedField: number); // Error: string ~> number
+
+/**
+ * Initialized fields can reference \`this\`.
+ */
+(o.base_initializedFieldWithThis: number);
+(o.base_initializedFieldWithThis: string); // Error: number ~> string
+(Child.base_initializedFieldWithThis: string);
+(Child.base_initializedFieldWithThis: number); // Error: string ~> number
+
+(o.child_initializedFieldWithThis: number);
+(o.child_initializedFieldWithThis: string); // Error: number ~> string
+(Child.child_initializedFieldWithThis: string);
+(Child.child_initializedFieldWithThis: number); // Error: string ~> number
+
+/**
+ * Initialized + annotated fields take the type of the annotation.
+ * (Note that this matters when the annotation is more general than the type of
+ *  the initializer)
+ */
+(o.base_annotatedInitializedFieldValid: ?number);
+(o.base_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+(Child.base_annotatedInitializedFieldValid: ?number);
+(Child.base_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+
+(o.child_annotatedInitializedFieldValid: ?number);
+(o.child_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+(Child.child_annotatedInitializedFieldValid: ?number);
+(Child.child_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+
+/**
+ * Initialized + annotated fields where the init/annot combo is a mismatch
+ * should assume the type of the annotation.
+ *
+ * (This happens in addition to erroring at the site of initialization)
+ */
+(o.base_annotatedInitializedFieldInvalid: number);
+(o.base_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+(Child.base_annotatedInitializedFieldInvalid: number);
+(Child.base_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+
+(o.child_annotatedInitializedFieldInvalid: number);
+(o.child_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+(Child.child_annotatedInitializedFieldInvalid: number);
+(Child.child_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+
+/**
+ * Derived fields without an initializer that shadow base fields *with* an
+ * initializer should have the type of the base field.
+ */
+(o.inherited_initializer: number);
+(o.inherited_initializer: string); // Error: number ~> string
+(Child.inherited_initializer: number);
+(Child.inherited_initializer: string); // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class Base {
+  base_unannotatedField;
+  base_annotatedField: number;
+  base_initializedField = 42;
+  base_initializedFieldWithThis = this.base_initializedField;
+  base_annotatedInitializedFieldValid: ?number = 42;
+  base_annotatedInitializedFieldInvalid: number = \"asdf\";// Error: string ~> number
+  static base_unannotatedField;
+  static base_annotatedField: number;
+  static base_initializedField = \"asdf\";
+  static base_initializedFieldWithThis = this.base_initializedField;
+  static base_annotatedInitializedFieldValid: ?number = 42;
+  static base_annotatedInitializedFieldInvalid: number = \"asdf\";// Error: string ~> number
+  inherited_initializer = 42;
+  static inherited_initializer = 42;
+}
+class Child extends Base {
+  child_unannotatedField;
+  child_annotatedField: number;
+  child_initializedField = 42;
+  child_initializedFieldWithThis = this.child_initializedField;
+  child_annotatedInitializedFieldValid: ?number = 42;
+  child_annotatedInitializedFieldInvalid: number = \"asdf\";// Error: string ~> number
+  static child_unannotatedField;
+  static child_annotatedField: number;
+  static child_initializedField = \"asdf\";
+  static child_initializedFieldWithThis = this.child_initializedField;
+  static child_annotatedInitializedFieldValid: ?number = 42;
+  static child_annotatedInitializedFieldInvalid: number = \"asdf\";// Error: string ~> number
+  inherited_initializer;
+  static inherited_initializer;
+}
+var o = new Child();
+/**
+ * Unannotated fields are open.
+ */
+(o.base_unannotatedField: string);
+(o.base_unannotatedField: number);
+(Child.base_unannotatedField: string);
+(Child.base_unannotatedField: number);
+(o.child_unannotatedField: string);
+(o.child_unannotatedField: number);
+(Child.child_unannotatedField: string);
+(Child.child_unannotatedField: number);
+/**
+ * Annotated (but uninitialized) fields still have a type.
+ */
+(o.base_annotatedField: number);
+(o.base_annotatedField: string);// Error: number ~> string
+(Child.base_annotatedField: number);
+(Child.base_annotatedField: string);// Error: number ~> string
+(o.child_annotatedField: number);
+(o.child_annotatedField: string);// Error: number ~> string
+(Child.child_annotatedField: number);
+(Child.child_annotatedField: string);// Error: number ~> string
+/**
+ * Initialized (but unannotated) fields assume the type of their initializer.
+ */
+(o.base_initializedField: number);
+(o.base_initializedField: string);// Error: number ~> string
+(Child.base_initializedField: string);
+(Child.base_initializedField: number);// Error: string ~> number
+(o.child_initializedField: number);
+(o.child_initializedField: string);// Error: number ~> string
+(Child.child_initializedField: string);
+(Child.child_initializedField: number);// Error: string ~> number
+/**
+ * Initialized fields can reference \`this\`.
+ */
+(o.base_initializedFieldWithThis: number);
+(o.base_initializedFieldWithThis: string);// Error: number ~> string
+(Child.base_initializedFieldWithThis: string);
+(Child.base_initializedFieldWithThis: number);// Error: string ~> number
+(o.child_initializedFieldWithThis: number);
+(o.child_initializedFieldWithThis: string);// Error: number ~> string
+(Child.child_initializedFieldWithThis: string);
+(Child.child_initializedFieldWithThis: number);// Error: string ~> number
+/**
+ * Initialized + annotated fields take the type of the annotation.
+ * (Note that this matters when the annotation is more general than the type of
+ *  the initializer)
+ */
+(o.base_annotatedInitializedFieldValid: ?number);
+(o.base_annotatedInitializedFieldValid: number);// Error: ?number ~> number
+(Child.base_annotatedInitializedFieldValid: ?number);
+(Child.base_annotatedInitializedFieldValid: number);// Error: ?number ~> number
+(o.child_annotatedInitializedFieldValid: ?number);
+(o.child_annotatedInitializedFieldValid: number);// Error: ?number ~> number
+(Child.child_annotatedInitializedFieldValid: ?number);
+(Child.child_annotatedInitializedFieldValid: number);// Error: ?number ~> number
+/**
+ * Initialized + annotated fields where the init/annot combo is a mismatch
+ * should assume the type of the annotation.
+ *
+ * (This happens in addition to erroring at the site of initialization)
+ */
+(o.base_annotatedInitializedFieldInvalid: number);
+(o.base_annotatedInitializedFieldInvalid: string);// Error: number ~> string
+(Child.base_annotatedInitializedFieldInvalid: number);
+(Child.base_annotatedInitializedFieldInvalid: string);// Error: number ~> string
+(o.child_annotatedInitializedFieldInvalid: number);
+(o.child_annotatedInitializedFieldInvalid: string);// Error: number ~> string
+(Child.child_annotatedInitializedFieldInvalid: number);
+(Child.child_annotatedInitializedFieldInvalid: string);// Error: number ~> string
+/**
+ * Derived fields without an initializer that shadow base fields *with* an
+ * initializer should have the type of the base field.
+ */
+(o.inherited_initializer: number);
+(o.inherited_initializer: string);// Error: number ~> string
+(Child.inherited_initializer: number);
+(Child.inherited_initializer: string);// Error: number ~> string
+
+"
+`;
+
+exports[`test generic_class.js 1`] = `
+"// @flow
+
+/**
+ * Fields annotated with a generic should assume a type once the type param
+ * is instantiated.
+ */
+class ClassAnnotated<T> {
+  p: T;
+  static p: T;
+}
+
+var o1 = new ClassAnnotated();
+o1.p = 42;
+(o1.p: number);
+(o1.p: string); // Error: number ~> string
+ClassAnnotated.p = 42;
+(ClassAnnotated.p: number);
+(ClassAnnotated.p: string); // Error: number ~> string
+
+
+/**
+ * It\'s always an error to initialized a generically-typed field with an
+ * expression of any type other than the generic itself.
+ */
+class ClassGenericInitialized<T, U> {
+  invalid: T = 42; // Error: number ~> Generic<T>
+  valid: T = ((42:any):T);
+
+  static invalid: T = 42; // Error: number ~> Generic<T>
+  static valid: T = ((42:any):T);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test scoping.js 1`] = `
+"// @flow
+
+var someVar = 42;
+
+class Foo {
+  outer = someVar;
+  selfTyped: Foo;
+  selfTypedInit = new Foo();
+
+  static outer = someVar;
+  static selfTyped: Foo;
+  static selfTypedInit = new Foo();
+
+  constructor() {
+    var someVar = \'asdf\';
+  }
+}
+
+/**
+ * Field initializers execute in a scope immediately under the scope outside the
+ * class definition.
+ */
+(new Foo().outer: number);
+(new Foo().outer: string); // Error: number ~> string
+(Foo.outer: number);
+(Foo.outer: string); // Error: number ~> string
+
+/**
+ * Field initializers should be able to refer to the class type in their type
+ * annotations.
+ */
+(new Foo().selfTyped: Foo);
+(new Foo().selfTyped: number); // Error: Foo ~> number
+(Foo.selfTyped: Foo);
+(Foo.selfTyped: number); // Error: Foo ~> number
+
+(new Foo().selfTypedInit: Foo);
+(new Foo().selfTypedInit: number); // Error: Foo ~> number
+(Foo.selfTypedInit: Foo);
+(Foo.selfTypedInit: number); // Error: Foo ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var someVar = 42;
+class Foo {
+  outer = someVar;
+  selfTyped: Foo;
+  selfTypedInit = new Foo();
+  static outer = someVar;
+  static selfTyped: Foo;
+  static selfTypedInit = new Foo();
+  constructor() {
+    var someVar = \"asdf\";
+  }
+}
+/**
+ * Field initializers execute in a scope immediately under the scope outside the
+ * class definition.
+ */
+(new Foo().outer: number);
+(new Foo().outer: string);// Error: number ~> string
+(Foo.outer: number);
+(Foo.outer: string);// Error: number ~> string
+/**
+ * Field initializers should be able to refer to the class type in their type
+ * annotations.
+ */
+(new Foo().selfTyped: Foo);
+(new Foo().selfTyped: number);// Error: Foo ~> number
+(Foo.selfTyped: Foo);
+(Foo.selfTyped: number);// Error: Foo ~> number
+(new Foo().selfTypedInit: Foo);
+(new Foo().selfTypedInit: number);// Error: Foo ~> number
+(Foo.selfTypedInit: Foo);
+(Foo.selfTypedInit: number);// Error: Foo ~> number
+
+"
+`;
diff --git a/tests/class_fields/base_class.js b/tests/class_fields/base_class.js
new file mode 100644
index 000000000000..b5ad46bcca31
--- /dev/null
+++ b/tests/class_fields/base_class.js
@@ -0,0 +1,72 @@
+// @flow
+
+class Base {
+  unannotatedField;
+  annotatedField: number;
+  initializedField = 42;
+  initializedFieldWithThis = this.initializedField;
+  annotatedInitializedFieldValid: ?number = 42;
+  annotatedInitializedFieldInvalid: number = 'asdf'; // Error: string ~> number
+
+  static unannotatedField;
+  static annotatedField: number;
+  static initializedField = 'asdf';
+  static initializedFieldWithThis = this.initializedField;
+  static annotatedInitializedFieldValid: ?number = 42;
+  static annotatedInitializedFieldInvalid: number = 'asdf'; // Error: string ~> number
+}
+
+var o = new Base();
+
+/**
+ * Unannotated fields are open.
+ */
+(o.unannotatedField: string);
+(o.unannotatedField: number);
+(Base.unannotatedField: string);
+(Base.unannotatedField: number);
+
+/**
+ * Annotated (but uninitialized) fields still have a type.
+ */
+(o.annotatedField: number);
+(o.annotatedField: string); // Error: number ~> string
+(Base.annotatedField: number);
+(Base.annotatedField: string); // Error: number ~> string
+
+/**
+ * Initialized (but unannotated) fields assume the type of their initializer.
+ */
+(o.initializedField: number);
+(o.initializedField: string); // Error: number ~> string
+(Base.initializedField: string);
+(Base.initializedField: number); // Error: string ~> number
+
+/**
+ * Initialized fields can reference `this`.
+ */
+(o.initializedFieldWithThis: number);
+(o.initializedFieldWithThis: string); // Error: number ~> string
+(Base.initializedFieldWithThis: string);
+(Base.initializedFieldWithThis: number); // Error: string ~> number
+
+/**
+ * Initialized + annotated fields take the type of the annotation.
+ * (Note that this matters when the annotation is more general than the type of
+ *  the initializer)
+ */
+(o.annotatedInitializedFieldValid: ?number);
+(o.annotatedInitializedFieldValid: number); // Error: ?number ~> number
+(Base.annotatedInitializedFieldValid: ?number);
+(Base.annotatedInitializedFieldValid: number); // Error: ?number ~> number
+
+/**
+ * Initialized + annotated fields where the init/annot combo is a mismatch
+ * should assume the type of the annotation.
+ *
+ * (This happens in addition to erroring at the site of initialization)
+ */
+(o.annotatedInitializedFieldInvalid: number);
+(o.annotatedInitializedFieldInvalid: string); // Error: number ~> string
+(Base.annotatedInitializedFieldInvalid: number);
+(Base.annotatedInitializedFieldInvalid: string); // Error: number ~> string
diff --git a/tests/class_fields/derived_class.js b/tests/class_fields/derived_class.js
new file mode 100644
index 000000000000..89b40c1664fd
--- /dev/null
+++ b/tests/class_fields/derived_class.js
@@ -0,0 +1,134 @@
+// @flow
+
+class Base {
+  base_unannotatedField;
+  base_annotatedField: number;
+  base_initializedField = 42;
+  base_initializedFieldWithThis = this.base_initializedField;
+  base_annotatedInitializedFieldValid: ?number = 42;
+  base_annotatedInitializedFieldInvalid: number = 'asdf'; // Error: string ~> number
+
+  static base_unannotatedField;
+  static base_annotatedField: number;
+  static base_initializedField = 'asdf';
+  static base_initializedFieldWithThis = this.base_initializedField;
+  static base_annotatedInitializedFieldValid: ?number = 42;
+  static base_annotatedInitializedFieldInvalid: number = 'asdf'; // Error: string ~> number
+
+  inherited_initializer = 42;
+  static inherited_initializer = 42;
+}
+
+class Child extends Base {
+  child_unannotatedField;
+  child_annotatedField: number;
+  child_initializedField = 42;
+  child_initializedFieldWithThis = this.child_initializedField;
+  child_annotatedInitializedFieldValid: ?number = 42;
+  child_annotatedInitializedFieldInvalid: number = 'asdf'; // Error: string ~> number
+
+  static child_unannotatedField;
+  static child_annotatedField: number;
+  static child_initializedField = 'asdf';
+  static child_initializedFieldWithThis = this.child_initializedField;
+  static child_annotatedInitializedFieldValid: ?number = 42;
+  static child_annotatedInitializedFieldInvalid: number = 'asdf'; // Error: string ~> number
+
+  inherited_initializer;
+  static inherited_initializer;
+}
+
+var o = new Child();
+
+/**
+ * Unannotated fields are open.
+ */
+(o.base_unannotatedField: string);
+(o.base_unannotatedField: number);
+(Child.base_unannotatedField: string);
+(Child.base_unannotatedField: number);
+
+(o.child_unannotatedField: string);
+(o.child_unannotatedField: number);
+(Child.child_unannotatedField: string);
+(Child.child_unannotatedField: number);
+
+
+/**
+ * Annotated (but uninitialized) fields still have a type.
+ */
+(o.base_annotatedField: number);
+(o.base_annotatedField: string); // Error: number ~> string
+(Child.base_annotatedField: number);
+(Child.base_annotatedField: string); // Error: number ~> string
+
+(o.child_annotatedField: number);
+(o.child_annotatedField: string); // Error: number ~> string
+(Child.child_annotatedField: number);
+(Child.child_annotatedField: string); // Error: number ~> string
+
+/**
+ * Initialized (but unannotated) fields assume the type of their initializer.
+ */
+(o.base_initializedField: number);
+(o.base_initializedField: string); // Error: number ~> string
+(Child.base_initializedField: string);
+(Child.base_initializedField: number); // Error: string ~> number
+
+(o.child_initializedField: number);
+(o.child_initializedField: string); // Error: number ~> string
+(Child.child_initializedField: string);
+(Child.child_initializedField: number); // Error: string ~> number
+
+/**
+ * Initialized fields can reference `this`.
+ */
+(o.base_initializedFieldWithThis: number);
+(o.base_initializedFieldWithThis: string); // Error: number ~> string
+(Child.base_initializedFieldWithThis: string);
+(Child.base_initializedFieldWithThis: number); // Error: string ~> number
+
+(o.child_initializedFieldWithThis: number);
+(o.child_initializedFieldWithThis: string); // Error: number ~> string
+(Child.child_initializedFieldWithThis: string);
+(Child.child_initializedFieldWithThis: number); // Error: string ~> number
+
+/**
+ * Initialized + annotated fields take the type of the annotation.
+ * (Note that this matters when the annotation is more general than the type of
+ *  the initializer)
+ */
+(o.base_annotatedInitializedFieldValid: ?number);
+(o.base_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+(Child.base_annotatedInitializedFieldValid: ?number);
+(Child.base_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+
+(o.child_annotatedInitializedFieldValid: ?number);
+(o.child_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+(Child.child_annotatedInitializedFieldValid: ?number);
+(Child.child_annotatedInitializedFieldValid: number); // Error: ?number ~> number
+
+/**
+ * Initialized + annotated fields where the init/annot combo is a mismatch
+ * should assume the type of the annotation.
+ *
+ * (This happens in addition to erroring at the site of initialization)
+ */
+(o.base_annotatedInitializedFieldInvalid: number);
+(o.base_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+(Child.base_annotatedInitializedFieldInvalid: number);
+(Child.base_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+
+(o.child_annotatedInitializedFieldInvalid: number);
+(o.child_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+(Child.child_annotatedInitializedFieldInvalid: number);
+(Child.child_annotatedInitializedFieldInvalid: string); // Error: number ~> string
+
+/**
+ * Derived fields without an initializer that shadow base fields *with* an
+ * initializer should have the type of the base field.
+ */
+(o.inherited_initializer: number);
+(o.inherited_initializer: string); // Error: number ~> string
+(Child.inherited_initializer: number);
+(Child.inherited_initializer: string); // Error: number ~> string
diff --git a/tests/class_fields/generic_class.js b/tests/class_fields/generic_class.js
new file mode 100644
index 000000000000..d214ff6ceee7
--- /dev/null
+++ b/tests/class_fields/generic_class.js
@@ -0,0 +1,31 @@
+// @flow
+
+/**
+ * Fields annotated with a generic should assume a type once the type param
+ * is instantiated.
+ */
+class ClassAnnotated<T> {
+  p: T;
+  static p: T;
+}
+
+var o1 = new ClassAnnotated();
+o1.p = 42;
+(o1.p: number);
+(o1.p: string); // Error: number ~> string
+ClassAnnotated.p = 42;
+(ClassAnnotated.p: number);
+(ClassAnnotated.p: string); // Error: number ~> string
+
+
+/**
+ * It's always an error to initialized a generically-typed field with an
+ * expression of any type other than the generic itself.
+ */
+class ClassGenericInitialized<T, U> {
+  invalid: T = 42; // Error: number ~> Generic<T>
+  valid: T = ((42:any):T);
+
+  static invalid: T = 42; // Error: number ~> Generic<T>
+  static valid: T = ((42:any):T);
+}
diff --git a/tests/class_fields/jsfmt.spec.js b/tests/class_fields/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/class_fields/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/class_fields/scoping.js b/tests/class_fields/scoping.js
new file mode 100644
index 000000000000..462b51293237
--- /dev/null
+++ b/tests/class_fields/scoping.js
@@ -0,0 +1,40 @@
+// @flow
+
+var someVar = 42;
+
+class Foo {
+  outer = someVar;
+  selfTyped: Foo;
+  selfTypedInit = new Foo();
+
+  static outer = someVar;
+  static selfTyped: Foo;
+  static selfTypedInit = new Foo();
+
+  constructor() {
+    var someVar = 'asdf';
+  }
+}
+
+/**
+ * Field initializers execute in a scope immediately under the scope outside the
+ * class definition.
+ */
+(new Foo().outer: number);
+(new Foo().outer: string); // Error: number ~> string
+(Foo.outer: number);
+(Foo.outer: string); // Error: number ~> string
+
+/**
+ * Field initializers should be able to refer to the class type in their type
+ * annotations.
+ */
+(new Foo().selfTyped: Foo);
+(new Foo().selfTyped: number); // Error: Foo ~> number
+(Foo.selfTyped: Foo);
+(Foo.selfTyped: number); // Error: Foo ~> number
+
+(new Foo().selfTypedInit: Foo);
+(new Foo().selfTypedInit: number); // Error: Foo ~> number
+(Foo.selfTypedInit: Foo);
+(Foo.selfTypedInit: number); // Error: Foo ~> number
diff --git a/tests/class_munging/__snapshots__/jsfmt.spec.js.snap b/tests/class_munging/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7e538f3c192d
--- /dev/null
+++ b/tests/class_munging/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,69 @@
+exports[`test with_munging.js 1`] = `
+"/**
+ * @flow
+ */
+
+class Foo {
+  _method(): string {
+    return 'this is private';
+  }
+}
+
+class Bar extends Foo {
+  test() {
+    (this._method(): string); // error
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class Foo {
+  _method(): string {
+    return "this is private";
+  }
+}
+class Bar extends Foo {
+  test() {
+    (this._method(): string);// error
+  }
+}
+
+"
+`;
+
+exports[`test without_munging.js 1`] = `
+"/**
+ * @flow
+ * @preventMunge
+ */
+
+class Foo {
+  _method(): string {
+    return 'this is not private';
+  }
+}
+
+class Bar extends Foo {
+  test() {
+    (this._method(): string); // ok
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ * @preventMunge
+ */
+class Foo {
+  _method(): string {
+    return "this is not private";
+  }
+}
+class Bar extends Foo {
+  test() {
+    (this._method(): string);// ok
+  }
+}
+
+"
+`;
diff --git a/tests/class_munging/jsfmt.spec.js b/tests/class_munging/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/class_munging/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/class_munging/with_munging.js b/tests/class_munging/with_munging.js
new file mode 100644
index 000000000000..ead68e9fbaba
--- /dev/null
+++ b/tests/class_munging/with_munging.js
@@ -0,0 +1,15 @@
+/**
+ * @flow
+ */
+
+class Foo {
+  _method(): string {
+    return 'this is private';
+  }
+}
+
+class Bar extends Foo {
+  test() {
+    (this._method(): string); // error
+  }
+}
diff --git a/tests/class_munging/without_munging.js b/tests/class_munging/without_munging.js
new file mode 100644
index 000000000000..400dcc84a81a
--- /dev/null
+++ b/tests/class_munging/without_munging.js
@@ -0,0 +1,16 @@
+/**
+ * @flow
+ * @preventMunge
+ */
+
+class Foo {
+  _method(): string {
+    return 'this is not private';
+  }
+}
+
+class Bar extends Foo {
+  test() {
+    (this._method(): string); // ok
+  }
+}
diff --git a/tests/class_statics/__snapshots__/jsfmt.spec.js.snap b/tests/class_statics/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9b81d21be6d0
--- /dev/null
+++ b/tests/class_statics/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,80 @@
+exports[`test test.js 1`] = `
+"class A {
+  static x: number;
+  static y: string;
+  static foo(x: number) { }
+  static bar(y: string) { }
+}
+A.qux = function(x: string) { } // error?
+
+class B extends A {
+  static x: string; // error?
+  static foo(x: string) { } // error?
+  static main() {
+    B.x = 0; // error
+    B.x = \"\";
+    B.foo(0); // error
+    B.foo(\"\");
+    B.y = 0; // error
+    B.bar(0); // error
+    B.qux(0); // error
+  }
+  static create(): A {
+    return new this();
+  }
+
+  static badCreate(): number {
+    return new this(); // error B ~> number
+  }
+}
+
+class C<X> {
+  static x: X;
+  static bar(x: X) { }
+  static create(): C<*> {
+    return new this();
+  }
+}
+
+class D extends C<string> {
+  static main() {
+    D.foo(0); // error?
+
+    D.bar(0);
+  }
+}
+
+var d: C<*> = D.create();
+(new A: typeof A);
+(B: typeof A);
+
+class E {
+  static x: number;
+  static foo(): string {
+    this.bar(); // error
+    return this.x; // error
+  }
+}
+
+// note: above classdefs are sufficiently annotated to export
+module.exports = {
+  A: A, B: B, C: C, D: D, E: E
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/class_statics/jsfmt.spec.js b/tests/class_statics/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/class_statics/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/class_statics/test.js b/tests/class_statics/test.js
new file mode 100644
index 000000000000..4fea29a3ed5b
--- /dev/null
+++ b/tests/class_statics/test.js
@@ -0,0 +1,61 @@
+class A {
+  static x: number;
+  static y: string;
+  static foo(x: number) { }
+  static bar(y: string) { }
+}
+A.qux = function(x: string) { } // error?
+
+class B extends A {
+  static x: string; // error?
+  static foo(x: string) { } // error?
+  static main() {
+    B.x = 0; // error
+    B.x = "";
+    B.foo(0); // error
+    B.foo("");
+    B.y = 0; // error
+    B.bar(0); // error
+    B.qux(0); // error
+  }
+  static create(): A {
+    return new this();
+  }
+
+  static badCreate(): number {
+    return new this(); // error B ~> number
+  }
+}
+
+class C<X> {
+  static x: X;
+  static bar(x: X) { }
+  static create(): C<*> {
+    return new this();
+  }
+}
+
+class D extends C<string> {
+  static main() {
+    D.foo(0); // error?
+
+    D.bar(0);
+  }
+}
+
+var d: C<*> = D.create();
+(new A: typeof A);
+(B: typeof A);
+
+class E {
+  static x: number;
+  static foo(): string {
+    this.bar(); // error
+    return this.x; // error
+  }
+}
+
+// note: above classdefs are sufficiently annotated to export
+module.exports = {
+  A: A, B: B, C: C, D: D, E: E
+}
diff --git a/tests/class_subtyping/__snapshots__/jsfmt.spec.js.snap b/tests/class_subtyping/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7d3266513137
--- /dev/null
+++ b/tests/class_subtyping/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,91 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+class A {}
+class B {}
+
+module.exports = { A, B };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class A {}
+class B {}
+module.exports = { A, B };
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"/* @flow */
+var I = require(\"./test.js\");
+
+class C extends I.A {}
+
+var x: I.A = new C();
+var y: I.B = new C();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var I = require(\"./test.js\");
+class C extends I.A {}
+var x: I.A = new C();
+var y: I.B = new C();
+
+"
+`;
+
+exports[`test test3.js 1`] = `
+"class A<X, Y, Z> {}
+class B extends A<string, number, bool> {}
+class C<X, Y, Z> extends B {}
+
+var c: C<number, string, Array<bool>> = new C; // none of the type args matter
+var a: A<string, number, Array<bool>> = c; // the third type arg is incorrect
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test4.js 1`] = `
+"class C<X> { x: X; }
+
+function foo<X>(c: C<X>, x: X) { }
+
+type O = { f: number };
+
+foo((new C: C<O>), { f_: 0 });
+
+class D extends C<O> {
+  bar() { this.x; }
+}
+
+foo(new D, { f_: 0 });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/class_subtyping/jsfmt.spec.js b/tests/class_subtyping/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/class_subtyping/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/class_subtyping/test.js b/tests/class_subtyping/test.js
new file mode 100644
index 000000000000..68aa0c6e71ae
--- /dev/null
+++ b/tests/class_subtyping/test.js
@@ -0,0 +1,5 @@
+/* @flow */
+class A {}
+class B {}
+
+module.exports = { A, B };
diff --git a/tests/class_subtyping/test2.js b/tests/class_subtyping/test2.js
new file mode 100644
index 000000000000..0601a3576687
--- /dev/null
+++ b/tests/class_subtyping/test2.js
@@ -0,0 +1,7 @@
+/* @flow */
+var I = require("./test.js");
+
+class C extends I.A {}
+
+var x: I.A = new C();
+var y: I.B = new C();
diff --git a/tests/class_subtyping/test3.js b/tests/class_subtyping/test3.js
new file mode 100644
index 000000000000..4f76d86d500f
--- /dev/null
+++ b/tests/class_subtyping/test3.js
@@ -0,0 +1,6 @@
+class A<X, Y, Z> {}
+class B extends A<string, number, bool> {}
+class C<X, Y, Z> extends B {}
+
+var c: C<number, string, Array<bool>> = new C; // none of the type args matter
+var a: A<string, number, Array<bool>> = c; // the third type arg is incorrect
diff --git a/tests/class_subtyping/test4.js b/tests/class_subtyping/test4.js
new file mode 100644
index 000000000000..9cd7abb32b4e
--- /dev/null
+++ b/tests/class_subtyping/test4.js
@@ -0,0 +1,13 @@
+class C<X> { x: X; }
+
+function foo<X>(c: C<X>, x: X) { }
+
+type O = { f: number };
+
+foo((new C: C<O>), { f_: 0 });
+
+class D extends C<O> {
+  bar() { this.x; }
+}
+
+foo(new D, { f_: 0 });
diff --git a/tests/class_type/__snapshots__/jsfmt.spec.js.snap b/tests/class_type/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..915e603e6b78
--- /dev/null
+++ b/tests/class_type/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,64 @@
+exports[`test test.js 1`] = `
+"class A { }
+function foo(x: Class<A>): A {
+  return new x(); // OK
+}
+
+class B {
+  constructor(_: any) { }
+}
+function bar(x: Class<B>): B {
+  return new x(); // error (too few args)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"// A function to typecheck values against their types. Covariance of Class<.>
+// makes it useless in such a function (when limited to classes and instances),
+// since everything can be trivially satisfied by going to \`mixed\`.
+declare function check<X>(cls: $Type<X>, inst: X): void;
+
+class A { }
+class B extends A { }
+class C { }
+
+check(B, new A);
+check(A, new B);
+check(C, new A);
+check(C, new B);
+check(B, new C);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/class_type/jsfmt.spec.js b/tests/class_type/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/class_type/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/class_type/test.js b/tests/class_type/test.js
new file mode 100644
index 000000000000..a72a3903bee0
--- /dev/null
+++ b/tests/class_type/test.js
@@ -0,0 +1,11 @@
+class A { }
+function foo(x: Class<A>): A {
+  return new x(); // OK
+}
+
+class B {
+  constructor(_: any) { }
+}
+function bar(x: Class<B>): B {
+  return new x(); // error (too few args)
+}
diff --git a/tests/class_type/test2.js b/tests/class_type/test2.js
new file mode 100644
index 000000000000..071653cd3db7
--- /dev/null
+++ b/tests/class_type/test2.js
@@ -0,0 +1,14 @@
+// A function to typecheck values against their types. Covariance of Class<.>
+// makes it useless in such a function (when limited to classes and instances),
+// since everything can be trivially satisfied by going to `mixed`.
+declare function check<X>(cls: $Type<X>, inst: X): void;
+
+class A { }
+class B extends A { }
+class C { }
+
+check(B, new A);
+check(A, new B);
+check(C, new A);
+check(C, new B);
+check(B, new C);
diff --git a/tests/classes/A.js b/tests/classes/A.js
new file mode 100644
index 000000000000..37bfb2d47616
--- /dev/null
+++ b/tests/classes/A.js
@@ -0,0 +1,5 @@
+class A {
+  foo(x:number):void { }
+}
+
+module.exports = A;
diff --git a/tests/classes/B.js b/tests/classes/B.js
new file mode 100644
index 000000000000..84a52066d088
--- /dev/null
+++ b/tests/classes/B.js
@@ -0,0 +1,8 @@
+var A = require('./A');
+
+class B extends A { }
+
+let b = new B();
+(b.foo: number); // error, number !~> function
+
+module.exports = B;
diff --git a/tests/classes/C.js b/tests/classes/C.js
new file mode 100644
index 000000000000..1837b2616d9b
--- /dev/null
+++ b/tests/classes/C.js
@@ -0,0 +1,10 @@
+var B = require('./B');
+
+class C extends B {
+  foo(x:string):void { }
+}
+
+let c = new C();
+(c.foo: number); // error, number !~> function
+
+module.exports = C;
diff --git a/tests/classes/D.js b/tests/classes/D.js
new file mode 100644
index 000000000000..5f4cae464ab3
--- /dev/null
+++ b/tests/classes/D.js
@@ -0,0 +1,3 @@
+class D { }
+class E { }
+new E().x
diff --git a/tests/classes/__snapshots__/jsfmt.spec.js.snap b/tests/classes/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1f1021805669
--- /dev/null
+++ b/tests/classes/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,249 @@
+exports[`test A.js 1`] = `
+"class A {
+  foo(x:number):void { }
+}
+
+module.exports = A;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {
+  foo(x: number): void {
+    
+  }
+}
+module.exports = A;
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"var A = require(\'./A\');
+
+class B extends A { }
+
+let b = new B();
+(b.foo: number); // error, number !~> function
+
+module.exports = B;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var A = require(\"./A\");
+class B extends A {}
+let b = new B();
+(b.foo: number);// error, number !~> function
+module.exports = B;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"var B = require(\'./B\');
+
+class C extends B {
+  foo(x:string):void { }
+}
+
+let c = new C();
+(c.foo: number); // error, number !~> function
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var B = require(\"./B\");
+class C extends B {
+  foo(x: string): void {
+    
+  }
+}
+let c = new C();
+(c.foo: number);// error, number !~> function
+module.exports = C;
+
+"
+`;
+
+exports[`test D.js 1`] = `
+"class D { }
+class E { }
+new E().x
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class D {}
+class E {}
+new E().x;
+
+"
+`;
+
+exports[`test class_shapes.js 1`] = `
+"/* @flow */
+
+type Foo = {
+  a: string;    // exists in TestClass
+  b: string;    // doesn\'t exist
+  c?: ?string;  // exists in TestClass, optional
+  d?: number;   // doesn\'t exist
+}
+
+class TestClass {
+  a: string;
+  c: ?string;
+}
+
+var x = new TestClass();
+
+x.a; // ok
+x.b; // error, TestClass has no b
+x.c; // ok
+x.d; // error, TestClass has no d
+
+var y : Foo = x;
+y.b; // error, doesn\'t exist in TestClass
+y.d; // ok, it\'s optional
+
+class Test2Superclass {
+  a: number;  // conflicts with cast to Foo
+  c: ?number; // conflicts with cast to Foo
+}
+class Test2Class extends Test2Superclass {
+  b: number;  // conflicts with cast to Foo
+}
+
+var z = new Test2Class();
+var w : Foo = z;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+type Foo = {
+  // exists in TestClass a: string,
+  // doesn\'t exist b: string,
+  // exists in TestClass, optional c?: ?string,
+  // doesn\'t exist d?: number
+};
+class TestClass {
+  a: string;
+  c: ?string;
+}
+var x = new TestClass();
+x.a;// ok
+x.b;// error, TestClass has no b
+x.c;// ok
+x.d;// error, TestClass has no d
+var y: Foo = x;
+y.b;// error, doesn\'t exist in TestClass
+y.d;// ok, it\'s optional
+class Test2Superclass {
+  a: number;// conflicts with cast to Foo
+  c: ?number;// conflicts with cast to Foo
+}
+class Test2Class extends Test2Superclass {
+  b: number;// conflicts with cast to Foo
+}
+var z = new Test2Class();
+var w: Foo = z;
+
+"
+`;
+
+exports[`test expr.js 1`] = `
+"var Bar = class Foo {
+  static factory(): Foo { // OK: Foo is a type in this scope
+    return new Foo()      // OK: Foo is a runtime binding in this scope
+  }
+};
+
+var bar1: Bar = new Bar() // OK
+var bar2: Bar = Bar.factory() // OK
+
+// NB: Don\'t write expected errors using Foo to avoid error collapse hiding an
+// unexpected failure in the above code.
+
+var B = class Baz { }
+var b = new Baz(); // error: Baz is not a runtime binding in this scope
+
+var C = class Qux { }
+var c: Qux = new C(); // error: Qux is not a type in this scope
+
+// OK: anon classes create no binding, but can be bound manually
+var Anon = class { }
+var anon: Anon = new Anon();
+
+class Alias { }
+var _Alias = class Alias {
+  static factory(): Alias {
+    return new Alias();
+  }
+}
+var alias1: Alias = new _Alias(); // error: bad pun
+var alias2: Alias = _Alias.factory(); // error: bad pun
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var Bar = class Foo {
+  factory(): Foo {
+    // OK: Foo is a type in this scope
+    return new Foo();// OK: Foo is a runtime binding in this scope
+  }
+};
+var bar1: Bar = new Bar();// OK
+var bar2: Bar = Bar.factory();// OK
+// NB: Don\'t write expected errors using Foo to avoid error collapse hiding an
+// unexpected failure in the above code.
+var B = class Baz {};
+var b = new Baz();// error: Baz is not a runtime binding in this scope
+var C = class Qux {};
+var c: Qux = new C();// error: Qux is not a type in this scope
+// OK: anon classes create no binding, but can be bound manually
+var Anon = class {};
+var anon: Anon = new Anon();
+class Alias {}
+var _Alias = class Alias {
+  factory(): Alias {
+    return new Alias();
+  }
+};
+var alias1: Alias = new _Alias();// error: bad pun
+var alias2: Alias = _Alias.factory();// error: bad pun
+
+"
+`;
+
+exports[`test loc.js 1`] = `
+"/* @flow */
+
+type Foo = number
+
+class Foo {} // error, shadows type Foo
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+type Foo = number;
+class Foo {}// error, shadows type Foo
+
+"
+`;
+
+exports[`test statics.js 1`] = `
+"/* @flow */
+
+class C {
+  static p: string;
+}
+C.p = \"hi\";
+
+// Class static fields are compatible with object types
+(C: {p:string}); // ok
+(C: {p:number}); // errors, string ~> number & vice versa (unify)
+
+declare var o: {p:number};
+(o: Class<C>); // error, object type incompatible with class type
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/classes/class_shapes.js b/tests/classes/class_shapes.js
new file mode 100644
index 000000000000..d35b273d6be5
--- /dev/null
+++ b/tests/classes/class_shapes.js
@@ -0,0 +1,35 @@
+/* @flow */
+
+type Foo = {
+  a: string;    // exists in TestClass
+  b: string;    // doesn't exist
+  c?: ?string;  // exists in TestClass, optional
+  d?: number;   // doesn't exist
+}
+
+class TestClass {
+  a: string;
+  c: ?string;
+}
+
+var x = new TestClass();
+
+x.a; // ok
+x.b; // error, TestClass has no b
+x.c; // ok
+x.d; // error, TestClass has no d
+
+var y : Foo = x;
+y.b; // error, doesn't exist in TestClass
+y.d; // ok, it's optional
+
+class Test2Superclass {
+  a: number;  // conflicts with cast to Foo
+  c: ?number; // conflicts with cast to Foo
+}
+class Test2Class extends Test2Superclass {
+  b: number;  // conflicts with cast to Foo
+}
+
+var z = new Test2Class();
+var w : Foo = z;
diff --git a/tests/classes/expr.js b/tests/classes/expr.js
new file mode 100644
index 000000000000..7fcca75c1f8f
--- /dev/null
+++ b/tests/classes/expr.js
@@ -0,0 +1,30 @@
+var Bar = class Foo {
+  static factory(): Foo { // OK: Foo is a type in this scope
+    return new Foo()      // OK: Foo is a runtime binding in this scope
+  }
+};
+
+var bar1: Bar = new Bar() // OK
+var bar2: Bar = Bar.factory() // OK
+
+// NB: Don't write expected errors using Foo to avoid error collapse hiding an
+// unexpected failure in the above code.
+
+var B = class Baz { }
+var b = new Baz(); // error: Baz is not a runtime binding in this scope
+
+var C = class Qux { }
+var c: Qux = new C(); // error: Qux is not a type in this scope
+
+// OK: anon classes create no binding, but can be bound manually
+var Anon = class { }
+var anon: Anon = new Anon();
+
+class Alias { }
+var _Alias = class Alias {
+  static factory(): Alias {
+    return new Alias();
+  }
+}
+var alias1: Alias = new _Alias(); // error: bad pun
+var alias2: Alias = _Alias.factory(); // error: bad pun
diff --git a/tests/classes/jsfmt.spec.js b/tests/classes/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/classes/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/classes/loc.js b/tests/classes/loc.js
new file mode 100644
index 000000000000..8f6066465e8f
--- /dev/null
+++ b/tests/classes/loc.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+type Foo = number
+
+class Foo {} // error, shadows type Foo
diff --git a/tests/classes/statics.js b/tests/classes/statics.js
new file mode 100644
index 000000000000..75c9d5e7bdef
--- /dev/null
+++ b/tests/classes/statics.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+class C {
+  static p: string;
+}
+C.p = "hi";
+
+// Class static fields are compatible with object types
+(C: {p:string}); // ok
+(C: {p:number}); // errors, string ~> number & vice versa (unify)
+
+declare var o: {p:number};
+(o: Class<C>); // error, object type incompatible with class type
diff --git a/tests/closure/Closure.js b/tests/closure/Closure.js
new file mode 100644
index 000000000000..baeae7811a1f
--- /dev/null
+++ b/tests/closure/Closure.js
@@ -0,0 +1,80 @@
+/***
+ * Test tracking of variable types across closure calls.
+ * @flow
+ */
+
+function takes_string(_:string) { }
+
+// global write from function
+//
+
+var global_x = "hello";
+
+function global_f() { }
+function global_g() { global_x = 42; }
+
+global_f();
+takes_string(global_x); // ok
+
+global_g();
+takes_string(global_x); // error
+
+global_x = 42;  // shouldn't pollute linear refinement
+
+// local write from function
+//
+
+function local_func() {
+
+  var local_x = "hello";
+
+  function local_f() { }
+  function local_g() { local_x = 42; }
+
+  local_f();
+  takes_string(local_x); // ok
+
+  local_g();
+  takes_string(local_x); // error
+
+  local_x = 42;  // shouldn't pollute linear refinement
+}
+
+// global write from method
+//
+
+var global_y = "hello";
+
+var global_o = {
+  f: function() { },
+  g: function() { global_y = 42; }
+}
+
+global_o.f();
+takes_string(global_y); // ok
+
+global_o.g();
+takes_string(global_y); // error
+
+global_y = 42;  // shouldn't pollute linear refinement
+
+// local write from method
+//
+
+function local_meth() {
+
+  var local_y = "hello";
+
+  var local_o = {
+    f: function() { },
+    g: function() { local_y = 42; }
+  }
+
+  local_o.f();
+  takes_string(local_y); // ok
+
+  local_o.g();
+  takes_string(local_y); // error
+
+  local_y = 42;  // shouldn't pollute linear refinement
+}
diff --git a/tests/closure/__snapshots__/jsfmt.spec.js.snap b/tests/closure/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e0f87eb8caa1
--- /dev/null
+++ b/tests/closure/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,256 @@
+exports[`test Closure.js 1`] = `
+"/***
+ * Test tracking of variable types across closure calls.
+ * @flow
+ */
+
+function takes_string(_:string) { }
+
+// global write from function
+//
+
+var global_x = \"hello\";
+
+function global_f() { }
+function global_g() { global_x = 42; }
+
+global_f();
+takes_string(global_x); // ok
+
+global_g();
+takes_string(global_x); // error
+
+global_x = 42;  // shouldn\'t pollute linear refinement
+
+// local write from function
+//
+
+function local_func() {
+
+  var local_x = \"hello\";
+
+  function local_f() { }
+  function local_g() { local_x = 42; }
+
+  local_f();
+  takes_string(local_x); // ok
+
+  local_g();
+  takes_string(local_x); // error
+
+  local_x = 42;  // shouldn\'t pollute linear refinement
+}
+
+// global write from method
+//
+
+var global_y = \"hello\";
+
+var global_o = {
+  f: function() { },
+  g: function() { global_y = 42; }
+}
+
+global_o.f();
+takes_string(global_y); // ok
+
+global_o.g();
+takes_string(global_y); // error
+
+global_y = 42;  // shouldn\'t pollute linear refinement
+
+// local write from method
+//
+
+function local_meth() {
+
+  var local_y = \"hello\";
+
+  var local_o = {
+    f: function() { },
+    g: function() { local_y = 42; }
+  }
+
+  local_o.f();
+  takes_string(local_y); // ok
+
+  local_o.g();
+  takes_string(local_y); // error
+
+  local_y = 42;  // shouldn\'t pollute linear refinement
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/***
+ * Test tracking of variable types across closure calls.
+ * @flow
+ */
+function takes_string(_: string) {
+  
+}
+// global write from function
+//
+var global_x = \"hello\";
+function global_f() {
+  
+}
+function global_g() {
+  global_x = 42;
+}
+global_f();
+takes_string(global_x);// ok
+global_g();
+takes_string(global_x);// error
+global_x = 42;// shouldn\'t pollute linear refinement
+// local write from function
+//
+function local_func() {
+  var local_x = \"hello\";
+  function local_f() {
+    
+  }
+  function local_g() {
+    local_x = 42;
+  }
+  local_f();
+  takes_string(local_x);// ok
+  local_g();
+  takes_string(local_x);// error
+  local_x = 42;// shouldn\'t pollute linear refinement
+}
+// global write from method
+//
+var global_y = \"hello\";
+var global_o = {
+  f: function() {
+    
+  },
+  g: function() {
+    global_y = 42;
+  }
+};
+global_o.f();
+takes_string(global_y);// ok
+global_o.g();
+takes_string(global_y);// error
+global_y = 42;// shouldn\'t pollute linear refinement
+// local write from method
+//
+function local_meth() {
+  var local_y = \"hello\";
+  var local_o = {
+    f: function() {
+      
+    },
+    g: function() {
+      local_y = 42;
+    }
+  };
+  local_o.f();
+  takes_string(local_y);// ok
+  local_o.g();
+  takes_string(local_y);// error
+  local_y = 42;// shouldn\'t pollute linear refinement
+}
+
+"
+`;
+
+exports[`test cond_havoc.js 1`] = `
+"// @flow
+
+// from sam, https://github.com/facebook/flow/issues/780
+// call to f() within if should properly havoc x.
+//
+function example(b: bool): number {
+  var x = 0;
+  function f() { x = \"\" }
+  if (b) {
+    f();
+  }
+  return x; // error, string ~/~> number (return type anno) TODO
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// from sam, https://github.com/facebook/flow/issues/780
+// call to f() within if should properly havoc x.
+//
+function example(b: boolean): number {
+  var x = 0;
+  function f() {
+    x = \"\";
+  }
+  if (b) {
+    f();
+  }
+  return x;// error, string ~/~> number (return type anno) TODO
+}
+
+"
+`;
+
+exports[`test const.js 1`] = `
+"/***
+ * consts retain refinements
+ * @flow
+ */
+
+// global, anybody can call it at any time
+var call_me: () => void = () => {};
+
+function g(x: ?number) {
+
+  const const_x = x;
+  if (const_x) {
+    // ok: if const_x is truthy here, it\'s truthy everywhere
+    call_me = () => { var y:number = const_x; };
+  }
+
+  var var_x = x;
+  if (var_x) {
+    // error: var_x might no longer be truthy when call_me is called
+    call_me = () => { var y:number = var_x; };  // error
+  }
+  var_x = null;
+}
+
+function h(x: number | string | boolean) {
+
+  const const_x = x;
+  if (typeof(const_x) == \"number\") {
+    call_me = () => { var y:number = const_x; };  // ok
+  } else if (typeof(const_x) == \"string\") {
+    call_me = () => { var y:string = const_x; };  // ok
+  } else if (typeof(const_x) == \"boolean\") {
+    call_me = () => { var y:boolean = const_x; };  // ok
+  }
+
+  var var_x = x;
+  if (typeof(var_x) == \"number\") {
+    call_me = () => { var y:number = var_x; };  // error
+  } else if (typeof(var_x) == \"string\") {
+    call_me = () => { var y:string = var_x; };  // error
+  } else if (typeof(var_x) == \"boolean\") {
+    call_me = () => { var y:boolean = var_x; };  // error
+  }
+}
+
+// in a galaxy far far away
+call_me();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/closure/cond_havoc.js b/tests/closure/cond_havoc.js
new file mode 100644
index 000000000000..d4364f3280a2
--- /dev/null
+++ b/tests/closure/cond_havoc.js
@@ -0,0 +1,13 @@
+// @flow
+
+// from sam, https://github.com/facebook/flow/issues/780
+// call to f() within if should properly havoc x.
+//
+function example(b: bool): number {
+  var x = 0;
+  function f() { x = "" }
+  if (b) {
+    f();
+  }
+  return x; // error, string ~/~> number (return type anno) TODO
+}
diff --git a/tests/closure/const.js b/tests/closure/const.js
new file mode 100644
index 000000000000..e16e12efc5c8
--- /dev/null
+++ b/tests/closure/const.js
@@ -0,0 +1,47 @@
+/***
+ * consts retain refinements
+ * @flow
+ */
+
+// global, anybody can call it at any time
+var call_me: () => void = () => {};
+
+function g(x: ?number) {
+
+  const const_x = x;
+  if (const_x) {
+    // ok: if const_x is truthy here, it's truthy everywhere
+    call_me = () => { var y:number = const_x; };
+  }
+
+  var var_x = x;
+  if (var_x) {
+    // error: var_x might no longer be truthy when call_me is called
+    call_me = () => { var y:number = var_x; };  // error
+  }
+  var_x = null;
+}
+
+function h(x: number | string | boolean) {
+
+  const const_x = x;
+  if (typeof(const_x) == "number") {
+    call_me = () => { var y:number = const_x; };  // ok
+  } else if (typeof(const_x) == "string") {
+    call_me = () => { var y:string = const_x; };  // ok
+  } else if (typeof(const_x) == "boolean") {
+    call_me = () => { var y:boolean = const_x; };  // ok
+  }
+
+  var var_x = x;
+  if (typeof(var_x) == "number") {
+    call_me = () => { var y:number = var_x; };  // error
+  } else if (typeof(var_x) == "string") {
+    call_me = () => { var y:string = var_x; };  // error
+  } else if (typeof(var_x) == "boolean") {
+    call_me = () => { var y:boolean = var_x; };  // error
+  }
+}
+
+// in a galaxy far far away
+call_me();
diff --git a/tests/closure/jsfmt.spec.js b/tests/closure/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/closure/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/commonjs/Abs.js b/tests/commonjs/Abs.js
new file mode 100644
index 000000000000..965e99f9f476
--- /dev/null
+++ b/tests/commonjs/Abs.js
@@ -0,0 +1,4 @@
+
+function f(x:string) { }
+
+module.exports = f;
diff --git a/tests/commonjs/Rel.js b/tests/commonjs/Rel.js
new file mode 100644
index 000000000000..f6b1b97972c4
--- /dev/null
+++ b/tests/commonjs/Rel.js
@@ -0,0 +1,4 @@
+
+var f = require('./Abs');
+
+f(0);
diff --git a/tests/commonjs/__snapshots__/jsfmt.spec.js.snap b/tests/commonjs/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e28e7d3eacff
--- /dev/null
+++ b/tests/commonjs/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test Abs.js 1`] = `
+"
+function f(x:string) { }
+
+module.exports = f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function f(x: string) {
+  
+}
+module.exports = f;
+
+"
+`;
+
+exports[`test Rel.js 1`] = `
+"
+var f = require('./Abs');
+
+f(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var f = require("./Abs");
+f(0);
+
+"
+`;
diff --git a/tests/commonjs/jsfmt.spec.js b/tests/commonjs/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/commonjs/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/computed_props/__snapshots__/jsfmt.spec.js.snap b/tests/computed_props/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b9d5978c4d68
--- /dev/null
+++ b/tests/computed_props/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,133 @@
+exports[`test test.js 1`] = `
+"var ColorId = {
+  RED: 'R',
+  GREEN: 'G',
+  BLUE: 'B',
+};
+
+var ColorNumber = {
+  RED: 'ff0000',
+  GREEN: '00ff00',
+  BLUE: '0000ff',
+};
+
+var ColorIdToNumber = {
+  [ColorId.RED]: ColorNumber.RED,
+  [ColorId.GREEN]: ColorNumber.GREEN,
+  [ColorId.BLUE]: ColorNumber.BLUE,
+};
+
+(ColorIdToNumber[ColorId.RED]: 'ffffff'); // oops
+
+ColorIdToNumber.XXX; // oops
+
+module.exports = { ColorId, ColorNumber };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var ColorId = { RED: "R", GREEN: "G", BLUE: "B" };
+var ColorNumber = { RED: "ff0000", GREEN: "00ff00", BLUE: "0000ff" };
+var ColorIdToNumber = {
+  [ColorId.RED]: ColorNumber.RED,
+  [ColorId.GREEN]: ColorNumber.GREEN,
+  [ColorId.BLUE]: ColorNumber.BLUE
+};
+(ColorIdToNumber[ColorId.RED]: "ffffff");// oops
+ColorIdToNumber.XXX;// oops
+module.exports = { ColorId, ColorNumber };
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"var { ColorId, ColorNumber } = require('./test');
+var ColorIdToNumber = {
+  [ColorId.RED]: ColorNumber.RED,
+  [ColorId.GREEN]: ColorNumber.GREEN,
+  [ColorId.BLUE]: ColorNumber.BLUE,
+};
+
+(ColorIdToNumber[ColorId.GREEN]: 'ffffff'); // oops
+
+module.exports = ColorIdToNumber;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var { ColorId, ColorNumber } = require("./test");
+var ColorIdToNumber = {
+  [ColorId.RED]: ColorNumber.RED,
+  [ColorId.GREEN]: ColorNumber.GREEN,
+  [ColorId.BLUE]: ColorNumber.BLUE
+};
+(ColorIdToNumber[ColorId.GREEN]: "ffffff");// oops
+module.exports = ColorIdToNumber;
+
+"
+`;
+
+exports[`test test3.js 1`] = `
+"var { ColorId } = require('./test');
+var ColorIdToNumber = require('./test2');
+
+(ColorIdToNumber[ColorId.BLUE]: 'ffffff'); // oops
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var { ColorId } = require("./test");
+var ColorIdToNumber = require("./test2");
+(ColorIdToNumber[ColorId.BLUE]: "ffffff");// oops
+
+"
+`;
+
+exports[`test test4.js 1`] = `
+"module.exports = 'hello';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = "hello";
+
+"
+`;
+
+exports[`test test5.js 1`] = `
+"var hello = require('./test4');
+var dummy = require('./test');
+module.exports = {
+  ...dummy,
+  [hello]: 'world',
+  ...dummy,
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var hello = require("./test4");
+var dummy = require("./test");
+module.exports = { ...dummy, [hello]: "world", ...dummy };
+
+"
+`;
+
+exports[`test test6.js 1`] = `
+"var o = require('./test5');
+(o.hello: 'nothing'); // oops
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = require("./test5");
+(o.hello: "nothing");// oops
+
+"
+`;
+
+exports[`test test7.js 1`] = `
+"var obj = {x: 0, m() { return this.x }}
+var x: string = obj['m'](); // error, number ~> string
+
+var arr = [function() { return this.length }];
+var y: string = arr[0](); // error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var obj = {
+  x: 0,
+  m() {
+    return this.x;
+  }
+};
+var x: string = obj["m"]();// error, number ~> string
+var arr = [
+  function() {
+    return this.length;
+  }
+];
+var y: string = arr[0]();// error: number ~> string
+
+"
+`;
diff --git a/tests/computed_props/jsfmt.spec.js b/tests/computed_props/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/computed_props/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/computed_props/test.js b/tests/computed_props/test.js
new file mode 100644
index 000000000000..4c65f895474e
--- /dev/null
+++ b/tests/computed_props/test.js
@@ -0,0 +1,23 @@
+var ColorId = {
+  RED: 'R',
+  GREEN: 'G',
+  BLUE: 'B',
+};
+
+var ColorNumber = {
+  RED: 'ff0000',
+  GREEN: '00ff00',
+  BLUE: '0000ff',
+};
+
+var ColorIdToNumber = {
+  [ColorId.RED]: ColorNumber.RED,
+  [ColorId.GREEN]: ColorNumber.GREEN,
+  [ColorId.BLUE]: ColorNumber.BLUE,
+};
+
+(ColorIdToNumber[ColorId.RED]: 'ffffff'); // oops
+
+ColorIdToNumber.XXX; // oops
+
+module.exports = { ColorId, ColorNumber };
diff --git a/tests/computed_props/test2.js b/tests/computed_props/test2.js
new file mode 100644
index 000000000000..02f05991d5ed
--- /dev/null
+++ b/tests/computed_props/test2.js
@@ -0,0 +1,10 @@
+var { ColorId, ColorNumber } = require('./test');
+var ColorIdToNumber = {
+  [ColorId.RED]: ColorNumber.RED,
+  [ColorId.GREEN]: ColorNumber.GREEN,
+  [ColorId.BLUE]: ColorNumber.BLUE,
+};
+
+(ColorIdToNumber[ColorId.GREEN]: 'ffffff'); // oops
+
+module.exports = ColorIdToNumber;
diff --git a/tests/computed_props/test3.js b/tests/computed_props/test3.js
new file mode 100644
index 000000000000..90bd0ad2a413
--- /dev/null
+++ b/tests/computed_props/test3.js
@@ -0,0 +1,4 @@
+var { ColorId } = require('./test');
+var ColorIdToNumber = require('./test2');
+
+(ColorIdToNumber[ColorId.BLUE]: 'ffffff'); // oops
diff --git a/tests/computed_props/test4.js b/tests/computed_props/test4.js
new file mode 100644
index 000000000000..76e8a568d58d
--- /dev/null
+++ b/tests/computed_props/test4.js
@@ -0,0 +1 @@
+module.exports = 'hello';
diff --git a/tests/computed_props/test5.js b/tests/computed_props/test5.js
new file mode 100644
index 000000000000..4979c54c80bd
--- /dev/null
+++ b/tests/computed_props/test5.js
@@ -0,0 +1,7 @@
+var hello = require('./test4');
+var dummy = require('./test');
+module.exports = {
+  ...dummy,
+  [hello]: 'world',
+  ...dummy,
+};
diff --git a/tests/computed_props/test6.js b/tests/computed_props/test6.js
new file mode 100644
index 000000000000..89ac05f48a7f
--- /dev/null
+++ b/tests/computed_props/test6.js
@@ -0,0 +1,2 @@
+var o = require('./test5');
+(o.hello: 'nothing'); // oops
diff --git a/tests/computed_props/test7.js b/tests/computed_props/test7.js
new file mode 100644
index 000000000000..003700429d8d
--- /dev/null
+++ b/tests/computed_props/test7.js
@@ -0,0 +1,5 @@
+var obj = {x: 0, m() { return this.x }}
+var x: string = obj['m'](); // error, number ~> string
+
+var arr = [function() { return this.length }];
+var y: string = arr[0](); // error: number ~> string
diff --git a/tests/conditional/__snapshots__/jsfmt.spec.js.snap b/tests/conditional/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a1d029d6c9ed
--- /dev/null
+++ b/tests/conditional/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,50 @@
+exports[`test conditional.js 1`] = `
+"/* @flow */
+
+function a(): number {
+  var x: ?string = null;
+  return x ? 1 : 0;
+}
+
+function b(): number {
+    var x: ?number = null;
+    return x != null ? x : 0;
+}
+
+function c(): number {
+  // equivalent to \`return (x && 1) || 0\`
+  var x = false;
+  var temp = (x ? 1 : x);
+  return temp ? temp : 0;
+}
+
+function d(): string { // expected \`: number | boolean\`
+  // equivalent to \`return x != null && x\`
+  var x: ?number = null;
+  return (x != null) ? x : (x != null);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function a(): number {
+  var x: ?string = null;
+  return (x ? 1 : 0);
+}
+function b(): number {
+  var x: ?number = null;
+  return (x != null ? x : 0);
+}
+function c(): number {
+  // equivalent to \`return (x && 1) || 0\`
+  var x = false;
+  var temp = (x ? 1 : x);
+  return (temp ? temp : 0);
+}
+function d(): string {
+  // expected \`: number | boolean\`
+  // equivalent to \`return x != null && x\`
+  var x: ?number = null;
+  return (x != null ? x : x != null);
+}
+
+"
+`;
diff --git a/tests/conditional/conditional.js b/tests/conditional/conditional.js
new file mode 100644
index 000000000000..b66892cfd1a2
--- /dev/null
+++ b/tests/conditional/conditional.js
@@ -0,0 +1,24 @@
+/* @flow */
+
+function a(): number {
+  var x: ?string = null;
+  return x ? 1 : 0;
+}
+
+function b(): number {
+    var x: ?number = null;
+    return x != null ? x : 0;
+}
+
+function c(): number {
+  // equivalent to `return (x && 1) || 0`
+  var x = false;
+  var temp = (x ? 1 : x);
+  return temp ? temp : 0;
+}
+
+function d(): string { // expected `: number | boolean`
+  // equivalent to `return x != null && x`
+  var x: ?number = null;
+  return (x != null) ? x : (x != null);
+}
diff --git a/tests/conditional/jsfmt.spec.js b/tests/conditional/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/conditional/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_all/__snapshots__/jsfmt.spec.js.snap b/tests/config_all/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..abf7e57cd722
--- /dev/null
+++ b/tests/config_all/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test no_at_flow.js 1`] = `
+"var x: number = "not a number"; // Error: string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: number = "not a number";// Error: string ~> number
+
+"
+`;
diff --git a/tests/config_all/jsfmt.spec.js b/tests/config_all/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_all/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_all/no_at_flow.js b/tests/config_all/no_at_flow.js
new file mode 100644
index 000000000000..3d01d67f0e7e
--- /dev/null
+++ b/tests/config_all/no_at_flow.js
@@ -0,0 +1 @@
+var x: number = "not a number"; // Error: string ~> number
diff --git a/tests/config_all_false/__snapshots__/jsfmt.spec.js.snap b/tests/config_all_false/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..dc6f37acc919
--- /dev/null
+++ b/tests/config_all_false/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test no_at_flow.js 1`] = `
+"var x: number = "not a number"; // No error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: number = "not a number";// No error
+
+"
+`;
diff --git a/tests/config_all_false/jsfmt.spec.js b/tests/config_all_false/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_all_false/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_all_false/no_at_flow.js b/tests/config_all_false/no_at_flow.js
new file mode 100644
index 000000000000..656a221a89c6
--- /dev/null
+++ b/tests/config_all_false/no_at_flow.js
@@ -0,0 +1 @@
+var x: number = "not a number"; // No error
diff --git a/tests/config_all_weak/__snapshots__/jsfmt.spec.js.snap b/tests/config_all_weak/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a9e1e0a2a26c
--- /dev/null
+++ b/tests/config_all_weak/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test no_at_flow.js 1`] = `
+"var x;
+
+x.length;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x;
+x.length;
+
+"
+`;
diff --git a/tests/config_all_weak/jsfmt.spec.js b/tests/config_all_weak/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_all_weak/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_all_weak/no_at_flow.js b/tests/config_all_weak/no_at_flow.js
new file mode 100644
index 000000000000..eacadf62df20
--- /dev/null
+++ b/tests/config_all_weak/no_at_flow.js
@@ -0,0 +1,3 @@
+var x;
+
+x.length;
diff --git a/tests/config_file_extensions/__snapshots__/jsfmt.spec.js.snap b/tests/config_file_extensions/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..dfca8fc58e4b
--- /dev/null
+++ b/tests/config_file_extensions/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test test.js 1`] = `
+"/*
+ * @flow
+ */
+
+function foo(x) {
+  var a: number = 'asdf';
+  return x * 10;
+}
+
+// This file should be ignored, so this should not result in an error
+foo('Hello, world!');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @flow
+ */
+function foo(x) {
+  var a: number = "asdf";
+  return x * 10;
+}
+// This file should be ignored, so this should not result in an error
+foo("Hello, world!");
+
+"
+`;
diff --git a/tests/config_file_extensions/jsfmt.spec.js b/tests/config_file_extensions/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_file_extensions/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_file_extensions/test.js b/tests/config_file_extensions/test.js
new file mode 100644
index 000000000000..ec34cbda765b
--- /dev/null
+++ b/tests/config_file_extensions/test.js
@@ -0,0 +1,11 @@
+/*
+ * @flow
+ */
+
+function foo(x) {
+  var a: number = 'asdf';
+  return x * 10;
+}
+
+// This file should be ignored, so this should not result in an error
+foo('Hello, world!');
diff --git a/tests/config_ignore/__snapshots__/jsfmt.spec.js.snap b/tests/config_ignore/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e2b382361017
--- /dev/null
+++ b/tests/config_ignore/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,12 @@
+exports[`test foo.js 1`] = `
+"/* @flow */
+
+// No error, this file is ignored
+var x: number = "string";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// No error, this file is ignored
+var x: number = "string";
+
+"
+`;
diff --git a/tests/config_ignore/dir/__snapshots__/jsfmt.spec.js.snap b/tests/config_ignore/dir/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d18373a3898c
--- /dev/null
+++ b/tests/config_ignore/dir/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test foo.js 1`] = `
+"/* @flow */
+
+var x: number = "string"; // Error string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var x: number = "string";// Error string ~> number
+
+"
+`;
diff --git a/tests/config_ignore/dir/foo.js b/tests/config_ignore/dir/foo.js
new file mode 100644
index 000000000000..b9901bd5b99b
--- /dev/null
+++ b/tests/config_ignore/dir/foo.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+var x: number = "string"; // Error string ~> number
diff --git a/tests/config_ignore/dir/jsfmt.spec.js b/tests/config_ignore/dir/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_ignore/dir/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_ignore/foo.js b/tests/config_ignore/foo.js
new file mode 100644
index 000000000000..1b0029abb16f
--- /dev/null
+++ b/tests/config_ignore/foo.js
@@ -0,0 +1,4 @@
+/* @flow */
+
+// No error, this file is ignored
+var x: number = "string";
diff --git a/tests/config_ignore/jsfmt.spec.js b/tests/config_ignore/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_ignore/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_name_mapper_PROJECT_ROOT-1.0/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..049efd334d2b
--- /dev/null
+++ b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test main.js 1`] = `
+"// @flow
+
+import {test} from 'testmodule';
+
+var a: number = test;
+var b: string = test; // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { test } from "testmodule";
+var a: number = test;
+var b: string = test;// Error: number ~> string
+
+"
+`;
diff --git a/tests/config_module_name_mapper_PROJECT_ROOT-1.0/jsfmt.spec.js b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_name_mapper_PROJECT_ROOT-1.0/main.js b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/main.js
new file mode 100644
index 000000000000..8168ba9c3ce0
--- /dev/null
+++ b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/main.js
@@ -0,0 +1,6 @@
+// @flow
+
+import {test} from 'testmodule';
+
+var a: number = test;
+var b: string = test; // Error: number ~> string
diff --git a/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8f51a9c7ac9d
--- /dev/null
+++ b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test testmodule.js 1`] = `
+"// @flow
+
+export let test = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export let test = 42;
+
+"
+`;
diff --git a/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/jsfmt.spec.js b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/testmodule.js b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/testmodule.js
new file mode 100644
index 000000000000..1e0fc93cca56
--- /dev/null
+++ b/tests/config_module_name_mapper_PROJECT_ROOT-1.0/src/testmodule.js
@@ -0,0 +1,3 @@
+// @flow
+
+export let test = 42;
diff --git a/tests/config_module_name_mapper_filetype/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_name_mapper_filetype/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2ad57396e31f
--- /dev/null
+++ b/tests/config_module_name_mapper_filetype/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,12 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+import {className} from "./SomeCSSFile.css";
+import {doesntExist} from "./SomeCSSFile.css"; // Error: \`doestExist\` isn't an export
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { className } from "./SomeCSSFile.css";
+import { doesntExist } from "./SomeCSSFile.css";// Error: \`doestExist\` isn't an export
+
+"
+`;
diff --git a/tests/config_module_name_mapper_filetype/jsfmt.spec.js b/tests/config_module_name_mapper_filetype/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_name_mapper_filetype/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_name_mapper_filetype/test.js b/tests/config_module_name_mapper_filetype/test.js
new file mode 100644
index 000000000000..8b209dd801c6
--- /dev/null
+++ b/tests/config_module_name_mapper_filetype/test.js
@@ -0,0 +1,4 @@
+// @flow
+
+import {className} from "./SomeCSSFile.css";
+import {doesntExist} from "./SomeCSSFile.css"; // Error: `doestExist` isn't an export
diff --git a/tests/config_module_name_rewrite_haste/A.js b/tests/config_module_name_rewrite_haste/A.js
new file mode 100644
index 000000000000..ca5185b4bcf6
--- /dev/null
+++ b/tests/config_module_name_rewrite_haste/A.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+var m1 = require('1DoesntExist');
+import {numVal as numVal1} from '1DoesntExist';
+var a_1: number = m1.numVal;
+var a_2: number = numVal1;
+
+// Error: 'Exists2' is not a valid module name
+//
+// This tests that, for haste, the first name_mapper regexp that happens to
+// match the given module name string is picked.
+var m2 = require('2DoesntExist'); // Error
+import {numVal as numVal2} from '3DoesntExist'; // Error
diff --git a/tests/config_module_name_rewrite_haste/Exists.js b/tests/config_module_name_rewrite_haste/Exists.js
new file mode 100644
index 000000000000..b91779d3ebe0
--- /dev/null
+++ b/tests/config_module_name_rewrite_haste/Exists.js
@@ -0,0 +1,8 @@
+/**
+ * @providesModule Exists
+ * @flow
+ */
+
+module.exports = {
+  numVal: 42
+};
diff --git a/tests/config_module_name_rewrite_haste/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_name_rewrite_haste/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6ccef0e73a9b
--- /dev/null
+++ b/tests/config_module_name_rewrite_haste/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,48 @@
+exports[`test A.js 1`] = `
+"/* @flow */
+
+var m1 = require('1DoesntExist');
+import {numVal as numVal1} from '1DoesntExist';
+var a_1: number = m1.numVal;
+var a_2: number = numVal1;
+
+// Error: 'Exists2' is not a valid module name
+//
+// This tests that, for haste, the first name_mapper regexp that happens to
+// match the given module name string is picked.
+var m2 = require('2DoesntExist'); // Error
+import {numVal as numVal2} from '3DoesntExist'; // Error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var m1 = require("1DoesntExist");
+import { numVal as numVal1 } from "1DoesntExist";
+var a_1: number = m1.numVal;
+var a_2: number = numVal1;
+// Error: 'Exists2' is not a valid module name
+//
+// This tests that, for haste, the first name_mapper regexp that happens to
+// match the given module name string is picked.
+var m2 = require("2DoesntExist");// Error
+import { numVal as numVal2 } from "3DoesntExist";// Error
+
+"
+`;
+
+exports[`test Exists.js 1`] = `
+"/**
+ * @providesModule Exists
+ * @flow
+ */
+
+module.exports = {
+  numVal: 42
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule Exists
+ * @flow
+ */
+module.exports = { numVal: 42 };
+
+"
+`;
diff --git a/tests/config_module_name_rewrite_haste/jsfmt.spec.js b/tests/config_module_name_rewrite_haste/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_name_rewrite_haste/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_name_rewrite_node/A.js b/tests/config_module_name_rewrite_node/A.js
new file mode 100644
index 000000000000..5f42adbf50d1
--- /dev/null
+++ b/tests/config_module_name_rewrite_node/A.js
@@ -0,0 +1,25 @@
+/* @flow */
+
+var m1 = require('./1DoesntExist');
+var a_1: number = m1.numVal;
+var a_2: string = m1.numVal; // Error: number ~> string
+import {numVal} from './1DoesntExist';
+var a_3: number = numVal;
+var a_4: string = numVal; // Error: number ~> string
+
+// This tests that, for node, the first name mapping that both matches *and*
+// results in a valid module filename is picked.
+var m2 = require('./2DoesntExist');
+var b_1: number = m2.numVal;
+var b_2: string = m2.numVal; // Error: number ~> string
+import {numVal as numVal2} from './3DoesntExist';
+var b_3: number = numVal2;
+var b_4: string = numVal2; // Error: number ~> string
+
+// node_modules/Exists/index.js
+var m3 = require('4DoesntExist');
+var c_1: number = m3.numVal;
+var c_2: string = m3.numVal; // Error: number ~> string
+import {numVal as numVal3} from '5DoesntExist';
+var c_3: number = numVal3;
+var c_4: string = numVal3; // Error: number ~> string
diff --git a/tests/config_module_name_rewrite_node/Exists.js b/tests/config_module_name_rewrite_node/Exists.js
new file mode 100644
index 000000000000..1b63e9c8bbf7
--- /dev/null
+++ b/tests/config_module_name_rewrite_node/Exists.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+module.exports = {
+  numVal: 42
+};
diff --git a/tests/config_module_name_rewrite_node/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_name_rewrite_node/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e8252c84db6e
--- /dev/null
+++ b/tests/config_module_name_rewrite_node/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,65 @@
+exports[`test A.js 1`] = `
+"/* @flow */
+
+var m1 = require('./1DoesntExist');
+var a_1: number = m1.numVal;
+var a_2: string = m1.numVal; // Error: number ~> string
+import {numVal} from './1DoesntExist';
+var a_3: number = numVal;
+var a_4: string = numVal; // Error: number ~> string
+
+// This tests that, for node, the first name mapping that both matches *and*
+// results in a valid module filename is picked.
+var m2 = require('./2DoesntExist');
+var b_1: number = m2.numVal;
+var b_2: string = m2.numVal; // Error: number ~> string
+import {numVal as numVal2} from './3DoesntExist';
+var b_3: number = numVal2;
+var b_4: string = numVal2; // Error: number ~> string
+
+// node_modules/Exists/index.js
+var m3 = require('4DoesntExist');
+var c_1: number = m3.numVal;
+var c_2: string = m3.numVal; // Error: number ~> string
+import {numVal as numVal3} from '5DoesntExist';
+var c_3: number = numVal3;
+var c_4: string = numVal3; // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var m1 = require("./1DoesntExist");
+var a_1: number = m1.numVal;
+var a_2: string = m1.numVal;// Error: number ~> string
+import { numVal } from "./1DoesntExist";
+var a_3: number = numVal;
+var a_4: string = numVal;// Error: number ~> string
+// This tests that, for node, the first name mapping that both matches *and*
+// results in a valid module filename is picked.
+var m2 = require("./2DoesntExist");
+var b_1: number = m2.numVal;
+var b_2: string = m2.numVal;// Error: number ~> string
+import { numVal as numVal2 } from "./3DoesntExist";
+var b_3: number = numVal2;
+var b_4: string = numVal2;// Error: number ~> string
+// node_modules/Exists/index.js
+var m3 = require("4DoesntExist");
+var c_1: number = m3.numVal;
+var c_2: string = m3.numVal;// Error: number ~> string
+import { numVal as numVal3 } from "5DoesntExist";
+var c_3: number = numVal3;
+var c_4: string = numVal3;// Error: number ~> string
+
+"
+`;
+
+exports[`test Exists.js 1`] = `
+"/* @flow */
+
+module.exports = {
+  numVal: 42
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports = { numVal: 42 };
+
+"
+`;
diff --git a/tests/config_module_name_rewrite_node/jsfmt.spec.js b/tests/config_module_name_rewrite_node/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_name_rewrite_node/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_system_node_resolve_dirname/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_system_node_resolve_dirname/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f6a5d798672e
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test toplevel.js 1`] = `
+"// @flow
+
+import {name} from "testproj";
+
+(name: "node_modules/testproj");
+(name: "custom_resolve_dir/testproj"); // Error: Resolve from node_modules first!
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { name } from "testproj";
+(name: "node_modules/testproj");
+(name: "custom_resolve_dir/testproj");// Error: Resolve from node_modules first!
+
+"
+`;
diff --git a/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..075fd4fa9f24
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test index.js 1`] = `
+"// @flow
+
+export var name: "otherdir/testproj" = "otherdir/testproj";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export var name: "otherdir/testproj" = "otherdir/testproj";
+
+"
+`;
diff --git a/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/index.js b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/index.js
new file mode 100644
index 000000000000..25037710b852
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/index.js
@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "otherdir/testproj" = "otherdir/testproj";
diff --git a/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/jsfmt.spec.js b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..23b55094cf43
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test index.js 1`] = `
+"// @flow
+
+export var name: "otherdir/testproj2" = "otherdir/testproj2";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export var name: "otherdir/testproj2" = "otherdir/testproj2";
+
+"
+`;
diff --git a/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/index.js b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/index.js
new file mode 100644
index 000000000000..ddd1f996f728
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/index.js
@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "otherdir/testproj2" = "otherdir/testproj2";
diff --git a/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/jsfmt.spec.js b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/custom_resolve_dir/testproj2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_system_node_resolve_dirname/jsfmt.spec.js b/tests/config_module_system_node_resolve_dirname/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_system_node_resolve_dirname/subdir/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_system_node_resolve_dirname/subdir/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a3e521c32436
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/subdir/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test sublevel.js 1`] = `
+"// @flow
+
+import {name} from "testproj2";
+
+(name: "node_modules/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+(name: "subdir/custom_resolve_dir/testproj2");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { name } from "testproj2";
+(name: "node_modules/testproj2");// Error: Resolve from sibling 'custom_resolve_dir' first!
+(name: "subdir/custom_resolve_dir/testproj2");
+
+"
+`;
diff --git a/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/__snapshots__/jsfmt.spec.js.snap b/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bec06490d473
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test index.js 1`] = `
+"// @flow
+
+export var name: "subdir/custom_resolve_dir/testproj2" = "subdir/custom_resolve_dir/testproj2";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export var name: "subdir/custom_resolve_dir/testproj2" = "subdir/custom_resolve_dir/testproj2";
+
+"
+`;
diff --git a/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/index.js b/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/index.js
new file mode 100644
index 000000000000..af4294a36c2a
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/index.js
@@ -0,0 +1,3 @@
+// @flow
+
+export var name: "subdir/custom_resolve_dir/testproj2" = "subdir/custom_resolve_dir/testproj2";
diff --git a/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/jsfmt.spec.js b/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/subdir/custom_resolve_dir/testproj2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_system_node_resolve_dirname/subdir/jsfmt.spec.js b/tests/config_module_system_node_resolve_dirname/subdir/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/subdir/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_module_system_node_resolve_dirname/subdir/sublevel.js b/tests/config_module_system_node_resolve_dirname/subdir/sublevel.js
new file mode 100644
index 000000000000..e080e5378dcd
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/subdir/sublevel.js
@@ -0,0 +1,6 @@
+// @flow
+
+import {name} from "testproj2";
+
+(name: "node_modules/testproj2"); // Error: Resolve from sibling 'custom_resolve_dir' first!
+(name: "subdir/custom_resolve_dir/testproj2");
diff --git a/tests/config_module_system_node_resolve_dirname/toplevel.js b/tests/config_module_system_node_resolve_dirname/toplevel.js
new file mode 100644
index 000000000000..5207c12bbba2
--- /dev/null
+++ b/tests/config_module_system_node_resolve_dirname/toplevel.js
@@ -0,0 +1,6 @@
+// @flow
+
+import {name} from "testproj";
+
+(name: "node_modules/testproj");
+(name: "custom_resolve_dir/testproj"); // Error: Resolve from node_modules first!
diff --git a/tests/config_munging_underscores/__snapshots__/jsfmt.spec.js.snap b/tests/config_munging_underscores/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9f42da9c160a
--- /dev/null
+++ b/tests/config_munging_underscores/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,98 @@
+exports[`test chain.js 1`] = `
+"/* @flow */
+
+class A {
+  _property1: number;
+  static _sProperty: number;
+
+  constructor() {
+    this._property1 = 5;
+  }
+  _method1(): number {
+    return 1;
+  }
+  static _sMethod(): string {
+    return "some string";
+  }
+}
+A._sProperty = 48;
+
+class B extends A {
+  _property1: string;
+  static _sProperty: string;
+
+  constructor() {
+    super();
+    this._property1 = "another string";
+  }
+  _method1(): string {
+    return "yet another string";
+  }
+  static _sMethod(): number {
+    return 23;
+  }
+}
+B._sProperty = "B._sProperty string";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class A {
+  _property1: number;
+  static _sProperty: number;
+  constructor() {
+    this._property1 = 5;
+  }
+  _method1(): number {
+    return 1;
+  }
+  _sMethod(): string {
+    return "some string";
+  }
+}
+A._sProperty = 48;
+class B extends A {
+  _property1: string;
+  static _sProperty: string;
+  constructor() {
+    super();
+    this._property1 = "another string";
+  }
+  _method1(): string {
+    return "yet another string";
+  }
+  _sMethod(): number {
+    return 23;
+  }
+}
+B._sProperty = "B._sProperty string";
+
+"
+`;
+
+exports[`test commonjs_export.js 1`] = `
+"/* @flow */
+
+class C {
+  _p: string;
+}
+
+module.exports = new C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class C {
+  _p: string;
+}
+module.exports = new C();
+
+"
+`;
+
+exports[`test commonjs_import.js 1`] = `
+"/* @flow */
+
+import {_p} from "./commonjs_export";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+import { _p } from "./commonjs_export";
+
+"
+`;
diff --git a/tests/config_munging_underscores/chain.js b/tests/config_munging_underscores/chain.js
new file mode 100644
index 000000000000..6eb45e480216
--- /dev/null
+++ b/tests/config_munging_underscores/chain.js
@@ -0,0 +1,34 @@
+/* @flow */
+
+class A {
+  _property1: number;
+  static _sProperty: number;
+
+  constructor() {
+    this._property1 = 5;
+  }
+  _method1(): number {
+    return 1;
+  }
+  static _sMethod(): string {
+    return "some string";
+  }
+}
+A._sProperty = 48;
+
+class B extends A {
+  _property1: string;
+  static _sProperty: string;
+
+  constructor() {
+    super();
+    this._property1 = "another string";
+  }
+  _method1(): string {
+    return "yet another string";
+  }
+  static _sMethod(): number {
+    return 23;
+  }
+}
+B._sProperty = "B._sProperty string";
diff --git a/tests/config_munging_underscores/commonjs_export.js b/tests/config_munging_underscores/commonjs_export.js
new file mode 100644
index 000000000000..bbecd1ae4574
--- /dev/null
+++ b/tests/config_munging_underscores/commonjs_export.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+class C {
+  _p: string;
+}
+
+module.exports = new C;
diff --git a/tests/config_munging_underscores/commonjs_import.js b/tests/config_munging_underscores/commonjs_import.js
new file mode 100644
index 000000000000..f63d24a7f7ad
--- /dev/null
+++ b/tests/config_munging_underscores/commonjs_import.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+import {_p} from "./commonjs_export";
diff --git a/tests/config_munging_underscores/jsfmt.spec.js b/tests/config_munging_underscores/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_munging_underscores/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/config_munging_underscores2/__snapshots__/jsfmt.spec.js.snap b/tests/config_munging_underscores2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..89fc8a4c07b3
--- /dev/null
+++ b/tests/config_munging_underscores2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,69 @@
+exports[`test chain.js 1`] = `
+"/* @flow */
+
+class A {
+  _property1: number;
+  static _sProperty: number;
+
+  constructor() {
+    this._property1 = 5;
+  }
+  _method1(): number {
+    return 1;
+  }
+  static _sMethod(): string {
+    return "some string";
+  }
+}
+A._sProperty = 48;
+
+class B extends A {
+  _property1: string;
+  static _sProperty: string;
+
+  constructor() {
+    super();
+    this._property1 = "another string";
+  }
+  _method1(): string {
+    return "yet another string";
+  }
+  static _sMethod(): number {
+    return 23;
+  }
+}
+B._sProperty = "B._sProperty string";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class A {
+  _property1: number;
+  static _sProperty: number;
+  constructor() {
+    this._property1 = 5;
+  }
+  _method1(): number {
+    return 1;
+  }
+  _sMethod(): string {
+    return "some string";
+  }
+}
+A._sProperty = 48;
+class B extends A {
+  _property1: string;
+  static _sProperty: string;
+  constructor() {
+    super();
+    this._property1 = "another string";
+  }
+  _method1(): string {
+    return "yet another string";
+  }
+  _sMethod(): number {
+    return 23;
+  }
+}
+B._sProperty = "B._sProperty string";
+
+"
+`;
diff --git a/tests/config_munging_underscores2/chain.js b/tests/config_munging_underscores2/chain.js
new file mode 100644
index 000000000000..6eb45e480216
--- /dev/null
+++ b/tests/config_munging_underscores2/chain.js
@@ -0,0 +1,34 @@
+/* @flow */
+
+class A {
+  _property1: number;
+  static _sProperty: number;
+
+  constructor() {
+    this._property1 = 5;
+  }
+  _method1(): number {
+    return 1;
+  }
+  static _sMethod(): string {
+    return "some string";
+  }
+}
+A._sProperty = 48;
+
+class B extends A {
+  _property1: string;
+  static _sProperty: string;
+
+  constructor() {
+    super();
+    this._property1 = "another string";
+  }
+  _method1(): string {
+    return "yet another string";
+  }
+  static _sMethod(): number {
+    return 23;
+  }
+}
+B._sProperty = "B._sProperty string";
diff --git a/tests/config_munging_underscores2/jsfmt.spec.js b/tests/config_munging_underscores2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/config_munging_underscores2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/const_params/__snapshots__/jsfmt.spec.js.snap b/tests/const_params/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..028d8606c6c4
--- /dev/null
+++ b/tests/const_params/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,63 @@
+exports[`test test.js 1`] = `
+"/**
+ * test handling of const params
+ * - reassignment prohibited
+ * - durable refinements
+ *
+ * Currently gated in .flowconfig:
+ *
+ * [options]
+ * experimental.const_params
+ *
+ * Syntax to follow
+ *
+ * @flow
+ */
+
+function cannot_reassign(x: string) {
+  x = "hey"; // error, const param cannot be reassigned
+}
+
+// Note: const params use the same machinery as explicit
+// const bindings, which are tested more extensively elsewhere.
+// Here we're just making sure the machinery is hooked up.
+//
+function durable_refi(x: ?number) {
+  if (x) {
+    // ok: if x is truthy here, it's truthy everywhere
+    return () => { var y:number = x; };
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * test handling of const params
+ * - reassignment prohibited
+ * - durable refinements
+ *
+ * Currently gated in .flowconfig:
+ *
+ * [options]
+ * experimental.const_params
+ *
+ * Syntax to follow
+ *
+ * @flow
+ */
+function cannot_reassign(x: string) {
+  x = "hey";// error, const param cannot be reassigned
+}
+// Note: const params use the same machinery as explicit
+// const bindings, which are tested more extensively elsewhere.
+// Here we're just making sure the machinery is hooked up.
+//
+function durable_refi(x: ?number) {
+  if (x) {
+    // ok: if x is truthy here, it's truthy everywhere
+    return () => {
+      var y: number = x;
+    };
+  }
+}
+
+"
+`;
diff --git a/tests/const_params/jsfmt.spec.js b/tests/const_params/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/const_params/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/const_params/test.js b/tests/const_params/test.js
new file mode 100644
index 000000000000..0f7838c3c1fa
--- /dev/null
+++ b/tests/const_params/test.js
@@ -0,0 +1,29 @@
+/**
+ * test handling of const params
+ * - reassignment prohibited
+ * - durable refinements
+ *
+ * Currently gated in .flowconfig:
+ *
+ * [options]
+ * experimental.const_params
+ *
+ * Syntax to follow
+ *
+ * @flow
+ */
+
+function cannot_reassign(x: string) {
+  x = "hey"; // error, const param cannot be reassigned
+}
+
+// Note: const params use the same machinery as explicit
+// const bindings, which are tested more extensively elsewhere.
+// Here we're just making sure the machinery is hooked up.
+//
+function durable_refi(x: ?number) {
+  if (x) {
+    // ok: if x is truthy here, it's truthy everywhere
+    return () => { var y:number = x; };
+  }
+}
diff --git a/tests/constructor/__snapshots__/jsfmt.spec.js.snap b/tests/constructor/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..038fdeca83c6
--- /dev/null
+++ b/tests/constructor/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test constructor.js 1`] = `
+"class C {
+    constructor() { }
+}
+
+class D {
+    constructor():number { }
+}
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  constructor() {
+    
+  }
+}
+class D {
+  constructor(): number {
+    
+  }
+}
+module.exports = C;
+
+"
+`;
diff --git a/tests/constructor/constructor.js b/tests/constructor/constructor.js
new file mode 100644
index 000000000000..92038b6e4e2d
--- /dev/null
+++ b/tests/constructor/constructor.js
@@ -0,0 +1,9 @@
+class C {
+    constructor() { }
+}
+
+class D {
+    constructor():number { }
+}
+
+module.exports = C;
diff --git a/tests/constructor/jsfmt.spec.js b/tests/constructor/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/constructor/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/constructor_annots/__snapshots__/jsfmt.spec.js.snap b/tests/constructor_annots/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b50f3d576333
--- /dev/null
+++ b/tests/constructor_annots/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,63 @@
+exports[`test constructors.js 1`] = `
+"// Foo is a class-like function
+function Foo() {
+  this.x = 0; // constructs objects with property x
+}
+Foo.y = 0; // has static property y
+Foo.prototype = { m() { return 0; } };
+
+// exporting Foo directly doesn\'t work
+// Foo\'s instance and static props are not picked up
+exports.Foo = Foo;
+
+// so you want to type Foo, by declaring it as a class
+interface IFooPrototype {
+  m: () => number;
+}
+interface IFoo extends IFooPrototype {
+  x: boolean; // error, should have declared x: number instead
+  static (): void;
+  static y: boolean; // error, should have declared static y: number instead
+}
+exports.Foo2 = (Foo: Class<IFoo>);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected : (19:9)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:33)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4424:8)
+    at Parser.pp$7.flowParseObjectType (/node_modules/babylon/lib/index.js:4809:27)
+    at Parser.pp$7.flowParseInterfaceish (/node_modules/babylon/lib/index.js:4575:20)
+    at Parser.pp$7.flowParseInterface (/node_modules/babylon/lib/index.js:4592:8)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5222:21)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test test.js 1`] = `
+"var Foo = require(\'./constructors\').Foo;
+var x: string = new Foo().x; // error, found number instead of string
+var y: string = Foo.y; // error, found number instead of string
+var z: string = new Foo().m();
+
+var Foo2 = require(\'./constructors\').Foo2;
+var x2: string = new Foo2().x; // error, found boolean instead of string
+var y2: string = Foo2.y; // error, found boolean instead of string
+var z2: string = new Foo2().m();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var Foo = require(\"./constructors\").Foo;
+var x: string = new Foo().x;// error, found number instead of string
+var y: string = Foo.y;// error, found number instead of string
+var z: string = new Foo().m();
+var Foo2 = require(\"./constructors\").Foo2;
+var x2: string = new Foo2().x;// error, found boolean instead of string
+var y2: string = Foo2.y;// error, found boolean instead of string
+var z2: string = new Foo2().m();
+
+"
+`;
diff --git a/tests/constructor_annots/constructors.js b/tests/constructor_annots/constructors.js
new file mode 100644
index 000000000000..dac947e6d829
--- /dev/null
+++ b/tests/constructor_annots/constructors.js
@@ -0,0 +1,21 @@
+// Foo is a class-like function
+function Foo() {
+  this.x = 0; // constructs objects with property x
+}
+Foo.y = 0; // has static property y
+Foo.prototype = { m() { return 0; } };
+
+// exporting Foo directly doesn't work
+// Foo's instance and static props are not picked up
+exports.Foo = Foo;
+
+// so you want to type Foo, by declaring it as a class
+interface IFooPrototype {
+  m: () => number;
+}
+interface IFoo extends IFooPrototype {
+  x: boolean; // error, should have declared x: number instead
+  static (): void;
+  static y: boolean; // error, should have declared static y: number instead
+}
+exports.Foo2 = (Foo: Class<IFoo>);
diff --git a/tests/constructor_annots/jsfmt.spec.js b/tests/constructor_annots/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/constructor_annots/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/constructor_annots/test.js b/tests/constructor_annots/test.js
new file mode 100644
index 000000000000..985cc8b19f36
--- /dev/null
+++ b/tests/constructor_annots/test.js
@@ -0,0 +1,9 @@
+var Foo = require('./constructors').Foo;
+var x: string = new Foo().x; // error, found number instead of string
+var y: string = Foo.y; // error, found number instead of string
+var z: string = new Foo().m();
+
+var Foo2 = require('./constructors').Foo2;
+var x2: string = new Foo2().x; // error, found boolean instead of string
+var y2: string = Foo2.y; // error, found boolean instead of string
+var z2: string = new Foo2().m();
diff --git a/tests/contents/ignore/__snapshots__/jsfmt.spec.js.snap b/tests/contents/ignore/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..71e57278fc6a
--- /dev/null
+++ b/tests/contents/ignore/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test dummy.js 1`] = `
+"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"require('./dummy');
+var xxx = 0;
+xxx
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./dummy");
+var xxx = 0;
+xxx;
+
+"
+`;
diff --git a/tests/contents/ignore/dummy.js b/tests/contents/ignore/dummy.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/contents/ignore/jsfmt.spec.js b/tests/contents/ignore/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/contents/ignore/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/contents/ignore/test.js b/tests/contents/ignore/test.js
new file mode 100644
index 000000000000..ac04887822df
--- /dev/null
+++ b/tests/contents/ignore/test.js
@@ -0,0 +1,3 @@
+require('./dummy');
+var xxx = 0;
+xxx
diff --git a/tests/contents/no_flow/__snapshots__/jsfmt.spec.js.snap b/tests/contents/no_flow/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..71e57278fc6a
--- /dev/null
+++ b/tests/contents/no_flow/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test dummy.js 1`] = `
+"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"require('./dummy');
+var xxx = 0;
+xxx
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./dummy");
+var xxx = 0;
+xxx;
+
+"
+`;
diff --git a/tests/contents/no_flow/dummy.js b/tests/contents/no_flow/dummy.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/contents/no_flow/jsfmt.spec.js b/tests/contents/no_flow/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/contents/no_flow/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/contents/no_flow/test.js b/tests/contents/no_flow/test.js
new file mode 100644
index 000000000000..ac04887822df
--- /dev/null
+++ b/tests/contents/no_flow/test.js
@@ -0,0 +1,3 @@
+require('./dummy');
+var xxx = 0;
+xxx
diff --git a/tests/core_tests/__snapshots__/jsfmt.spec.js.snap b/tests/core_tests/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8d649a93948a
--- /dev/null
+++ b/tests/core_tests/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,253 @@
+exports[`test boolean.js 1`] = `
+"// @flow
+
+// Boolean (the class) tests. booleans (the literals) are not part of core.js
+
+let tests = [
+  // constructor
+  function() {
+    new Boolean();
+    new Boolean(0);
+    new Boolean(-0);
+    new Boolean(null);
+    new Boolean(false);
+    new Boolean(NaN);
+    new Boolean(undefined);
+    new Boolean(\"\");
+  },
+
+  // toString
+  function() {
+    (true).toString();
+    let x: boolean = false;
+    x.toString();
+    (new Boolean(true)).toString();
+  },
+
+  // valueOf
+  function() {
+    ((new Boolean(0)).valueOf(): boolean);
+  },
+
+  // casting
+  function() {
+    Boolean();
+    Boolean(0);
+    Boolean(-0);
+    Boolean(null);
+    Boolean(false);
+    Boolean(NaN);
+    Boolean(undefined);
+    Boolean(\"\");
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// Boolean (the class) tests. booleans (the literals) are not part of core.js
+let tests = [
+  // constructor
+  function() {
+    new Boolean();
+    new Boolean(0);
+    new Boolean(-0);
+    new Boolean(null);
+    new Boolean(false);
+    new Boolean(NaN);
+    new Boolean(undefined);
+    new Boolean(\"\");
+  },
+  // toString
+  function() {
+    true.toString();
+    let x: boolean = false;
+    x.toString();
+    new Boolean(true).toString();
+  },
+  // valueOf
+  function() {
+    (new Boolean(0).valueOf(): boolean);
+  },
+  // casting
+  function() {
+    Boolean();
+    Boolean(0);
+    Boolean(-0);
+    Boolean(null);
+    Boolean(false);
+    Boolean(NaN);
+    Boolean(undefined);
+    Boolean(\"\");
+  }
+];
+
+"
+`;
+
+exports[`test map.js 1`] = `
+"// @flow
+
+function* generator(): Iterable<[string, number]> {
+  while (true) {
+    yield [\'foo\', 123];
+  }
+}
+
+let tests = [
+  // good constructors
+  function() {
+    let w = new Map();
+    let x = new Map(null);
+    let y = new Map([[\'foo\', 123]]);
+    let z = new Map(generator());
+    let a: Map<string, number> = new Map();
+    let b: Map<string, number> = new Map([[\'foo\', 123]]);
+    let c: Map<string, number> = new Map(generator());
+  },
+
+  // bad constructors
+  function() {
+    let x = new Map([\'foo\', 123]); // error
+    let y: Map<number, string> = new Map([[\'foo\', 123]]); // error
+  },
+
+  // get()
+  function(x: Map<string, number>) {
+    (x.get(\'foo\'): boolean); // error, string | void
+    x.get(123); // error, wrong key type
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test regexp.js 1`] = `
+"// @flow
+
+let tests = [
+  // constructor
+  function() {
+    new RegExp(\'foo\');
+    new RegExp(/foo/);
+    new RegExp(\'foo\', \'i\');
+    new RegExp(\'foo\', \'ig\');
+    new RegExp(/foo/, \'i\'); // invalid in ES5, valid in ES6
+    new RegExp(/foo/g, \'i\'); // invalid in ES5, valid in ES6
+  },
+
+  // called as a function (equivalent to the constructor per ES6 21.2.3)
+  function() {
+    RegExp(\'foo\');
+    RegExp(/foo/);
+    RegExp(\'foo\', \'i\');
+    RegExp(\'foo\', \'ig\');
+    RegExp(/foo/, \'i\'); // invalid in ES5, valid in ES6
+    RegExp(/foo/g, \'i\'); // invalid in ES5, valid in ES6
+  },
+
+  // invalid flags
+  function() {
+    RegExp(\'foo\', \'z\'); // error
+    new RegExp(\'foo\', \'z\'); // error
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // constructor
+  function() {
+    new RegExp(\"foo\");
+    new RegExp(/foo/);
+    new RegExp(\"foo\", \"i\");
+    new RegExp(\"foo\", \"ig\");
+    new RegExp(/foo/, \"i\");// invalid in ES5, valid in ES6
+    new RegExp(/foo/g, \"i\");// invalid in ES5, valid in ES6
+  },
+  // called as a function (equivalent to the constructor per ES6 21.2.3)
+  function() {
+    RegExp(\"foo\");
+    RegExp(/foo/);
+    RegExp(\"foo\", \"i\");
+    RegExp(\"foo\", \"ig\");
+    RegExp(/foo/, \"i\");// invalid in ES5, valid in ES6
+    RegExp(/foo/g, \"i\");// invalid in ES5, valid in ES6
+  },
+  // invalid flags
+  function() {
+    RegExp(\"foo\", \"z\");// error
+    new RegExp(\"foo\", \"z\");// error
+  }
+];
+
+"
+`;
+
+exports[`test weakset.js 1`] = `
+"// @flow
+
+let ws = new WeakSet();
+let obj: Object = {};
+let dict: {foo: string} = {foo: \'bar\'};
+
+ws.add(window);
+ws.add(obj);
+ws.add(dict);
+ws.has(window);
+ws.has(obj);
+ws.has(dict);
+ws.delete(window);
+ws.delete(obj);
+ws.delete(dict);
+
+let ws2 = new WeakSet([obj, dict]);
+
+let ws3 = new WeakSet([1, 2, 3]); // error, must be objects
+
+function* generator(): Iterable<{foo: string}> {
+  while (true) {
+    yield {foo: \'bar\'};
+  }
+}
+
+let ws4 = new WeakSet(generator());
+
+function* numbers(): Iterable<number> {
+  let i = 0;
+  while (true) {
+    yield i++;
+  }
+}
+
+let ws5 = new WeakSet(numbers()); // error, must be objects
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/core_tests/boolean.js b/tests/core_tests/boolean.js
new file mode 100644
index 000000000000..6917378f95bc
--- /dev/null
+++ b/tests/core_tests/boolean.js
@@ -0,0 +1,42 @@
+// @flow
+
+// Boolean (the class) tests. booleans (the literals) are not part of core.js
+
+let tests = [
+  // constructor
+  function() {
+    new Boolean();
+    new Boolean(0);
+    new Boolean(-0);
+    new Boolean(null);
+    new Boolean(false);
+    new Boolean(NaN);
+    new Boolean(undefined);
+    new Boolean("");
+  },
+
+  // toString
+  function() {
+    (true).toString();
+    let x: boolean = false;
+    x.toString();
+    (new Boolean(true)).toString();
+  },
+
+  // valueOf
+  function() {
+    ((new Boolean(0)).valueOf(): boolean);
+  },
+
+  // casting
+  function() {
+    Boolean();
+    Boolean(0);
+    Boolean(-0);
+    Boolean(null);
+    Boolean(false);
+    Boolean(NaN);
+    Boolean(undefined);
+    Boolean("");
+  },
+];
diff --git a/tests/core_tests/jsfmt.spec.js b/tests/core_tests/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/core_tests/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/core_tests/map.js b/tests/core_tests/map.js
new file mode 100644
index 000000000000..414b794c74c0
--- /dev/null
+++ b/tests/core_tests/map.js
@@ -0,0 +1,32 @@
+// @flow
+
+function* generator(): Iterable<[string, number]> {
+  while (true) {
+    yield ['foo', 123];
+  }
+}
+
+let tests = [
+  // good constructors
+  function() {
+    let w = new Map();
+    let x = new Map(null);
+    let y = new Map([['foo', 123]]);
+    let z = new Map(generator());
+    let a: Map<string, number> = new Map();
+    let b: Map<string, number> = new Map([['foo', 123]]);
+    let c: Map<string, number> = new Map(generator());
+  },
+
+  // bad constructors
+  function() {
+    let x = new Map(['foo', 123]); // error
+    let y: Map<number, string> = new Map([['foo', 123]]); // error
+  },
+
+  // get()
+  function(x: Map<string, number>) {
+    (x.get('foo'): boolean); // error, string | void
+    x.get(123); // error, wrong key type
+  },
+];
diff --git a/tests/core_tests/regexp.js b/tests/core_tests/regexp.js
new file mode 100644
index 000000000000..d3bca655cb91
--- /dev/null
+++ b/tests/core_tests/regexp.js
@@ -0,0 +1,29 @@
+// @flow
+
+let tests = [
+  // constructor
+  function() {
+    new RegExp('foo');
+    new RegExp(/foo/);
+    new RegExp('foo', 'i');
+    new RegExp('foo', 'ig');
+    new RegExp(/foo/, 'i'); // invalid in ES5, valid in ES6
+    new RegExp(/foo/g, 'i'); // invalid in ES5, valid in ES6
+  },
+
+  // called as a function (equivalent to the constructor per ES6 21.2.3)
+  function() {
+    RegExp('foo');
+    RegExp(/foo/);
+    RegExp('foo', 'i');
+    RegExp('foo', 'ig');
+    RegExp(/foo/, 'i'); // invalid in ES5, valid in ES6
+    RegExp(/foo/g, 'i'); // invalid in ES5, valid in ES6
+  },
+
+  // invalid flags
+  function() {
+    RegExp('foo', 'z'); // error
+    new RegExp('foo', 'z'); // error
+  }
+];
diff --git a/tests/core_tests/weakset.js b/tests/core_tests/weakset.js
new file mode 100644
index 000000000000..76d7ae1ee83c
--- /dev/null
+++ b/tests/core_tests/weakset.js
@@ -0,0 +1,36 @@
+// @flow
+
+let ws = new WeakSet();
+let obj: Object = {};
+let dict: {foo: string} = {foo: 'bar'};
+
+ws.add(window);
+ws.add(obj);
+ws.add(dict);
+ws.has(window);
+ws.has(obj);
+ws.has(dict);
+ws.delete(window);
+ws.delete(obj);
+ws.delete(dict);
+
+let ws2 = new WeakSet([obj, dict]);
+
+let ws3 = new WeakSet([1, 2, 3]); // error, must be objects
+
+function* generator(): Iterable<{foo: string}> {
+  while (true) {
+    yield {foo: 'bar'};
+  }
+}
+
+let ws4 = new WeakSet(generator());
+
+function* numbers(): Iterable<number> {
+  let i = 0;
+  while (true) {
+    yield i++;
+  }
+}
+
+let ws5 = new WeakSet(numbers()); // error, must be objects
diff --git a/tests/covariance/__snapshots__/jsfmt.spec.js.snap b/tests/covariance/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..491e6e935231
--- /dev/null
+++ b/tests/covariance/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,68 @@
+exports[`test test.js 1`] = `
+"type CovArrayVerbose<X,Y:X> = Array<Y>;
+var b: CovArrayVerbose<number,*> = [];
+var y: CovArrayVerbose<mixed,*> = b;
+y[0] = \"\"; // error
+
+class NVerbose<E,I:E> {
+    x: CovArrayVerbose<E,I>;
+    foo(): CovArrayVerbose<mixed,I> { return this.x; }
+}
+
+var nv: NVerbose<number,*> = new NVerbose;
+nv.x = [0];
+(nv.x[0]: string); // error
+(nv.foo()[0]: string); // error
+
+/* TODO: use existentials for non-verbose covariance?
+
+type CovArray<X> = Array<*:X>;
+var c: CovArray<number> = [0];
+var z: CovArray<string> = c; // error
+
+var d: CovArray<number> = [];
+var w: CovArray<mixed> = d;
+w[0] = \"\"; // error
+
+type P<X> = CovArray<X>;
+var p: P<mixed> = [];
+(p[0]: number); // not an error!
+p[0] = \"\"; // error
+
+class M {
+    x: CovArray<number>;
+    foo(): CovArray<mixed> { return this.x; }
+    bar(x: string) { this.foo()[0] = x; } // error
+}
+
+class N<E> {
+    x: CovArray<E>;
+    foo(): CovArray<mixed> { return this.x; }
+    bar(e: string) { this.foo()[0] = e; } // error
+    qux(e: E) { this.foo()[0] = e; }
+}
+
+var n: N<number> = new N;
+n.x = [0];
+(n.x[0]: string); // error
+(n.foo()[0]: string); // not an error!
+
+*/
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/covariance/jsfmt.spec.js b/tests/covariance/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/covariance/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/covariance/test.js b/tests/covariance/test.js
new file mode 100644
index 000000000000..9383b247fc8d
--- /dev/null
+++ b/tests/covariance/test.js
@@ -0,0 +1,49 @@
+type CovArrayVerbose<X,Y:X> = Array<Y>;
+var b: CovArrayVerbose<number,*> = [];
+var y: CovArrayVerbose<mixed,*> = b;
+y[0] = ""; // error
+
+class NVerbose<E,I:E> {
+    x: CovArrayVerbose<E,I>;
+    foo(): CovArrayVerbose<mixed,I> { return this.x; }
+}
+
+var nv: NVerbose<number,*> = new NVerbose;
+nv.x = [0];
+(nv.x[0]: string); // error
+(nv.foo()[0]: string); // error
+
+/* TODO: use existentials for non-verbose covariance?
+
+type CovArray<X> = Array<*:X>;
+var c: CovArray<number> = [0];
+var z: CovArray<string> = c; // error
+
+var d: CovArray<number> = [];
+var w: CovArray<mixed> = d;
+w[0] = ""; // error
+
+type P<X> = CovArray<X>;
+var p: P<mixed> = [];
+(p[0]: number); // not an error!
+p[0] = ""; // error
+
+class M {
+    x: CovArray<number>;
+    foo(): CovArray<mixed> { return this.x; }
+    bar(x: string) { this.foo()[0] = x; } // error
+}
+
+class N<E> {
+    x: CovArray<E>;
+    foo(): CovArray<mixed> { return this.x; }
+    bar(e: string) { this.foo()[0] = e; } // error
+    qux(e: E) { this.foo()[0] = e; }
+}
+
+var n: N<number> = new N;
+n.x = [0];
+(n.x[0]: string); // error
+(n.foo()[0]: string); // not an error!
+
+*/
diff --git a/tests/coverage/__snapshots__/jsfmt.spec.js.snap b/tests/coverage/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5343f59a1e2e
--- /dev/null
+++ b/tests/coverage/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,80 @@
+exports[`test crash.js 1`] = `
+"// This file triggers a violation of the "disjoint-or-nested ranges invariant"
+// that we implicitly assume in type-at-pos and coverage implementations. In
+// particular, when unchecked it causes a crash with coverage --color.
+
+declare module foo {
+}
+
+declare module bar {
+}
+
+// TODO
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// This file triggers a violation of the "disjoint-or-nested ranges invariant"
+// that we implicitly assume in type-at-pos and coverage implementations. In
+// particular, when unchecked it causes a crash with coverage --color.
+declare module foo {
+  
+}
+declare module bar {
+  
+}// TODO
+
+"
+`;
+
+exports[`test declare_module.js 1`] = `
+"// check coverage of declare module
+
+declare module foo {
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// check coverage of declare module
+declare module foo {
+  
+}
+
+"
+`;
+
+exports[`test no_pragma.js 1`] = `
+"let x = 0;
+(x: string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let x = 0;
+(x: string);
+
+"
+`;
+
+exports[`test non-termination.js 1`] = `
+"// This file triggers a violation of the "disjoint-or-nested ranges invariant"
+// that we implicitly assume in type-at-pos and coverage implementations. In
+// particular, when unchecked it causes non-termination with coverage --color.
+
+declare module foo {
+}
+
+declare module bar {
+}
+
+// TODO
+
+declare class qux {
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// This file triggers a violation of the "disjoint-or-nested ranges invariant"
+// that we implicitly assume in type-at-pos and coverage implementations. In
+// particular, when unchecked it causes non-termination with coverage --color.
+declare module foo {
+  
+}
+declare module bar {
+  
+}
+// TODO
+declare class qux {}
+
+"
+`;
diff --git a/tests/coverage/crash.js b/tests/coverage/crash.js
new file mode 100644
index 000000000000..16aa9e752c9d
--- /dev/null
+++ b/tests/coverage/crash.js
@@ -0,0 +1,11 @@
+// This file triggers a violation of the "disjoint-or-nested ranges invariant"
+// that we implicitly assume in type-at-pos and coverage implementations. In
+// particular, when unchecked it causes a crash with coverage --color.
+
+declare module foo {
+}
+
+declare module bar {
+}
+
+// TODO
diff --git a/tests/coverage/declare_module.js b/tests/coverage/declare_module.js
new file mode 100644
index 000000000000..88ad5dab23f2
--- /dev/null
+++ b/tests/coverage/declare_module.js
@@ -0,0 +1,4 @@
+// check coverage of declare module
+
+declare module foo {
+}
diff --git a/tests/coverage/jsfmt.spec.js b/tests/coverage/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/coverage/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/coverage/no_pragma.js b/tests/coverage/no_pragma.js
new file mode 100644
index 000000000000..865e412c16d6
--- /dev/null
+++ b/tests/coverage/no_pragma.js
@@ -0,0 +1,2 @@
+let x = 0;
+(x: string);
diff --git a/tests/coverage/non-termination.js b/tests/coverage/non-termination.js
new file mode 100644
index 000000000000..86e8c24301ff
--- /dev/null
+++ b/tests/coverage/non-termination.js
@@ -0,0 +1,14 @@
+// This file triggers a violation of the "disjoint-or-nested ranges invariant"
+// that we implicitly assume in type-at-pos and coverage implementations. In
+// particular, when unchecked it causes non-termination with coverage --color.
+
+declare module foo {
+}
+
+declare module bar {
+}
+
+// TODO
+
+declare class qux {
+}
diff --git a/tests/cycle/A.js b/tests/cycle/A.js
new file mode 100644
index 000000000000..a49a8f290e31
--- /dev/null
+++ b/tests/cycle/A.js
@@ -0,0 +1,5 @@
+var B = require('./B');
+
+class A extends B { }
+
+module.exports = A;
diff --git a/tests/cycle/B.js b/tests/cycle/B.js
new file mode 100644
index 000000000000..e5c1da823f74
--- /dev/null
+++ b/tests/cycle/B.js
@@ -0,0 +1,5 @@
+var A = require('./A');
+
+//class B extends A { }
+
+module.exports = B;
diff --git a/tests/cycle/__snapshots__/jsfmt.spec.js.snap b/tests/cycle/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4986c12b758a
--- /dev/null
+++ b/tests/cycle/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test A.js 1`] = `
+"var B = require('./B');
+
+class A extends B { }
+
+module.exports = A;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var B = require("./B");
+class A extends B {}
+module.exports = A;
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"var A = require('./A');
+
+//class B extends A { }
+
+module.exports = B;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var A = require("./A");
+//class B extends A { }
+module.exports = B;
+
+"
+`;
diff --git a/tests/cycle/jsfmt.spec.js b/tests/cycle/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/cycle/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/date/__snapshots__/jsfmt.spec.js.snap b/tests/date/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a79fda0e82f2
--- /dev/null
+++ b/tests/date/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,57 @@
+exports[`test date.js 1`] = `
+"var d = new Date(0);
+var x:string = d.getTime();
+
+var y:number = d;
+
+// valid constructors
+new Date();
+new Date(1234567890);
+new Date('2015/06/18');
+new Date(2015, 6);
+new Date(2015, 6, 18);
+new Date(2015, 6, 18, 11);
+new Date(2015, 6, 18, 11, 55);
+new Date(2015, 6, 18, 11, 55, 42);
+new Date(2015, 6, 18, 11, 55, 42, 999);
+
+// invalid constructors
+new Date({});
+new Date(2015, '6');
+new Date(2015, 6, '18');
+new Date(2015, 6, 18, '11');
+new Date(2015, 6, 18, 11, '55');
+new Date(2015, 6, 18, 11, 55, '42');
+new Date(2015, 6, 18, 11, 55, 42, '999');
+
+// invalid constructors that we incorrectly consider valid
+new Date('2015', 6);
+new Date(2015, 6, 18, 11, 55, 42, 999, 'hahaha');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var d = new Date(0);
+var x: string = d.getTime();
+var y: number = d;
+// valid constructors
+new Date();
+new Date(1234567890);
+new Date("2015/06/18");
+new Date(2015, 6);
+new Date(2015, 6, 18);
+new Date(2015, 6, 18, 11);
+new Date(2015, 6, 18, 11, 55);
+new Date(2015, 6, 18, 11, 55, 42);
+new Date(2015, 6, 18, 11, 55, 42, 999);
+// invalid constructors
+new Date({});
+new Date(2015, "6");
+new Date(2015, 6, "18");
+new Date(2015, 6, 18, "11");
+new Date(2015, 6, 18, 11, "55");
+new Date(2015, 6, 18, 11, 55, "42");
+new Date(2015, 6, 18, 11, 55, 42, "999");
+// invalid constructors that we incorrectly consider valid
+new Date("2015", 6);
+new Date(2015, 6, 18, 11, 55, 42, 999, "hahaha");
+
+"
+`;
diff --git a/tests/date/date.js b/tests/date/date.js
new file mode 100644
index 000000000000..dddd8aa08d2b
--- /dev/null
+++ b/tests/date/date.js
@@ -0,0 +1,28 @@
+var d = new Date(0);
+var x:string = d.getTime();
+
+var y:number = d;
+
+// valid constructors
+new Date();
+new Date(1234567890);
+new Date('2015/06/18');
+new Date(2015, 6);
+new Date(2015, 6, 18);
+new Date(2015, 6, 18, 11);
+new Date(2015, 6, 18, 11, 55);
+new Date(2015, 6, 18, 11, 55, 42);
+new Date(2015, 6, 18, 11, 55, 42, 999);
+
+// invalid constructors
+new Date({});
+new Date(2015, '6');
+new Date(2015, 6, '18');
+new Date(2015, 6, 18, '11');
+new Date(2015, 6, 18, 11, '55');
+new Date(2015, 6, 18, 11, 55, '42');
+new Date(2015, 6, 18, 11, 55, 42, '999');
+
+// invalid constructors that we incorrectly consider valid
+new Date('2015', 6);
+new Date(2015, 6, 18, 11, 55, 42, 999, 'hahaha');
diff --git a/tests/date/jsfmt.spec.js b/tests/date/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/date/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_haste/ExplicitProvidesModuleDifferentName.js b/tests/declaration_files_haste/ExplicitProvidesModuleDifferentName.js
new file mode 100644
index 000000000000..90fdd624d92e
--- /dev/null
+++ b/tests/declaration_files_haste/ExplicitProvidesModuleDifferentName.js
@@ -0,0 +1,6 @@
+/*
+ * @providesModule ExplicitProvidesModuleDifferentName
+ * @flow
+ */
+
+module.exports.fun = (): string => "hello there";
diff --git a/tests/declaration_files_haste/ExplicitProvidesModuleSameName.js b/tests/declaration_files_haste/ExplicitProvidesModuleSameName.js
new file mode 100644
index 000000000000..420b439f46c9
--- /dev/null
+++ b/tests/declaration_files_haste/ExplicitProvidesModuleSameName.js
@@ -0,0 +1,6 @@
+/*
+ * @providesModule ExplicitProvidesModuleSameName
+ * @flow
+ */
+
+module.exports.fun = (): string => "hello there";
diff --git a/tests/declaration_files_haste/ImplicitProvidesModule.js b/tests/declaration_files_haste/ImplicitProvidesModule.js
new file mode 100644
index 000000000000..9fa3b2cc07d6
--- /dev/null
+++ b/tests/declaration_files_haste/ImplicitProvidesModule.js
@@ -0,0 +1,6 @@
+/*
+ * @providesModule ImplicitProvidesModule
+ * @flow
+ */
+
+module.exports.fun = (): string => "hello there";
diff --git a/tests/declaration_files_haste/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_haste/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..53ece1a8733a
--- /dev/null
+++ b/tests/declaration_files_haste/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,81 @@
+exports[`test ExplicitProvidesModuleDifferentName.js 1`] = `
+"/*
+ * @providesModule ExplicitProvidesModuleDifferentName
+ * @flow
+ */
+
+module.exports.fun = (): string => "hello there";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @providesModule ExplicitProvidesModuleDifferentName
+ * @flow
+ */
+module.exports.fun = (): string => "hello there";
+
+"
+`;
+
+exports[`test ExplicitProvidesModuleSameName.js 1`] = `
+"/*
+ * @providesModule ExplicitProvidesModuleSameName
+ * @flow
+ */
+
+module.exports.fun = (): string => "hello there";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @providesModule ExplicitProvidesModuleSameName
+ * @flow
+ */
+module.exports.fun = (): string => "hello there";
+
+"
+`;
+
+exports[`test ImplicitProvidesModule.js 1`] = `
+"/*
+ * @providesModule ImplicitProvidesModule
+ * @flow
+ */
+
+module.exports.fun = (): string => "hello there";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @providesModule ImplicitProvidesModule
+ * @flow
+ */
+module.exports.fun = (): string => "hello there";
+
+"
+`;
+
+exports[`test md5.js 1`] = `
+"/* @providesModule md5 */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"/* @flow */
+
+var Implicit = require('ImplicitProvidesModule');
+(Implicit.fun(): string);
+
+var ExplicitSameName = require('ExplicitProvidesModuleSameName');
+(ExplicitSameName.fun(): string);
+
+var ExplicitDifferentName = require('ExplicitProvidesModuleDifferentName');
+(ExplicitDifferentName.fun(): string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var Implicit = require("ImplicitProvidesModule");
+(Implicit.fun(): string);
+var ExplicitSameName = require("ExplicitProvidesModuleSameName");
+(ExplicitSameName.fun(): string);
+var ExplicitDifferentName = require("ExplicitProvidesModuleDifferentName");
+(ExplicitDifferentName.fun(): string);
+
+"
+`;
diff --git a/tests/declaration_files_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8eedeb757628
--- /dev/null
+++ b/tests/declaration_files_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test min.js 1`] = `
+"module.exports.fun = (): string => "hello there";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports.fun = (): string => "hello there";
+
+"
+`;
diff --git a/tests/declaration_files_haste/external/_d3/jsfmt.spec.js b/tests/declaration_files_haste/external/_d3/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_haste/external/_d3/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_haste/external/_d3/min.js b/tests/declaration_files_haste/external/_d3/min.js
new file mode 100644
index 000000000000..94884777ff10
--- /dev/null
+++ b/tests/declaration_files_haste/external/_d3/min.js
@@ -0,0 +1 @@
+module.exports.fun = (): string => "hello there";
diff --git a/tests/declaration_files_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ac5bbc602ad1
--- /dev/null
+++ b/tests/declaration_files_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,28 @@
+exports[`test nested_test.js 1`] = `
+"/* @flow */
+
+var docblock = require('qux/docblock');
+var min = require('d3/min.js');
+var corge = require('qux/corge');
+
+// make sure we don't pick up non-header @providesModule
+// annotations - see node_modules/qux/docblock.js
+var unreachable = require('annotation');
+
+(docblock.fun(): string);
+(min.fun(): string);
+(corge.fun(): string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var docblock = require("qux/docblock");
+var min = require("d3/min.js");
+var corge = require("qux/corge");
+// make sure we don't pick up non-header @providesModule
+// annotations - see node_modules/qux/docblock.js
+var unreachable = require("annotation");
+(docblock.fun(): string);
+(min.fun(): string);
+(corge.fun(): string);
+
+"
+`;
diff --git a/tests/declaration_files_haste/foo/bar/jsfmt.spec.js b/tests/declaration_files_haste/foo/bar/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_haste/foo/bar/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_haste/foo/bar/nested_test.js b/tests/declaration_files_haste/foo/bar/nested_test.js
new file mode 100644
index 000000000000..c9522bc6e6b5
--- /dev/null
+++ b/tests/declaration_files_haste/foo/bar/nested_test.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+var docblock = require('qux/docblock');
+var min = require('d3/min.js');
+var corge = require('qux/corge');
+
+// make sure we don't pick up non-header @providesModule
+// annotations - see node_modules/qux/docblock.js
+var unreachable = require('annotation');
+
+(docblock.fun(): string);
+(min.fun(): string);
+(corge.fun(): string);
diff --git a/tests/declaration_files_haste/jsfmt.spec.js b/tests/declaration_files_haste/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_haste/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_haste/md5.js b/tests/declaration_files_haste/md5.js
new file mode 100644
index 000000000000..c358d72168a6
--- /dev/null
+++ b/tests/declaration_files_haste/md5.js
@@ -0,0 +1 @@
+/* @providesModule md5 */
diff --git a/tests/declaration_files_haste/test.js b/tests/declaration_files_haste/test.js
new file mode 100644
index 000000000000..88fe21f03875
--- /dev/null
+++ b/tests/declaration_files_haste/test.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+var Implicit = require('ImplicitProvidesModule');
+(Implicit.fun(): string);
+
+var ExplicitSameName = require('ExplicitProvidesModuleSameName');
+(ExplicitSameName.fun(): string);
+
+var ExplicitDifferentName = require('ExplicitProvidesModuleDifferentName');
+(ExplicitDifferentName.fun(): string);
diff --git a/tests/declaration_files_haste/ws/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_haste/ws/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..72caaf084cb1
--- /dev/null
+++ b/tests/declaration_files_haste/ws/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,6 @@
+exports[`test index.js 1`] = `
+"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/declaration_files_haste/ws/index.js b/tests/declaration_files_haste/ws/index.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/declaration_files_haste/ws/jsfmt.spec.js b/tests/declaration_files_haste/ws/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_haste/ws/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_haste/ws/test/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_haste/ws/test/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f54d0216ceb7
--- /dev/null
+++ b/tests/declaration_files_haste/ws/test/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test client.js 1`] = `
+"var ws = require('../');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var ws = require("../");
+
+"
+`;
diff --git a/tests/declaration_files_haste/ws/test/client.js b/tests/declaration_files_haste/ws/test/client.js
new file mode 100644
index 000000000000..2fb0ed6d4dfd
--- /dev/null
+++ b/tests/declaration_files_haste/ws/test/client.js
@@ -0,0 +1 @@
+var ws = require('../');
diff --git a/tests/declaration_files_haste/ws/test/jsfmt.spec.js b/tests/declaration_files_haste/ws/test/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_haste/ws/test/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_haste/A.js b/tests/declaration_files_incremental_haste/A.js
new file mode 100644
index 000000000000..9ad347d2c7b9
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/A.js
@@ -0,0 +1,3 @@
+/* @providesModule A */
+class Implementation {}
+export function foo(): Implementation { return new Implementation; }
diff --git a/tests/declaration_files_incremental_haste/ExplicitProvidesModuleDifferentName.js b/tests/declaration_files_incremental_haste/ExplicitProvidesModuleDifferentName.js
new file mode 100644
index 000000000000..b31795b56a69
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ExplicitProvidesModuleDifferentName.js
@@ -0,0 +1,7 @@
+/*
+ * @providesModule ExplicitProvidesModuleDifferentName
+ * @flow
+ */
+
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
diff --git a/tests/declaration_files_incremental_haste/ExplicitProvidesModuleSameName.js b/tests/declaration_files_incremental_haste/ExplicitProvidesModuleSameName.js
new file mode 100644
index 000000000000..2b8762f7b39d
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ExplicitProvidesModuleSameName.js
@@ -0,0 +1,7 @@
+/*
+ * @providesModule ExplicitProvidesModuleSameName
+ * @flow
+ */
+
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
diff --git a/tests/declaration_files_incremental_haste/ImplicitProvidesModule.js b/tests/declaration_files_incremental_haste/ImplicitProvidesModule.js
new file mode 100644
index 000000000000..855ff08d972d
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ImplicitProvidesModule.js
@@ -0,0 +1,7 @@
+/*
+ * @providesModule ImplicitProvidesModule
+ * @flow
+ */
+
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
diff --git a/tests/declaration_files_incremental_haste/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_incremental_haste/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3abccda6a355
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,101 @@
+exports[`test A.js 1`] = `
+"/* @providesModule A */
+class Implementation {}
+export function foo(): Implementation { return new Implementation; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule A */
+class Implementation {}
+export function foo(): Implementation {
+  return new Implementation();
+}
+
+"
+`;
+
+exports[`test ExplicitProvidesModuleDifferentName.js 1`] = `
+"/*
+ * @providesModule ExplicitProvidesModuleDifferentName
+ * @flow
+ */
+
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @providesModule ExplicitProvidesModuleDifferentName
+ * @flow
+ */
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation();
+
+"
+`;
+
+exports[`test ExplicitProvidesModuleSameName.js 1`] = `
+"/*
+ * @providesModule ExplicitProvidesModuleSameName
+ * @flow
+ */
+
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @providesModule ExplicitProvidesModuleSameName
+ * @flow
+ */
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation();
+
+"
+`;
+
+exports[`test ImplicitProvidesModule.js 1`] = `
+"/*
+ * @providesModule ImplicitProvidesModule
+ * @flow
+ */
+
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * @providesModule ImplicitProvidesModule
+ * @flow
+ */
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation();
+
+"
+`;
+
+exports[`test md5.js 1`] = `
+"/* @providesModule md5 */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"/* @flow */
+
+var Implicit = require('ImplicitProvidesModule');
+(Implicit.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+
+var ExplicitSameName = require('ExplicitProvidesModuleSameName');
+(ExplicitSameName.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+
+var ExplicitDifferentName = require('ExplicitProvidesModuleDifferentName');
+(ExplicitDifferentName.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var Implicit = require("ImplicitProvidesModule");
+(Implicit.fun(): boolean);// Error: Either Implementation ~> boolean or Declaration ~> boolean
+var ExplicitSameName = require("ExplicitProvidesModuleSameName");
+(ExplicitSameName.fun(): boolean);// Error: Either Implementation ~> boolean or Declaration ~> boolean
+var ExplicitDifferentName = require("ExplicitProvidesModuleDifferentName");
+(ExplicitDifferentName.fun(): boolean);// Error: Either Implementation ~> boolean or Declaration ~> boolean
+
+"
+`;
diff --git a/tests/declaration_files_incremental_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_incremental_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..67b927b140c4
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test min.js 1`] = `
+"class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation();
+
+"
+`;
diff --git a/tests/declaration_files_incremental_haste/external/_d3/jsfmt.spec.js b/tests/declaration_files_incremental_haste/external/_d3/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/external/_d3/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_haste/external/_d3/min.js b/tests/declaration_files_incremental_haste/external/_d3/min.js
new file mode 100644
index 000000000000..330a5d7de8ca
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/external/_d3/min.js
@@ -0,0 +1,2 @@
+class Implementation {}
+module.exports.fun = (): Implementation => new Implementation;
diff --git a/tests/declaration_files_incremental_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_incremental_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b213b5938c18
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,21 @@
+exports[`test nested_test.js 1`] = `
+"/* @flow */
+
+var docblock = require('qux/docblock');
+var min = require('d3/min.js');
+var corge = require('qux/corge');
+
+(docblock.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+(min.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+(corge.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var docblock = require("qux/docblock");
+var min = require("d3/min.js");
+var corge = require("qux/corge");
+(docblock.fun(): boolean);// Error: Either Implementation ~> boolean or Declaration ~> boolean
+(min.fun(): boolean);// Error: Either Implementation ~> boolean or Declaration ~> boolean
+(corge.fun(): boolean);// Error: Either Implementation ~> boolean or Declaration ~> boolean
+
+"
+`;
diff --git a/tests/declaration_files_incremental_haste/foo/bar/jsfmt.spec.js b/tests/declaration_files_incremental_haste/foo/bar/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/foo/bar/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_haste/foo/bar/nested_test.js b/tests/declaration_files_incremental_haste/foo/bar/nested_test.js
new file mode 100644
index 000000000000..ffc6bac4625a
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/foo/bar/nested_test.js
@@ -0,0 +1,9 @@
+/* @flow */
+
+var docblock = require('qux/docblock');
+var min = require('d3/min.js');
+var corge = require('qux/corge');
+
+(docblock.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+(min.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+(corge.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
diff --git a/tests/declaration_files_incremental_haste/jsfmt.spec.js b/tests/declaration_files_incremental_haste/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_haste/md5.js b/tests/declaration_files_incremental_haste/md5.js
new file mode 100644
index 000000000000..c358d72168a6
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/md5.js
@@ -0,0 +1 @@
+/* @providesModule md5 */
diff --git a/tests/declaration_files_incremental_haste/test.js b/tests/declaration_files_incremental_haste/test.js
new file mode 100644
index 000000000000..c139d4c41746
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/test.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+var Implicit = require('ImplicitProvidesModule');
+(Implicit.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+
+var ExplicitSameName = require('ExplicitProvidesModuleSameName');
+(ExplicitSameName.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
+
+var ExplicitDifferentName = require('ExplicitProvidesModuleDifferentName');
+(ExplicitDifferentName.fun(): boolean); // Error: Either Implementation ~> boolean or Declaration ~> boolean
diff --git a/tests/declaration_files_incremental_haste/ws/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_incremental_haste/ws/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..72caaf084cb1
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ws/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,6 @@
+exports[`test index.js 1`] = `
+"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/declaration_files_incremental_haste/ws/index.js b/tests/declaration_files_incremental_haste/ws/index.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/declaration_files_incremental_haste/ws/jsfmt.spec.js b/tests/declaration_files_incremental_haste/ws/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ws/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_haste/ws/test/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_incremental_haste/ws/test/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f54d0216ceb7
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ws/test/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test client.js 1`] = `
+"var ws = require('../');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var ws = require("../");
+
+"
+`;
diff --git a/tests/declaration_files_incremental_haste/ws/test/client.js b/tests/declaration_files_incremental_haste/ws/test/client.js
new file mode 100644
index 000000000000..2fb0ed6d4dfd
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ws/test/client.js
@@ -0,0 +1 @@
+var ws = require('../');
diff --git a/tests/declaration_files_incremental_haste/ws/test/jsfmt.spec.js b/tests/declaration_files_incremental_haste/ws/test/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_incremental_haste/ws/test/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_node/A.js b/tests/declaration_files_incremental_node/A.js
new file mode 100644
index 000000000000..e1abbb2ca677
--- /dev/null
+++ b/tests/declaration_files_incremental_node/A.js
@@ -0,0 +1,2 @@
+class Implementation {}
+export function foo(): Implementation { return new Implementation; }
diff --git a/tests/declaration_files_incremental_node/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_incremental_node/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..77b78352e073
--- /dev/null
+++ b/tests/declaration_files_incremental_node/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,98 @@
+exports[`test A.js 1`] = `
+"class Implementation {}
+export function foo(): Implementation { return new Implementation; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class Implementation {}
+export function foo(): Implementation {
+  return new Implementation();
+}
+
+"
+`;
+
+exports[`test test_absolute.js 1`] = `
+"/* @flow */
+
+// This will require ./node_modules/B.js.flow
+var B1 = require('B');
+(B1.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+// This will require ./node_modules/B.js.flow
+var B2 = require('B.js');
+(B2.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var C = require('package_with_full_main');
+(C.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var D = require('package_with_partial_main');
+(D.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var E = require('package_with_no_package_json');
+(E.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var F = require('package_with_dir_main');
+(F.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+// This will require ./node_modules/B.js.flow
+var B1 = require('B');
+(B1.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+// This will require ./node_modules/B.js.flow
+var B2 = require('B.js');
+(B2.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var C = require('package_with_full_main');
+(C.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var D = require('package_with_partial_main');
+(D.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var E = require('package_with_no_package_json');
+(E.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var F = require('package_with_dir_main');
+(F.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// This will require ./node_modules/B.js.flow
+var B1 = require("B");
+(B1.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+// This will require ./node_modules/B.js.flow
+var B2 = require("B.js");
+(B2.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var C = require("package_with_full_main");
+(C.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var D = require("package_with_partial_main");
+(D.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var E = require("package_with_no_package_json");
+(E.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var F = require("package_with_dir_main");
+(F.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+// This will require ./node_modules/B.js.flow
+var B1 = require("B");
+(B1.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+// This will require ./node_modules/B.js.flow
+var B2 = require("B.js");
+(B2.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var C = require("package_with_full_main");
+(C.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var D = require("package_with_partial_main");
+(D.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var E = require("package_with_no_package_json");
+(E.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+var F = require("package_with_dir_main");
+(F.fun(): boolean);// Error either Implementation ~> boolean or Declaration ~> boolean
+
+"
+`;
+
+exports[`test test_relative.js 1`] = `
+"import { foo } from './A';
+
+(foo(): boolean); // Error: either Implementation ~> boolean or Definition ~> boolean
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+import { foo } from "./A";
+(foo(): boolean);// Error: either Implementation ~> boolean or Definition ~> boolean
+
+"
+`;
diff --git a/tests/declaration_files_incremental_node/jsfmt.spec.js b/tests/declaration_files_incremental_node/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_incremental_node/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_incremental_node/test_absolute.js b/tests/declaration_files_incremental_node/test_absolute.js
new file mode 100644
index 000000000000..ec99b67abe32
--- /dev/null
+++ b/tests/declaration_files_incremental_node/test_absolute.js
@@ -0,0 +1,41 @@
+/* @flow */
+
+// This will require ./node_modules/B.js.flow
+var B1 = require('B');
+(B1.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+// This will require ./node_modules/B.js.flow
+var B2 = require('B.js');
+(B2.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var C = require('package_with_full_main');
+(C.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var D = require('package_with_partial_main');
+(D.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var E = require('package_with_no_package_json');
+(E.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var F = require('package_with_dir_main');
+(F.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+// This will require ./node_modules/B.js.flow
+var B1 = require('B');
+(B1.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+// This will require ./node_modules/B.js.flow
+var B2 = require('B.js');
+(B2.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var C = require('package_with_full_main');
+(C.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var D = require('package_with_partial_main');
+(D.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var E = require('package_with_no_package_json');
+(E.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
+
+var F = require('package_with_dir_main');
+(F.fun(): boolean); // Error either Implementation ~> boolean or Declaration ~> boolean
diff --git a/tests/declaration_files_incremental_node/test_relative.js b/tests/declaration_files_incremental_node/test_relative.js
new file mode 100644
index 000000000000..abd7f0b8ca8f
--- /dev/null
+++ b/tests/declaration_files_incremental_node/test_relative.js
@@ -0,0 +1,3 @@
+import { foo } from './A';
+
+(foo(): boolean); // Error: either Implementation ~> boolean or Definition ~> boolean
diff --git a/tests/declaration_files_node/A.js b/tests/declaration_files_node/A.js
new file mode 100644
index 000000000000..d948c87f95a2
--- /dev/null
+++ b/tests/declaration_files_node/A.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+module.exports.fun = (): string => 'hello there!';
diff --git a/tests/declaration_files_node/CJS.js b/tests/declaration_files_node/CJS.js
new file mode 100644
index 000000000000..a0dfc0144a62
--- /dev/null
+++ b/tests/declaration_files_node/CJS.js
@@ -0,0 +1,2 @@
+// @flow
+module.exports = 42;
diff --git a/tests/declaration_files_node/__snapshots__/jsfmt.spec.js.snap b/tests/declaration_files_node/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2b9e69b03631
--- /dev/null
+++ b/tests/declaration_files_node/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,91 @@
+exports[`test A.js 1`] = `
+"/* @flow */
+
+module.exports.fun = (): string => 'hello there!';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports.fun = (): string => "hello there!";
+
+"
+`;
+
+exports[`test CJS.js 1`] = `
+"// @flow
+module.exports = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+module.exports = 42;
+
+"
+`;
+
+exports[`test test_absolute.js 1`] = `
+"/* @flow */
+
+// This will require ./node_modules/B.js.flow
+var B1 = require('B');
+(B1.fun(): string); // Error number ~> string
+
+// This will require ./node_modules/B.js.flow
+var B2 = require('B.js');
+(B2.fun(): string); // Error number ~> string
+
+var C = require('package_with_full_main');
+(C.fun(): string); // Error number ~> string
+
+var D = require('package_with_partial_main');
+(D.fun(): string); // Error number ~> string
+
+var E = require('package_with_no_package_json');
+(E.fun(): string); // Error number ~> string
+
+var F = require('package_with_dir_main');
+(F.fun(): string); // Error number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// This will require ./node_modules/B.js.flow
+var B1 = require("B");
+(B1.fun(): string);// Error number ~> string
+// This will require ./node_modules/B.js.flow
+var B2 = require("B.js");
+(B2.fun(): string);// Error number ~> string
+var C = require("package_with_full_main");
+(C.fun(): string);// Error number ~> string
+var D = require("package_with_partial_main");
+(D.fun(): string);// Error number ~> string
+var E = require("package_with_no_package_json");
+(E.fun(): string);// Error number ~> string
+var F = require("package_with_dir_main");
+(F.fun(): string);// Error number ~> string
+
+"
+`;
+
+exports[`test test_relative.js 1`] = `
+"/* @flow */
+
+// This will require ./A.js.flow
+var A1 = require('./A');
+(A1.fun(): string); // Error number ~> string
+
+// This will require ./A.js.flow
+var A2 = require('./A.js');
+(A2.fun(): string); // Error number ~> string
+
+var CJS = require('./CJS.js');
+(CJS: string);
+(CJS: number); // Error: string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// This will require ./A.js.flow
+var A1 = require("./A");
+(A1.fun(): string);// Error number ~> string
+// This will require ./A.js.flow
+var A2 = require("./A.js");
+(A2.fun(): string);// Error number ~> string
+var CJS = require("./CJS.js");
+(CJS: string);
+(CJS: number);// Error: string ~> number
+
+"
+`;
diff --git a/tests/declaration_files_node/jsfmt.spec.js b/tests/declaration_files_node/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declaration_files_node/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declaration_files_node/test_absolute.js b/tests/declaration_files_node/test_absolute.js
new file mode 100644
index 000000000000..cf562b0f1254
--- /dev/null
+++ b/tests/declaration_files_node/test_absolute.js
@@ -0,0 +1,21 @@
+/* @flow */
+
+// This will require ./node_modules/B.js.flow
+var B1 = require('B');
+(B1.fun(): string); // Error number ~> string
+
+// This will require ./node_modules/B.js.flow
+var B2 = require('B.js');
+(B2.fun(): string); // Error number ~> string
+
+var C = require('package_with_full_main');
+(C.fun(): string); // Error number ~> string
+
+var D = require('package_with_partial_main');
+(D.fun(): string); // Error number ~> string
+
+var E = require('package_with_no_package_json');
+(E.fun(): string); // Error number ~> string
+
+var F = require('package_with_dir_main');
+(F.fun(): string); // Error number ~> string
diff --git a/tests/declaration_files_node/test_relative.js b/tests/declaration_files_node/test_relative.js
new file mode 100644
index 000000000000..340a3f68cdfe
--- /dev/null
+++ b/tests/declaration_files_node/test_relative.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+// This will require ./A.js.flow
+var A1 = require('./A');
+(A1.fun(): string); // Error number ~> string
+
+// This will require ./A.js.flow
+var A2 = require('./A.js');
+(A2.fun(): string); // Error number ~> string
+
+var CJS = require('./CJS.js');
+(CJS: string);
+(CJS: number); // Error: string ~> number
diff --git a/tests/declare_class/__snapshots__/jsfmt.spec.js.snap b/tests/declare_class/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ed66b2e693cc
--- /dev/null
+++ b/tests/declare_class/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,29 @@
+exports[`test declare_class.js 1`] = `
+"declare class C {
+    static x: number;
+    static foo(x: number): void;
+}
+
+C.x = \"\";
+C.foo(\"\");
+
+(C.name: string);
+(C.name: number); // error, it\'s a string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/declare_class/declare_class.js b/tests/declare_class/declare_class.js
new file mode 100644
index 000000000000..3096c97af9fd
--- /dev/null
+++ b/tests/declare_class/declare_class.js
@@ -0,0 +1,10 @@
+declare class C {
+    static x: number;
+    static foo(x: number): void;
+}
+
+C.x = "";
+C.foo("");
+
+(C.name: string);
+(C.name: number); // error, it's a string
diff --git a/tests/declare_class/jsfmt.spec.js b/tests/declare_class/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_class/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_class/lib/__snapshots__/jsfmt.spec.js.snap b/tests/declare_class/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fcb6db09e975
--- /dev/null
+++ b/tests/declare_class/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,28 @@
+exports[`test test.js 1`] = `
+"declare class _C {
+  foo(): number;
+}
+declare var _module: {
+  C: Class<_C>;
+}
+declare class D extends _module.C {
+  foo(): string;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/declare_class/lib/jsfmt.spec.js b/tests/declare_class/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_class/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_class/lib/test.js b/tests/declare_class/lib/test.js
new file mode 100644
index 000000000000..03ce578f62fc
--- /dev/null
+++ b/tests/declare_class/lib/test.js
@@ -0,0 +1,9 @@
+declare class _C {
+  foo(): number;
+}
+declare var _module: {
+  C: Class<_C>;
+}
+declare class D extends _module.C {
+  foo(): string;
+}
diff --git a/tests/declare_export/B.js b/tests/declare_export/B.js
new file mode 100644
index 000000000000..e4d0f1b41f44
--- /dev/null
+++ b/tests/declare_export/B.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+exports.numberValue = 42;
diff --git a/tests/declare_export/C.js b/tests/declare_export/C.js
new file mode 100644
index 000000000000..e667c4717b69
--- /dev/null
+++ b/tests/declare_export/C.js
@@ -0,0 +1 @@
+/* @flow */
diff --git a/tests/declare_export/CommonJS_Clobbering_Class.js b/tests/declare_export/CommonJS_Clobbering_Class.js
new file mode 100644
index 000000000000..4fbd96118432
--- /dev/null
+++ b/tests/declare_export/CommonJS_Clobbering_Class.js
@@ -0,0 +1,21 @@
+/**
+ * @providesModule CommonJS_Clobbering_Class
+ * @flow
+ */
+
+class Base {
+  static baseProp: number;
+}
+
+class Test extends Base {
+  static childProp: number;
+
+  static staticNumber1():number { return 1; }
+  static staticNumber2():number { return 2; }
+  static staticNumber3():number { return 3; }
+
+  instNumber1():number { return 1; }
+  instNumber2():number { return 2; }
+};
+
+module.exports = Test;
diff --git a/tests/declare_export/CommonJS_Clobbering_Lit.js b/tests/declare_export/CommonJS_Clobbering_Lit.js
new file mode 100644
index 000000000000..991b7bc37c12
--- /dev/null
+++ b/tests/declare_export/CommonJS_Clobbering_Lit.js
@@ -0,0 +1,12 @@
+/**
+ * @providesModule CommonJS_Clobbering_Lit
+ * @flow
+ */
+
+module.exports = {
+  numberValue1: 1,
+  numberValue2: 2,
+  numberValue3: 3,
+  numberValue4: 4,
+  numberValue5: 5
+};
diff --git a/tests/declare_export/CommonJS_Named.js b/tests/declare_export/CommonJS_Named.js
new file mode 100644
index 000000000000..698ec4f05276
--- /dev/null
+++ b/tests/declare_export/CommonJS_Named.js
@@ -0,0 +1,10 @@
+/**
+ * @providesModule CommonJS_Named
+ * @flow
+ */
+
+exports.numberValue1 = 1;
+exports.numberValue2 = 2;
+exports.numberValue3 = 3;
+exports.numberValue4 = 4;
+exports.numberValue5 = 5;
diff --git a/tests/declare_export/ES6_DefaultAndNamed.js b/tests/declare_export/ES6_DefaultAndNamed.js
new file mode 100644
index 000000000000..afa31fd3ea2c
--- /dev/null
+++ b/tests/declare_export/ES6_DefaultAndNamed.js
@@ -0,0 +1,4 @@
+/* @flow */
+
+declare export default number;
+declare export var str: string;
diff --git a/tests/declare_export/ES6_Default_AnonFunction1.js b/tests/declare_export/ES6_Default_AnonFunction1.js
new file mode 100644
index 000000000000..d93d3f0a1feb
--- /dev/null
+++ b/tests/declare_export/ES6_Default_AnonFunction1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_AnonFunction1
+ * @flow
+ */
+
+declare export default () => number;
diff --git a/tests/declare_export/ES6_Default_AnonFunction2.js b/tests/declare_export/ES6_Default_AnonFunction2.js
new file mode 100644
index 000000000000..f539ad3c1ec7
--- /dev/null
+++ b/tests/declare_export/ES6_Default_AnonFunction2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_AnonFunction2
+ * @flow
+ */
+
+declare export default () =>number;
diff --git a/tests/declare_export/ES6_Default_NamedClass1.js b/tests/declare_export/ES6_Default_NamedClass1.js
new file mode 100644
index 000000000000..7779c6081957
--- /dev/null
+++ b/tests/declare_export/ES6_Default_NamedClass1.js
@@ -0,0 +1,12 @@
+/**
+ * @providesModule ES6_Default_NamedClass1
+ * @flow
+ */
+
+declare export default class FooImpl { givesANum(): number; };
+
+// Regression test for https://github.com/facebook/flow/issues/511
+//
+// Default-exported class should also be available in local scope
+declare export { FooImpl as Foo }
+declare export function getAFoo(): FooImpl;
diff --git a/tests/declare_export/ES6_Default_NamedClass2.js b/tests/declare_export/ES6_Default_NamedClass2.js
new file mode 100644
index 000000000000..9c27f1f9b9eb
--- /dev/null
+++ b/tests/declare_export/ES6_Default_NamedClass2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_NamedClass2
+ * @flow
+ */
+
+declare export default class Foo { givesANum(): number; };
diff --git a/tests/declare_export/ES6_Default_NamedFunction1.js b/tests/declare_export/ES6_Default_NamedFunction1.js
new file mode 100644
index 000000000000..186dcb632069
--- /dev/null
+++ b/tests/declare_export/ES6_Default_NamedFunction1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_NamedFunction1
+ * @flow
+ */
+
+declare export default function foo():number;
diff --git a/tests/declare_export/ES6_Default_NamedFunction2.js b/tests/declare_export/ES6_Default_NamedFunction2.js
new file mode 100644
index 000000000000..87b3d290d93c
--- /dev/null
+++ b/tests/declare_export/ES6_Default_NamedFunction2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_NamedFunction2
+ * @flow
+ */
+
+declare export default function foo():number;
diff --git a/tests/declare_export/ES6_ExportAllFromMulti.js b/tests/declare_export/ES6_ExportAllFromMulti.js
new file mode 100644
index 000000000000..b0f1d15ffaa4
--- /dev/null
+++ b/tests/declare_export/ES6_ExportAllFromMulti.js
@@ -0,0 +1,4 @@
+// @flow
+
+declare export * from "./ES6_ExportAllFrom_Source1";
+declare export * from "./ES6_ExportAllFrom_Source2";
diff --git a/tests/declare_export/ES6_ExportAllFrom_Intermediary1.js b/tests/declare_export/ES6_ExportAllFrom_Intermediary1.js
new file mode 100644
index 000000000000..7fc67e38b8eb
--- /dev/null
+++ b/tests/declare_export/ES6_ExportAllFrom_Intermediary1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Intermediary1
+ * @flow
+ */
+
+declare export * from "ES6_ExportAllFrom_Source1";
diff --git a/tests/declare_export/ES6_ExportAllFrom_Intermediary2.js b/tests/declare_export/ES6_ExportAllFrom_Intermediary2.js
new file mode 100644
index 000000000000..5239b4ec9b3f
--- /dev/null
+++ b/tests/declare_export/ES6_ExportAllFrom_Intermediary2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Intermediary2
+ * @flow
+ */
+
+declare export * from "ES6_ExportAllFrom_Source2";
diff --git a/tests/declare_export/ES6_ExportAllFrom_Source1.js b/tests/declare_export/ES6_ExportAllFrom_Source1.js
new file mode 100644
index 000000000000..349a2519ab5a
--- /dev/null
+++ b/tests/declare_export/ES6_ExportAllFrom_Source1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Source1
+ * @flow
+ */
+
+declare export var numberValue1: number;
diff --git a/tests/declare_export/ES6_ExportAllFrom_Source2.js b/tests/declare_export/ES6_ExportAllFrom_Source2.js
new file mode 100644
index 000000000000..b048c4c660af
--- /dev/null
+++ b/tests/declare_export/ES6_ExportAllFrom_Source2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Source2
+ * @flow
+ */
+
+declare export var numberValue2: number;
diff --git a/tests/declare_export/ES6_ExportFrom_Intermediary1.js b/tests/declare_export/ES6_ExportFrom_Intermediary1.js
new file mode 100644
index 000000000000..42deb8f3cab4
--- /dev/null
+++ b/tests/declare_export/ES6_ExportFrom_Intermediary1.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule ES6_ExportFrom_Intermediary1
+ * @flow
+ */
+
+declare export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed
+} from "ES6_ExportFrom_Source1";
diff --git a/tests/declare_export/ES6_ExportFrom_Intermediary2.js b/tests/declare_export/ES6_ExportFrom_Intermediary2.js
new file mode 100644
index 000000000000..bb52574f5f76
--- /dev/null
+++ b/tests/declare_export/ES6_ExportFrom_Intermediary2.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule ES6_ExportFrom_Intermediary2
+ * @flow
+ */
+
+declare export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed2
+} from "ES6_ExportFrom_Source2";
diff --git a/tests/declare_export/ES6_ExportFrom_Source1.js b/tests/declare_export/ES6_ExportFrom_Source1.js
new file mode 100644
index 000000000000..519dacde3334
--- /dev/null
+++ b/tests/declare_export/ES6_ExportFrom_Source1.js
@@ -0,0 +1,7 @@
+/**
+ * @providesModule ES6_ExportFrom_Source1
+ * @flow
+ */
+
+declare export var numberValue1: number;
+declare export var numberValue2: number;
diff --git a/tests/declare_export/ES6_ExportFrom_Source2.js b/tests/declare_export/ES6_ExportFrom_Source2.js
new file mode 100644
index 000000000000..71ba5d456098
--- /dev/null
+++ b/tests/declare_export/ES6_ExportFrom_Source2.js
@@ -0,0 +1,7 @@
+/**
+ * @providesModule ES6_ExportFrom_Source2
+ * @flow
+ */
+
+declare export var numberValue1: number;
+declare export var numberValue2: number;
diff --git a/tests/declare_export/ES6_Named1.js b/tests/declare_export/ES6_Named1.js
new file mode 100644
index 000000000000..b448ee324be3
--- /dev/null
+++ b/tests/declare_export/ES6_Named1.js
@@ -0,0 +1,21 @@
+/**
+ * @providesModule ES6_Named1
+ * @flow
+ */
+
+var specifierNumber1 = 1;
+var specifierNumber2 = 2;
+var specifierNumber3 = 3;
+var groupedSpecifierNumber1 = 1;
+var groupedSpecifierNumber2 = 2;
+
+declare export {specifierNumber1};
+declare export {specifierNumber2 as specifierNumber2Renamed};
+declare export {specifierNumber3};
+declare export {groupedSpecifierNumber1, groupedSpecifierNumber2};
+
+declare export function givesANumber(): number;
+declare export class NumberGenerator { givesANumber(): number; };
+
+declare export var varDeclNumber1: number;
+declare export var varDeclNumber2: number;
diff --git a/tests/declare_export/ES6_Named2.js b/tests/declare_export/ES6_Named2.js
new file mode 100644
index 000000000000..5f29921f40b5
--- /dev/null
+++ b/tests/declare_export/ES6_Named2.js
@@ -0,0 +1,19 @@
+/**
+ * @providesModule ES6_Named2
+ * @flow
+ */
+
+var specifierNumber4 = 1;
+var specifierNumber5 = 2;
+var groupedSpecifierNumber3 = 1;
+var groupedSpecifierNumber4 = 2;
+
+declare export {specifierNumber4};
+declare export {specifierNumber5 as specifierNumber5Renamed};
+declare export {groupedSpecifierNumber3, groupedSpecifierNumber4};
+
+declare export function givesANumber2(): number;
+declare export class NumberGenerator2 { givesANumber(): number; };
+
+declare export var varDeclNumber3: number;
+declare export var varDeclNumber4: number;
diff --git a/tests/declare_export/ProvidesModuleA.js b/tests/declare_export/ProvidesModuleA.js
new file mode 100644
index 000000000000..f2cbd52ce005
--- /dev/null
+++ b/tests/declare_export/ProvidesModuleA.js
@@ -0,0 +1,10 @@
+/**
+ * @providesModule A
+ * @flow
+ */
+
+exports.numberValue1 = 42;
+exports.numberValue2 = 42;
+exports.numberValue3 = 42;
+exports.numberValue4 = 42;
+exports.stringValue = "str";
diff --git a/tests/declare_export/ProvidesModuleCJSDefault.js b/tests/declare_export/ProvidesModuleCJSDefault.js
new file mode 100644
index 000000000000..a3d9c135a2c1
--- /dev/null
+++ b/tests/declare_export/ProvidesModuleCJSDefault.js
@@ -0,0 +1,8 @@
+/**
+ * @providesModule CJSDefault
+ * @flow
+ */
+
+module.exports = {
+  numberValue: 42
+};
diff --git a/tests/declare_export/ProvidesModuleD.js b/tests/declare_export/ProvidesModuleD.js
new file mode 100644
index 000000000000..a4d5ee842062
--- /dev/null
+++ b/tests/declare_export/ProvidesModuleD.js
@@ -0,0 +1,4 @@
+/**
+ * @providesModule D
+ * @flow
+ */
diff --git a/tests/declare_export/ProvidesModuleES6Default.js b/tests/declare_export/ProvidesModuleES6Default.js
new file mode 100644
index 000000000000..636a1946109c
--- /dev/null
+++ b/tests/declare_export/ProvidesModuleES6Default.js
@@ -0,0 +1,10 @@
+/**
+ * @providesModule ES6Default
+ * @flow
+ */
+
+/*
+export default {
+  numberValue: 42,
+};
+*/
diff --git a/tests/declare_export/SideEffects.js b/tests/declare_export/SideEffects.js
new file mode 100644
index 000000000000..e667c4717b69
--- /dev/null
+++ b/tests/declare_export/SideEffects.js
@@ -0,0 +1 @@
+/* @flow */
diff --git a/tests/declare_export/__snapshots__/jsfmt.spec.js.snap b/tests/declare_export/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..829bbe76b0ee
--- /dev/null
+++ b/tests/declare_export/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,1212 @@
+exports[`test B.js 1`] = `
+"/* @flow */
+
+exports.numberValue = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+exports.numberValue = 42;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"/* @flow */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test CommonJS_Clobbering_Class.js 1`] = `
+"/**
+ * @providesModule CommonJS_Clobbering_Class
+ * @flow
+ */
+
+class Base {
+  static baseProp: number;
+}
+
+class Test extends Base {
+  static childProp: number;
+
+  static staticNumber1():number { return 1; }
+  static staticNumber2():number { return 2; }
+  static staticNumber3():number { return 3; }
+
+  instNumber1():number { return 1; }
+  instNumber2():number { return 2; }
+};
+
+module.exports = Test;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Clobbering_Class
+ * @flow
+ */
+class Base {
+  static baseProp: number;
+}
+class Test extends Base {
+  static childProp: number;
+  staticNumber1(): number {
+    return 1;
+  }
+  staticNumber2(): number {
+    return 2;
+  }
+  staticNumber3(): number {
+    return 3;
+  }
+  instNumber1(): number {
+    return 1;
+  }
+  instNumber2(): number {
+    return 2;
+  }
+}
+module.exports = Test;
+
+"
+`;
+
+exports[`test CommonJS_Clobbering_Lit.js 1`] = `
+"/**
+ * @providesModule CommonJS_Clobbering_Lit
+ * @flow
+ */
+
+module.exports = {
+  numberValue1: 1,
+  numberValue2: 2,
+  numberValue3: 3,
+  numberValue4: 4,
+  numberValue5: 5
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Clobbering_Lit
+ * @flow
+ */
+module.exports = {
+  numberValue1: 1,
+  numberValue2: 2,
+  numberValue3: 3,
+  numberValue4: 4,
+  numberValue5: 5
+};
+
+"
+`;
+
+exports[`test CommonJS_Named.js 1`] = `
+"/**
+ * @providesModule CommonJS_Named
+ * @flow
+ */
+
+exports.numberValue1 = 1;
+exports.numberValue2 = 2;
+exports.numberValue3 = 3;
+exports.numberValue4 = 4;
+exports.numberValue5 = 5;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Named
+ * @flow
+ */
+exports.numberValue1 = 1;
+exports.numberValue2 = 2;
+exports.numberValue3 = 3;
+exports.numberValue4 = 4;
+exports.numberValue5 = 5;
+
+"
+`;
+
+exports[`test ES6_Default_AnonFunction1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_AnonFunction1
+ * @flow
+ */
+
+declare export default () => number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Default_AnonFunction2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_AnonFunction2
+ * @flow
+ */
+
+declare export default () =>number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Default_NamedClass1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedClass1
+ * @flow
+ */
+
+declare export default class FooImpl { givesANum(): number; };
+
+// Regression test for https://github.com/facebook/flow/issues/511
+//
+// Default-exported class should also be available in local scope
+declare export { FooImpl as Foo }
+declare export function getAFoo(): FooImpl;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Default_NamedClass2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedClass2
+ * @flow
+ */
+
+declare export default class Foo { givesANum(): number; };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Default_NamedFunction1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedFunction1
+ * @flow
+ */
+
+declare export default function foo():number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Default_NamedFunction2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedFunction2
+ * @flow
+ */
+
+declare export default function foo():number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_DefaultAndNamed.js 1`] = `
+"/* @flow */
+
+declare export default number;
+declare export var str: string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Intermediary1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Intermediary1
+ * @flow
+ */
+
+declare export * from \"ES6_ExportAllFrom_Source1\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Intermediary2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Intermediary2
+ * @flow
+ */
+
+declare export * from \"ES6_ExportAllFrom_Source2\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Source1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Source1
+ * @flow
+ */
+
+declare export var numberValue1: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Source2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Source2
+ * @flow
+ */
+
+declare export var numberValue2: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportAllFromMulti.js 1`] = `
+"// @flow
+
+declare export * from \"./ES6_ExportAllFrom_Source1\";
+declare export * from \"./ES6_ExportAllFrom_Source2\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportFrom_Intermediary1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Intermediary1
+ * @flow
+ */
+
+declare export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed
+} from \"ES6_ExportFrom_Source1\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportFrom_Intermediary2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Intermediary2
+ * @flow
+ */
+
+declare export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed2
+} from \"ES6_ExportFrom_Source2\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportFrom_Source1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Source1
+ * @flow
+ */
+
+declare export var numberValue1: number;
+declare export var numberValue2: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_ExportFrom_Source2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Source2
+ * @flow
+ */
+
+declare export var numberValue1: number;
+declare export var numberValue2: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (6:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Named1.js 1`] = `
+"/**
+ * @providesModule ES6_Named1
+ * @flow
+ */
+
+var specifierNumber1 = 1;
+var specifierNumber2 = 2;
+var specifierNumber3 = 3;
+var groupedSpecifierNumber1 = 1;
+var groupedSpecifierNumber2 = 2;
+
+declare export {specifierNumber1};
+declare export {specifierNumber2 as specifierNumber2Renamed};
+declare export {specifierNumber3};
+declare export {groupedSpecifierNumber1, groupedSpecifierNumber2};
+
+declare export function givesANumber(): number;
+declare export class NumberGenerator { givesANumber(): number; };
+
+declare export var varDeclNumber1: number;
+declare export var varDeclNumber2: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (12:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ES6_Named2.js 1`] = `
+"/**
+ * @providesModule ES6_Named2
+ * @flow
+ */
+
+var specifierNumber4 = 1;
+var specifierNumber5 = 2;
+var groupedSpecifierNumber3 = 1;
+var groupedSpecifierNumber4 = 2;
+
+declare export {specifierNumber4};
+declare export {specifierNumber5 as specifierNumber5Renamed};
+declare export {groupedSpecifierNumber3, groupedSpecifierNumber4};
+
+declare export function givesANumber2(): number;
+declare export class NumberGenerator2 { givesANumber(): number; };
+
+declare export var varDeclNumber3: number;
+declare export var varDeclNumber4: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (11:8)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseExpressionStatement (/node_modules/babylon/lib/index.js:2109:8)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5246:20)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+"
+`;
+
+exports[`test ProvidesModuleA.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+
+exports.numberValue1 = 42;
+exports.numberValue2 = 42;
+exports.numberValue3 = 42;
+exports.numberValue4 = 42;
+exports.stringValue = \"str\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule A
+ * @flow
+ */
+exports.numberValue1 = 42;
+exports.numberValue2 = 42;
+exports.numberValue3 = 42;
+exports.numberValue4 = 42;
+exports.stringValue = \"str\";
+
+"
+`;
+
+exports[`test ProvidesModuleCJSDefault.js 1`] = `
+"/**
+ * @providesModule CJSDefault
+ * @flow
+ */
+
+module.exports = {
+  numberValue: 42
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CJSDefault
+ * @flow
+ */
+module.exports = { numberValue: 42 };
+
+"
+`;
+
+exports[`test ProvidesModuleD.js 1`] = `
+"/**
+ * @providesModule D
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test ProvidesModuleES6Default.js 1`] = `
+"/**
+ * @providesModule ES6Default
+ * @flow
+ */
+
+/*
+export default {
+  numberValue: 42,
+};
+*/
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test SideEffects.js 1`] = `
+"/* @flow */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test es6modules.js 1`] = `
+"/* @flow */
+
+// ===================== //
+// == Path Resolution == //
+// ===================== //
+
+// @providesModule
+import * as DefaultA from \"A\";
+var a1: number = DefaultA.numberValue1;
+var a2: string = DefaultA.numberValue1; // Error: number ~> string
+
+// File path
+import * as DefaultB from \"./B\";
+var b1: number = DefaultB.numberValue;
+var b2: string = DefaultB.numberValue; // Error: number ~> string
+
+// C.js exists, but not as a providesModule
+import DefaultC from \"C\"; // Error: No such module
+
+// @providesModule D exists, but not as a filename
+import DefaultD from \"./D\"; // Error: No such module
+
+// ================================================ //
+// == CommonJS Clobbering Literal Exports -> ES6 == //
+// ================================================ //
+
+import {doesntExist1} from \"CommonJS_Clobbering_Lit\"; // Error: Not an exported binding
+
+import {numberValue1} from \"CommonJS_Clobbering_Lit\";
+var c1: number = numberValue1;
+var c2: string = numberValue1; // Error: number ~> string
+
+import {numberValue2 as numVal1} from \"CommonJS_Clobbering_Lit\";
+var d1: number = numVal1;
+var d2: string = numVal1; // Error: number ~> string
+
+import CJS_Clobb_Lit from \"CommonJS_Clobbering_Lit\";
+var e1: number = CJS_Clobb_Lit.numberValue3;
+var e2: string = CJS_Clobb_Lit.numberValue3; // Error: number ~> string
+CJS_Clobb_Lit.doesntExist; // Error: doesntExist isn\'t a property
+
+import * as CJS_Clobb_Lit_NS from \"CommonJS_Clobbering_Lit\";
+var f1: number = CJS_Clobb_Lit_NS.numberValue4;
+var f2: number = CJS_Clobb_Lit_NS.default.numberValue4;
+CJS_Clobb_Lit_NS.default.default; // Error: No \'default\' property on the exported obj
+var f3: string = CJS_Clobb_Lit_NS.numberValue4; // Error: number ~> string
+var f4: string = CJS_Clobb_Lit_NS.default.numberValue5; // Error: number ~> string
+
+// ============================================== //
+// == CommonJS Clobbering Class Exports -> ES6 == //
+// ============================================== //
+
+import {doesntExist2} from \"CommonJS_Clobbering_Class\"; // Error: Not an exported binding
+
+// The following import should error because class statics are not turned into
+// named exports for now. This avoids complexities with polymorphic static
+// members (where the polymophism is defined on the class itself rather than the
+// method).
+import {staticNumber1, baseProp, childProp} from \"CommonJS_Clobbering_Class\"; // Error
+
+import CJS_Clobb_Class from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class();
+new CJS_Clobb_Class().doesntExist; // Error: Class has no \`doesntExist\` property
+var h1: number = CJS_Clobb_Class.staticNumber2();
+var h2: string = CJS_Clobb_Class.staticNumber2(); // Error: number ~> string
+var h3: number = new CJS_Clobb_Class().instNumber1();
+var h4: string = new CJS_Clobb_Class().instNumber1(); // Error: number ~> string
+
+import * as CJS_Clobb_Class_NS from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class_NS(); // Error: Namespace object isn\'t constructable
+var i1: number = CJS_Clobb_Class_NS.staticNumber3(); // Error: Class statics not copied to Namespace object
+var i2: number = new CJS_Clobb_Class_NS.default().instNumber2();
+var i3: string = new CJS_Clobb_Class_NS.default().instNumber2(); // Error: number ~> string
+
+// =================================== //
+// == CommonJS Named Exports -> ES6 == //
+// =================================== //
+
+import {doesntExist3} from \"CommonJS_Named\"; // Error: Not an exported binding
+
+import {numberValue2} from \"CommonJS_Named\";
+var j1: number = numberValue2;
+var j2: string = numberValue2; // Error: number ~> string
+
+import {numberValue3 as numVal3} from \"CommonJS_Named\";
+var k1: number = numVal3;
+var k2: string = numVal3; // Error: number ~> string
+
+import * as CJS_Named from \"CommonJS_Named\";
+var l1: number = CJS_Named.numberValue1;
+var l2: string = CJS_Named.numberValue1; // Error: number ~> string
+CJS_Named.doesntExist; // Error: doesntExist isn\'t a property
+
+import * as CJS_Named_NS from \"CommonJS_Named\";
+var m1: number = CJS_Named_NS.numberValue4;
+var m2: string = CJS_Named_NS.default.numberValue4; // Error: CommonJS_Named has no default export
+var m3: string = CJS_Named_NS.numberValue4; // Error: number ~> string
+
+//////////////////////////////
+// == ES6 Default -> ES6 == //
+//////////////////////////////
+
+import {doesntExist4} from \"ES6_Default_AnonFunction1\"; // Error: Not an exported binding
+
+import ES6_Def_AnonFunc1 from \"ES6_Default_AnonFunction1\";
+var n1: number = ES6_Def_AnonFunc1();
+var n2: string = ES6_Def_AnonFunc1(); // Error: number ~> string
+
+import ES6_Def_NamedFunc1 from \"ES6_Default_NamedFunction1\";
+var o1: number = ES6_Def_NamedFunc1();
+var o2: string = ES6_Def_NamedFunc1(); // Error: number ~> string
+
+
+
+
+
+import ES6_Def_NamedClass1 from \"ES6_Default_NamedClass1\";
+var q1: number = new ES6_Def_NamedClass1().givesANum();
+var q2: string = new ES6_Def_NamedClass1().givesANum(); // Error: number ~> string
+
+////////////////////////////
+// == ES6 Named -> ES6 == //
+////////////////////////////
+
+import doesntExist5 from \"ES6_Named1\"; // Error: Not an exported binding
+
+import {specifierNumber1 as specifierNumber1_1} from \"ES6_Named1\";
+var r1: number = specifierNumber1_1;
+var r2: string = specifierNumber1_1; // Error: number ~> string
+
+import {specifierNumber2Renamed} from \"ES6_Named1\";
+var s1: number = specifierNumber2Renamed;
+var s2: string = specifierNumber2Renamed; // Error: number ~> string
+
+import {specifierNumber3 as specifierNumber3Renamed} from \"ES6_Named1\";
+var t1: number = specifierNumber3Renamed;
+var t2: string = specifierNumber3Renamed; // Error: number ~> string
+
+import {groupedSpecifierNumber1, groupedSpecifierNumber2} from \"ES6_Named1\";
+var u1: number = groupedSpecifierNumber1;
+var u2: number = groupedSpecifierNumber2;
+var u3: string = groupedSpecifierNumber1; // Error: number ~> string
+var u4: string = groupedSpecifierNumber2; // Error: number ~> string
+
+import {givesANumber} from \"ES6_Named1\";
+var v1: number = givesANumber();
+var v2: string = givesANumber(); // Error: number ~> string
+
+import {NumberGenerator} from \"ES6_Named1\";
+var w1: number = new NumberGenerator().givesANumber();
+var w2: string = new NumberGenerator().givesANumber(); // Error: number ~> string
+
+import {varDeclNumber1, varDeclNumber2} from \"ES6_Named1\";
+var x1: number = varDeclNumber1;
+var x2: number = varDeclNumber2;
+var x3: string = varDeclNumber1; // Error: number ~> string
+var x4: string = varDeclNumber2; // Error: number ~> string
+
+
+
+
+
+
+
+
+
+import {numberValue1 as numberValue4} from \"ES6_ExportFrom_Intermediary1\";
+var aa1: number = numberValue4;
+var aa2: string = numberValue4; // Error: number ~> string
+
+import {numberValue2_renamed} from \"ES6_ExportFrom_Intermediary1\";
+var ab1: number = numberValue2_renamed;
+var ab2: string = numberValue2_renamed; // Error: number ~> string
+
+import {numberValue1 as numberValue5} from \"ES6_ExportAllFrom_Intermediary1\";
+var ac1: number = numberValue5;
+var ac2: string = numberValue5; // Error: number ~> string
+
+///////////////////////////////////
+// == ES6 Default -> CommonJS == //
+///////////////////////////////////
+
+require(\'ES6_Default_AnonFunction2\').doesntExist; // Error: \'doesntExist\' isn\'t an export
+
+var ES6_Def_AnonFunc2 = require(\"ES6_Default_AnonFunction2\").default;
+var ad1: number = ES6_Def_AnonFunc2();
+var ad2: string = ES6_Def_AnonFunc2(); // Error: number ~> string
+
+var ES6_Def_NamedFunc2 = require(\"ES6_Default_NamedFunction2\").default;
+var ae1: number = ES6_Def_NamedFunc2();
+var ae2: string = ES6_Def_NamedFunc2(); // Error: number ~> string
+
+
+
+
+
+var ES6_Def_NamedClass2 = require(\"ES6_Default_NamedClass2\").default;
+var ag1: number = new ES6_Def_NamedClass2().givesANum();
+var ag2: string = new ES6_Def_NamedClass2().givesANum(); // Error: number ~> string
+
+/////////////////////////////////
+// == ES6 Named -> CommonJS == //
+/////////////////////////////////
+
+var specifierNumber4 = require(\"ES6_Named2\").specifierNumber4;
+var ah1: number = specifierNumber4;
+var ah2: string = specifierNumber4; // Error: number ~> string
+
+var specifierNumber5Renamed = require(\"ES6_Named2\").specifierNumber5Renamed;
+var ai1: number = specifierNumber5Renamed;
+var ai2: string = specifierNumber5Renamed; // Error: number ~> string
+
+var groupedSpecifierNumber3 = require(\"ES6_Named2\").groupedSpecifierNumber3;
+var groupedSpecifierNumber4 = require(\"ES6_Named2\").groupedSpecifierNumber4;
+var aj1: number = groupedSpecifierNumber3;
+var aj2: number = groupedSpecifierNumber4;
+var aj3: string = groupedSpecifierNumber3; // Error: number ~> string
+var aj4: string = groupedSpecifierNumber4; // Error: number ~> string
+
+var givesANumber2 = require(\"ES6_Named2\").givesANumber2;
+var ak1: number = givesANumber2();
+var ak2: string = givesANumber2(); // Error: number ~> string
+
+var NumberGenerator2 = require(\"ES6_Named2\").NumberGenerator2;
+var al1: number = new NumberGenerator2().givesANumber();
+var al2: string = new NumberGenerator2().givesANumber(); // Error: number ~> string
+
+var varDeclNumber3 = require(\"ES6_Named2\").varDeclNumber3;
+var varDeclNumber4 = require(\"ES6_Named2\").varDeclNumber4;
+var am1: number = varDeclNumber3;
+var am2: number = varDeclNumber4;
+var am3: string = varDeclNumber3; // Error: number ~> string
+var am4: string = varDeclNumber4; // Error: number ~> string
+
+
+
+
+
+
+
+
+
+var numberValue6 = require(\"ES6_ExportFrom_Intermediary2\").numberValue1;
+var ap1: number = numberValue6;
+var ap2: string = numberValue6; // Error: number ~> string
+
+var numberValue2_renamed2 = require(\"ES6_ExportFrom_Intermediary2\").numberValue2_renamed2;
+var aq1: number = numberValue2_renamed2;
+var aq2: string = numberValue2_renamed2; // Error: number ~> string
+
+var numberValue7 = require(\"ES6_ExportAllFrom_Intermediary2\").numberValue2;
+var ar1: number = numberValue7;
+var ar2: string = numberValue7; // Error: number ~> string
+
+////////////////////////////////////////////////////////
+// == ES6 Default+Named -> ES6 import Default+Named== //
+////////////////////////////////////////////////////////
+
+import defaultNum, {str as namedStr} from \"./ES6_DefaultAndNamed\";
+
+var as1: number = defaultNum;
+var as2: string = defaultNum; // Error: number ~> string
+
+var as3: string = namedStr;
+var as4: number = namedStr; // Error: string ~> number
+
+////////////////////////////////////////
+// == Side-effect only ES6 imports == //
+////////////////////////////////////////
+
+import \"./SideEffects\";
+
+//////////////////////////////////////////////
+// == Suggest export name on likely typo == //
+//////////////////////////////////////////////
+import specifierNumber1 from \"ES6_Named1\"; // Error: Did you mean \`import {specifierNumber1} from ...\`?
+import {specifierNumber} from \"ES6_Named1\"; // Error: Did you mean \`specifierNumber1\`?
+
+///////////////////////////////////////////////////
+// == Multi \`export *\` should combine exports == //
+///////////////////////////////////////////////////
+import {
+  numberValue1 as numberValue8,
+  numberValue2 as numberValue9
+} from \"./ES6_ExportAllFromMulti\";
+
+var at1: number = numberValue8;
+var at2: string = numberValue8; // Error: number ~> string
+
+var at3: number = numberValue9;
+var at4: string = numberValue9; // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// ===================== //
+// == Path Resolution == //
+// ===================== //
+// @providesModule
+import * as DefaultA from \"A\";
+var a1: number = DefaultA.numberValue1;
+var a2: string = DefaultA.numberValue1;// Error: number ~> string
+// File path
+import * as DefaultB from \"./B\";
+var b1: number = DefaultB.numberValue;
+var b2: string = DefaultB.numberValue;// Error: number ~> string
+// C.js exists, but not as a providesModule
+import DefaultC from \"C\";// Error: No such module
+// @providesModule D exists, but not as a filename
+import DefaultD from \"./D\";// Error: No such module
+// ================================================ //
+// == CommonJS Clobbering Literal Exports -> ES6 == //
+// ================================================ //
+import { doesntExist1 } from \"CommonJS_Clobbering_Lit\";// Error: Not an exported binding
+import { numberValue1 } from \"CommonJS_Clobbering_Lit\";
+var c1: number = numberValue1;
+var c2: string = numberValue1;// Error: number ~> string
+import { numberValue2 as numVal1 } from \"CommonJS_Clobbering_Lit\";
+var d1: number = numVal1;
+var d2: string = numVal1;// Error: number ~> string
+import CJS_Clobb_Lit from \"CommonJS_Clobbering_Lit\";
+var e1: number = CJS_Clobb_Lit.numberValue3;
+var e2: string = CJS_Clobb_Lit.numberValue3;// Error: number ~> string
+CJS_Clobb_Lit.doesntExist;// Error: doesntExist isn\'t a property
+import * as CJS_Clobb_Lit_NS from \"CommonJS_Clobbering_Lit\";
+var f1: number = CJS_Clobb_Lit_NS.numberValue4;
+var f2: number = CJS_Clobb_Lit_NS.default.numberValue4;
+CJS_Clobb_Lit_NS.default.default;// Error: No \'default\' property on the exported obj
+var f3: string = CJS_Clobb_Lit_NS.numberValue4;// Error: number ~> string
+var f4: string = CJS_Clobb_Lit_NS.default.numberValue5;// Error: number ~> string
+// ============================================== //
+// == CommonJS Clobbering Class Exports -> ES6 == //
+// ============================================== //
+import { doesntExist2 } from \"CommonJS_Clobbering_Class\";// Error: Not an exported binding
+// The following import should error because class statics are not turned into
+// named exports for now. This avoids complexities with polymorphic static
+// members (where the polymophism is defined on the class itself rather than the
+// method).
+import { staticNumber1, baseProp, childProp } from \"CommonJS_Clobbering_Class\";// Error
+import CJS_Clobb_Class from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class();
+new CJS_Clobb_Class().doesntExist;// Error: Class has no \`doesntExist\` property
+var h1: number = CJS_Clobb_Class.staticNumber2();
+var h2: string = CJS_Clobb_Class.staticNumber2();// Error: number ~> string
+var h3: number = new CJS_Clobb_Class().instNumber1();
+var h4: string = new CJS_Clobb_Class().instNumber1();// Error: number ~> string
+import * as CJS_Clobb_Class_NS from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class_NS();// Error: Namespace object isn\'t constructable
+var i1: number = CJS_Clobb_Class_NS.staticNumber3();// Error: Class statics not copied to Namespace object
+var i2: number = new CJS_Clobb_Class_NS.default().instNumber2();
+var i3: string = new CJS_Clobb_Class_NS.default().instNumber2();// Error: number ~> string
+// =================================== //
+// == CommonJS Named Exports -> ES6 == //
+// =================================== //
+import { doesntExist3 } from \"CommonJS_Named\";// Error: Not an exported binding
+import { numberValue2 } from \"CommonJS_Named\";
+var j1: number = numberValue2;
+var j2: string = numberValue2;// Error: number ~> string
+import { numberValue3 as numVal3 } from \"CommonJS_Named\";
+var k1: number = numVal3;
+var k2: string = numVal3;// Error: number ~> string
+import * as CJS_Named from \"CommonJS_Named\";
+var l1: number = CJS_Named.numberValue1;
+var l2: string = CJS_Named.numberValue1;// Error: number ~> string
+CJS_Named.doesntExist;// Error: doesntExist isn\'t a property
+import * as CJS_Named_NS from \"CommonJS_Named\";
+var m1: number = CJS_Named_NS.numberValue4;
+var m2: string = CJS_Named_NS.default.numberValue4;// Error: CommonJS_Named has no default export
+var m3: string = CJS_Named_NS.numberValue4;// Error: number ~> string
+//////////////////////////////
+// == ES6 Default -> ES6 == //
+//////////////////////////////
+import { doesntExist4 } from \"ES6_Default_AnonFunction1\";// Error: Not an exported binding
+import ES6_Def_AnonFunc1 from \"ES6_Default_AnonFunction1\";
+var n1: number = ES6_Def_AnonFunc1();
+var n2: string = ES6_Def_AnonFunc1();// Error: number ~> string
+import ES6_Def_NamedFunc1 from \"ES6_Default_NamedFunction1\";
+var o1: number = ES6_Def_NamedFunc1();
+var o2: string = ES6_Def_NamedFunc1();// Error: number ~> string
+import ES6_Def_NamedClass1 from \"ES6_Default_NamedClass1\";
+var q1: number = new ES6_Def_NamedClass1().givesANum();
+var q2: string = new ES6_Def_NamedClass1().givesANum();// Error: number ~> string
+////////////////////////////
+// == ES6 Named -> ES6 == //
+////////////////////////////
+import doesntExist5 from \"ES6_Named1\";// Error: Not an exported binding
+import { specifierNumber1 as specifierNumber1_1 } from \"ES6_Named1\";
+var r1: number = specifierNumber1_1;
+var r2: string = specifierNumber1_1;// Error: number ~> string
+import { specifierNumber2Renamed } from \"ES6_Named1\";
+var s1: number = specifierNumber2Renamed;
+var s2: string = specifierNumber2Renamed;// Error: number ~> string
+import { specifierNumber3 as specifierNumber3Renamed } from \"ES6_Named1\";
+var t1: number = specifierNumber3Renamed;
+var t2: string = specifierNumber3Renamed;// Error: number ~> string
+import { groupedSpecifierNumber1, groupedSpecifierNumber2 } from \"ES6_Named1\";
+var u1: number = groupedSpecifierNumber1;
+var u2: number = groupedSpecifierNumber2;
+var u3: string = groupedSpecifierNumber1;// Error: number ~> string
+var u4: string = groupedSpecifierNumber2;// Error: number ~> string
+import { givesANumber } from \"ES6_Named1\";
+var v1: number = givesANumber();
+var v2: string = givesANumber();// Error: number ~> string
+import { NumberGenerator } from \"ES6_Named1\";
+var w1: number = new NumberGenerator().givesANumber();
+var w2: string = new NumberGenerator().givesANumber();// Error: number ~> string
+import { varDeclNumber1, varDeclNumber2 } from \"ES6_Named1\";
+var x1: number = varDeclNumber1;
+var x2: number = varDeclNumber2;
+var x3: string = varDeclNumber1;// Error: number ~> string
+var x4: string = varDeclNumber2;// Error: number ~> string
+import { numberValue1 as numberValue4 } from \"ES6_ExportFrom_Intermediary1\";
+var aa1: number = numberValue4;
+var aa2: string = numberValue4;// Error: number ~> string
+import { numberValue2_renamed } from \"ES6_ExportFrom_Intermediary1\";
+var ab1: number = numberValue2_renamed;
+var ab2: string = numberValue2_renamed;// Error: number ~> string
+import { numberValue1 as numberValue5 } from \"ES6_ExportAllFrom_Intermediary1\";
+var ac1: number = numberValue5;
+var ac2: string = numberValue5;// Error: number ~> string
+///////////////////////////////////
+// == ES6 Default -> CommonJS == //
+///////////////////////////////////
+require(
+  \"ES6_Default_AnonFunction2\"
+).doesntExist;// Error: \'doesntExist\' isn\'t an export
+var ES6_Def_AnonFunc2 = require(\"ES6_Default_AnonFunction2\").default;
+var ad1: number = ES6_Def_AnonFunc2();
+var ad2: string = ES6_Def_AnonFunc2();// Error: number ~> string
+var ES6_Def_NamedFunc2 = require(\"ES6_Default_NamedFunction2\").default;
+var ae1: number = ES6_Def_NamedFunc2();
+var ae2: string = ES6_Def_NamedFunc2();// Error: number ~> string
+var ES6_Def_NamedClass2 = require(\"ES6_Default_NamedClass2\").default;
+var ag1: number = new ES6_Def_NamedClass2().givesANum();
+var ag2: string = new ES6_Def_NamedClass2().givesANum();// Error: number ~> string
+/////////////////////////////////
+// == ES6 Named -> CommonJS == //
+/////////////////////////////////
+var specifierNumber4 = require(\"ES6_Named2\").specifierNumber4;
+var ah1: number = specifierNumber4;
+var ah2: string = specifierNumber4;// Error: number ~> string
+var specifierNumber5Renamed = require(\"ES6_Named2\").specifierNumber5Renamed;
+var ai1: number = specifierNumber5Renamed;
+var ai2: string = specifierNumber5Renamed;// Error: number ~> string
+var groupedSpecifierNumber3 = require(\"ES6_Named2\").groupedSpecifierNumber3;
+var groupedSpecifierNumber4 = require(\"ES6_Named2\").groupedSpecifierNumber4;
+var aj1: number = groupedSpecifierNumber3;
+var aj2: number = groupedSpecifierNumber4;
+var aj3: string = groupedSpecifierNumber3;// Error: number ~> string
+var aj4: string = groupedSpecifierNumber4;// Error: number ~> string
+var givesANumber2 = require(\"ES6_Named2\").givesANumber2;
+var ak1: number = givesANumber2();
+var ak2: string = givesANumber2();// Error: number ~> string
+var NumberGenerator2 = require(\"ES6_Named2\").NumberGenerator2;
+var al1: number = new NumberGenerator2().givesANumber();
+var al2: string = new NumberGenerator2().givesANumber();// Error: number ~> string
+var varDeclNumber3 = require(\"ES6_Named2\").varDeclNumber3;
+var varDeclNumber4 = require(\"ES6_Named2\").varDeclNumber4;
+var am1: number = varDeclNumber3;
+var am2: number = varDeclNumber4;
+var am3: string = varDeclNumber3;// Error: number ~> string
+var am4: string = varDeclNumber4;// Error: number ~> string
+var numberValue6 = require(\"ES6_ExportFrom_Intermediary2\").numberValue1;
+var ap1: number = numberValue6;
+var ap2: string = numberValue6;// Error: number ~> string
+var numberValue2_renamed2 = require(
+  \"ES6_ExportFrom_Intermediary2\"
+).numberValue2_renamed2;
+var aq1: number = numberValue2_renamed2;
+var aq2: string = numberValue2_renamed2;// Error: number ~> string
+var numberValue7 = require(\"ES6_ExportAllFrom_Intermediary2\").numberValue2;
+var ar1: number = numberValue7;
+var ar2: string = numberValue7;// Error: number ~> string
+////////////////////////////////////////////////////////
+// == ES6 Default+Named -> ES6 import Default+Named== //
+////////////////////////////////////////////////////////
+import defaultNum, { str as namedStr } from \"./ES6_DefaultAndNamed\";
+var as1: number = defaultNum;
+var as2: string = defaultNum;// Error: number ~> string
+var as3: string = namedStr;
+var as4: number = namedStr;// Error: string ~> number
+////////////////////////////////////////
+// == Side-effect only ES6 imports == //
+////////////////////////////////////////
+import \"./SideEffects\";
+//////////////////////////////////////////////
+// == Suggest export name on likely typo == //
+//////////////////////////////////////////////
+import specifierNumber1 from \"ES6_Named1\";// Error: Did you mean \`import {specifierNumber1} from ...\`?
+import { specifierNumber } from \"ES6_Named1\";// Error: Did you mean \`specifierNumber1\`?
+///////////////////////////////////////////////////
+// == Multi \`export *\` should combine exports == //
+///////////////////////////////////////////////////
+import { numberValue1 as numberValue8, numberValue2 as numberValue9 } from \"./ES6_ExportAllFromMulti\";
+var at1: number = numberValue8;
+var at2: string = numberValue8;// Error: number ~> string
+var at3: number = numberValue9;
+var at4: string = numberValue9;// Error: number ~> string
+
+"
+`;
diff --git a/tests/declare_export/es6modules.js b/tests/declare_export/es6modules.js
new file mode 100644
index 000000000000..a6a52fe441cb
--- /dev/null
+++ b/tests/declare_export/es6modules.js
@@ -0,0 +1,291 @@
+/* @flow */
+
+// ===================== //
+// == Path Resolution == //
+// ===================== //
+
+// @providesModule
+import * as DefaultA from "A";
+var a1: number = DefaultA.numberValue1;
+var a2: string = DefaultA.numberValue1; // Error: number ~> string
+
+// File path
+import * as DefaultB from "./B";
+var b1: number = DefaultB.numberValue;
+var b2: string = DefaultB.numberValue; // Error: number ~> string
+
+// C.js exists, but not as a providesModule
+import DefaultC from "C"; // Error: No such module
+
+// @providesModule D exists, but not as a filename
+import DefaultD from "./D"; // Error: No such module
+
+// ================================================ //
+// == CommonJS Clobbering Literal Exports -> ES6 == //
+// ================================================ //
+
+import {doesntExist1} from "CommonJS_Clobbering_Lit"; // Error: Not an exported binding
+
+import {numberValue1} from "CommonJS_Clobbering_Lit";
+var c1: number = numberValue1;
+var c2: string = numberValue1; // Error: number ~> string
+
+import {numberValue2 as numVal1} from "CommonJS_Clobbering_Lit";
+var d1: number = numVal1;
+var d2: string = numVal1; // Error: number ~> string
+
+import CJS_Clobb_Lit from "CommonJS_Clobbering_Lit";
+var e1: number = CJS_Clobb_Lit.numberValue3;
+var e2: string = CJS_Clobb_Lit.numberValue3; // Error: number ~> string
+CJS_Clobb_Lit.doesntExist; // Error: doesntExist isn't a property
+
+import * as CJS_Clobb_Lit_NS from "CommonJS_Clobbering_Lit";
+var f1: number = CJS_Clobb_Lit_NS.numberValue4;
+var f2: number = CJS_Clobb_Lit_NS.default.numberValue4;
+CJS_Clobb_Lit_NS.default.default; // Error: No 'default' property on the exported obj
+var f3: string = CJS_Clobb_Lit_NS.numberValue4; // Error: number ~> string
+var f4: string = CJS_Clobb_Lit_NS.default.numberValue5; // Error: number ~> string
+
+// ============================================== //
+// == CommonJS Clobbering Class Exports -> ES6 == //
+// ============================================== //
+
+import {doesntExist2} from "CommonJS_Clobbering_Class"; // Error: Not an exported binding
+
+// The following import should error because class statics are not turned into
+// named exports for now. This avoids complexities with polymorphic static
+// members (where the polymophism is defined on the class itself rather than the
+// method).
+import {staticNumber1, baseProp, childProp} from "CommonJS_Clobbering_Class"; // Error
+
+import CJS_Clobb_Class from "CommonJS_Clobbering_Class";
+new CJS_Clobb_Class();
+new CJS_Clobb_Class().doesntExist; // Error: Class has no `doesntExist` property
+var h1: number = CJS_Clobb_Class.staticNumber2();
+var h2: string = CJS_Clobb_Class.staticNumber2(); // Error: number ~> string
+var h3: number = new CJS_Clobb_Class().instNumber1();
+var h4: string = new CJS_Clobb_Class().instNumber1(); // Error: number ~> string
+
+import * as CJS_Clobb_Class_NS from "CommonJS_Clobbering_Class";
+new CJS_Clobb_Class_NS(); // Error: Namespace object isn't constructable
+var i1: number = CJS_Clobb_Class_NS.staticNumber3(); // Error: Class statics not copied to Namespace object
+var i2: number = new CJS_Clobb_Class_NS.default().instNumber2();
+var i3: string = new CJS_Clobb_Class_NS.default().instNumber2(); // Error: number ~> string
+
+// =================================== //
+// == CommonJS Named Exports -> ES6 == //
+// =================================== //
+
+import {doesntExist3} from "CommonJS_Named"; // Error: Not an exported binding
+
+import {numberValue2} from "CommonJS_Named";
+var j1: number = numberValue2;
+var j2: string = numberValue2; // Error: number ~> string
+
+import {numberValue3 as numVal3} from "CommonJS_Named";
+var k1: number = numVal3;
+var k2: string = numVal3; // Error: number ~> string
+
+import * as CJS_Named from "CommonJS_Named";
+var l1: number = CJS_Named.numberValue1;
+var l2: string = CJS_Named.numberValue1; // Error: number ~> string
+CJS_Named.doesntExist; // Error: doesntExist isn't a property
+
+import * as CJS_Named_NS from "CommonJS_Named";
+var m1: number = CJS_Named_NS.numberValue4;
+var m2: string = CJS_Named_NS.default.numberValue4; // Error: CommonJS_Named has no default export
+var m3: string = CJS_Named_NS.numberValue4; // Error: number ~> string
+
+//////////////////////////////
+// == ES6 Default -> ES6 == //
+//////////////////////////////
+
+import {doesntExist4} from "ES6_Default_AnonFunction1"; // Error: Not an exported binding
+
+import ES6_Def_AnonFunc1 from "ES6_Default_AnonFunction1";
+var n1: number = ES6_Def_AnonFunc1();
+var n2: string = ES6_Def_AnonFunc1(); // Error: number ~> string
+
+import ES6_Def_NamedFunc1 from "ES6_Default_NamedFunction1";
+var o1: number = ES6_Def_NamedFunc1();
+var o2: string = ES6_Def_NamedFunc1(); // Error: number ~> string
+
+
+
+
+
+import ES6_Def_NamedClass1 from "ES6_Default_NamedClass1";
+var q1: number = new ES6_Def_NamedClass1().givesANum();
+var q2: string = new ES6_Def_NamedClass1().givesANum(); // Error: number ~> string
+
+////////////////////////////
+// == ES6 Named -> ES6 == //
+////////////////////////////
+
+import doesntExist5 from "ES6_Named1"; // Error: Not an exported binding
+
+import {specifierNumber1 as specifierNumber1_1} from "ES6_Named1";
+var r1: number = specifierNumber1_1;
+var r2: string = specifierNumber1_1; // Error: number ~> string
+
+import {specifierNumber2Renamed} from "ES6_Named1";
+var s1: number = specifierNumber2Renamed;
+var s2: string = specifierNumber2Renamed; // Error: number ~> string
+
+import {specifierNumber3 as specifierNumber3Renamed} from "ES6_Named1";
+var t1: number = specifierNumber3Renamed;
+var t2: string = specifierNumber3Renamed; // Error: number ~> string
+
+import {groupedSpecifierNumber1, groupedSpecifierNumber2} from "ES6_Named1";
+var u1: number = groupedSpecifierNumber1;
+var u2: number = groupedSpecifierNumber2;
+var u3: string = groupedSpecifierNumber1; // Error: number ~> string
+var u4: string = groupedSpecifierNumber2; // Error: number ~> string
+
+import {givesANumber} from "ES6_Named1";
+var v1: number = givesANumber();
+var v2: string = givesANumber(); // Error: number ~> string
+
+import {NumberGenerator} from "ES6_Named1";
+var w1: number = new NumberGenerator().givesANumber();
+var w2: string = new NumberGenerator().givesANumber(); // Error: number ~> string
+
+import {varDeclNumber1, varDeclNumber2} from "ES6_Named1";
+var x1: number = varDeclNumber1;
+var x2: number = varDeclNumber2;
+var x3: string = varDeclNumber1; // Error: number ~> string
+var x4: string = varDeclNumber2; // Error: number ~> string
+
+
+
+
+
+
+
+
+
+import {numberValue1 as numberValue4} from "ES6_ExportFrom_Intermediary1";
+var aa1: number = numberValue4;
+var aa2: string = numberValue4; // Error: number ~> string
+
+import {numberValue2_renamed} from "ES6_ExportFrom_Intermediary1";
+var ab1: number = numberValue2_renamed;
+var ab2: string = numberValue2_renamed; // Error: number ~> string
+
+import {numberValue1 as numberValue5} from "ES6_ExportAllFrom_Intermediary1";
+var ac1: number = numberValue5;
+var ac2: string = numberValue5; // Error: number ~> string
+
+///////////////////////////////////
+// == ES6 Default -> CommonJS == //
+///////////////////////////////////
+
+require('ES6_Default_AnonFunction2').doesntExist; // Error: 'doesntExist' isn't an export
+
+var ES6_Def_AnonFunc2 = require("ES6_Default_AnonFunction2").default;
+var ad1: number = ES6_Def_AnonFunc2();
+var ad2: string = ES6_Def_AnonFunc2(); // Error: number ~> string
+
+var ES6_Def_NamedFunc2 = require("ES6_Default_NamedFunction2").default;
+var ae1: number = ES6_Def_NamedFunc2();
+var ae2: string = ES6_Def_NamedFunc2(); // Error: number ~> string
+
+
+
+
+
+var ES6_Def_NamedClass2 = require("ES6_Default_NamedClass2").default;
+var ag1: number = new ES6_Def_NamedClass2().givesANum();
+var ag2: string = new ES6_Def_NamedClass2().givesANum(); // Error: number ~> string
+
+/////////////////////////////////
+// == ES6 Named -> CommonJS == //
+/////////////////////////////////
+
+var specifierNumber4 = require("ES6_Named2").specifierNumber4;
+var ah1: number = specifierNumber4;
+var ah2: string = specifierNumber4; // Error: number ~> string
+
+var specifierNumber5Renamed = require("ES6_Named2").specifierNumber5Renamed;
+var ai1: number = specifierNumber5Renamed;
+var ai2: string = specifierNumber5Renamed; // Error: number ~> string
+
+var groupedSpecifierNumber3 = require("ES6_Named2").groupedSpecifierNumber3;
+var groupedSpecifierNumber4 = require("ES6_Named2").groupedSpecifierNumber4;
+var aj1: number = groupedSpecifierNumber3;
+var aj2: number = groupedSpecifierNumber4;
+var aj3: string = groupedSpecifierNumber3; // Error: number ~> string
+var aj4: string = groupedSpecifierNumber4; // Error: number ~> string
+
+var givesANumber2 = require("ES6_Named2").givesANumber2;
+var ak1: number = givesANumber2();
+var ak2: string = givesANumber2(); // Error: number ~> string
+
+var NumberGenerator2 = require("ES6_Named2").NumberGenerator2;
+var al1: number = new NumberGenerator2().givesANumber();
+var al2: string = new NumberGenerator2().givesANumber(); // Error: number ~> string
+
+var varDeclNumber3 = require("ES6_Named2").varDeclNumber3;
+var varDeclNumber4 = require("ES6_Named2").varDeclNumber4;
+var am1: number = varDeclNumber3;
+var am2: number = varDeclNumber4;
+var am3: string = varDeclNumber3; // Error: number ~> string
+var am4: string = varDeclNumber4; // Error: number ~> string
+
+
+
+
+
+
+
+
+
+var numberValue6 = require("ES6_ExportFrom_Intermediary2").numberValue1;
+var ap1: number = numberValue6;
+var ap2: string = numberValue6; // Error: number ~> string
+
+var numberValue2_renamed2 = require("ES6_ExportFrom_Intermediary2").numberValue2_renamed2;
+var aq1: number = numberValue2_renamed2;
+var aq2: string = numberValue2_renamed2; // Error: number ~> string
+
+var numberValue7 = require("ES6_ExportAllFrom_Intermediary2").numberValue2;
+var ar1: number = numberValue7;
+var ar2: string = numberValue7; // Error: number ~> string
+
+////////////////////////////////////////////////////////
+// == ES6 Default+Named -> ES6 import Default+Named== //
+////////////////////////////////////////////////////////
+
+import defaultNum, {str as namedStr} from "./ES6_DefaultAndNamed";
+
+var as1: number = defaultNum;
+var as2: string = defaultNum; // Error: number ~> string
+
+var as3: string = namedStr;
+var as4: number = namedStr; // Error: string ~> number
+
+////////////////////////////////////////
+// == Side-effect only ES6 imports == //
+////////////////////////////////////////
+
+import "./SideEffects";
+
+//////////////////////////////////////////////
+// == Suggest export name on likely typo == //
+//////////////////////////////////////////////
+import specifierNumber1 from "ES6_Named1"; // Error: Did you mean `import {specifierNumber1} from ...`?
+import {specifierNumber} from "ES6_Named1"; // Error: Did you mean `specifierNumber1`?
+
+///////////////////////////////////////////////////
+// == Multi `export *` should combine exports == //
+///////////////////////////////////////////////////
+import {
+  numberValue1 as numberValue8,
+  numberValue2 as numberValue9
+} from "./ES6_ExportAllFromMulti";
+
+var at1: number = numberValue8;
+var at2: string = numberValue8; // Error: number ~> string
+
+var at3: number = numberValue9;
+var at4: string = numberValue9; // Error: number ~> string
diff --git a/tests/declare_export/jsfmt.spec.js b/tests/declare_export/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_export/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_fun/__snapshots__/jsfmt.spec.js.snap b/tests/declare_fun/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1d896985749f
--- /dev/null
+++ b/tests/declare_fun/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test test.js 1`] = `
+"declare function foo(x: number): string;
+declare function foo(x: string): number;
+declare function foo<X>(x: X): X;
+
+(foo(0): string); // OK
+(foo(\"hello\"): number); // OK
+(foo(false): void); // error, boolean ~/~ undefined
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/declare_fun/jsfmt.spec.js b/tests/declare_fun/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_fun/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_fun/test.js b/tests/declare_fun/test.js
new file mode 100644
index 000000000000..db8a37324764
--- /dev/null
+++ b/tests/declare_fun/test.js
@@ -0,0 +1,7 @@
+declare function foo(x: number): string;
+declare function foo(x: string): number;
+declare function foo<X>(x: X): X;
+
+(foo(0): string); // OK
+(foo("hello"): number); // OK
+(foo(false): void); // error, boolean ~/~ undefined
diff --git a/tests/declare_module_exports/__snapshots__/jsfmt.spec.js.snap b/tests/declare_module_exports/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fd7fb86fc55f
--- /dev/null
+++ b/tests/declare_module_exports/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,49 @@
+exports[`test main.js 1`] = `
+"// @flow
+
+import declare_module_exports from "declare_module_exports";
+(declare_module_exports: number);
+(declare_module_exports: string); // Error: number ~> string
+
+// Error: Has no named export "str"!
+import {str} from "declare_m_e_with_other_value_declares";
+
+import type {str2} from "declare_m_e_with_other_type_declares";
+("asdf": str2);
+(42: str2); // Error: number ~> string
+
+/**
+ * \`declare var exports\` is deprecated, so we have a grace period where both
+ * syntaxes will work.
+ */
+
+import DEPRECATED__declare_var_exports from "DEPRECATED__declare_var_exports";
+(DEPRECATED__declare_var_exports: number);
+(DEPRECATED__declare_var_exports: string); // Error: number ~> string
+
+import declare_m_e_with_declare_var_e from "declare_m_e_with_declare_var_e";
+(declare_m_e_with_declare_var_e: number);
+(declare_m_e_with_declare_var_e: string); // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import declare_module_exports from "declare_module_exports";
+(declare_module_exports: number);
+(declare_module_exports: string);// Error: number ~> string
+// Error: Has no named export "str"!
+import { str } from "declare_m_e_with_other_value_declares";
+import type { str2 } from "declare_m_e_with_other_type_declares";
+("asdf": str2);
+(42: str2);// Error: number ~> string
+/**
+ * \`declare var exports\` is deprecated, so we have a grace period where both
+ * syntaxes will work.
+ */
+import DEPRECATED__declare_var_exports from "DEPRECATED__declare_var_exports";
+(DEPRECATED__declare_var_exports: number);
+(DEPRECATED__declare_var_exports: string);// Error: number ~> string
+import declare_m_e_with_declare_var_e from "declare_m_e_with_declare_var_e";
+(declare_m_e_with_declare_var_e: number);
+(declare_m_e_with_declare_var_e: string);// Error: number ~> string
+
+"
+`;
diff --git a/tests/declare_module_exports/flow-typed/__snapshots__/jsfmt.spec.js.snap b/tests/declare_module_exports/flow-typed/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..610dfff48baf
--- /dev/null
+++ b/tests/declare_module_exports/flow-typed/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,60 @@
+exports[`test libs.js 1`] = `
+"declare module "declare_module_exports" {
+  declare module.exports: number;
+}
+
+declare module "declare_m_e_with_other_value_declares" {
+  declare module.exports: number;
+  declare var str: string;
+}
+
+declare module "declare_m_e_with_other_type_declares" {
+  declare module.exports: number;
+  declare type str2 = string;
+}
+
+/**
+ * \`declare var exports\` is deprecated, so we have a grace period where both
+ * syntaxes will work.
+ */
+
+declare module "DEPRECATED__declare_var_exports" {
+  declare var exports: number;
+}
+
+/**
+ * Ensure that, if both are present, \`declare module.exports\` wins
+ */
+declare module "declare_m_e_with_declare_var_e" {
+  declare module.exports: number;
+  declare var exports: string;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare module "declare_module_exports" {
+  declare module.exports: number
+}
+declare module "declare_m_e_with_other_value_declares" {
+  declare module.exports: number
+  declare var str: string;
+}
+declare module "declare_m_e_with_other_type_declares" {
+  declare module.exports: number
+  type str2 = string;
+}
+/**
+ * \`declare var exports\` is deprecated, so we have a grace period where both
+ * syntaxes will work.
+ */
+declare module "DEPRECATED__declare_var_exports" {
+  declare var exports: number;
+}
+/**
+ * Ensure that, if both are present, \`declare module.exports\` wins
+ */
+declare module "declare_m_e_with_declare_var_e" {
+  declare module.exports: number
+  declare var exports: string;
+}
+
+"
+`;
diff --git a/tests/declare_module_exports/flow-typed/jsfmt.spec.js b/tests/declare_module_exports/flow-typed/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_module_exports/flow-typed/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_module_exports/flow-typed/libs.js b/tests/declare_module_exports/flow-typed/libs.js
new file mode 100644
index 000000000000..25ee31b0a922
--- /dev/null
+++ b/tests/declare_module_exports/flow-typed/libs.js
@@ -0,0 +1,30 @@
+declare module "declare_module_exports" {
+  declare module.exports: number;
+}
+
+declare module "declare_m_e_with_other_value_declares" {
+  declare module.exports: number;
+  declare var str: string;
+}
+
+declare module "declare_m_e_with_other_type_declares" {
+  declare module.exports: number;
+  declare type str2 = string;
+}
+
+/**
+ * `declare var exports` is deprecated, so we have a grace period where both
+ * syntaxes will work.
+ */
+
+declare module "DEPRECATED__declare_var_exports" {
+  declare var exports: number;
+}
+
+/**
+ * Ensure that, if both are present, `declare module.exports` wins
+ */
+declare module "declare_m_e_with_declare_var_e" {
+  declare module.exports: number;
+  declare var exports: string;
+}
diff --git a/tests/declare_module_exports/jsfmt.spec.js b/tests/declare_module_exports/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_module_exports/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_module_exports/main.js b/tests/declare_module_exports/main.js
new file mode 100644
index 000000000000..7c9cce2c344d
--- /dev/null
+++ b/tests/declare_module_exports/main.js
@@ -0,0 +1,25 @@
+// @flow
+
+import declare_module_exports from "declare_module_exports";
+(declare_module_exports: number);
+(declare_module_exports: string); // Error: number ~> string
+
+// Error: Has no named export "str"!
+import {str} from "declare_m_e_with_other_value_declares";
+
+import type {str2} from "declare_m_e_with_other_type_declares";
+("asdf": str2);
+(42: str2); // Error: number ~> string
+
+/**
+ * `declare var exports` is deprecated, so we have a grace period where both
+ * syntaxes will work.
+ */
+
+import DEPRECATED__declare_var_exports from "DEPRECATED__declare_var_exports";
+(DEPRECATED__declare_var_exports: number);
+(DEPRECATED__declare_var_exports: string); // Error: number ~> string
+
+import declare_m_e_with_declare_var_e from "declare_m_e_with_declare_var_e";
+(declare_m_e_with_declare_var_e: number);
+(declare_m_e_with_declare_var_e: string); // Error: number ~> string
diff --git a/tests/declare_type/__snapshots__/jsfmt.spec.js.snap b/tests/declare_type/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..70ade6b61551
--- /dev/null
+++ b/tests/declare_type/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,49 @@
+exports[`test import_declare_type.js 1`] = `
+"/**
+ * @flow
+ */
+
+////////////////////////////////////////////////////////////
+// == Import Declared Type Alias From Declared Module == //
+//////////////////////////////////////////////////////////
+import type {baz} from \"ModuleAliasFoo\";
+import {foo} from \"ModuleAliasFoo\";
+var k1: baz = 42;
+var k2: baz = \"shab\"; // Error: string to int
+var k3: toz = foo(k1); // works
+
+import type {toz} from \"ModuleAliasFoo\";
+var k4: toz = foo(k1); // works
+
+//////////////////////////////////////////////////////////
+// == Declared Module with exports prop (issue 880) == //
+////////////////////////////////////////////////////////
+
+import blah from \'foo\';
+import type { Foo, Bar, Id } from \'foo\';
+
+blah(0, 0);
+
+({toz:3} : Foo); // error : {toz : number} ~> string
+
+(3 : Bar); // error : number ~> A
+
+(\"lol\" : Id<number>); // error : string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/declare_type/import_declare_type.js b/tests/declare_type/import_declare_type.js
new file mode 100644
index 000000000000..3cd90be747b0
--- /dev/null
+++ b/tests/declare_type/import_declare_type.js
@@ -0,0 +1,30 @@
+/**
+ * @flow
+ */
+
+////////////////////////////////////////////////////////////
+// == Import Declared Type Alias From Declared Module == //
+//////////////////////////////////////////////////////////
+import type {baz} from "ModuleAliasFoo";
+import {foo} from "ModuleAliasFoo";
+var k1: baz = 42;
+var k2: baz = "shab"; // Error: string to int
+var k3: toz = foo(k1); // works
+
+import type {toz} from "ModuleAliasFoo";
+var k4: toz = foo(k1); // works
+
+//////////////////////////////////////////////////////////
+// == Declared Module with exports prop (issue 880) == //
+////////////////////////////////////////////////////////
+
+import blah from 'foo';
+import type { Foo, Bar, Id } from 'foo';
+
+blah(0, 0);
+
+({toz:3} : Foo); // error : {toz : number} ~> string
+
+(3 : Bar); // error : number ~> A
+
+("lol" : Id<number>); // error : string ~> number
diff --git a/tests/declare_type/jsfmt.spec.js b/tests/declare_type/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_type/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/declare_type/lib/DeclareModule_TypeAlias.js b/tests/declare_type/lib/DeclareModule_TypeAlias.js
new file mode 100644
index 000000000000..325d344de110
--- /dev/null
+++ b/tests/declare_type/lib/DeclareModule_TypeAlias.js
@@ -0,0 +1,9 @@
+/**
+ * @flow
+ */
+
+declare module ModuleAliasFoo {
+    declare type baz = number;
+    declare type toz = string;
+    declare function foo(bar : baz) : toz;
+}
diff --git a/tests/declare_type/lib/__snapshots__/jsfmt.spec.js.snap b/tests/declare_type/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ae6ef708d866
--- /dev/null
+++ b/tests/declare_type/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,65 @@
+exports[`test DeclareModule_TypeAlias.js 1`] = `
+"/**
+ * @flow
+ */
+
+declare module ModuleAliasFoo {
+    declare type baz = number;
+    declare type toz = string;
+    declare function foo(bar : baz) : toz;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test declare_type_exports.js 1`] = `
+"/* @flow */
+
+declare module \'foo\' {
+    declare class A {
+        toz : number
+    }
+
+    declare var n : string;
+
+    declare type Foo = typeof n;
+    declare type Bar = A;
+    declare type Id<T> = T;
+
+    declare var exports : {
+        (a : number, b : number) : number
+    };
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/declare_type/lib/declare_type_exports.js b/tests/declare_type/lib/declare_type_exports.js
new file mode 100644
index 000000000000..dac1a6bd9a92
--- /dev/null
+++ b/tests/declare_type/lib/declare_type_exports.js
@@ -0,0 +1,17 @@
+/* @flow */
+
+declare module 'foo' {
+    declare class A {
+        toz : number
+    }
+
+    declare var n : string;
+
+    declare type Foo = typeof n;
+    declare type Bar = A;
+    declare type Id<T> = T;
+
+    declare var exports : {
+        (a : number, b : number) : number
+    };
+}
diff --git a/tests/declare_type/lib/jsfmt.spec.js b/tests/declare_type/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/declare_type/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/def_site_variance/__snapshots__/jsfmt.spec.js.snap b/tests/def_site_variance/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..cd46d9b9ba9b
--- /dev/null
+++ b/tests/def_site_variance/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,50 @@
+exports[`test test.js 1`] = `
+"class Variance<+Out,-In> {
+  foo(x: Out): Out { return x; }
+  bar(y: In): In { return y; }
+}
+
+class A { }
+class B extends A { }
+
+function subtyping(
+  v1: Variance<A,B>,
+  v2: Variance<B,A>
+) {
+  (v1: Variance<B,A>); // error on both targs (A ~/~> B)
+  (v2: Variance<A,B>); // OK for both targs (B ~> A)
+}
+
+class PropVariance<+Out,-In> {
+  inv1: Out; // error
+  inv2: In; // error
+  -co1: Out; // error
+  -co2: In; // ok
+  +con1: Out; // ok
+  +con2: In; // error
+
+  inv_dict1: {[k:string]: Out}; // error
+  inv_dict2: {[k:string]: In}; // error
+  co_dict1: {+[k:string]: Out}; // ok
+  co_dict2: {+[k:string]: In}; // error
+  con_dict1: {-[k:string]: Out}; // error
+  con_dict2: {-[k:string]: In}; // ok
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/def_site_variance/jsfmt.spec.js b/tests/def_site_variance/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/def_site_variance/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/def_site_variance/test.js b/tests/def_site_variance/test.js
new file mode 100644
index 000000000000..72f756eeaa21
--- /dev/null
+++ b/tests/def_site_variance/test.js
@@ -0,0 +1,31 @@
+class Variance<+Out,-In> {
+  foo(x: Out): Out { return x; }
+  bar(y: In): In { return y; }
+}
+
+class A { }
+class B extends A { }
+
+function subtyping(
+  v1: Variance<A,B>,
+  v2: Variance<B,A>
+) {
+  (v1: Variance<B,A>); // error on both targs (A ~/~> B)
+  (v2: Variance<A,B>); // OK for both targs (B ~> A)
+}
+
+class PropVariance<+Out,-In> {
+  inv1: Out; // error
+  inv2: In; // error
+  -co1: Out; // error
+  -co2: In; // ok
+  +con1: Out; // ok
+  +con2: In; // error
+
+  inv_dict1: {[k:string]: Out}; // error
+  inv_dict2: {[k:string]: In}; // error
+  co_dict1: {+[k:string]: Out}; // ok
+  co_dict2: {+[k:string]: In}; // error
+  con_dict1: {-[k:string]: Out}; // error
+  con_dict2: {-[k:string]: In}; // ok
+}
diff --git a/tests/demo/1/__snapshots__/jsfmt.spec.js.snap b/tests/demo/1/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6a6eab1a73fe
--- /dev/null
+++ b/tests/demo/1/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,20 @@
+exports[`test f.js 1`] = `
+"/* demo */
+
+function f(x) { return 42/x; }
+
+var x = null;
+//...
+
+f(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* demo */
+function f(x) {
+  return 42 / x;
+}
+var x = null;
+//...
+f(x);
+
+"
+`;
diff --git a/tests/demo/1/f.js b/tests/demo/1/f.js
new file mode 100644
index 000000000000..fd73a91e9cc9
--- /dev/null
+++ b/tests/demo/1/f.js
@@ -0,0 +1,8 @@
+/* demo */
+
+function f(x) { return 42/x; }
+
+var x = null;
+//...
+
+f(x);
diff --git a/tests/demo/1/jsfmt.spec.js b/tests/demo/1/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/demo/1/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/demo/2/A.js b/tests/demo/2/A.js
new file mode 100644
index 000000000000..b0281e07e714
--- /dev/null
+++ b/tests/demo/2/A.js
@@ -0,0 +1,19 @@
+/* @providesModule Demo */
+
+class A {
+  x: number; // instance field declaration
+  constructor(x) { this.x = x; }
+
+  getX() { return this.x; }
+
+  onLoad(callback) {
+    return callback(this.getX());
+  }
+}
+
+function callback(x: string) { return x.length; }
+
+var a = new A(42);
+a.onLoad(callback);
+
+module.exports = A;
diff --git a/tests/demo/2/B.js b/tests/demo/2/B.js
new file mode 100644
index 000000000000..4c44780b9e90
--- /dev/null
+++ b/tests/demo/2/B.js
@@ -0,0 +1,3 @@
+var A = require('Demo');
+
+var z = new A("42").getX();
diff --git a/tests/demo/2/__snapshots__/jsfmt.spec.js.snap b/tests/demo/2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..faf41ca9a6bd
--- /dev/null
+++ b/tests/demo/2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,54 @@
+exports[`test A.js 1`] = `
+"/* @providesModule Demo */
+
+class A {
+  x: number; // instance field declaration
+  constructor(x) { this.x = x; }
+
+  getX() { return this.x; }
+
+  onLoad(callback) {
+    return callback(this.getX());
+  }
+}
+
+function callback(x: string) { return x.length; }
+
+var a = new A(42);
+a.onLoad(callback);
+
+module.exports = A;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Demo */
+class A {
+  x: number;// instance field declaration
+  constructor(x) {
+    this.x = x;
+  }
+  getX() {
+    return this.x;
+  }
+  onLoad(callback) {
+    return callback(this.getX());
+  }
+}
+function callback(x: string) {
+  return x.length;
+}
+var a = new A(42);
+a.onLoad(callback);
+module.exports = A;
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"var A = require('Demo');
+
+var z = new A("42").getX();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var A = require("Demo");
+var z = new A("42").getX();
+
+"
+`;
diff --git a/tests/demo/2/jsfmt.spec.js b/tests/demo/2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/demo/2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/deps/A.js b/tests/deps/A.js
new file mode 100644
index 000000000000..5a8c55d5bf63
--- /dev/null
+++ b/tests/deps/A.js
@@ -0,0 +1 @@
+require('./C');
diff --git a/tests/deps/B.js b/tests/deps/B.js
new file mode 100644
index 000000000000..5a8c55d5bf63
--- /dev/null
+++ b/tests/deps/B.js
@@ -0,0 +1 @@
+require('./C');
diff --git a/tests/deps/C.js b/tests/deps/C.js
new file mode 100644
index 000000000000..a006ecb7fb7d
--- /dev/null
+++ b/tests/deps/C.js
@@ -0,0 +1,4 @@
+require('./D');
+require('./E');
+require('./F');
+require('./G');
diff --git a/tests/deps/D.js b/tests/deps/D.js
new file mode 100644
index 000000000000..c5dbbb7bc2e4
--- /dev/null
+++ b/tests/deps/D.js
@@ -0,0 +1 @@
+require('./I');
diff --git a/tests/deps/E.js b/tests/deps/E.js
new file mode 100644
index 000000000000..c5dbbb7bc2e4
--- /dev/null
+++ b/tests/deps/E.js
@@ -0,0 +1 @@
+require('./I');
diff --git a/tests/deps/F.js b/tests/deps/F.js
new file mode 100644
index 000000000000..8b1a393741c9
--- /dev/null
+++ b/tests/deps/F.js
@@ -0,0 +1 @@
+// empty
diff --git a/tests/deps/G.js b/tests/deps/G.js
new file mode 100644
index 000000000000..4c21ad55c16d
--- /dev/null
+++ b/tests/deps/G.js
@@ -0,0 +1 @@
+require('./H');
diff --git a/tests/deps/H.js b/tests/deps/H.js
new file mode 100644
index 000000000000..8b1a393741c9
--- /dev/null
+++ b/tests/deps/H.js
@@ -0,0 +1 @@
+// empty
diff --git a/tests/deps/I.js b/tests/deps/I.js
new file mode 100644
index 000000000000..39ab86c96453
--- /dev/null
+++ b/tests/deps/I.js
@@ -0,0 +1 @@
+require('./A');
diff --git a/tests/deps/__snapshots__/jsfmt.spec.js.snap b/tests/deps/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d5665196b01d
--- /dev/null
+++ b/tests/deps/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,77 @@
+exports[`test A.js 1`] = `
+"require('./C');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./C");
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"require('./C');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./C");
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"require('./D');
+require('./E');
+require('./F');
+require('./G');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./D");
+require("./E");
+require("./F");
+require("./G");
+
+"
+`;
+
+exports[`test D.js 1`] = `
+"require('./I');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./I");
+
+"
+`;
+
+exports[`test E.js 1`] = `
+"require('./I');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./I");
+
+"
+`;
+
+exports[`test F.js 1`] = `
+"// empty
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test G.js 1`] = `
+"require('./H');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./H");
+
+"
+`;
+
+exports[`test H.js 1`] = `
+"// empty
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test I.js 1`] = `
+"require('./A');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+require("./A");
+
+"
+`;
diff --git a/tests/deps/jsfmt.spec.js b/tests/deps/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/deps/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/destructuring/__snapshots__/jsfmt.spec.js.snap b/tests/destructuring/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..874ac970940b
--- /dev/null
+++ b/tests/destructuring/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,480 @@
+exports[`test array_rest.js 1`] = `
+"let xs = [0, \"\", true];
+let [a, ...ys] = xs;
+let [b, ...zs] = ys;
+let c = zs[0]; // retain tuple info
+let d = zs[1]; // run off the end
+
+(a: void); // error: number ~> void
+(b: void); // error: string ~> void
+(c: void); // error: boolean ~> void
+(d: void); // error: number|string|boolean ~> void
+
+let [...e] = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+let xs = [ 0, \"\", true ];
+let [ a, ...ys ] = xs;
+let [ b, ...zs ] = ys;
+let c = zs[0];// retain tuple info
+let d = zs[1];// run off the end
+(a: void);// error: number ~> void
+(b: void);// error: string ~> void
+(c: void);// error: boolean ~> void
+(d: void);// error: number|string|boolean ~> void
+let [ ...e ] = 0;
+
+"
+`;
+
+exports[`test computed.js 1`] = `
+"var { [\"key\"]: val1 } = { key: \"val\" };
+(val1: void); // error: string ~> void
+
+var key: string = \"key\";
+var { [key]: val2 } = { key: \"val\" };
+(val2: void); // ok (gasp!) by existing StrT -> ElemT rule
+
+var { [\"key\"]: val3, ...spread } = { key: \"val\" };
+(spread.key: void); // error (gasp!) in general we don\'t know if a computed prop should be excluded from spread
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var { [\"key\"]: val1 } = { key: \"val\" };
+(val1: void);// error: string ~> void
+var key: string = \"key\";
+var { [key]: val2 } = { key: \"val\" };
+(val2: void);// ok (gasp!) by existing StrT -> ElemT rule
+var { [\"key\"]: val3, ...spread } = { key: \"val\" };
+(spread.key: void);// error (gasp!) in general we don\'t know if a computed prop should be excluded from spread
+
+"
+`;
+
+exports[`test defaults.js 1`] = `
+"/* @flow */
+
+function obj_prop_fun({p:{q=0}={q:true}}={p:{q:\"\"}}) {
+  // errors:
+  // * number  ~> void, from default on _.p.q
+  // * boolean ~> void, from default on _.p
+  // * string  ~> void, from default on _
+  // * null    ~> void, from call below
+  (q:void);
+}
+obj_prop_fun(); // ok
+obj_prop_fun({}); // ok
+obj_prop_fun({p:{}}); // ok
+obj_prop_fun({p:{q:null}}); // ok, provides add\'l lower bound
+
+function obj_prop_var(o={p:{q:\"\"}}) {
+  var {p:{q=0}={q:true}} = o;
+  // errors:
+  // * number  ~> void, from default on o.p.q
+  // * boolean ~> void, from default on o.p
+  // * string  ~> void, from default on o
+  // * null    ~> void, from call below
+  (q:void);
+}
+obj_prop_var(); // ok
+obj_prop_var({}); // ok
+obj_prop_var({p:{}}); // ok
+obj_prop_var({p:{q:null}}); // ok, provides add\'l lower bound
+
+function obj_rest({p:{q,...o}={q:0,r:0}}={p:{q:0,r:\"\"}}) {
+  // errors:
+  // * number  ~> void, from default on _.p
+  // * string  ~> void, from default on _
+  // * null    ~> void, from call below
+  (o.r:void);
+}
+obj_rest(); // ok
+obj_rest({}); // ok
+obj_rest({p:{}}); // ok
+obj_rest({p:{q:0,r:null}});
+
+function obj_prop_annot({
+  p = true // error: boolean ~> string
+}: {
+  p: string
+} = {
+  p: 0 // error: number ~> string
+}) {
+  (p:void); // error: string ~> void
+}
+
+var {
+  p = true // error: boolean ~> string
+}: {
+  p: string
+} = {
+  p: 0 // error: number ~> string
+};
+(p:void); // error: string ~> void
+
+function obj_prop_err({x:{y}}=null) {} // error: property \`x\` cannot be accessed on null
+function obj_rest_err({...o}=0) {} // error: expected object instead of number
+function arr_elem_err([x]=null) {} // error: element 0 cannot be accessed on null
+function arr_rest_err([...a]=null) {} // error: expected array instead of null
+
+function gen<T>(x:T,{p=x}:{p:T}):T {
+  return p;
+}
+
+// Default values in destructuring unwrap optional types
+obj_prop_fun(({} : {p?:{q?:null}})); // ok
+obj_prop_var(({} : {p?:{q?:null}})); // ok
+
+// union-like upper bounds preserved through destructuring
+function obj_prop_opt({p}:{p?:string}={p:0}) {}
+function obj_prop_maybe({p}:{p:?string}={p:0}) {}
+function obj_prop_union({p}:{p:number|string}={p:true}) {}
+
+// TODO: union-of-objects upper bounds preserved through destructuring
+function obj_prop_union2({p}:{p:number}|{p:string}={p:true}) {}
+
+function default_expr_scope({a, b = a}) {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test destructuring.js 1`] = `
+"declare var a:string;
+declare var b:string;
+declare var c:string;
+[{a1:a, b},c] = [{a1:0, b:1},2];
+
+var {m} = {m:0};
+({m} = {m:m});
+
+var obj;
+({n: obj.x} = {n:3});
+[obj.x] = [\'foo\'];
+
+function foo({p, z:[r]}) {
+    a = p;
+    b = z;
+    c = r;
+}
+foo({p:0, z:[1,2]});
+
+[a,,b,...c] = [0,1,true,3];
+
+function bar({x, ...z}) {
+    var o:{x: string; y: number;} = z;
+}
+bar({x:\"\",y:0});
+
+var spread = {y:\"\"};
+var extend: {x:number; y:string; z: boolean} = {x:0, ...spread};
+
+function qux(_: {a:number}) { }
+qux({a:\"\"});
+function corge({b}: {b:string}) { }
+corge({b:0});
+
+var {n}:{n: number} = {n: \"\"}
+
+function test() {
+  var {foo} = {bar: 123}; // error on foo
+  var {bar, baz} = {bar: 123} // error on baz
+}
+
+function test() {
+  var x = {foo: \'abc\', bar: 123};
+  var {foo, ...rest} = x;
+  (x.baz: string); // error, baz doesn\'t exist
+  (rest.baz: string); // no error, rest is unsealed
+}
+
+module.exports = corge;
+
+class Base {
+  baseprop1: number;
+  baseprop2: number;
+}
+
+class Child extends Base {
+  childprop1: number;
+  childprop2: number;
+}
+
+var {baseprop1, childprop1, ...others} = new Child();
+
+var bp1: number = baseprop1;
+var bp1_err: string = baseprop1; // Error: number ~> string
+var bp2: number = others.baseprop2;
+var bp2_err: string = others.baseprop2; // Error: number ~> string
+
+var cp1: number = childprop1;
+var cp1_err: string = childprop1; // Error: number ~> string
+var cp2: number = others.childprop1;
+var cp2_err: string = others.childprop2; // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare var a: string;
+declare var b: string;
+declare var c: string;
+[ { a1: a, b }, c ] = [ { a1: 0, b: 1 }, 2 ];
+var { m } = { m: 0 };
+{ m } = { m: m };
+var obj;
+{ n: obj.x } = { n: 3 };
+[ obj.x ] = [ \"foo\" ];
+function foo({ p, z: [ r ] }) {
+  a = p;
+  b = z;
+  c = r;
+}
+foo({ p: 0, z: [ 1, 2 ] });
+[ a, , b, ...c ] = [ 0, 1, true, 3 ];
+function bar({ x, ...z }) {
+  var o: { x: string, y: number } = z;
+}
+bar({ x: \"\", y: 0 });
+var spread = { y: \"\" };
+var extend: { x: number, y: string, z: boolean } = { x: 0, ...spread };
+function qux(_: { a: number }) {
+  
+}
+qux({ a: \"\" });
+function corge({ b }) {
+  
+}
+corge({ b: 0 });
+var { n } = { n: \"\" };
+function test() {
+  var { foo } = { bar: 123 };// error on foo
+  var { bar, baz } = { bar: 123 };// error on baz
+}
+function test() {
+  var x = { foo: \"abc\", bar: 123 };
+  var { foo, ...rest } = x;
+  (x.baz: string);// error, baz doesn\'t exist
+  (rest.baz: string);// no error, rest is unsealed
+}
+module.exports = corge;
+class Base {
+  baseprop1: number;
+  baseprop2: number;
+}
+class Child extends Base {
+  childprop1: number;
+  childprop2: number;
+}
+var { baseprop1, childprop1, ...others } = new Child();
+var bp1: number = baseprop1;
+var bp1_err: string = baseprop1;// Error: number ~> string
+var bp2: number = others.baseprop2;
+var bp2_err: string = others.baseprop2;// Error: number ~> string
+var cp1: number = childprop1;
+var cp1_err: string = childprop1;// Error: number ~> string
+var cp2: number = others.childprop1;
+var cp2_err: string = others.childprop2;// Error: number ~> string
+
+"
+`;
+
+exports[`test destructuring_init.js 1`] = `
+"var {foo};
+var [bar];
+var [];
+var {};
+var [], {toz};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Complex binding patterns require an initialization value (1:9)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$1.parseVar (/node_modules/babylon/lib/index.js:2215:12)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2042:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+    at Object.parse (/index.js:34:26)
+"
+`;
+
+exports[`test destructuring_param.js 1`] = `
+"function f(a, { b }) {
+  return a + b;
+}
+
+function g(a, { a }) {
+  return a;
+}
+
+function h({ a, { b } }, { c }, { { d } }) {
+  return a + b + c + d;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Argument name clash in strict mode (5:16)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$2.checkLVal (/node_modules/babylon/lib/index.js:3007:16)
+    at Parser.checkLVal (/node_modules/babylon/lib/index.js:5446:22)
+    at Parser.pp$2.checkLVal (/node_modules/babylon/lib/index.js:3034:14)
+    at Parser.checkLVal (/node_modules/babylon/lib/index.js:5446:22)
+    at Parser.pp$3.parseFunctionBody (/node_modules/babylon/lib/index.js:4072:12)
+    at Parser.parseFunctionBody (/node_modules/babylon/lib/index.js:5211:20)
+    at Parser.pp$1.parseFunction (/node_modules/babylon/lib/index.js:2257:8)
+    at Parser.pp$1.parseFunctionStatement (/node_modules/babylon/lib/index.js:1926:15)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1712:19)
+"
+`;
+
+exports[`test eager.js 1`] = `
+"var x;
+({x} = null); // error, property \`x\` can not be accessed on \`null\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x;
+{ x } = null;// error, property \`x\` can not be accessed on \`null\`
+
+"
+`;
+
+exports[`test poly.js 1`] = `
+"// @flow
+
+function obj_pattern<X>({ prop } : { prop: X }) {} // prop: X
+type Prop<X> = { prop: X };
+function obj_pattern2<X>({ prop } : Prop<X>) {} // prop: X
+
+function arr_pattern<X>([ elem ] : X[]) {} // elem: X
+type Elem<X> = X[];
+function arr_pattern2<X>([ elem ] : Elem<X>) {} // elem: X
+
+function tup_pattern<X>([ proj ] : [X]) {} // proj: X
+type Proj<X> = [X];
+function tup_pattern2<X>([ proj ] : Proj<X>) {} // proj: X
+
+function rest_antipattern<T>(...t: T) {} // nonsense
+function rest_pattern<X>(...r: X[]) {} // r: X[]
+
+function obj_rest_pattern<X>({ _, ...o } : { _: any, x: X }) { // o: { x: X }
+  o.x;
+}
+type ObjRest<X> = { _: any, x: X };
+function obj_rest_pattern<X>({ _, ...o } : ObjRest<X>) { // o: { x: X }
+  o.x;
+}
+
+function arr_rest_pattern<X>([ _, ...a ] : [ any, X ]) { // a: [X]
+  a[0];
+}
+type ArrRest<X> = [ any, X ];
+function arr_rest_pattern<X>([ _, ...a ] : ArrRest<X>) { // a: [X]
+  a[0];
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test rec.js 1`] = `
+"// @flow
+
+// Make sure that destructuring doesn\'t cause infinite loops when combined with
+// funny doses of repositioning
+
+let foo = (i: number) => [i];
+
+const bar = (i: number) => {
+  [i] = foo(i);
+  return [i];
+};
+
+foo = (i: number) => {
+  return bar(i);
+};
+
+// Also make sure that the following doesn\'t loop
+
+declare var o;
+var { x: o } = o;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// Make sure that destructuring doesn\'t cause infinite loops when combined with
+// funny doses of repositioning
+let foo = (i: number) => [ i ];
+const bar = (i: number) => {
+  [ i ] = foo(i);
+  return [ i ];
+};
+foo = (i: number) => {
+  return bar(i);
+};
+// Also make sure that the following doesn\'t loop
+declare var o;
+var { x: o } = o;
+
+"
+`;
+
+exports[`test string_lit.js 1`] = `
+"var { \"key\": val } = { key: \"val\" };
+(val: void); // error: string ~> void
+
+var { \"with-dash\": with_dash } = { \"with-dash\": \"motivating example\" };
+(with_dash: \"motivating example\"); // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var { \"key\": val } = { key: \"val\" };
+(val: void);// error: string ~> void
+var { \"with-dash\": with_dash } = { \"with-dash\": \"motivating example\" };
+(with_dash: \"motivating example\");// ok
+
+"
+`;
+
+exports[`test unannotated.js 1`] = `
+"// @flow
+
+var { x } = {
+  x: { foo: \"foo\" }
+};
+
+function bar() {
+  x.bar
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var { x } = { x: { foo: \"foo\" } };
+function bar() {
+  x.bar;
+}
+
+"
+`;
diff --git a/tests/destructuring/array_rest.js b/tests/destructuring/array_rest.js
new file mode 100644
index 000000000000..df9c2364fef7
--- /dev/null
+++ b/tests/destructuring/array_rest.js
@@ -0,0 +1,12 @@
+let xs = [0, "", true];
+let [a, ...ys] = xs;
+let [b, ...zs] = ys;
+let c = zs[0]; // retain tuple info
+let d = zs[1]; // run off the end
+
+(a: void); // error: number ~> void
+(b: void); // error: string ~> void
+(c: void); // error: boolean ~> void
+(d: void); // error: number|string|boolean ~> void
+
+let [...e] = 0;
diff --git a/tests/destructuring/computed.js b/tests/destructuring/computed.js
new file mode 100644
index 000000000000..5f5f2d241152
--- /dev/null
+++ b/tests/destructuring/computed.js
@@ -0,0 +1,9 @@
+var { ["key"]: val1 } = { key: "val" };
+(val1: void); // error: string ~> void
+
+var key: string = "key";
+var { [key]: val2 } = { key: "val" };
+(val2: void); // ok (gasp!) by existing StrT -> ElemT rule
+
+var { ["key"]: val3, ...spread } = { key: "val" };
+(spread.key: void); // error (gasp!) in general we don't know if a computed prop should be excluded from spread
diff --git a/tests/destructuring/defaults.js b/tests/destructuring/defaults.js
new file mode 100644
index 000000000000..0c5fcfb358bc
--- /dev/null
+++ b/tests/destructuring/defaults.js
@@ -0,0 +1,82 @@
+/* @flow */
+
+function obj_prop_fun({p:{q=0}={q:true}}={p:{q:""}}) {
+  // errors:
+  // * number  ~> void, from default on _.p.q
+  // * boolean ~> void, from default on _.p
+  // * string  ~> void, from default on _
+  // * null    ~> void, from call below
+  (q:void);
+}
+obj_prop_fun(); // ok
+obj_prop_fun({}); // ok
+obj_prop_fun({p:{}}); // ok
+obj_prop_fun({p:{q:null}}); // ok, provides add'l lower bound
+
+function obj_prop_var(o={p:{q:""}}) {
+  var {p:{q=0}={q:true}} = o;
+  // errors:
+  // * number  ~> void, from default on o.p.q
+  // * boolean ~> void, from default on o.p
+  // * string  ~> void, from default on o
+  // * null    ~> void, from call below
+  (q:void);
+}
+obj_prop_var(); // ok
+obj_prop_var({}); // ok
+obj_prop_var({p:{}}); // ok
+obj_prop_var({p:{q:null}}); // ok, provides add'l lower bound
+
+function obj_rest({p:{q,...o}={q:0,r:0}}={p:{q:0,r:""}}) {
+  // errors:
+  // * number  ~> void, from default on _.p
+  // * string  ~> void, from default on _
+  // * null    ~> void, from call below
+  (o.r:void);
+}
+obj_rest(); // ok
+obj_rest({}); // ok
+obj_rest({p:{}}); // ok
+obj_rest({p:{q:0,r:null}});
+
+function obj_prop_annot({
+  p = true // error: boolean ~> string
+}: {
+  p: string
+} = {
+  p: 0 // error: number ~> string
+}) {
+  (p:void); // error: string ~> void
+}
+
+var {
+  p = true // error: boolean ~> string
+}: {
+  p: string
+} = {
+  p: 0 // error: number ~> string
+};
+(p:void); // error: string ~> void
+
+function obj_prop_err({x:{y}}=null) {} // error: property `x` cannot be accessed on null
+function obj_rest_err({...o}=0) {} // error: expected object instead of number
+function arr_elem_err([x]=null) {} // error: element 0 cannot be accessed on null
+function arr_rest_err([...a]=null) {} // error: expected array instead of null
+
+function gen<T>(x:T,{p=x}:{p:T}):T {
+  return p;
+}
+
+// Default values in destructuring unwrap optional types
+obj_prop_fun(({} : {p?:{q?:null}})); // ok
+obj_prop_var(({} : {p?:{q?:null}})); // ok
+
+// union-like upper bounds preserved through destructuring
+function obj_prop_opt({p}:{p?:string}={p:0}) {}
+function obj_prop_maybe({p}:{p:?string}={p:0}) {}
+function obj_prop_union({p}:{p:number|string}={p:true}) {}
+
+// TODO: union-of-objects upper bounds preserved through destructuring
+function obj_prop_union2({p}:{p:number}|{p:string}={p:true}) {}
+
+function default_expr_scope({a, b = a}) {}
diff --git a/tests/destructuring/destructuring.js b/tests/destructuring/destructuring.js
new file mode 100644
index 000000000000..697454b1fceb
--- /dev/null
+++ b/tests/destructuring/destructuring.js
@@ -0,0 +1,71 @@
+declare var a:string;
+declare var b:string;
+declare var c:string;
+[{a1:a, b},c] = [{a1:0, b:1},2];
+
+var {m} = {m:0};
+({m} = {m:m});
+
+var obj;
+({n: obj.x} = {n:3});
+[obj.x] = ['foo'];
+
+function foo({p, z:[r]}) {
+    a = p;
+    b = z;
+    c = r;
+}
+foo({p:0, z:[1,2]});
+
+[a,,b,...c] = [0,1,true,3];
+
+function bar({x, ...z}) {
+    var o:{x: string; y: number;} = z;
+}
+bar({x:"",y:0});
+
+var spread = {y:""};
+var extend: {x:number; y:string; z: boolean} = {x:0, ...spread};
+
+function qux(_: {a:number}) { }
+qux({a:""});
+function corge({b}: {b:string}) { }
+corge({b:0});
+
+var {n}:{n: number} = {n: ""}
+
+function test() {
+  var {foo} = {bar: 123}; // error on foo
+  var {bar, baz} = {bar: 123} // error on baz
+}
+
+function test() {
+  var x = {foo: 'abc', bar: 123};
+  var {foo, ...rest} = x;
+  (x.baz: string); // error, baz doesn't exist
+  (rest.baz: string); // no error, rest is unsealed
+}
+
+module.exports = corge;
+
+class Base {
+  baseprop1: number;
+  baseprop2: number;
+}
+
+class Child extends Base {
+  childprop1: number;
+  childprop2: number;
+}
+
+var {baseprop1, childprop1, ...others} = new Child();
+
+var bp1: number = baseprop1;
+var bp1_err: string = baseprop1; // Error: number ~> string
+var bp2: number = others.baseprop2;
+var bp2_err: string = others.baseprop2; // Error: number ~> string
+
+var cp1: number = childprop1;
+var cp1_err: string = childprop1; // Error: number ~> string
+var cp2: number = others.childprop1;
+var cp2_err: string = others.childprop2; // Error: number ~> string
diff --git a/tests/destructuring/destructuring_init.js b/tests/destructuring/destructuring_init.js
new file mode 100644
index 000000000000..2a62fe4344d4
--- /dev/null
+++ b/tests/destructuring/destructuring_init.js
@@ -0,0 +1,5 @@
+var {foo};
+var [bar];
+var [];
+var {};
+var [], {toz};
diff --git a/tests/destructuring/destructuring_param.js b/tests/destructuring/destructuring_param.js
new file mode 100644
index 000000000000..85b6a5d42888
--- /dev/null
+++ b/tests/destructuring/destructuring_param.js
@@ -0,0 +1,11 @@
+function f(a, { b }) {
+  return a + b;
+}
+
+function g(a, { a }) {
+  return a;
+}
+
+function h({ a, { b } }, { c }, { { d } }) {
+  return a + b + c + d;
+}
diff --git a/tests/destructuring/eager.js b/tests/destructuring/eager.js
new file mode 100644
index 000000000000..5b668bb68003
--- /dev/null
+++ b/tests/destructuring/eager.js
@@ -0,0 +1,2 @@
+var x;
+({x} = null); // error, property `x` can not be accessed on `null`
diff --git a/tests/destructuring/jsfmt.spec.js b/tests/destructuring/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/destructuring/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/destructuring/poly.js b/tests/destructuring/poly.js
new file mode 100644
index 000000000000..bbfb5ccf7761
--- /dev/null
+++ b/tests/destructuring/poly.js
@@ -0,0 +1,32 @@
+// @flow
+
+function obj_pattern<X>({ prop } : { prop: X }) {} // prop: X
+type Prop<X> = { prop: X };
+function obj_pattern2<X>({ prop } : Prop<X>) {} // prop: X
+
+function arr_pattern<X>([ elem ] : X[]) {} // elem: X
+type Elem<X> = X[];
+function arr_pattern2<X>([ elem ] : Elem<X>) {} // elem: X
+
+function tup_pattern<X>([ proj ] : [X]) {} // proj: X
+type Proj<X> = [X];
+function tup_pattern2<X>([ proj ] : Proj<X>) {} // proj: X
+
+function rest_antipattern<T>(...t: T) {} // nonsense
+function rest_pattern<X>(...r: X[]) {} // r: X[]
+
+function obj_rest_pattern<X>({ _, ...o } : { _: any, x: X }) { // o: { x: X }
+  o.x;
+}
+type ObjRest<X> = { _: any, x: X };
+function obj_rest_pattern<X>({ _, ...o } : ObjRest<X>) { // o: { x: X }
+  o.x;
+}
+
+function arr_rest_pattern<X>([ _, ...a ] : [ any, X ]) { // a: [X]
+  a[0];
+}
+type ArrRest<X> = [ any, X ];
+function arr_rest_pattern<X>([ _, ...a ] : ArrRest<X>) { // a: [X]
+  a[0];
+}
diff --git a/tests/destructuring/rec.js b/tests/destructuring/rec.js
new file mode 100644
index 000000000000..8dcd432df6cc
--- /dev/null
+++ b/tests/destructuring/rec.js
@@ -0,0 +1,20 @@
+// @flow
+
+// Make sure that destructuring doesn't cause infinite loops when combined with
+// funny doses of repositioning
+
+let foo = (i: number) => [i];
+
+const bar = (i: number) => {
+  [i] = foo(i);
+  return [i];
+};
+
+foo = (i: number) => {
+  return bar(i);
+};
+
+// Also make sure that the following doesn't loop
+
+declare var o;
+var { x: o } = o;
diff --git a/tests/destructuring/string_lit.js b/tests/destructuring/string_lit.js
new file mode 100644
index 000000000000..95da8eaf33b8
--- /dev/null
+++ b/tests/destructuring/string_lit.js
@@ -0,0 +1,5 @@
+var { "key": val } = { key: "val" };
+(val: void); // error: string ~> void
+
+var { "with-dash": with_dash } = { "with-dash": "motivating example" };
+(with_dash: "motivating example"); // ok
diff --git a/tests/destructuring/unannotated.js b/tests/destructuring/unannotated.js
new file mode 100644
index 000000000000..fc2d27a34661
--- /dev/null
+++ b/tests/destructuring/unannotated.js
@@ -0,0 +1,9 @@
+// @flow
+
+var { x } = {
+  x: { foo: "foo" }
+};
+
+function bar() {
+  x.bar
+}
diff --git a/tests/dictionary/__snapshots__/jsfmt.spec.js.snap b/tests/dictionary/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..599e2a272cb1
--- /dev/null
+++ b/tests/dictionary/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,561 @@
+exports[`test any.js 1`] = `
+"/* @flow */
+
+const dict: {[key: string]: number} = {}
+const k: any = \'foo\'
+const val: string = dict[k] // error: number incompatible with string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+const dict: { [key: string]: number } = {};
+const k: any = \"foo\";
+const val: string = dict[k];// error: number incompatible with string
+
+"
+`;
+
+exports[`test compatible.js 1`] = `
+"/* @flow */
+
+function foo0(x: Array<{[key: string]: mixed}>): Array<{[key: string]: mixed}> {
+  // this adds a fooBar property to the param type, which should NOT cause
+  // an error in the return type because it is a dictionary.
+  x[0].fooBar = \'foobar\';
+  return x;
+}
+
+function foo2(
+  x: {[key: string]: number}
+): {[key: string]: number, +toString: () => string} {
+  // x\'s prototype has a toString method
+  return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test dictionary.js 1`] = `
+"/* Dictionary types are object types that include an indexer, which specifies a
+ * key type and a value type. The presence of an indexer makes the object type
+ * unsealed, but all added properties must be consistent with the indexer
+ * signature.
+ *
+ * Dictionaries can be used to represent the common idiom of objects used as
+ * maps. They can also be used to represent array-like objects, e.g., NodeList
+ * from the DOM API.
+ *
+ * A dictionary is assumed to have every property described by it\'s key type.
+ * This behavior is similar to the behavior of arrays, which are assumed to have
+ * a value at every index.
+ *
+ * @flow
+ */
+
+// Some logic is variance-sensitive.
+class A {}
+class B extends A {}
+class C extends B {}
+
+// Just a couple of short type names. Compare to string/number.
+class X {}
+class Y {}
+
+// Any property can be set on a dict with string keys.
+function set_prop_to_string_key(
+  o: {[k:string]:any},
+) {
+  o.prop = \"ok\";
+}
+
+// **UNSOUND**
+// This is allowed by design. We don\'t track get/set and we don\'t wrap the
+// return type in a maybe.
+function unsound_dict_has_every_key(
+  o: {[k:string]:X},
+) {
+  (o.p: X); // ok
+  (o[\"p\"]: X); // ok
+}
+
+// As with any object type, we can assign subtypes to properties.
+function set_prop_covariant(
+  o: {[k:string]:B},
+) {
+  o.p = new A; // error, A ~> B
+  o.p = new B; // ok
+  o.p = new C; // ok
+}
+
+// This isn\'t specific behavior to dictionaries, but for completeness...
+function get_prop_contravariant(
+  o: {[k:string]:B},
+) {
+  (o.p: A); // ok
+  (o.p: B); // ok
+  (o.p: C); // error, C ~> B
+}
+
+// Dot-notation can not be used to add properties to dictionaries with
+// non-string keys, because keys are strings.
+function add_prop_to_nonstring_key_dot(
+  o: {[k:number]:any},
+) {
+  o.prop = \"err\"; // error: string ~> number
+}
+
+// Bracket notation can be used to add properties to dictionaries with
+// non-string keys, even though all keys are strings. This is a convenient
+// affordance.
+function add_prop_to_nonstring_key_bracket(
+  o: {[k:number]:any},
+) {
+  o[0] = \"ok\";
+}
+
+// Objects can be part dict, part not by mixing an indexer with declared props.
+function mix_with_declared_props(
+  o: {[k:number]:X,p:Y},
+  x: X,
+  y: Y,
+) {
+  (o[0]: X); // ok
+  (o.p: Y); // ok
+  o[0] = x; // ok
+  o.p = y; // ok
+}
+
+// Indeed, dict types are still Objects and have Object.prototype stuff
+function object_prototype(
+  o: {[k:string]:number},
+): {[k:string]:number, +toString: () => string} {
+  (o.toString(): boolean); // error: string ~> boolean
+  return o; // ok
+}
+
+// **UNSOUND**
+// Because we support non-string props w/ bracket notation, it\'s possible to
+// write into a declared prop unsoundly.
+function unsound_string_conversion_alias_declared_prop(
+  o: {[k:number]:any, \"0\":X},
+) {
+  o[0] = \"not-x\"; // a[\"0\"] no longer X
+}
+
+function unification_dict_values_invariant(
+  x: Array<{[k:string]:B}>,
+) {
+  let a: Array<{[k:string]:A}> = x; // error
+  a[0].p = new A; // in[0].p no longer B
+
+  let b: Array<{[k:string]:B}> = x; // ok
+
+  let c: Array<{[k:string]:C}> = x; // error
+  (x[0].p: C); // not true
+}
+
+function subtype_dict_values_invariant(
+  x: {[k:string]:B},
+) {
+  let a: {[k:string]:A} = x; // error
+  a.p = new A; // x[0].p no longer B
+
+  let b: {[k:string]:B} = x; // ok
+
+  let c: {[k:string]:C} = x; // error
+  (x.p: C); // not true
+}
+
+function subtype_dict_values_fresh_exception() {
+  let a: {[k:string]:A} = {
+    a: new A, // ok, A == A
+    b: new B, // ok, B <: A
+    c: new C, // ok, C <: A
+  };
+
+  let b: {[k:string]:B} = {
+    a: new A, // error, A not <: B
+    b: new B, // ok, B == B
+    c: new C, // ok, C <: A
+  };
+
+  let c: {[k:string]:C} = {
+    a: new A, // error, A not <: C
+    b: new B, // error, A not <: C
+    c: new C, // ok, C == C
+  };
+}
+
+// Actually, unsound_string_conversion_alias_declared_prop behavior makes an
+// argument that we shouldn\'t really care about this, since we ignore the fact
+// that coercing values to string keys can cause unintended aliasing in general.
+// Barring some compelling use case for that in this context, though, we choose
+// to be strict.
+function unification_dict_keys_invariant(
+  x: Array<{[k:B]:any}>,
+) {
+  let a: Array<{[k:A]:any}> = x; // error
+  let b: Array<{[k:B]:any}> = x; // ok
+  let c: Array<{[k:C]:any}> = x; // error
+}
+
+function subtype_dict_keys_invariant(
+  x: {[k:B]:any},
+) {
+  let a: {[k:A]:any} = x; // error
+  let b: {[k:B]:any} = x; // ok
+  let c: {[k:C]:any} = x; // error
+}
+
+function unification_mix_with_declared_props_invariant_l(
+  x: Array<{[k:string]:B}>,
+) {
+  let a: Array<{[k:string]:B, p:A}> = x; // error: A ~> B
+  a[0].p = new A; // x[0].p no longer B
+
+  let b: Array<{[k:string]:B, p:B}> = x; // ok
+
+  let c: Array<{[k:string]:B, p:C}> = x; // error
+  (x[0].p: C); // not true
+}
+
+function unification_mix_with_declared_props_invariant_r(
+  xa: Array<{[k:string]:A, p:B}>,
+  xb: Array<{[k:string]:B, p:B}>,
+  xc: Array<{[k:string]:C, p:B}>,
+) {
+  let a: Array<{[k:string]:A}> = xa; // error
+  a[0].p = new A; // xa[0].p no longer B
+
+  let b: Array<{[k:string]:B}> = xb; // ok
+
+  let c: Array<{[k:string]:C}> = xc; // error
+  (xc[0].p: C); // not true
+}
+
+function subtype_mix_with_declared_props_invariant_l(
+  x: {[k:string]:B},
+) {
+  let a: {[k:string]:B, p:A} = x; // error: A ~> B
+  a.p = new A; // x.p no longer B
+
+  let b: {[k:string]:B, p:B} = x; // ok
+
+  let c: {[k:string]:B, p:C} = x; // error
+  (x.p: C); // not true
+}
+
+function subtype_mix_with_declared_props_invariant_r(
+  xa: {[k:string]:A, p:B},
+  xb: {[k:string]:B, p:B},
+  xc: {[k:string]:C, p:B},
+) {
+  let a: {[k:string]:A} = xa; // error
+  a.p = new A; // xa.p no longer B
+
+  let b: {[k:string]:B} = xb; // ok
+
+  let c: {[k:string]:C} = xc; // error
+  (xc.p: C); // not true
+}
+
+function unification_dict_to_obj(
+  x: Array<{[k:string]:X}>,
+): Array<{p:X}> {
+  return x; // error: if allowed, could write {p:X,q:Y} into \`x\`
+}
+
+function unification_obj_to_dict(
+  x: Array<{p:X}>,
+): Array<{[k:string]:X}> {
+  return x; // error: if allowed, could write {p:X,q:Y} into returned array
+}
+
+function subtype_dict_to_obj(
+  x: {[k:string]:B},
+) {
+  let a: {p:A} = x; // error
+  a.p = new A; // x.p no longer B
+
+  let b: {p:B} = x; // ok
+
+  let c: {p:C} = x; // error
+  (x.p: C); // not true
+}
+
+function subtype_obj_to_dict(
+  x: {p:B},
+) {
+  let a: {[k:string]:A} = x; // error
+  a.p = new A; // x.p no longer B
+
+  let b: {[k:string]:B} = x;
+
+  let c: {[k:string]:C} = x; // error
+  (x.p: C); // not true
+}
+
+// Only props in l which are not in u must match indexer, but must do so
+// exactly.
+function subtype_obj_to_mixed(
+  x: {p:B, x:X},
+) {
+  let a: {[k:string]:A,x:X} = x; // error (as above), but exclusive of x
+  let b: {[k:string]:B,x:X} = x; // ok,
+  let c: {[k:string]:C,x:X} = x; // error (as above), but exclusive of x
+}
+
+function unification_dict_to_mixed(
+  x: Array<{[k:string]:B}>,
+) {
+  let a: Array<{[k:string]:B, p:A}> = x; // error
+  let b: Array<{[k:string]:B, p:B}> = x; // ok
+  let c: Array<{[k:string]:B, p:C}> = x; // error
+}
+
+function subtype_dict_to_mixed(
+  x: {[k:string]:B},
+) {
+  let a: {[k:string]:B, p:A} = x; // error
+  let b: {[k:string]:B, p:B} = x; // ok
+  let c: {[k:string]:B, p:C} = x; // error
+}
+
+function subtype_dict_to_optional_a(
+  x: {[k:string]:B},
+) {
+  let a: {p?:A} = x; // error
+}
+
+function subtype_dict_to_optional_b(
+  x: {[k:string]:B},
+) {
+  let b: {p?:B} = x; // ok
+}
+
+function subtype_dict_to_optional_c(
+  x: {[k:string]:B},
+) {
+  let c: {p?:C} = x; // error
+}
+
+function subtype_optional_a_to_dict(
+  x: {p?:A},
+): {[k:string]:B} { // error: A ~> B
+  return x;
+}
+
+function subtype_optional_b_to_dict(
+  x: {p?:B},
+): {[k:string]:B} { // ok
+  return x;
+}
+
+function subtype_optional_c_to_dict(
+  x: {p?:C},
+): {[k:string]:B} { // error: C ~> B
+  return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test incompatible.js 1`] = `
+"/* @flow */
+
+var x : {[key: string]: string} = {};
+var y : {[key: string]: number} = x; // 2 errors, number !~> string & vice versa
+var z : {[key: number]: string} = x; // 2 errors, string !~> number & vice versa
+
+var a : {[key: string]: ?string} = {};
+var b : {[key: string]: string} = a; // 2 errors (null & undefined)
+var c : {[key: string]: ?string} = b; // 2 errors, since c[\'x\'] = null updates b
+
+// 2 errors (number !~> string, string !~> number)
+function foo0(x: Array<{[key: string]: number}>): Array<{[key: string]: string}> {
+  return x;
+}
+
+// error, fooBar:string !~> number (x\'s dictionary)
+function foo1(
+  x: Array<{[key: string]: number}>
+): Array<{[key: string]: number, fooBar: string}> {
+  return x;
+}
+
+function foo2(
+  x: Array<{[key: string]: mixed}>
+): Array<{[key: string]: mixed, fooBar: string}> {
+  x[0].fooBar = 123; // OK, since number ~> mixed (x elem\'s dictionary)
+  return x; // error: mixed ~> string
+}
+
+// OK, since we assume dictionaries have every key
+function foo3(x: {[key: string]: number}): {foo: number} {
+  return x;
+}
+
+// error: foo can\'t exist in x
+function foo4(x: {[key: string]: number}): {[key: string]: number, foo: string} {
+  return x;
+}
+
+// error, some prop in x could be incompatible (covariance)
+function foo5(x: Array<{[key: string]: number}>): Array<{foo: number}> {
+  return x;
+}
+
+// error, some prop in return could be incompatible
+function foo6(x: Array<{foo: number}>): Array<{[key: string]: number}> {
+  return x;
+}
+
+function foo7(x: {bar: string, [key: string]: number}) {
+  (x.bar: string);
+}
+
+function foo8(x: {[key: string]: number}) {
+  (x.foo: string); // error
+  (x.foo: number);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1745.js 1`] = `
+"/* @flow */
+
+class A {
+  x: {[k:string]: number};
+
+  m1() {
+    this.x = { bar: 0 }; // no error
+  }
+
+  m2() {
+    this.x.foo = 0; // no error
+  }
+}
+
+class B {
+  x: {[k:string]: number};
+
+  m2() {
+    this.x.foo = 0; // no error
+  }
+
+  m1() {
+    this.x = { bar: 0 }; // no error
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class A {
+  x: { [k: string]: number };
+  m1() {
+    this.x = { bar: 0 };// no error
+  }
+  m2() {
+    this.x.foo = 0;// no error
+  }
+}
+class B {
+  x: { [k: string]: number };
+  m2() {
+    this.x.foo = 0;// no error
+  }
+  m1() {
+    this.x = { bar: 0 };// no error
+  }
+}
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"type Params = {count: number; [name: string]: string};
+type QueryFunction = (params: Params) => string;
+
+var o: { foo: QueryFunction } = {
+  foo(params) {
+    return params.count; // error, number ~/~ string
+  }
+};
+
+module.exports = o;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test_client.js 1`] = `
+"var o = require(\'./test\');
+
+o.foo = function (params) {
+  return params.count; // error, number ~/~ string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = require(\"./test\");
+o.foo = function(params) {
+  return params.count;// error, number ~/~ string
+};
+
+"
+`;
diff --git a/tests/dictionary/any.js b/tests/dictionary/any.js
new file mode 100644
index 000000000000..b8b846674dab
--- /dev/null
+++ b/tests/dictionary/any.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+const dict: {[key: string]: number} = {}
+const k: any = 'foo'
+const val: string = dict[k] // error: number incompatible with string
diff --git a/tests/dictionary/compatible.js b/tests/dictionary/compatible.js
new file mode 100644
index 000000000000..87299c2ca1d9
--- /dev/null
+++ b/tests/dictionary/compatible.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+function foo0(x: Array<{[key: string]: mixed}>): Array<{[key: string]: mixed}> {
+  // this adds a fooBar property to the param type, which should NOT cause
+  // an error in the return type because it is a dictionary.
+  x[0].fooBar = 'foobar';
+  return x;
+}
+
+function foo2(
+  x: {[key: string]: number}
+): {[key: string]: number, +toString: () => string} {
+  // x's prototype has a toString method
+  return x;
+}
diff --git a/tests/dictionary/dictionary.js b/tests/dictionary/dictionary.js
new file mode 100644
index 000000000000..0a7150fa447a
--- /dev/null
+++ b/tests/dictionary/dictionary.js
@@ -0,0 +1,320 @@
+/* Dictionary types are object types that include an indexer, which specifies a
+ * key type and a value type. The presence of an indexer makes the object type
+ * unsealed, but all added properties must be consistent with the indexer
+ * signature.
+ *
+ * Dictionaries can be used to represent the common idiom of objects used as
+ * maps. They can also be used to represent array-like objects, e.g., NodeList
+ * from the DOM API.
+ *
+ * A dictionary is assumed to have every property described by it's key type.
+ * This behavior is similar to the behavior of arrays, which are assumed to have
+ * a value at every index.
+ *
+ * @flow
+ */
+
+// Some logic is variance-sensitive.
+class A {}
+class B extends A {}
+class C extends B {}
+
+// Just a couple of short type names. Compare to string/number.
+class X {}
+class Y {}
+
+// Any property can be set on a dict with string keys.
+function set_prop_to_string_key(
+  o: {[k:string]:any},
+) {
+  o.prop = "ok";
+}
+
+// **UNSOUND**
+// This is allowed by design. We don't track get/set and we don't wrap the
+// return type in a maybe.
+function unsound_dict_has_every_key(
+  o: {[k:string]:X},
+) {
+  (o.p: X); // ok
+  (o["p"]: X); // ok
+}
+
+// As with any object type, we can assign subtypes to properties.
+function set_prop_covariant(
+  o: {[k:string]:B},
+) {
+  o.p = new A; // error, A ~> B
+  o.p = new B; // ok
+  o.p = new C; // ok
+}
+
+// This isn't specific behavior to dictionaries, but for completeness...
+function get_prop_contravariant(
+  o: {[k:string]:B},
+) {
+  (o.p: A); // ok
+  (o.p: B); // ok
+  (o.p: C); // error, C ~> B
+}
+
+// Dot-notation can not be used to add properties to dictionaries with
+// non-string keys, because keys are strings.
+function add_prop_to_nonstring_key_dot(
+  o: {[k:number]:any},
+) {
+  o.prop = "err"; // error: string ~> number
+}
+
+// Bracket notation can be used to add properties to dictionaries with
+// non-string keys, even though all keys are strings. This is a convenient
+// affordance.
+function add_prop_to_nonstring_key_bracket(
+  o: {[k:number]:any},
+) {
+  o[0] = "ok";
+}
+
+// Objects can be part dict, part not by mixing an indexer with declared props.
+function mix_with_declared_props(
+  o: {[k:number]:X,p:Y},
+  x: X,
+  y: Y,
+) {
+  (o[0]: X); // ok
+  (o.p: Y); // ok
+  o[0] = x; // ok
+  o.p = y; // ok
+}
+
+// Indeed, dict types are still Objects and have Object.prototype stuff
+function object_prototype(
+  o: {[k:string]:number},
+): {[k:string]:number, +toString: () => string} {
+  (o.toString(): boolean); // error: string ~> boolean
+  return o; // ok
+}
+
+// **UNSOUND**
+// Because we support non-string props w/ bracket notation, it's possible to
+// write into a declared prop unsoundly.
+function unsound_string_conversion_alias_declared_prop(
+  o: {[k:number]:any, "0":X},
+) {
+  o[0] = "not-x"; // a["0"] no longer X
+}
+
+function unification_dict_values_invariant(
+  x: Array<{[k:string]:B}>,
+) {
+  let a: Array<{[k:string]:A}> = x; // error
+  a[0].p = new A; // in[0].p no longer B
+
+  let b: Array<{[k:string]:B}> = x; // ok
+
+  let c: Array<{[k:string]:C}> = x; // error
+  (x[0].p: C); // not true
+}
+
+function subtype_dict_values_invariant(
+  x: {[k:string]:B},
+) {
+  let a: {[k:string]:A} = x; // error
+  a.p = new A; // x[0].p no longer B
+
+  let b: {[k:string]:B} = x; // ok
+
+  let c: {[k:string]:C} = x; // error
+  (x.p: C); // not true
+}
+
+function subtype_dict_values_fresh_exception() {
+  let a: {[k:string]:A} = {
+    a: new A, // ok, A == A
+    b: new B, // ok, B <: A
+    c: new C, // ok, C <: A
+  };
+
+  let b: {[k:string]:B} = {
+    a: new A, // error, A not <: B
+    b: new B, // ok, B == B
+    c: new C, // ok, C <: A
+  };
+
+  let c: {[k:string]:C} = {
+    a: new A, // error, A not <: C
+    b: new B, // error, A not <: C
+    c: new C, // ok, C == C
+  };
+}
+
+// Actually, unsound_string_conversion_alias_declared_prop behavior makes an
+// argument that we shouldn't really care about this, since we ignore the fact
+// that coercing values to string keys can cause unintended aliasing in general.
+// Barring some compelling use case for that in this context, though, we choose
+// to be strict.
+function unification_dict_keys_invariant(
+  x: Array<{[k:B]:any}>,
+) {
+  let a: Array<{[k:A]:any}> = x; // error
+  let b: Array<{[k:B]:any}> = x; // ok
+  let c: Array<{[k:C]:any}> = x; // error
+}
+
+function subtype_dict_keys_invariant(
+  x: {[k:B]:any},
+) {
+  let a: {[k:A]:any} = x; // error
+  let b: {[k:B]:any} = x; // ok
+  let c: {[k:C]:any} = x; // error
+}
+
+function unification_mix_with_declared_props_invariant_l(
+  x: Array<{[k:string]:B}>,
+) {
+  let a: Array<{[k:string]:B, p:A}> = x; // error: A ~> B
+  a[0].p = new A; // x[0].p no longer B
+
+  let b: Array<{[k:string]:B, p:B}> = x; // ok
+
+  let c: Array<{[k:string]:B, p:C}> = x; // error
+  (x[0].p: C); // not true
+}
+
+function unification_mix_with_declared_props_invariant_r(
+  xa: Array<{[k:string]:A, p:B}>,
+  xb: Array<{[k:string]:B, p:B}>,
+  xc: Array<{[k:string]:C, p:B}>,
+) {
+  let a: Array<{[k:string]:A}> = xa; // error
+  a[0].p = new A; // xa[0].p no longer B
+
+  let b: Array<{[k:string]:B}> = xb; // ok
+
+  let c: Array<{[k:string]:C}> = xc; // error
+  (xc[0].p: C); // not true
+}
+
+function subtype_mix_with_declared_props_invariant_l(
+  x: {[k:string]:B},
+) {
+  let a: {[k:string]:B, p:A} = x; // error: A ~> B
+  a.p = new A; // x.p no longer B
+
+  let b: {[k:string]:B, p:B} = x; // ok
+
+  let c: {[k:string]:B, p:C} = x; // error
+  (x.p: C); // not true
+}
+
+function subtype_mix_with_declared_props_invariant_r(
+  xa: {[k:string]:A, p:B},
+  xb: {[k:string]:B, p:B},
+  xc: {[k:string]:C, p:B},
+) {
+  let a: {[k:string]:A} = xa; // error
+  a.p = new A; // xa.p no longer B
+
+  let b: {[k:string]:B} = xb; // ok
+
+  let c: {[k:string]:C} = xc; // error
+  (xc.p: C); // not true
+}
+
+function unification_dict_to_obj(
+  x: Array<{[k:string]:X}>,
+): Array<{p:X}> {
+  return x; // error: if allowed, could write {p:X,q:Y} into `x`
+}
+
+function unification_obj_to_dict(
+  x: Array<{p:X}>,
+): Array<{[k:string]:X}> {
+  return x; // error: if allowed, could write {p:X,q:Y} into returned array
+}
+
+function subtype_dict_to_obj(
+  x: {[k:string]:B},
+) {
+  let a: {p:A} = x; // error
+  a.p = new A; // x.p no longer B
+
+  let b: {p:B} = x; // ok
+
+  let c: {p:C} = x; // error
+  (x.p: C); // not true
+}
+
+function subtype_obj_to_dict(
+  x: {p:B},
+) {
+  let a: {[k:string]:A} = x; // error
+  a.p = new A; // x.p no longer B
+
+  let b: {[k:string]:B} = x;
+
+  let c: {[k:string]:C} = x; // error
+  (x.p: C); // not true
+}
+
+// Only props in l which are not in u must match indexer, but must do so
+// exactly.
+function subtype_obj_to_mixed(
+  x: {p:B, x:X},
+) {
+  let a: {[k:string]:A,x:X} = x; // error (as above), but exclusive of x
+  let b: {[k:string]:B,x:X} = x; // ok,
+  let c: {[k:string]:C,x:X} = x; // error (as above), but exclusive of x
+}
+
+function unification_dict_to_mixed(
+  x: Array<{[k:string]:B}>,
+) {
+  let a: Array<{[k:string]:B, p:A}> = x; // error
+  let b: Array<{[k:string]:B, p:B}> = x; // ok
+  let c: Array<{[k:string]:B, p:C}> = x; // error
+}
+
+function subtype_dict_to_mixed(
+  x: {[k:string]:B},
+) {
+  let a: {[k:string]:B, p:A} = x; // error
+  let b: {[k:string]:B, p:B} = x; // ok
+  let c: {[k:string]:B, p:C} = x; // error
+}
+
+function subtype_dict_to_optional_a(
+  x: {[k:string]:B},
+) {
+  let a: {p?:A} = x; // error
+}
+
+function subtype_dict_to_optional_b(
+  x: {[k:string]:B},
+) {
+  let b: {p?:B} = x; // ok
+}
+
+function subtype_dict_to_optional_c(
+  x: {[k:string]:B},
+) {
+  let c: {p?:C} = x; // error
+}
+
+function subtype_optional_a_to_dict(
+  x: {p?:A},
+): {[k:string]:B} { // error: A ~> B
+  return x;
+}
+
+function subtype_optional_b_to_dict(
+  x: {p?:B},
+): {[k:string]:B} { // ok
+  return x;
+}
+
+function subtype_optional_c_to_dict(
+  x: {p?:C},
+): {[k:string]:B} { // error: C ~> B
+  return x;
+}
diff --git a/tests/dictionary/incompatible.js b/tests/dictionary/incompatible.js
new file mode 100644
index 000000000000..dc73b7e71422
--- /dev/null
+++ b/tests/dictionary/incompatible.js
@@ -0,0 +1,57 @@
+/* @flow */
+
+var x : {[key: string]: string} = {};
+var y : {[key: string]: number} = x; // 2 errors, number !~> string & vice versa
+var z : {[key: number]: string} = x; // 2 errors, string !~> number & vice versa
+
+var a : {[key: string]: ?string} = {};
+var b : {[key: string]: string} = a; // 2 errors (null & undefined)
+var c : {[key: string]: ?string} = b; // 2 errors, since c['x'] = null updates b
+
+// 2 errors (number !~> string, string !~> number)
+function foo0(x: Array<{[key: string]: number}>): Array<{[key: string]: string}> {
+  return x;
+}
+
+// error, fooBar:string !~> number (x's dictionary)
+function foo1(
+  x: Array<{[key: string]: number}>
+): Array<{[key: string]: number, fooBar: string}> {
+  return x;
+}
+
+function foo2(
+  x: Array<{[key: string]: mixed}>
+): Array<{[key: string]: mixed, fooBar: string}> {
+  x[0].fooBar = 123; // OK, since number ~> mixed (x elem's dictionary)
+  return x; // error: mixed ~> string
+}
+
+// OK, since we assume dictionaries have every key
+function foo3(x: {[key: string]: number}): {foo: number} {
+  return x;
+}
+
+// error: foo can't exist in x
+function foo4(x: {[key: string]: number}): {[key: string]: number, foo: string} {
+  return x;
+}
+
+// error, some prop in x could be incompatible (covariance)
+function foo5(x: Array<{[key: string]: number}>): Array<{foo: number}> {
+  return x;
+}
+
+// error, some prop in return could be incompatible
+function foo6(x: Array<{foo: number}>): Array<{[key: string]: number}> {
+  return x;
+}
+
+function foo7(x: {bar: string, [key: string]: number}) {
+  (x.bar: string);
+}
+
+function foo8(x: {[key: string]: number}) {
+  (x.foo: string); // error
+  (x.foo: number);
+}
diff --git a/tests/dictionary/issue-1745.js b/tests/dictionary/issue-1745.js
new file mode 100644
index 000000000000..cef88e22aa47
--- /dev/null
+++ b/tests/dictionary/issue-1745.js
@@ -0,0 +1,25 @@
+/* @flow */
+
+class A {
+  x: {[k:string]: number};
+
+  m1() {
+    this.x = { bar: 0 }; // no error
+  }
+
+  m2() {
+    this.x.foo = 0; // no error
+  }
+}
+
+class B {
+  x: {[k:string]: number};
+
+  m2() {
+    this.x.foo = 0; // no error
+  }
+
+  m1() {
+    this.x = { bar: 0 }; // no error
+  }
+}
diff --git a/tests/dictionary/jsfmt.spec.js b/tests/dictionary/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/dictionary/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/dictionary/test.js b/tests/dictionary/test.js
new file mode 100644
index 000000000000..8b2b99223b98
--- /dev/null
+++ b/tests/dictionary/test.js
@@ -0,0 +1,10 @@
+type Params = {count: number; [name: string]: string};
+type QueryFunction = (params: Params) => string;
+
+var o: { foo: QueryFunction } = {
+  foo(params) {
+    return params.count; // error, number ~/~ string
+  }
+};
+
+module.exports = o;
diff --git a/tests/dictionary/test_client.js b/tests/dictionary/test_client.js
new file mode 100644
index 000000000000..28e9c5808816
--- /dev/null
+++ b/tests/dictionary/test_client.js
@@ -0,0 +1,5 @@
+var o = require('./test');
+
+o.foo = function (params) {
+  return params.count; // error, number ~/~ string
+}
diff --git a/tests/disjoint-union-perf/__snapshots__/jsfmt.spec.js.snap b/tests/disjoint-union-perf/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2afb93d5ec39
--- /dev/null
+++ b/tests/disjoint-union-perf/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,840 @@
+exports[`test ast.js 1`] = `
+"/**
+ * @flow
+ */
+
+export type InferredType =
+  | \'unknown\'
+  | \'gender\'
+  | \'enum\'
+  | \'number-or-string\'
+  | \'number\'
+  | \'string\'
+  | \'error\'
+;
+
+export type Pos = {
+  firstLine: number,
+  firstColumn: number,
+  lastLine: number,
+  lastColumn: number,
+};
+
+export type TypedBinaryOpNode = {
+  exprNodeType: \'binary_op\',
+  binaryOp: \'plus\' | \'multiply\' | \'divide\' | \'minus\',
+  lhs: TypedNode,
+  rhs: TypedNode,
+  pos: Pos,
+  exprType: InferredType,
+  typed: true,
+}
+
+export type TypedUnaryMinusNode = {
+  exprNodeType: \'unary_minus\',
+  op: TypedNode,
+  pos: Pos,
+  exprType: InferredType,
+  typed: true,
+}
+
+export type TypedNumberNode = {
+  exprNodeType: \'number\',
+  value: number,
+  pos: Pos,
+  exprType: \'number\',
+  typed: true,
+}
+
+export type TypedStringLiteralNode = {
+  exprNodeType: \'string_literal\',
+  value: string,
+  pos: Pos,
+  exprType: \'string\',
+  typed: true,
+}
+
+export type TypedVariableNode = {
+  exprNodeType: \'variable\',
+  name: string,
+  pos: Pos,
+  exprType: InferredType,
+  typed: true,
+};
+
+export type TypedFunctionInvocationNode = {
+  exprNodeType: \'function_invocation\',
+  name: string,
+  parameters: TypedNode[],
+  pos: Pos,
+  exprType: \'error\' | \'string\',
+  typed: true,
+}
+
+export type TypedNode =
+  | TypedBinaryOpNode
+  | TypedUnaryMinusNode
+  | TypedNumberNode
+  | TypedStringLiteralNode
+  | TypedVariableNode
+  | TypedFunctionInvocationNode
+;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test emit.js 1`] = `
+"/**
+ * @flow
+ */
+import * as t from \'./jsAst\';
+
+const b = t.builders;
+
+import type {
+        TypedNode
+} from \'./ast\';
+
+function getBinaryOp(op: \'plus\' | \'minus\' | \'divide\' | \'multiply\') : \'+\' | \'-\' | \'*\' | \'/\' {
+  switch (op) {
+  case \'plus\':
+    return \'+\';
+  case \'minus\':
+    return \'-\';
+  case \'divide\':
+    return \'/\';
+  case \'multiply\':
+    return \'*\';
+  default:
+    throw new Error(\'Invalid binary operator: \' + op);
+  }
+}
+
+export function emitExpression(node: TypedNode) : t.Expression {
+  switch (node.exprNodeType) {
+  case \'string_literal\': // FALLTHROUGH
+  case \'number\':
+    return b.literal(node.value);
+  case \'variable\':
+    return b.memberExpression(
+      b.identifier(\'vars\'),
+      b.identifier(node.name),
+      false
+    );
+  case \'binary_op\': {
+    const lhs = emitExpression(node.lhs);
+    const rhs = emitExpression(node.rhs);
+
+    const op = getBinaryOp(node.binaryOp);
+    return b.binaryExpression(op, lhs, rhs);
+  }
+  case \'unary_minus\': {
+    const operand = emitExpression(node.op);
+    return b.unaryExpression(\'-\', operand, true);
+  }
+  case \'function_invocation\': {
+    const callee = b.memberExpression(
+      b.identifier(\'fns\'),
+      b.identifier(node.name),
+      false
+    );
+
+    const args = node.parameters.map(
+      (n) => emitExpression(n)
+    );
+
+    return b.callExpression(callee, args);
+  }
+  default:
+    throw new Error(\'Unknown expression type: \' + node.type);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test jsAst.js 1`] = `
+"/**
+ * @flow
+ */
+export type Comment = {
+  loc: ?SourceLocation,
+  value: string,
+  leading: boolean,
+  trailing: boolean,
+};
+
+export type SourceLocation = {
+  start: SourcePosition,
+  end: SourcePosition,
+  source: ?string,
+};
+
+export type SourcePosition = {
+  line: number,
+  column: number,
+};
+
+export type File = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'File\',
+  program: Program,
+}
+
+export type Program = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'Program\',
+  body: Statement[],
+}
+
+export type BinaryOperator =
+  |\'==\'
+  | \'!=\'
+  | \'===\'
+  | \'!==\'
+  | \'<\'
+  | \'<=\'
+  | \'>\'
+  | \'>=\'
+  | \'<<\'
+  | \'>>\'
+  | \'>>>\'
+  | \'+\'
+  | \'-\'
+  | \'*\'
+  | \'/\'
+  | \'%\'
+  | \'&\' // TODO Missing from the Parser API.
+  | \'|\'
+  | \'^\'
+  | \'in\'
+  | \'instanceof\'
+  | \'..\'
+;
+
+export type UnaryOperator =
+  | \'-\'
+  | \'+\'
+  | \'!\'
+  | \'~\'
+  | \'typeof\'
+  | \'void\'
+  | \'delete\'
+;
+
+export type AssignmentOperator =
+  | \'=\'
+  | \'+=\'
+  | \'-=\'
+  | \'*=\'
+  | \'/=\'
+  | \'%=\'
+  | \'<<=\'
+  | \'>>=\'
+  | \'>>>=\'
+  | \'|=\'
+  | \'^=\'
+  | \'&=\'
+;
+
+export type UpdateOperator =
+  | \'++\'
+  | \'--\'
+;
+
+export type LogicalOperator =
+  | \'&&\'
+  | \'||\'
+;
+
+export type Node =
+  | EmptyStatement
+  | BlockStatement
+  | ExpressionStatement
+  | IfStatement
+  | BreakStatement
+  | ContinueStatement
+  | ReturnStatement
+  | ThrowStatement
+  | WhileStatement
+  | ForStatement
+  | ForInStatement
+  | TryStatement
+  | CatchClause
+  | Identifier
+  | Literal
+  | ThisExpression
+  | ArrayExpression
+  | ObjectExpreession
+  | Property
+  | FunctionExpression
+  | BinaryExpression
+  | UnaryExpression
+  | AssignmentExpression
+  | UpdateExpression
+  | LogicalExpression
+  | ConditionalExpression
+  | NewExpression
+  | CallExpression
+  | MemberExpression
+  | VariableDeclaration
+  | FunctionDeclaration
+  | VariableDeclarator
+;
+
+export type Statement =
+  | BlockStatement
+  | EmptyStatement
+  | ExpressionStatement
+  | IfStatement
+  | BreakStatement
+  | ContinueStatement
+  | ReturnStatement
+  | ThrowStatement
+  | WhileStatement
+  | ForStatement
+  | ForInStatement
+  | TryStatement
+  | Declaration
+;
+
+export type EmptyStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'EmptyStatement\',
+}
+
+export type BlockStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'BlockStatement\',
+  body: Statement[],
+}
+
+export type ExpressionStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ExpressionStatement\',
+  expression: Expression,
+}
+
+export type IfStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'IfStatement\',
+  test: Expression,
+  consequent: Statement,
+  alternate: ?Statement,
+}
+
+export type BreakStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'BreakStatement\',
+  label: ?Identifier,
+}
+
+export type ContinueStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ContinueStatement\',
+  label: ?Identifier,
+}
+
+export type ReturnStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ReturnStatement\',
+  argument: ?Expression,
+}
+
+export type ThrowStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ThrowStatement\',
+  argument: ?Expression,
+}
+
+export type WhileStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'WhileStatement\',
+  test: Expression,
+  body: Statement,
+}
+
+export type ForStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ForStatement\',
+  init: ?(VariableDeclaration | Expression),
+  test: ?Expression,
+  update: ?Expression,
+  body: Statement,
+}
+
+export type ForInStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ForInStatement\',
+  left: VariableDeclaration | Expression,
+  right: Expression,
+  body: Statement,
+}
+
+export type TryStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'TryStatement\',
+  block: BlockStatement,
+  handler: ?CatchClause,
+  handlers: CatchClause[],
+  finalizer: ?BlockStatement,
+};
+
+export type CatchClause = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'CatchClause\',
+  param: Pattern,
+  guard: ?Expression,
+  body: BlockStatement,
+};
+
+export type Expression =
+  | Identifier
+  | ThisExpression
+  | Literal
+  | FunctionExpression
+  | BinaryExpression
+  | UnaryExpression
+  | AssignmentExpression
+  | UpdateExpression
+  | LogicalExpression
+  | ConditionalExpression
+  | NewExpression
+  | CallExpression
+  | MemberExpression
+  | ArrayExpression
+  | ObjectExpreession
+;
+
+export type Identifier = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'Identifier\',
+  name: string,
+}
+
+export type Literal = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'Literal\',
+  value: ?(string | boolean | number | RegExp),
+  regex: ?{ pattern: string, flags: string },
+}
+
+export type ThisExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ThisExpression\',
+}
+
+export type ArrayExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ArrayExpression\',
+  elements: Expression[],
+}
+
+export type ObjectExpreession = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ObjectExpression\',
+  properties: Property[],
+}
+
+export type Property = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'Property\',
+  kind: \'init\' | \'get\' | \'set\',
+  key: Literal | Identifier,
+  value: Expression,
+};
+
+export type FunctionExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'FunctionExpression\',
+  id: ?Identifier,
+  params: Pattern[],
+  body: BlockStatement,
+}
+
+export type BinaryExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'BinaryExpression\',
+  operator: BinaryOperator,
+  left: Expression,
+  right: Expression,
+}
+
+export type UnaryExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'UnaryExpression\',
+  operator: UnaryOperator,
+  argument: Expression,
+  prefix: boolean,
+};
+
+export type AssignmentExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'AssignmentExpression\',
+  operator: AssignmentOperator,
+  left: Pattern,
+  right: Expression,
+};
+
+export type UpdateExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'UpdateExpression\',
+  operator: UpdateOperator,
+  argument: Expression,
+  prefix: boolean,
+};
+
+export type LogicalExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'LogicalExpression\',
+  operator: LogicalOperator,
+  left: Expression,
+  right: Expression,
+};
+
+export type ConditionalExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'ConditionalExpression\',
+  test: Expression,
+  consequent: Expression,
+  alternate: Expression,
+};
+
+export type NewExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'NewExpression\',
+  callee: Expression,
+  arguments: Expression[],
+};
+
+export type CallExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'CallExpression\',
+  callee: Expression,
+  arguments: Expression[],
+};
+
+export type MemberExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'MemberExpression\',
+  object: Expression,
+  property: Identifier | Expression,
+  computed: bool,
+}
+// ast-types exports all expressions as patterns.
+// That seems not like it was intended.
+export type Pattern =
+  | Identifier
+;
+
+export type Declaration =
+  | VariableDeclaration
+  | FunctionDeclaration
+;
+
+export type VariableDeclaration = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'VariableDeclaration\',
+  kind: \'var\' | \'let\' | \'const\',
+  declarations: VariableDeclarator[],
+}
+
+export type FunctionDeclaration = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'FunctionDeclaration\',
+  id: Identifier,
+  body: BlockStatement,
+  params: Pattern[],
+}
+
+export type VariableDeclarator = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: \'VariableDeclarator\',
+  id: Pattern,
+  init: ?Expression,
+}
+
+const a : any = null;
+
+export const builders : {
+  emptyStatement() : EmptyStatement,
+  blockStatement(
+    body: Statement[]
+  ) : BlockStatement,
+  expressionStatement(
+    expression: Expression
+  ) : ExpressionStatement,
+  ifStatement(
+    test: Expression,
+    consequent: Statement,
+    alternate?: Statement
+  ) : IfStatement,
+  breakStatement(
+    label?: Identifier
+  ) : BreakStatement,
+  continueStatement(
+    label?: Identifier
+  ) : ContinueStatement,
+  returnStatement(
+    argument: ?Expression
+  ) : ReturnStatement,
+  throwStatement(
+    argument: ?Expression
+  ) : ThrowStatement,
+  whileStatement(
+    test: Expression,
+    body: Statement
+  ) : WhileStatement,
+  forStatement(
+    init: ?(VariableDeclaration | Expression),
+    test: ?Expression,
+    update: ?Expression,
+    body: Statement
+  ) : ForStatement,
+  forInStatement(
+    left: VariableDeclaration | Expression,
+    right: Expression,
+    body: Statement
+  ) : ForInStatement,
+  tryStatement(
+    block: BlockStatement,
+    handler: ?CatchClause,
+    handlers: CatchClause[],
+    finalizer?: BlockStatement
+  ) : TryStatement,
+  catchClause(
+    param: Pattern,
+    guard: ?Expression,
+    body: BlockStatement
+  ) : CatchClause,
+  identifier(
+    name: string
+  ) : Identifier,
+  literal(
+    value: ?(string | boolean | number | RegExp),
+    regex?: { pattern: string, flags: string }
+  ) : Literal,
+  thisExpression() : ThisExpression,
+  arrayExpression(
+    elements: Expression[]
+  ) : ArrayExpression,
+  objectExpreession(
+    properties: Property[]
+  ) : ObjectExpreession,
+  property(
+    kind: \'init\' | \'get\' | \'set\',
+    key: Literal | Identifier,
+    value: Expression
+  ) : Property,
+  functionExpression(
+    id: ?Identifier,
+    params: Pattern[],
+    body: BlockStatement
+  ) : FunctionExpression,
+  binaryExpression(
+    operator: BinaryOperator,
+    left: Expression,
+    right: Expression
+  ) : BinaryExpression,
+  unaryExpression(
+    operator: UnaryOperator,
+    argument: Expression,
+    prefix: boolean
+  ) : UnaryExpression,
+  assignmentExpression(
+    operator: AssignmentOperator,
+    left: Pattern,
+    right: Expression
+  ) : AssignmentExpression,
+  updateExpression(
+    operator: UpdateOperator,
+    argument: Expression,
+    prefix: boolean
+  ) : UpdateExpression,
+  logicalExpression(
+    operator: LogicalOperator,
+    left: Expression,
+    right: Expression
+  ) : LogicalExpression,
+  conditionalExpression(
+    test: Expression,
+    consequent: Expression,
+    alternate: Expression
+  ) : ConditionalExpression,
+  newExpression(
+    callee: Expression,
+    arguments: Expression[]
+  ) : NewExpression,
+  callExpression(
+    callee: Expression,
+    arguments: Expression[]
+  ) : CallExpression,
+  memberExpression(
+    object: Expression,
+    property: Identifier | Expression,
+    computed: bool
+  ) : MemberExpression,
+  variableDeclaration(
+    kind: \'var\' | \'let\' | \'const\',
+    declarations: VariableDeclarator[]
+  ) : VariableDeclaration,
+  functionDeclaration(
+    id: Identifier,
+    body: BlockStatement,
+    params: Pattern[]
+  ) : FunctionDeclaration,
+  variableDeclarator(
+    id: Pattern,
+    init?: Expression
+  ) : VariableDeclarator,
+} = a;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/disjoint-union-perf/ast.js b/tests/disjoint-union-perf/ast.js
new file mode 100644
index 000000000000..8705bde03415
--- /dev/null
+++ b/tests/disjoint-union-perf/ast.js
@@ -0,0 +1,80 @@
+/**
+ * @flow
+ */
+
+export type InferredType =
+  | 'unknown'
+  | 'gender'
+  | 'enum'
+  | 'number-or-string'
+  | 'number'
+  | 'string'
+  | 'error'
+;
+
+export type Pos = {
+  firstLine: number,
+  firstColumn: number,
+  lastLine: number,
+  lastColumn: number,
+};
+
+export type TypedBinaryOpNode = {
+  exprNodeType: 'binary_op',
+  binaryOp: 'plus' | 'multiply' | 'divide' | 'minus',
+  lhs: TypedNode,
+  rhs: TypedNode,
+  pos: Pos,
+  exprType: InferredType,
+  typed: true,
+}
+
+export type TypedUnaryMinusNode = {
+  exprNodeType: 'unary_minus',
+  op: TypedNode,
+  pos: Pos,
+  exprType: InferredType,
+  typed: true,
+}
+
+export type TypedNumberNode = {
+  exprNodeType: 'number',
+  value: number,
+  pos: Pos,
+  exprType: 'number',
+  typed: true,
+}
+
+export type TypedStringLiteralNode = {
+  exprNodeType: 'string_literal',
+  value: string,
+  pos: Pos,
+  exprType: 'string',
+  typed: true,
+}
+
+export type TypedVariableNode = {
+  exprNodeType: 'variable',
+  name: string,
+  pos: Pos,
+  exprType: InferredType,
+  typed: true,
+};
+
+export type TypedFunctionInvocationNode = {
+  exprNodeType: 'function_invocation',
+  name: string,
+  parameters: TypedNode[],
+  pos: Pos,
+  exprType: 'error' | 'string',
+  typed: true,
+}
+
+export type TypedNode =
+  | TypedBinaryOpNode
+  | TypedUnaryMinusNode
+  | TypedNumberNode
+  | TypedStringLiteralNode
+  | TypedVariableNode
+  | TypedFunctionInvocationNode
+;
diff --git a/tests/disjoint-union-perf/emit.js b/tests/disjoint-union-perf/emit.js
new file mode 100644
index 000000000000..49bef648e63c
--- /dev/null
+++ b/tests/disjoint-union-perf/emit.js
@@ -0,0 +1,65 @@
+/**
+ * @flow
+ */
+import * as t from './jsAst';
+
+const b = t.builders;
+
+import type {
+        TypedNode
+} from './ast';
+
+function getBinaryOp(op: 'plus' | 'minus' | 'divide' | 'multiply') : '+' | '-' | '*' | '/' {
+  switch (op) {
+  case 'plus':
+    return '+';
+  case 'minus':
+    return '-';
+  case 'divide':
+    return '/';
+  case 'multiply':
+    return '*';
+  default:
+    throw new Error('Invalid binary operator: ' + op);
+  }
+}
+
+export function emitExpression(node: TypedNode) : t.Expression {
+  switch (node.exprNodeType) {
+  case 'string_literal': // FALLTHROUGH
+  case 'number':
+    return b.literal(node.value);
+  case 'variable':
+    return b.memberExpression(
+      b.identifier('vars'),
+      b.identifier(node.name),
+      false
+    );
+  case 'binary_op': {
+    const lhs = emitExpression(node.lhs);
+    const rhs = emitExpression(node.rhs);
+
+    const op = getBinaryOp(node.binaryOp);
+    return b.binaryExpression(op, lhs, rhs);
+  }
+  case 'unary_minus': {
+    const operand = emitExpression(node.op);
+    return b.unaryExpression('-', operand, true);
+  }
+  case 'function_invocation': {
+    const callee = b.memberExpression(
+      b.identifier('fns'),
+      b.identifier(node.name),
+      false
+    );
+
+    const args = node.parameters.map(
+      (n) => emitExpression(n)
+    );
+
+    return b.callExpression(callee, args);
+  }
+  default:
+    throw new Error('Unknown expression type: ' + node.type);
+  }
+}
diff --git a/tests/disjoint-union-perf/jsAst.js b/tests/disjoint-union-perf/jsAst.js
new file mode 100644
index 000000000000..4ca78a03e62d
--- /dev/null
+++ b/tests/disjoint-union-perf/jsAst.js
@@ -0,0 +1,636 @@
+/**
+ * @flow
+ */
+export type Comment = {
+  loc: ?SourceLocation,
+  value: string,
+  leading: boolean,
+  trailing: boolean,
+};
+
+export type SourceLocation = {
+  start: SourcePosition,
+  end: SourcePosition,
+  source: ?string,
+};
+
+export type SourcePosition = {
+  line: number,
+  column: number,
+};
+
+export type File = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'File',
+  program: Program,
+}
+
+export type Program = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'Program',
+  body: Statement[],
+}
+
+export type BinaryOperator =
+  |'=='
+  | '!='
+  | '==='
+  | '!=='
+  | '<'
+  | '<='
+  | '>'
+  | '>='
+  | '<<'
+  | '>>'
+  | '>>>'
+  | '+'
+  | '-'
+  | '*'
+  | '/'
+  | '%'
+  | '&' // TODO Missing from the Parser API.
+  | '|'
+  | '^'
+  | 'in'
+  | 'instanceof'
+  | '..'
+;
+
+export type UnaryOperator =
+  | '-'
+  | '+'
+  | '!'
+  | '~'
+  | 'typeof'
+  | 'void'
+  | 'delete'
+;
+
+export type AssignmentOperator =
+  | '='
+  | '+='
+  | '-='
+  | '*='
+  | '/='
+  | '%='
+  | '<<='
+  | '>>='
+  | '>>>='
+  | '|='
+  | '^='
+  | '&='
+;
+
+export type UpdateOperator =
+  | '++'
+  | '--'
+;
+
+export type LogicalOperator =
+  | '&&'
+  | '||'
+;
+
+export type Node =
+  | EmptyStatement
+  | BlockStatement
+  | ExpressionStatement
+  | IfStatement
+  | BreakStatement
+  | ContinueStatement
+  | ReturnStatement
+  | ThrowStatement
+  | WhileStatement
+  | ForStatement
+  | ForInStatement
+  | TryStatement
+  | CatchClause
+  | Identifier
+  | Literal
+  | ThisExpression
+  | ArrayExpression
+  | ObjectExpreession
+  | Property
+  | FunctionExpression
+  | BinaryExpression
+  | UnaryExpression
+  | AssignmentExpression
+  | UpdateExpression
+  | LogicalExpression
+  | ConditionalExpression
+  | NewExpression
+  | CallExpression
+  | MemberExpression
+  | VariableDeclaration
+  | FunctionDeclaration
+  | VariableDeclarator
+;
+
+export type Statement =
+  | BlockStatement
+  | EmptyStatement
+  | ExpressionStatement
+  | IfStatement
+  | BreakStatement
+  | ContinueStatement
+  | ReturnStatement
+  | ThrowStatement
+  | WhileStatement
+  | ForStatement
+  | ForInStatement
+  | TryStatement
+  | Declaration
+;
+
+export type EmptyStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'EmptyStatement',
+}
+
+export type BlockStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'BlockStatement',
+  body: Statement[],
+}
+
+export type ExpressionStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ExpressionStatement',
+  expression: Expression,
+}
+
+export type IfStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'IfStatement',
+  test: Expression,
+  consequent: Statement,
+  alternate: ?Statement,
+}
+
+export type BreakStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'BreakStatement',
+  label: ?Identifier,
+}
+
+export type ContinueStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ContinueStatement',
+  label: ?Identifier,
+}
+
+export type ReturnStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ReturnStatement',
+  argument: ?Expression,
+}
+
+export type ThrowStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ThrowStatement',
+  argument: ?Expression,
+}
+
+export type WhileStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'WhileStatement',
+  test: Expression,
+  body: Statement,
+}
+
+export type ForStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ForStatement',
+  init: ?(VariableDeclaration | Expression),
+  test: ?Expression,
+  update: ?Expression,
+  body: Statement,
+}
+
+export type ForInStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ForInStatement',
+  left: VariableDeclaration | Expression,
+  right: Expression,
+  body: Statement,
+}
+
+export type TryStatement = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'TryStatement',
+  block: BlockStatement,
+  handler: ?CatchClause,
+  handlers: CatchClause[],
+  finalizer: ?BlockStatement,
+};
+
+export type CatchClause = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'CatchClause',
+  param: Pattern,
+  guard: ?Expression,
+  body: BlockStatement,
+};
+
+export type Expression =
+  | Identifier
+  | ThisExpression
+  | Literal
+  | FunctionExpression
+  | BinaryExpression
+  | UnaryExpression
+  | AssignmentExpression
+  | UpdateExpression
+  | LogicalExpression
+  | ConditionalExpression
+  | NewExpression
+  | CallExpression
+  | MemberExpression
+  | ArrayExpression
+  | ObjectExpreession
+;
+
+export type Identifier = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'Identifier',
+  name: string,
+}
+
+export type Literal = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'Literal',
+  value: ?(string | boolean | number | RegExp),
+  regex: ?{ pattern: string, flags: string },
+}
+
+export type ThisExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ThisExpression',
+}
+
+export type ArrayExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ArrayExpression',
+  elements: Expression[],
+}
+
+export type ObjectExpreession = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ObjectExpression',
+  properties: Property[],
+}
+
+export type Property = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'Property',
+  kind: 'init' | 'get' | 'set',
+  key: Literal | Identifier,
+  value: Expression,
+};
+
+export type FunctionExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'FunctionExpression',
+  id: ?Identifier,
+  params: Pattern[],
+  body: BlockStatement,
+}
+
+export type BinaryExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'BinaryExpression',
+  operator: BinaryOperator,
+  left: Expression,
+  right: Expression,
+}
+
+export type UnaryExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'UnaryExpression',
+  operator: UnaryOperator,
+  argument: Expression,
+  prefix: boolean,
+};
+
+export type AssignmentExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'AssignmentExpression',
+  operator: AssignmentOperator,
+  left: Pattern,
+  right: Expression,
+};
+
+export type UpdateExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'UpdateExpression',
+  operator: UpdateOperator,
+  argument: Expression,
+  prefix: boolean,
+};
+
+export type LogicalExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'LogicalExpression',
+  operator: LogicalOperator,
+  left: Expression,
+  right: Expression,
+};
+
+export type ConditionalExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'ConditionalExpression',
+  test: Expression,
+  consequent: Expression,
+  alternate: Expression,
+};
+
+export type NewExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'NewExpression',
+  callee: Expression,
+  arguments: Expression[],
+};
+
+export type CallExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'CallExpression',
+  callee: Expression,
+  arguments: Expression[],
+};
+
+export type MemberExpression = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'MemberExpression',
+  object: Expression,
+  property: Identifier | Expression,
+  computed: bool,
+}
+// ast-types exports all expressions as patterns.
+// That seems not like it was intended.
+export type Pattern =
+  | Identifier
+;
+
+export type Declaration =
+  | VariableDeclaration
+  | FunctionDeclaration
+;
+
+export type VariableDeclaration = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'VariableDeclaration',
+  kind: 'var' | 'let' | 'const',
+  declarations: VariableDeclarator[],
+}
+
+export type FunctionDeclaration = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'FunctionDeclaration',
+  id: Identifier,
+  body: BlockStatement,
+  params: Pattern[],
+}
+
+export type VariableDeclarator = {
+  source: ?string,
+  start: SourcePosition,
+  end: SourcePosition,
+  comments: ?Array<Comment>,
+  type: 'VariableDeclarator',
+  id: Pattern,
+  init: ?Expression,
+}
+
+const a : any = null;
+
+export const builders : {
+  emptyStatement() : EmptyStatement,
+  blockStatement(
+    body: Statement[]
+  ) : BlockStatement,
+  expressionStatement(
+    expression: Expression
+  ) : ExpressionStatement,
+  ifStatement(
+    test: Expression,
+    consequent: Statement,
+    alternate?: Statement
+  ) : IfStatement,
+  breakStatement(
+    label?: Identifier
+  ) : BreakStatement,
+  continueStatement(
+    label?: Identifier
+  ) : ContinueStatement,
+  returnStatement(
+    argument: ?Expression
+  ) : ReturnStatement,
+  throwStatement(
+    argument: ?Expression
+  ) : ThrowStatement,
+  whileStatement(
+    test: Expression,
+    body: Statement
+  ) : WhileStatement,
+  forStatement(
+    init: ?(VariableDeclaration | Expression),
+    test: ?Expression,
+    update: ?Expression,
+    body: Statement
+  ) : ForStatement,
+  forInStatement(
+    left: VariableDeclaration | Expression,
+    right: Expression,
+    body: Statement
+  ) : ForInStatement,
+  tryStatement(
+    block: BlockStatement,
+    handler: ?CatchClause,
+    handlers: CatchClause[],
+    finalizer?: BlockStatement
+  ) : TryStatement,
+  catchClause(
+    param: Pattern,
+    guard: ?Expression,
+    body: BlockStatement
+  ) : CatchClause,
+  identifier(
+    name: string
+  ) : Identifier,
+  literal(
+    value: ?(string | boolean | number | RegExp),
+    regex?: { pattern: string, flags: string }
+  ) : Literal,
+  thisExpression() : ThisExpression,
+  arrayExpression(
+    elements: Expression[]
+  ) : ArrayExpression,
+  objectExpreession(
+    properties: Property[]
+  ) : ObjectExpreession,
+  property(
+    kind: 'init' | 'get' | 'set',
+    key: Literal | Identifier,
+    value: Expression
+  ) : Property,
+  functionExpression(
+    id: ?Identifier,
+    params: Pattern[],
+    body: BlockStatement
+  ) : FunctionExpression,
+  binaryExpression(
+    operator: BinaryOperator,
+    left: Expression,
+    right: Expression
+  ) : BinaryExpression,
+  unaryExpression(
+    operator: UnaryOperator,
+    argument: Expression,
+    prefix: boolean
+  ) : UnaryExpression,
+  assignmentExpression(
+    operator: AssignmentOperator,
+    left: Pattern,
+    right: Expression
+  ) : AssignmentExpression,
+  updateExpression(
+    operator: UpdateOperator,
+    argument: Expression,
+    prefix: boolean
+  ) : UpdateExpression,
+  logicalExpression(
+    operator: LogicalOperator,
+    left: Expression,
+    right: Expression
+  ) : LogicalExpression,
+  conditionalExpression(
+    test: Expression,
+    consequent: Expression,
+    alternate: Expression
+  ) : ConditionalExpression,
+  newExpression(
+    callee: Expression,
+    arguments: Expression[]
+  ) : NewExpression,
+  callExpression(
+    callee: Expression,
+    arguments: Expression[]
+  ) : CallExpression,
+  memberExpression(
+    object: Expression,
+    property: Identifier | Expression,
+    computed: bool
+  ) : MemberExpression,
+  variableDeclaration(
+    kind: 'var' | 'let' | 'const',
+    declarations: VariableDeclarator[]
+  ) : VariableDeclaration,
+  functionDeclaration(
+    id: Identifier,
+    body: BlockStatement,
+    params: Pattern[]
+  ) : FunctionDeclaration,
+  variableDeclarator(
+    id: Pattern,
+    init?: Expression
+  ) : VariableDeclarator,
+} = a;
diff --git a/tests/disjoint-union-perf/jsfmt.spec.js b/tests/disjoint-union-perf/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/disjoint-union-perf/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/docblock_flow/__snapshots__/jsfmt.spec.js.snap b/tests/docblock_flow/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3994c269287c
--- /dev/null
+++ b/tests/docblock_flow/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,108 @@
+exports[`test license_with_flow.js 1`] = `
+"/* Copyright example */
+/* @flow */
+
+("": void); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* Copyright example */
+/* @flow */
+("": void);// error
+
+"
+`;
+
+exports[`test max_header_tokens.js 1`] = `
+"/* @flow */
+/* second token */
+/* third token */
+/**
+ * After max_header_tokens (in .flowconfig), we no longer care:
+ *
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test multiple_flows_1.js 1`] = `
+"/* @flow */
+/* @flow */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test multiple_flows_2.js 1`] = `
+"/**
+ * @flow
+ * @noflow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test multiple_providesModule_1.js 1`] = `
+"/**
+ * @providesModule Foo
+ * @providesModule Bar
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test multiple_providesModule_2.js 1`] = `
+"/**
+ * @providesModule Foo
+ * @flow
+ */
+/**
+ * @providesModule Bar
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test use_strict_with_flow.js 1`] = `
+""use strict";
+/* @flow */
+
+("": void); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+"use strict";
+/* @flow */
+("": void);// error
+
+"
+`;
+
+exports[`test with_flow.js 1`] = `
+"/* @flow */
+
+("": void); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+("": void);// error
+
+"
+`;
+
+exports[`test without_flow.js 1`] = `
+"/* some other comment */
+
+("": void); // no error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* some other comment */
+("": void);// no error
+
+"
+`;
diff --git a/tests/docblock_flow/jsfmt.spec.js b/tests/docblock_flow/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/docblock_flow/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/docblock_flow/license_with_flow.js b/tests/docblock_flow/license_with_flow.js
new file mode 100644
index 000000000000..8b3cd6be2a8d
--- /dev/null
+++ b/tests/docblock_flow/license_with_flow.js
@@ -0,0 +1,4 @@
+/* Copyright example */
+/* @flow */
+
+("": void); // error
diff --git a/tests/docblock_flow/max_header_tokens.js b/tests/docblock_flow/max_header_tokens.js
new file mode 100644
index 000000000000..c8eb64fe8886
--- /dev/null
+++ b/tests/docblock_flow/max_header_tokens.js
@@ -0,0 +1,8 @@
+/* @flow */
+/* second token */
+/* third token */
+/**
+ * After max_header_tokens (in .flowconfig), we no longer care:
+ *
+ * @flow
+ */
diff --git a/tests/docblock_flow/multiple_flows_1.js b/tests/docblock_flow/multiple_flows_1.js
new file mode 100644
index 000000000000..205d73fd152c
--- /dev/null
+++ b/tests/docblock_flow/multiple_flows_1.js
@@ -0,0 +1,2 @@
+/* @flow */
+/* @flow */
diff --git a/tests/docblock_flow/multiple_flows_2.js b/tests/docblock_flow/multiple_flows_2.js
new file mode 100644
index 000000000000..421903b00b29
--- /dev/null
+++ b/tests/docblock_flow/multiple_flows_2.js
@@ -0,0 +1,4 @@
+/**
+ * @flow
+ * @noflow
+ */
diff --git a/tests/docblock_flow/multiple_providesModule_1.js b/tests/docblock_flow/multiple_providesModule_1.js
new file mode 100644
index 000000000000..5d78d1deb91c
--- /dev/null
+++ b/tests/docblock_flow/multiple_providesModule_1.js
@@ -0,0 +1,5 @@
+/**
+ * @providesModule Foo
+ * @providesModule Bar
+ * @flow
+ */
diff --git a/tests/docblock_flow/multiple_providesModule_2.js b/tests/docblock_flow/multiple_providesModule_2.js
new file mode 100644
index 000000000000..01b86e701744
--- /dev/null
+++ b/tests/docblock_flow/multiple_providesModule_2.js
@@ -0,0 +1,7 @@
+/**
+ * @providesModule Foo
+ * @flow
+ */
+/**
+ * @providesModule Bar
+ */
diff --git a/tests/docblock_flow/use_strict_with_flow.js b/tests/docblock_flow/use_strict_with_flow.js
new file mode 100644
index 000000000000..5d065b6a9452
--- /dev/null
+++ b/tests/docblock_flow/use_strict_with_flow.js
@@ -0,0 +1,4 @@
+"use strict";
+/* @flow */
+
+("": void); // error
diff --git a/tests/docblock_flow/with_flow.js b/tests/docblock_flow/with_flow.js
new file mode 100644
index 000000000000..83ee2f86af06
--- /dev/null
+++ b/tests/docblock_flow/with_flow.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+("": void); // error
diff --git a/tests/docblock_flow/without_flow.js b/tests/docblock_flow/without_flow.js
new file mode 100644
index 000000000000..d8ba64110515
--- /dev/null
+++ b/tests/docblock_flow/without_flow.js
@@ -0,0 +1,3 @@
+/* some other comment */
+
+("": void); // no error
diff --git a/tests/dom/CanvasRenderingContext2D.js b/tests/dom/CanvasRenderingContext2D.js
new file mode 100644
index 000000000000..f6af4fc4f579
--- /dev/null
+++ b/tests/dom/CanvasRenderingContext2D.js
@@ -0,0 +1,13 @@
+// @flow
+
+let tests = [
+  // fillRect
+  function(ctx: CanvasRenderingContext2D) {
+    ctx.fillRect(0, 0, 200, 100);
+  },
+
+  // moveTo
+  function(ctx: CanvasRenderingContext2D) {
+    ctx.moveTo('0', '1');  // error: should be numbers
+  },
+];
diff --git a/tests/dom/CustomEvent.js b/tests/dom/CustomEvent.js
new file mode 100644
index 000000000000..4c73a4d8f5bb
--- /dev/null
+++ b/tests/dom/CustomEvent.js
@@ -0,0 +1,9 @@
+// @flow
+
+let tests = [
+  // CustomEvent
+  function(document: Document) {
+    const event = document.createEvent('CustomEvent');
+    event.initCustomEvent('butts', true, false, { nice: 42 });
+  }
+];
diff --git a/tests/dom/Document.js b/tests/dom/Document.js
new file mode 100644
index 000000000000..7bf234607fe1
--- /dev/null
+++ b/tests/dom/Document.js
@@ -0,0 +1,11 @@
+// @flow
+
+let tests = [
+  // createElement
+  function(document: Document) {
+    (document.createElement('canvas'): HTMLCanvasElement);
+    (document.createElement('link'): HTMLLinkElement);
+    (document.createElement('option'): HTMLOptionElement);
+    (document.createElement('select'): HTMLSelectElement);
+  }
+];
diff --git a/tests/dom/Element.js b/tests/dom/Element.js
new file mode 100644
index 000000000000..9f8c65c2fc6e
--- /dev/null
+++ b/tests/dom/Element.js
@@ -0,0 +1,18 @@
+// @flow
+
+let tests = [
+  // scrollIntoView
+  function(element: Element) {
+    element.scrollIntoView();
+    element.scrollIntoView(false);
+    element.scrollIntoView({});
+    element.scrollIntoView({ behavior: 'smooth', block: 'end' });
+    element.scrollIntoView({ block: 'end' });
+    element.scrollIntoView({ behavior: 'smooth' });
+
+    // fails
+    element.scrollIntoView({ behavior: 'invalid' });
+    element.scrollIntoView({ block: 'invalid' });
+    element.scrollIntoView(1);
+  }
+];
diff --git a/tests/dom/HTMLCanvasElement.js b/tests/dom/HTMLCanvasElement.js
new file mode 100644
index 000000000000..1bad9066f73e
--- /dev/null
+++ b/tests/dom/HTMLCanvasElement.js
@@ -0,0 +1,8 @@
+// @flow
+
+let tests = [
+  // getContext
+  function(el: HTMLCanvasElement) {
+    (el.getContext('2d'): ?CanvasRenderingContext2D);
+  }
+];
diff --git a/tests/dom/HTMLElement.js b/tests/dom/HTMLElement.js
new file mode 100644
index 000000000000..d3942a275710
--- /dev/null
+++ b/tests/dom/HTMLElement.js
@@ -0,0 +1,18 @@
+// @flow
+
+let tests = [
+  // scrollIntoView
+  function(element: HTMLElement) {
+    element.scrollIntoView();
+    element.scrollIntoView(false);
+    element.scrollIntoView({});
+    element.scrollIntoView({ behavior: 'smooth', block: 'end' });
+    element.scrollIntoView({ block: 'end' });
+    element.scrollIntoView({ behavior: 'smooth' });
+
+    // fails
+    element.scrollIntoView({ behavior: 'invalid' });
+    element.scrollIntoView({ block: 'invalid' });
+    element.scrollIntoView(1);
+  }
+];
diff --git a/tests/dom/HTMLInputElement.js b/tests/dom/HTMLInputElement.js
new file mode 100644
index 000000000000..48f1413addc9
--- /dev/null
+++ b/tests/dom/HTMLInputElement.js
@@ -0,0 +1,12 @@
+// @flow
+
+let tests = [
+  // setRangeText
+  function(el: HTMLInputElement) {
+    el.setRangeText('foo');
+    el.setRangeText('foo', 123); // end is required
+    el.setRangeText('foo', 123, 234);
+    el.setRangeText('foo', 123, 234, 'select');
+    el.setRangeText('foo', 123, 234, 'bogus'); // invalid value
+  }
+];
diff --git a/tests/dom/URL.js b/tests/dom/URL.js
new file mode 100644
index 000000000000..ecba845d56da
--- /dev/null
+++ b/tests/dom/URL.js
@@ -0,0 +1,20 @@
+/* @flow */
+
+const a = new URL('http://flowtype.org/'); // correct
+const b = new URL('/docs', a); // correct
+const c = new URL('/docs', 'http://flowtype.org/'); // correct
+
+const d: URLSearchParams = c.searchParams; // correct
+const e: string = c.path; // not correct
+const f: string = c.pathname; // correct
+const g: string = c.hash; // correct
+const h: string = c.host; // correct
+const i: string = c.hostname; // correct
+const j: string = c.href; // correct
+const l: string = c.origin; // correct
+const m: string = c.password; // correct
+const n: string = c.pathname; // correct
+const o: string = c.port; // correct
+const p: string = c.protocol; // correct
+const q: string = c.search; // correct
+const r: string = c.username; // correct
diff --git a/tests/dom/__snapshots__/jsfmt.spec.js.snap b/tests/dom/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9e1cc90c0e46
--- /dev/null
+++ b/tests/dom/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,700 @@
+exports[`test CanvasRenderingContext2D.js 1`] = `
+"// @flow
+
+let tests = [
+  // fillRect
+  function(ctx: CanvasRenderingContext2D) {
+    ctx.fillRect(0, 0, 200, 100);
+  },
+
+  // moveTo
+  function(ctx: CanvasRenderingContext2D) {
+    ctx.moveTo(\'0\', \'1\');  // error: should be numbers
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // fillRect
+  function(ctx: CanvasRenderingContext2D) {
+    ctx.fillRect(0, 0, 200, 100);
+  },
+  // moveTo
+  function(ctx: CanvasRenderingContext2D) {
+    ctx.moveTo(\"0\", \"1\");// error: should be numbers
+  }
+];
+
+"
+`;
+
+exports[`test CustomEvent.js 1`] = `
+"// @flow
+
+let tests = [
+  // CustomEvent
+  function(document: Document) {
+    const event = document.createEvent(\'CustomEvent\');
+    event.initCustomEvent(\'butts\', true, false, { nice: 42 });
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // CustomEvent
+  function(document: Document) {
+    const event = document.createEvent(\"CustomEvent\");
+    event.initCustomEvent(\"butts\", true, false, { nice: 42 });
+  }
+];
+
+"
+`;
+
+exports[`test Document.js 1`] = `
+"// @flow
+
+let tests = [
+  // createElement
+  function(document: Document) {
+    (document.createElement(\'canvas\'): HTMLCanvasElement);
+    (document.createElement(\'link\'): HTMLLinkElement);
+    (document.createElement(\'option\'): HTMLOptionElement);
+    (document.createElement(\'select\'): HTMLSelectElement);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // createElement
+  function(document: Document) {
+    (document.createElement(\"canvas\"): HTMLCanvasElement);
+    (document.createElement(\"link\"): HTMLLinkElement);
+    (document.createElement(\"option\"): HTMLOptionElement);
+    (document.createElement(\"select\"): HTMLSelectElement);
+  }
+];
+
+"
+`;
+
+exports[`test Element.js 1`] = `
+"// @flow
+
+let tests = [
+  // scrollIntoView
+  function(element: Element) {
+    element.scrollIntoView();
+    element.scrollIntoView(false);
+    element.scrollIntoView({});
+    element.scrollIntoView({ behavior: \'smooth\', block: \'end\' });
+    element.scrollIntoView({ block: \'end\' });
+    element.scrollIntoView({ behavior: \'smooth\' });
+
+    // fails
+    element.scrollIntoView({ behavior: \'invalid\' });
+    element.scrollIntoView({ block: \'invalid\' });
+    element.scrollIntoView(1);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // scrollIntoView
+  function(element: Element) {
+    element.scrollIntoView();
+    element.scrollIntoView(false);
+    element.scrollIntoView({});
+    element.scrollIntoView({ behavior: \"smooth\", block: \"end\" });
+    element.scrollIntoView({ block: \"end\" });
+    element.scrollIntoView({ behavior: \"smooth\" });
+    // fails
+    element.scrollIntoView({ behavior: \"invalid\" });
+    element.scrollIntoView({ block: \"invalid\" });
+    element.scrollIntoView(1);
+  }
+];
+
+"
+`;
+
+exports[`test HTMLCanvasElement.js 1`] = `
+"// @flow
+
+let tests = [
+  // getContext
+  function(el: HTMLCanvasElement) {
+    (el.getContext(\'2d\'): ?CanvasRenderingContext2D);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // getContext
+  function(el: HTMLCanvasElement) {
+    (el.getContext(\"2d\"): ?CanvasRenderingContext2D);
+  }
+];
+
+"
+`;
+
+exports[`test HTMLElement.js 1`] = `
+"// @flow
+
+let tests = [
+  // scrollIntoView
+  function(element: HTMLElement) {
+    element.scrollIntoView();
+    element.scrollIntoView(false);
+    element.scrollIntoView({});
+    element.scrollIntoView({ behavior: \'smooth\', block: \'end\' });
+    element.scrollIntoView({ block: \'end\' });
+    element.scrollIntoView({ behavior: \'smooth\' });
+
+    // fails
+    element.scrollIntoView({ behavior: \'invalid\' });
+    element.scrollIntoView({ block: \'invalid\' });
+    element.scrollIntoView(1);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // scrollIntoView
+  function(element: HTMLElement) {
+    element.scrollIntoView();
+    element.scrollIntoView(false);
+    element.scrollIntoView({});
+    element.scrollIntoView({ behavior: \"smooth\", block: \"end\" });
+    element.scrollIntoView({ block: \"end\" });
+    element.scrollIntoView({ behavior: \"smooth\" });
+    // fails
+    element.scrollIntoView({ behavior: \"invalid\" });
+    element.scrollIntoView({ block: \"invalid\" });
+    element.scrollIntoView(1);
+  }
+];
+
+"
+`;
+
+exports[`test HTMLInputElement.js 1`] = `
+"// @flow
+
+let tests = [
+  // setRangeText
+  function(el: HTMLInputElement) {
+    el.setRangeText(\'foo\');
+    el.setRangeText(\'foo\', 123); // end is required
+    el.setRangeText(\'foo\', 123, 234);
+    el.setRangeText(\'foo\', 123, 234, \'select\');
+    el.setRangeText(\'foo\', 123, 234, \'bogus\'); // invalid value
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // setRangeText
+  function(el: HTMLInputElement) {
+    el.setRangeText(\"foo\");
+    el.setRangeText(\"foo\", 123);// end is required
+    el.setRangeText(\"foo\", 123, 234);
+    el.setRangeText(\"foo\", 123, 234, \"select\");
+    el.setRangeText(\"foo\", 123, 234, \"bogus\");// invalid value
+  }
+];
+
+"
+`;
+
+exports[`test URL.js 1`] = `
+"/* @flow */
+
+const a = new URL(\'http://flowtype.org/\'); // correct
+const b = new URL(\'/docs\', a); // correct
+const c = new URL(\'/docs\', \'http://flowtype.org/\'); // correct
+
+const d: URLSearchParams = c.searchParams; // correct
+const e: string = c.path; // not correct
+const f: string = c.pathname; // correct
+const g: string = c.hash; // correct
+const h: string = c.host; // correct
+const i: string = c.hostname; // correct
+const j: string = c.href; // correct
+const l: string = c.origin; // correct
+const m: string = c.password; // correct
+const n: string = c.pathname; // correct
+const o: string = c.port; // correct
+const p: string = c.protocol; // correct
+const q: string = c.search; // correct
+const r: string = c.username; // correct
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+const a = new URL(\"http://flowtype.org/\");// correct
+const b = new URL(\"/docs\", a);// correct
+const c = new URL(\"/docs\", \"http://flowtype.org/\");// correct
+const d: URLSearchParams = c.searchParams;// correct
+const e: string = c.path;// not correct
+const f: string = c.pathname;// correct
+const g: string = c.hash;// correct
+const h: string = c.host;// correct
+const i: string = c.hostname;// correct
+const j: string = c.href;// correct
+const l: string = c.origin;// correct
+const m: string = c.password;// correct
+const n: string = c.pathname;// correct
+const o: string = c.port;// correct
+const p: string = c.protocol;// correct
+const q: string = c.search;// correct
+const r: string = c.username;// correct
+
+"
+`;
+
+exports[`test eventtarget.js 1`] = `
+"// @flow
+
+let listener: EventListener = function (event: Event) :void {};
+
+let tests = [
+  // attachEvent
+  function() {
+    let target = new EventTarget();
+    (target.attachEvent(\'foo\', listener): void); // invalid, may be undefined
+    (target.attachEvent && target.attachEvent(\'foo\', listener): void); // valid
+  },
+
+  // detachEvent
+  function() {
+    let target = new EventTarget();
+    (target.detachEvent(\'foo\', listener): void); // invalid, may be undefined
+    (target.detachEvent && target.detachEvent(\'foo\', listener): void); // valid
+  },
+
+  function() {
+    window.onmessage = (event: MessageEvent) => {
+      (event.target: window);
+    };
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let listener: EventListener = function(event: Event): void {
+  
+};
+let tests = [
+  // attachEvent
+  function() {
+    let target = new EventTarget();
+    (target.attachEvent(\"foo\", listener): void);// invalid, may be undefined
+    (target.attachEvent && target.attachEvent(\"foo\", listener): void);// valid
+  },
+  // detachEvent
+  function() {
+    let target = new EventTarget();
+    (target.detachEvent(\"foo\", listener): void);// invalid, may be undefined
+    (target.detachEvent && target.detachEvent(\"foo\", listener): void);// valid
+  },
+  function() {
+    window.onmessage = (event: MessageEvent) => {
+      (event.target: window);
+    };
+  }
+];
+
+"
+`;
+
+exports[`test path2d.js 1`] = `
+"// @flow
+
+let tests = [
+  // arcTo
+  function() {
+    let path = new Path2D();
+    (path.arcTo(0, 0, 0, 0, 10): void); // valid
+    (path.arcTo(0, 0, 0, 0, 10, 20, 5): void); // valid
+    (path.arcTo(0, 0, 0, 0, 10, \'20\', 5): void); // invalid
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // arcTo
+  function() {
+    let path = new Path2D();
+    (path.arcTo(0, 0, 0, 0, 10): void);// valid
+    (path.arcTo(0, 0, 0, 0, 10, 20, 5): void);// valid
+    (path.arcTo(0, 0, 0, 0, 10, \"20\", 5): void);// invalid
+  }
+];
+
+"
+`;
+
+exports[`test registerElement.js 1`] = `
+"// @flow
+
+let tests = [
+  // should work with Object.create()
+  function() {
+    document.registerElement(\'custom-element\', {
+      prototype: Object.create(HTMLElement.prototype, {
+        createdCallback: { value: function createdCallback () {
+        }},
+        attachedCallback: { value: function attachedCallback () {
+        }},
+        detachedCallback: { value: function detachedCallback () {
+        }},
+        attributeChangedCallback: {
+          value: function attributeChangedCallback (
+            attributeLocalName,
+            oldAttributeValue,
+            newAttributeValue,
+            attributeNamespace
+          ) {
+          }
+        }
+      })
+    })
+  },
+  // or with Object.assign()
+  function() {
+    document.registerElement(\'custom-element\', {
+      prototype: Object.assign(Object.create(HTMLElement.prototype), {
+        createdCallback () {
+        },
+        attachedCallback () {
+        },
+        detachedCallback () {
+        },
+        attributeChangedCallback (
+          attributeLocalName,
+          oldAttributeValue,
+          newAttributeValue,
+          attributeNamespace
+        ) {
+        }
+      })
+    })
+  },
+  // should complain about invalid callback parameters
+  function() {
+    document.registerElement(\'custom-element\', {
+      prototype: {
+        attributeChangedCallback(
+          localName: string,
+          oldVal: string, // Error: This might be null
+          newVal: string, // Error: This might be null
+          namespace: string) {}
+      },
+    });
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // should work with Object.create()
+  function() {
+    document.registerElement(
+      \"custom-element\",
+      {
+        prototype: Object.create(
+          HTMLElement.prototype,
+          {
+            createdCallback: {
+              value: function createdCallback() {
+                
+              }
+            },
+            attachedCallback: {
+              value: function attachedCallback() {
+                
+              }
+            },
+            detachedCallback: {
+              value: function detachedCallback() {
+                
+              }
+            },
+            attributeChangedCallback: {
+              value: function attributeChangedCallback(
+                attributeLocalName,
+                oldAttributeValue,
+                newAttributeValue,
+                attributeNamespace
+              ) {
+                
+              }
+            }
+          }
+        )
+      }
+    );
+  },
+  // or with Object.assign()
+  function() {
+    document.registerElement(
+      \"custom-element\",
+      {
+        prototype: Object.assign(
+          Object.create(HTMLElement.prototype),
+          {
+            createdCallback() {
+              
+            },
+            attachedCallback() {
+              
+            },
+            detachedCallback() {
+              
+            },
+            attributeChangedCallback(attributeLocalName,
+            oldAttributeValue,
+            newAttributeValue,
+            attributeNamespace) {
+              
+            }
+          }
+        )
+      }
+    );
+  },
+  // should complain about invalid callback parameters
+  function() {
+    document.registerElement(
+      \"custom-element\",
+      {
+        prototype: {
+          attributeChangedCallback(localName: string,
+          // Error: This might be null
+          oldVal: string,
+          // Error: This might be null
+          newVal: string,
+          namespace: string) {
+            
+          }
+        }
+      }
+    );
+  }
+];
+
+"
+`;
+
+exports[`test traversal.js 1`] = `
+"// @flow
+
+let tests = [
+  // basic functionality
+  function() {
+    const i: NodeIterator<*,*> = document.createNodeIterator(document.body);
+    const filter: NodeFilter = i.filter;
+    const response:
+      typeof NodeFilter.FILTER_ACCEPT |
+      typeof NodeFilter.FILTER_REJECT |
+      typeof NodeFilter.FILTER_SKIP =
+      filter.acceptNode(document.body);
+  },
+  function() {
+    const w: TreeWalker<*,*> = document.createTreeWalker(document.body);
+    const filter: NodeFilter = w.filter;
+    const response:
+      typeof NodeFilter.FILTER_ACCEPT |
+      typeof NodeFilter.FILTER_REJECT |
+      typeof NodeFilter.FILTER_SKIP =
+      filter.acceptNode(document.body);
+  },
+  // rootNode must be a Node
+  function() {
+    document.createNodeIterator(document.body); // valid
+    document.createNodeIterator({}); // invalid
+  },
+  function() {
+    document.createTreeWalker(document.body);
+    document.createTreeWalker({}); // invalid
+  },
+  // Type Parameters
+  function() {
+    const _root = document.body;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_ELEMENT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Element = i.referenceNode;
+    const previousNode: Element | null = i.previousNode();
+    const nextNode: Element | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body.attributes[0];
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_ATTRIBUTE);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Attr = i.referenceNode
+    const previousNode: Attr | null = i.previousNode();
+    const nextNode: Attr | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_TEXT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Text = i.referenceNode;
+    const previousNode: Text | null = i.previousNode();
+    const nextNode: Text | null = i.nextNode();
+  },
+  function() {
+    const _root = document;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_DOCUMENT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Document = i.referenceNode;
+    const previousNode: Document | null = i.previousNode();
+    const nextNode: Document | null = i.nextNode();
+  },
+  function() {
+    const _root = document;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_DOCUMENT_TYPE);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | DocumentType = i.referenceNode;
+    const previousNode: DocumentType | null = i.previousNode();
+    const nextNode: DocumentType | null = i.nextNode();
+  },
+  function() {
+    const _root = document.createDocumentFragment();
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_DOCUMENT_FRAGMENT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | DocumentFragment = i.referenceNode;
+    const previousNode: DocumentFragment | null = i.previousNode();
+    const nextNode: DocumentFragment | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_ALL);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Node = i.referenceNode;
+    const previousNode: Node | null = i.previousNode();
+    const nextNode: Node | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_ELEMENT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Element = w.currentNode;
+    const parentNode: Element | null = w.parentNode();
+    const firstChild: Element | null = w.firstChild();
+    const lastChild: Element | null = w.lastChild();
+    const previousSibling: Element | null = w.previousSibling();
+    const nextSibling: Element | null = w.nextSibling();
+    const previousNode: Element | null = w.previousNode();
+    const nextNode: Element | null = w.nextNode();
+  },
+  function() {
+    const _root = document.body.attributes[0];
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_ATTRIBUTE);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Attr = w.currentNode;
+    const parentNode: Attr | null = w.parentNode();
+    const firstChild: Attr | null = w.firstChild();
+    const lastChild: Attr | null = w.lastChild();
+    const previousSibling: Attr | null = w.previousSibling();
+    const nextSibling: Attr | null = w.nextSibling();
+    const previousNode: Attr | null = w.previousNode();
+    const nextNode: Attr | null = w.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_TEXT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Text = w.currentNode;
+    const parentNode: Text | null = w.parentNode();
+    const firstChild: Text | null = w.firstChild();
+    const lastChild: Text | null = w.lastChild();
+    const previousSibling: Text | null = w.previousSibling();
+    const nextSibling: Text | null = w.nextSibling();
+    const previousNode: Text | null = w.previousNode();
+    const nextNode: Text | null = w.nextNode();
+  },
+  function() {
+    const _root = document;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_DOCUMENT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Document = w.currentNode;
+    const parentNode: Document | null = w.parentNode();
+    const firstChild: Document | null = w.firstChild();
+    const lastChild: Document | null = w.lastChild();
+    const previousSibling: Document | null = w.previousSibling();
+    const nextSibling: Document | null = w.nextSibling();
+    const previousNode: Document | null = w.previousNode();
+    const nextNode: Document | null = w.nextNode();
+  },
+  function() {
+    const _root = document;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_DOCUMENT_TYPE);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | DocumentType = w.currentNode;
+    const parentNode: DocumentType | null = w.parentNode();
+    const firstChild: DocumentType | null = w.firstChild();
+    const lastChild: DocumentType | null = w.lastChild();
+    const previousSibling: DocumentType | null = w.previousSibling();
+    const nextSibling: DocumentType | null = w.nextSibling();
+    const previousNode: DocumentType | null = w.previousNode();
+    const nextNode: DocumentType | null = w.nextNode();
+  },
+  function() {
+    const _root = document.createDocumentFragment();
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_DOCUMENT_FRAGMENT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | DocumentFragment = w.currentNode;
+    const parentNode: DocumentFragment | null = w.parentNode();
+    const firstChild: DocumentFragment | null = w.firstChild();
+    const lastChild: DocumentFragment | null = w.lastChild();
+    const previousSibling: DocumentFragment | null = w.previousSibling();
+    const nextSibling: DocumentFragment | null = w.nextSibling();
+    const previousNode: DocumentFragment | null = w.previousNode();
+    const nextNode: DocumentFragment | null = w.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_ALL);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Node = w.currentNode;
+    const parentNode: Node | null = w.parentNode();
+    const firstChild: Node | null = w.firstChild();
+    const lastChild: Node | null = w.lastChild();
+    const previousSibling: Node | null = w.previousSibling();
+    const nextSibling: Node | null = w.nextSibling();
+    const previousNode: Node | null = w.previousNode();
+    const nextNode: Node | null = w.nextNode();
+  },
+  // NodeFilterInterface
+  function() {
+    document.createNodeIterator(document.body, -1, node => NodeFilter.FILTER_ACCEPT); // valid
+    document.createNodeIterator(document.body, -1, node => \'accept\'); // invalid
+    document.createNodeIterator(document.body, -1, { accept: node => NodeFilter.FILTER_ACCEPT }); // valid
+    document.createNodeIterator(document.body, -1, { accept: node => \'accept\' }); // invalid
+    document.createNodeIterator(document.body, -1, {}); // invalid
+  },
+  function() {
+    document.createTreeWalker(document.body, -1, node => NodeFilter.FILTER_ACCEPT); // valid
+    document.createTreeWalker(document.body, -1, node => \'accept\'); // invalid
+    document.createTreeWalker(document.body, -1, { accept: node => NodeFilter.FILTER_ACCEPT }); // valid
+    document.createTreeWalker(document.body, -1, { accept: node => \'accept\' }); // invalid
+    document.createTreeWalker(document.body, -1, {}); // invalid
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/dom/eventtarget.js b/tests/dom/eventtarget.js
new file mode 100644
index 000000000000..42a732475a6b
--- /dev/null
+++ b/tests/dom/eventtarget.js
@@ -0,0 +1,25 @@
+// @flow
+
+let listener: EventListener = function (event: Event) :void {};
+
+let tests = [
+  // attachEvent
+  function() {
+    let target = new EventTarget();
+    (target.attachEvent('foo', listener): void); // invalid, may be undefined
+    (target.attachEvent && target.attachEvent('foo', listener): void); // valid
+  },
+
+  // detachEvent
+  function() {
+    let target = new EventTarget();
+    (target.detachEvent('foo', listener): void); // invalid, may be undefined
+    (target.detachEvent && target.detachEvent('foo', listener): void); // valid
+  },
+
+  function() {
+    window.onmessage = (event: MessageEvent) => {
+      (event.target: window);
+    };
+  },
+];
diff --git a/tests/dom/jsfmt.spec.js b/tests/dom/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/dom/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/dom/path2d.js b/tests/dom/path2d.js
new file mode 100644
index 000000000000..5610e88c5343
--- /dev/null
+++ b/tests/dom/path2d.js
@@ -0,0 +1,11 @@
+// @flow
+
+let tests = [
+  // arcTo
+  function() {
+    let path = new Path2D();
+    (path.arcTo(0, 0, 0, 0, 10): void); // valid
+    (path.arcTo(0, 0, 0, 0, 10, 20, 5): void); // valid
+    (path.arcTo(0, 0, 0, 0, 10, '20', 5): void); // invalid
+  },
+];
diff --git a/tests/dom/registerElement.js b/tests/dom/registerElement.js
new file mode 100644
index 000000000000..f42bec596fce
--- /dev/null
+++ b/tests/dom/registerElement.js
@@ -0,0 +1,58 @@
+// @flow
+
+let tests = [
+  // should work with Object.create()
+  function() {
+    document.registerElement('custom-element', {
+      prototype: Object.create(HTMLElement.prototype, {
+        createdCallback: { value: function createdCallback () {
+        }},
+        attachedCallback: { value: function attachedCallback () {
+        }},
+        detachedCallback: { value: function detachedCallback () {
+        }},
+        attributeChangedCallback: {
+          value: function attributeChangedCallback (
+            attributeLocalName,
+            oldAttributeValue,
+            newAttributeValue,
+            attributeNamespace
+          ) {
+          }
+        }
+      })
+    })
+  },
+  // or with Object.assign()
+  function() {
+    document.registerElement('custom-element', {
+      prototype: Object.assign(Object.create(HTMLElement.prototype), {
+        createdCallback () {
+        },
+        attachedCallback () {
+        },
+        detachedCallback () {
+        },
+        attributeChangedCallback (
+          attributeLocalName,
+          oldAttributeValue,
+          newAttributeValue,
+          attributeNamespace
+        ) {
+        }
+      })
+    })
+  },
+  // should complain about invalid callback parameters
+  function() {
+    document.registerElement('custom-element', {
+      prototype: {
+        attributeChangedCallback(
+          localName: string,
+          oldVal: string, // Error: This might be null
+          newVal: string, // Error: This might be null
+          namespace: string) {}
+      },
+    });
+  },
+];
diff --git a/tests/dom/traversal.js b/tests/dom/traversal.js
new file mode 100644
index 000000000000..a78ae27468e3
--- /dev/null
+++ b/tests/dom/traversal.js
@@ -0,0 +1,195 @@
+// @flow
+
+let tests = [
+  // basic functionality
+  function() {
+    const i: NodeIterator<*,*> = document.createNodeIterator(document.body);
+    const filter: NodeFilter = i.filter;
+    const response:
+      typeof NodeFilter.FILTER_ACCEPT |
+      typeof NodeFilter.FILTER_REJECT |
+      typeof NodeFilter.FILTER_SKIP =
+      filter.acceptNode(document.body);
+  },
+  function() {
+    const w: TreeWalker<*,*> = document.createTreeWalker(document.body);
+    const filter: NodeFilter = w.filter;
+    const response:
+      typeof NodeFilter.FILTER_ACCEPT |
+      typeof NodeFilter.FILTER_REJECT |
+      typeof NodeFilter.FILTER_SKIP =
+      filter.acceptNode(document.body);
+  },
+  // rootNode must be a Node
+  function() {
+    document.createNodeIterator(document.body); // valid
+    document.createNodeIterator({}); // invalid
+  },
+  function() {
+    document.createTreeWalker(document.body);
+    document.createTreeWalker({}); // invalid
+  },
+  // Type Parameters
+  function() {
+    const _root = document.body;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_ELEMENT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Element = i.referenceNode;
+    const previousNode: Element | null = i.previousNode();
+    const nextNode: Element | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body.attributes[0];
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_ATTRIBUTE);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Attr = i.referenceNode
+    const previousNode: Attr | null = i.previousNode();
+    const nextNode: Attr | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_TEXT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Text = i.referenceNode;
+    const previousNode: Text | null = i.previousNode();
+    const nextNode: Text | null = i.nextNode();
+  },
+  function() {
+    const _root = document;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_DOCUMENT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Document = i.referenceNode;
+    const previousNode: Document | null = i.previousNode();
+    const nextNode: Document | null = i.nextNode();
+  },
+  function() {
+    const _root = document;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_DOCUMENT_TYPE);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | DocumentType = i.referenceNode;
+    const previousNode: DocumentType | null = i.previousNode();
+    const nextNode: DocumentType | null = i.nextNode();
+  },
+  function() {
+    const _root = document.createDocumentFragment();
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_DOCUMENT_FRAGMENT);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | DocumentFragment = i.referenceNode;
+    const previousNode: DocumentFragment | null = i.previousNode();
+    const nextNode: DocumentFragment | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const i = document.createNodeIterator(_root, NodeFilter.SHOW_ALL);
+    const root: typeof _root = i.root;
+    const referenceNode: typeof _root | Node = i.referenceNode;
+    const previousNode: Node | null = i.previousNode();
+    const nextNode: Node | null = i.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_ELEMENT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Element = w.currentNode;
+    const parentNode: Element | null = w.parentNode();
+    const firstChild: Element | null = w.firstChild();
+    const lastChild: Element | null = w.lastChild();
+    const previousSibling: Element | null = w.previousSibling();
+    const nextSibling: Element | null = w.nextSibling();
+    const previousNode: Element | null = w.previousNode();
+    const nextNode: Element | null = w.nextNode();
+  },
+  function() {
+    const _root = document.body.attributes[0];
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_ATTRIBUTE);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Attr = w.currentNode;
+    const parentNode: Attr | null = w.parentNode();
+    const firstChild: Attr | null = w.firstChild();
+    const lastChild: Attr | null = w.lastChild();
+    const previousSibling: Attr | null = w.previousSibling();
+    const nextSibling: Attr | null = w.nextSibling();
+    const previousNode: Attr | null = w.previousNode();
+    const nextNode: Attr | null = w.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_TEXT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Text = w.currentNode;
+    const parentNode: Text | null = w.parentNode();
+    const firstChild: Text | null = w.firstChild();
+    const lastChild: Text | null = w.lastChild();
+    const previousSibling: Text | null = w.previousSibling();
+    const nextSibling: Text | null = w.nextSibling();
+    const previousNode: Text | null = w.previousNode();
+    const nextNode: Text | null = w.nextNode();
+  },
+  function() {
+    const _root = document;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_DOCUMENT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Document = w.currentNode;
+    const parentNode: Document | null = w.parentNode();
+    const firstChild: Document | null = w.firstChild();
+    const lastChild: Document | null = w.lastChild();
+    const previousSibling: Document | null = w.previousSibling();
+    const nextSibling: Document | null = w.nextSibling();
+    const previousNode: Document | null = w.previousNode();
+    const nextNode: Document | null = w.nextNode();
+  },
+  function() {
+    const _root = document;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_DOCUMENT_TYPE);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | DocumentType = w.currentNode;
+    const parentNode: DocumentType | null = w.parentNode();
+    const firstChild: DocumentType | null = w.firstChild();
+    const lastChild: DocumentType | null = w.lastChild();
+    const previousSibling: DocumentType | null = w.previousSibling();
+    const nextSibling: DocumentType | null = w.nextSibling();
+    const previousNode: DocumentType | null = w.previousNode();
+    const nextNode: DocumentType | null = w.nextNode();
+  },
+  function() {
+    const _root = document.createDocumentFragment();
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_DOCUMENT_FRAGMENT);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | DocumentFragment = w.currentNode;
+    const parentNode: DocumentFragment | null = w.parentNode();
+    const firstChild: DocumentFragment | null = w.firstChild();
+    const lastChild: DocumentFragment | null = w.lastChild();
+    const previousSibling: DocumentFragment | null = w.previousSibling();
+    const nextSibling: DocumentFragment | null = w.nextSibling();
+    const previousNode: DocumentFragment | null = w.previousNode();
+    const nextNode: DocumentFragment | null = w.nextNode();
+  },
+  function() {
+    const _root = document.body;
+    const w = document.createTreeWalker(_root, NodeFilter.SHOW_ALL);
+    const root: typeof _root = w.root;
+    const currentNode: typeof _root | Node = w.currentNode;
+    const parentNode: Node | null = w.parentNode();
+    const firstChild: Node | null = w.firstChild();
+    const lastChild: Node | null = w.lastChild();
+    const previousSibling: Node | null = w.previousSibling();
+    const nextSibling: Node | null = w.nextSibling();
+    const previousNode: Node | null = w.previousNode();
+    const nextNode: Node | null = w.nextNode();
+  },
+  // NodeFilterInterface
+  function() {
+    document.createNodeIterator(document.body, -1, node => NodeFilter.FILTER_ACCEPT); // valid
+    document.createNodeIterator(document.body, -1, node => 'accept'); // invalid
+    document.createNodeIterator(document.body, -1, { accept: node => NodeFilter.FILTER_ACCEPT }); // valid
+    document.createNodeIterator(document.body, -1, { accept: node => 'accept' }); // invalid
+    document.createNodeIterator(document.body, -1, {}); // invalid
+  },
+  function() {
+    document.createTreeWalker(document.body, -1, node => NodeFilter.FILTER_ACCEPT); // valid
+    document.createTreeWalker(document.body, -1, node => 'accept'); // invalid
+    document.createTreeWalker(document.body, -1, { accept: node => NodeFilter.FILTER_ACCEPT }); // valid
+    document.createTreeWalker(document.body, -1, { accept: node => 'accept' }); // invalid
+    document.createTreeWalker(document.body, -1, {}); // invalid
+  },
+];
diff --git a/tests/dump-types/__snapshots__/jsfmt.spec.js.snap b/tests/dump-types/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..56a9c6930a86
--- /dev/null
+++ b/tests/dump-types/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,58 @@
+exports[`test import.js 1`] = `
+"// @flow
+var num = 42;
+function bar() { }
+bar();
+module.exports = num;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var num = 42;
+function bar() {
+  
+}
+bar();
+module.exports = num;
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"// @flow
+var num = require(\'./import\');
+function foo(x) { }
+foo(0);
+var a:string = num;
+
+function unannotated(x) {
+  return x;
+}
+
+// test deduping of inferred types
+const nullToUndefined = val => val === null ? undefined : val;
+
+function f0(x: ?Object) { return nullToUndefined(x); }
+function f1(x: ?Object) { return nullToUndefined(x); }
+function f2(x: ?string) { return nullToUndefined(x); }
+function f3(x: ?string) { return nullToUndefined(x); }
+
+declare var idx: $Facebookism$Idx;
+declare var obj: {a?: {b: ?{c: null | {d: number}}}};
+const idxResult = idx(obj, obj => obj.a.b.c.d);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/dump-types/import.js b/tests/dump-types/import.js
new file mode 100644
index 000000000000..9a49778fd59d
--- /dev/null
+++ b/tests/dump-types/import.js
@@ -0,0 +1,5 @@
+// @flow
+var num = 42;
+function bar() { }
+bar();
+module.exports = num;
diff --git a/tests/dump-types/jsfmt.spec.js b/tests/dump-types/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/dump-types/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/dump-types/test.js b/tests/dump-types/test.js
new file mode 100644
index 000000000000..579402b464c0
--- /dev/null
+++ b/tests/dump-types/test.js
@@ -0,0 +1,21 @@
+// @flow
+var num = require('./import');
+function foo(x) { }
+foo(0);
+var a:string = num;
+
+function unannotated(x) {
+  return x;
+}
+
+// test deduping of inferred types
+const nullToUndefined = val => val === null ? undefined : val;
+
+function f0(x: ?Object) { return nullToUndefined(x); }
+function f1(x: ?Object) { return nullToUndefined(x); }
+function f2(x: ?string) { return nullToUndefined(x); }
+function f3(x: ?string) { return nullToUndefined(x); }
+
+declare var idx: $Facebookism$Idx;
+declare var obj: {a?: {b: ?{c: null | {d: number}}}};
+const idxResult = idx(obj, obj => obj.a.b.c.d);
diff --git a/tests/duplicate_methods/__snapshots__/jsfmt.spec.js.snap b/tests/duplicate_methods/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..01ab603de59f
--- /dev/null
+++ b/tests/duplicate_methods/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,88 @@
+exports[`test test.js 1`] = `
+"class C1 {
+  m() { }
+  m() { }
+}
+
+new C1().m();
+
+class C2 {
+  get m() { return 42; }
+  m() { }
+}
+
+new C2().m();
+
+class C3 {
+  set m(x) { }
+  m() { }
+}
+
+new C3().m();
+
+class C4 {
+  get m() { return 42; }
+  set m(x: number) { }
+}
+
+new C4().m = new C4().m - 42;
+
+class C5 {
+  m() { }
+  get m() { return 42; }
+  set m(x: number) { }
+}
+
+new C5().m = new C5().m - 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C1 {
+  m() {
+    
+  }
+  m() {
+    
+  }
+}
+new C1().m();
+class C2 {
+  get m() {
+    return 42;
+  }
+  m() {
+    
+  }
+}
+new C2().m();
+class C3 {
+  set m(x) {
+    
+  }
+  m() {
+    
+  }
+}
+new C3().m();
+class C4 {
+  get m() {
+    return 42;
+  }
+  set m(x: number) {
+    
+  }
+}
+new C4().m = new C4().m - 42;
+class C5 {
+  m() {
+    
+  }
+  get m() {
+    return 42;
+  }
+  set m(x: number) {
+    
+  }
+}
+new C5().m = new C5().m - 42;
+
+"
+`;
diff --git a/tests/duplicate_methods/jsfmt.spec.js b/tests/duplicate_methods/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/duplicate_methods/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/duplicate_methods/test.js b/tests/duplicate_methods/test.js
new file mode 100644
index 000000000000..3c2aa61999b7
--- /dev/null
+++ b/tests/duplicate_methods/test.js
@@ -0,0 +1,35 @@
+class C1 {
+  m() { }
+  m() { }
+}
+
+new C1().m();
+
+class C2 {
+  get m() { return 42; }
+  m() { }
+}
+
+new C2().m();
+
+class C3 {
+  set m(x) { }
+  m() { }
+}
+
+new C3().m();
+
+class C4 {
+  get m() { return 42; }
+  set m(x: number) { }
+}
+
+new C4().m = new C4().m - 42;
+
+class C5 {
+  m() { }
+  get m() { return 42; }
+  set m(x: number) { }
+}
+
+new C5().m = new C5().m - 42;
diff --git a/tests/encaps/__snapshots__/jsfmt.spec.js.snap b/tests/encaps/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3277d93da996
--- /dev/null
+++ b/tests/encaps/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,34 @@
+exports[`test encaps.js 1`] = `
+"class A { }
+var a = new A();
+var s1 = \`l\${a.x}r\`; // error: no prop x in A
+
+function tag(strings,...values) {
+    var x:number = strings[0]; // error: string ~> number
+    return x;
+}
+var s2 = tag \`l\${42}r\`;
+
+function tag2(strings,...values) {
+  return { foo: "" }; // ok: tagged templates can return whatever
+}
+
+var s3 = tag2 \`la la la\`;
+(s3.foo: number); // error: string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {}
+var a = new A();
+var s1 = \`l\${a.x}r\`;// error: no prop x in A
+function tag(strings, ...values) {
+  var x: number = strings[0];// error: string ~> number
+  return x;
+}
+var s2 = tag\`l\${42}r\`;
+function tag2(strings, ...values) {
+  return { foo: "" };// ok: tagged templates can return whatever
+}
+var s3 = tag2\`la la la\`;
+(s3.foo: number);// error: string ~> number
+
+"
+`;
diff --git a/tests/encaps/encaps.js b/tests/encaps/encaps.js
new file mode 100644
index 000000000000..1f1127b42137
--- /dev/null
+++ b/tests/encaps/encaps.js
@@ -0,0 +1,16 @@
+class A { }
+var a = new A();
+var s1 = `l${a.x}r`; // error: no prop x in A
+
+function tag(strings,...values) {
+    var x:number = strings[0]; // error: string ~> number
+    return x;
+}
+var s2 = tag `l${42}r`;
+
+function tag2(strings,...values) {
+  return { foo: "" }; // ok: tagged templates can return whatever
+}
+
+var s3 = tag2 `la la la`;
+(s3.foo: number); // error: string ~> number
diff --git a/tests/encaps/jsfmt.spec.js b/tests/encaps/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/encaps/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/enumerror/__snapshots__/jsfmt.spec.js.snap b/tests/enumerror/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..77a0f8471311
--- /dev/null
+++ b/tests/enumerror/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,45 @@
+exports[`test enumerror.js 1`] = `
+"/** @flow */
+
+function isActive(ad: {state: $Keys<{
+    PAUSED: string;
+    ACTIVE: string;
+    DELETED: string;
+}>}): boolean {
+    return ad.state === \'ACTIVE\';
+};
+isActive({state: \'PAUSE\'});
+
+var MyStates = {
+    PAUSED: \'PAUSED\',
+    ACTIVE: \'ACTIVE\',
+    DELETED: \'DELETED\',
+};
+function isActive2(ad: {state: $Keys<typeof MyStates>}): boolean {
+    return ad.state === MyStates.ACTIVE;
+};
+isActive2({state: \'PAUSE\'});
+
+type Keys = $Keys<{ x: any, y: any }>;
+type Union = \"x\" | \"y\"
+
+function keys2union(s: Keys): Union { return s; } // ok
+function union2keys(s: Union): Keys { return s; } // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/enumerror/enumerror.js b/tests/enumerror/enumerror.js
new file mode 100644
index 000000000000..ea4d96907a0e
--- /dev/null
+++ b/tests/enumerror/enumerror.js
@@ -0,0 +1,26 @@
+/** @flow */
+
+function isActive(ad: {state: $Keys<{
+    PAUSED: string;
+    ACTIVE: string;
+    DELETED: string;
+}>}): boolean {
+    return ad.state === 'ACTIVE';
+};
+isActive({state: 'PAUSE'});
+
+var MyStates = {
+    PAUSED: 'PAUSED',
+    ACTIVE: 'ACTIVE',
+    DELETED: 'DELETED',
+};
+function isActive2(ad: {state: $Keys<typeof MyStates>}): boolean {
+    return ad.state === MyStates.ACTIVE;
+};
+isActive2({state: 'PAUSE'});
+
+type Keys = $Keys<{ x: any, y: any }>;
+type Union = "x" | "y"
+
+function keys2union(s: Keys): Union { return s; } // ok
+function union2keys(s: Union): Keys { return s; } // ok
diff --git a/tests/enumerror/jsfmt.spec.js b/tests/enumerror/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/enumerror/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/equals/__snapshots__/jsfmt.spec.js.snap b/tests/equals/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..450ed18fa059
--- /dev/null
+++ b/tests/equals/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test equals.js 1`] = `
+"/* @flow */
+
+(1 == 1);
+("foo" == "bar");
+(1 == null);
+(null == 1);
+(1 == ""); // error
+("" == 1); // error
+
+var x = (null : ?number);
+(x == 1);
+(1 == x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+1 == 1;
+"foo" == "bar";
+1 == null;
+null == 1;
+1 == "";// error
+"" == 1;// error
+var x = (null: ?number);
+x == 1;
+1 == x;
+
+"
+`;
diff --git a/tests/equals/equals.js b/tests/equals/equals.js
new file mode 100644
index 000000000000..0e1f7297cce6
--- /dev/null
+++ b/tests/equals/equals.js
@@ -0,0 +1,12 @@
+/* @flow */
+
+(1 == 1);
+("foo" == "bar");
+(1 == null);
+(null == 1);
+(1 == ""); // error
+("" == 1); // error
+
+var x = (null : ?number);
+(x == 1);
+(1 == x);
diff --git a/tests/equals/jsfmt.spec.js b/tests/equals/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/equals/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/error_messages/__snapshots__/jsfmt.spec.js.snap b/tests/error_messages/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..68bde87c7fcd
--- /dev/null
+++ b/tests/error_messages/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test errors.js 1`] = `
+"if (typeof define === 'function' && define.amd) { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+if (typeof define === "function" && define.amd) {
+  
+}
+
+"
+`;
diff --git a/tests/error_messages/errors.js b/tests/error_messages/errors.js
new file mode 100644
index 000000000000..6d1c725fc570
--- /dev/null
+++ b/tests/error_messages/errors.js
@@ -0,0 +1 @@
+if (typeof define === 'function' && define.amd) { }
diff --git a/tests/error_messages/jsfmt.spec.js b/tests/error_messages/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/error_messages/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/es6modules/B.js b/tests/es6modules/B.js
new file mode 100644
index 000000000000..e4d0f1b41f44
--- /dev/null
+++ b/tests/es6modules/B.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+exports.numberValue = 42;
diff --git a/tests/es6modules/C.js b/tests/es6modules/C.js
new file mode 100644
index 000000000000..e667c4717b69
--- /dev/null
+++ b/tests/es6modules/C.js
@@ -0,0 +1 @@
+/* @flow */
diff --git a/tests/es6modules/CommonJS_Clobbering_Class.js b/tests/es6modules/CommonJS_Clobbering_Class.js
new file mode 100644
index 000000000000..4fbd96118432
--- /dev/null
+++ b/tests/es6modules/CommonJS_Clobbering_Class.js
@@ -0,0 +1,21 @@
+/**
+ * @providesModule CommonJS_Clobbering_Class
+ * @flow
+ */
+
+class Base {
+  static baseProp: number;
+}
+
+class Test extends Base {
+  static childProp: number;
+
+  static staticNumber1():number { return 1; }
+  static staticNumber2():number { return 2; }
+  static staticNumber3():number { return 3; }
+
+  instNumber1():number { return 1; }
+  instNumber2():number { return 2; }
+};
+
+module.exports = Test;
diff --git a/tests/es6modules/CommonJS_Clobbering_Frozen.js b/tests/es6modules/CommonJS_Clobbering_Frozen.js
new file mode 100644
index 000000000000..322f60abeee2
--- /dev/null
+++ b/tests/es6modules/CommonJS_Clobbering_Frozen.js
@@ -0,0 +1,8 @@
+/**
+ * @providesModule CommonJS_Clobbering_Frozen
+ * @flow
+ */
+
+module.exports = Object.freeze({
+  numberValue1: 1,
+});
diff --git a/tests/es6modules/CommonJS_Clobbering_Lit.js b/tests/es6modules/CommonJS_Clobbering_Lit.js
new file mode 100644
index 000000000000..991b7bc37c12
--- /dev/null
+++ b/tests/es6modules/CommonJS_Clobbering_Lit.js
@@ -0,0 +1,12 @@
+/**
+ * @providesModule CommonJS_Clobbering_Lit
+ * @flow
+ */
+
+module.exports = {
+  numberValue1: 1,
+  numberValue2: 2,
+  numberValue3: 3,
+  numberValue4: 4,
+  numberValue5: 5
+};
diff --git a/tests/es6modules/CommonJS_Named.js b/tests/es6modules/CommonJS_Named.js
new file mode 100644
index 000000000000..698ec4f05276
--- /dev/null
+++ b/tests/es6modules/CommonJS_Named.js
@@ -0,0 +1,10 @@
+/**
+ * @providesModule CommonJS_Named
+ * @flow
+ */
+
+exports.numberValue1 = 1;
+exports.numberValue2 = 2;
+exports.numberValue3 = 3;
+exports.numberValue4 = 4;
+exports.numberValue5 = 5;
diff --git a/tests/es6modules/ES6_DefaultAndNamed.js b/tests/es6modules/ES6_DefaultAndNamed.js
new file mode 100644
index 000000000000..82df6c20aaa8
--- /dev/null
+++ b/tests/es6modules/ES6_DefaultAndNamed.js
@@ -0,0 +1,4 @@
+/* @flow */
+
+export default 42;
+export var str = 'asdf';
diff --git a/tests/es6modules/ES6_Default_AnonClass1.js b/tests/es6modules/ES6_Default_AnonClass1.js
new file mode 100644
index 000000000000..2890acbb2843
--- /dev/null
+++ b/tests/es6modules/ES6_Default_AnonClass1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_AnonClass1
+ * @flow
+ */
+
+export default class { givesANum(): number { return 42; }};
diff --git a/tests/es6modules/ES6_Default_AnonClass2.js b/tests/es6modules/ES6_Default_AnonClass2.js
new file mode 100644
index 000000000000..1debca797b18
--- /dev/null
+++ b/tests/es6modules/ES6_Default_AnonClass2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_AnonClass2
+ * @flow
+ */
+
+export default class { givesANum(): number { return 42; }};
diff --git a/tests/es6modules/ES6_Default_AnonFunction1.js b/tests/es6modules/ES6_Default_AnonFunction1.js
new file mode 100644
index 000000000000..ab2e1bbd8721
--- /dev/null
+++ b/tests/es6modules/ES6_Default_AnonFunction1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_AnonFunction1
+ * @flow
+ */
+
+export default function():number { return 42; }
diff --git a/tests/es6modules/ES6_Default_AnonFunction2.js b/tests/es6modules/ES6_Default_AnonFunction2.js
new file mode 100644
index 000000000000..2c60dbbe7c5c
--- /dev/null
+++ b/tests/es6modules/ES6_Default_AnonFunction2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_AnonFunction2
+ * @flow
+ */
+
+export default function():number { return 42; }
diff --git a/tests/es6modules/ES6_Default_NamedClass1.js b/tests/es6modules/ES6_Default_NamedClass1.js
new file mode 100644
index 000000000000..d903c252bca6
--- /dev/null
+++ b/tests/es6modules/ES6_Default_NamedClass1.js
@@ -0,0 +1,11 @@
+/**
+ * @providesModule ES6_Default_NamedClass1
+ * @flow
+ */
+
+export default class Foo { givesANum(): number { return 42; }};
+
+// Regression test for https://github.com/facebook/flow/issues/511
+//
+// Default-exported class should also be available in local scope
+new Foo();
diff --git a/tests/es6modules/ES6_Default_NamedClass2.js b/tests/es6modules/ES6_Default_NamedClass2.js
new file mode 100644
index 000000000000..a42af92016a6
--- /dev/null
+++ b/tests/es6modules/ES6_Default_NamedClass2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_NamedClass2
+ * @flow
+ */
+
+export default class Foo { givesANum(): number { return 42; }};
diff --git a/tests/es6modules/ES6_Default_NamedFunction1.js b/tests/es6modules/ES6_Default_NamedFunction1.js
new file mode 100644
index 000000000000..40fb4f30dda7
--- /dev/null
+++ b/tests/es6modules/ES6_Default_NamedFunction1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_NamedFunction1
+ * @flow
+ */
+
+export default function foo():number { return 42; }
diff --git a/tests/es6modules/ES6_Default_NamedFunction2.js b/tests/es6modules/ES6_Default_NamedFunction2.js
new file mode 100644
index 000000000000..5f3b5e9e03e0
--- /dev/null
+++ b/tests/es6modules/ES6_Default_NamedFunction2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_Default_NamedFunction2
+ * @flow
+ */
+
+export default function foo():number { return 42; }
diff --git a/tests/es6modules/ES6_ExportAllFromMulti.js b/tests/es6modules/ES6_ExportAllFromMulti.js
new file mode 100644
index 000000000000..9153402a64d5
--- /dev/null
+++ b/tests/es6modules/ES6_ExportAllFromMulti.js
@@ -0,0 +1,4 @@
+// @flow
+
+export * from "./ES6_ExportAllFrom_Source1";
+export * from "./ES6_ExportAllFrom_Source2";
diff --git a/tests/es6modules/ES6_ExportAllFrom_Intermediary1.js b/tests/es6modules/ES6_ExportAllFrom_Intermediary1.js
new file mode 100644
index 000000000000..8d2469c08c42
--- /dev/null
+++ b/tests/es6modules/ES6_ExportAllFrom_Intermediary1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Intermediary1
+ * @flow
+ */
+
+export * from "ES6_ExportAllFrom_Source1";
diff --git a/tests/es6modules/ES6_ExportAllFrom_Intermediary2.js b/tests/es6modules/ES6_ExportAllFrom_Intermediary2.js
new file mode 100644
index 000000000000..fcd626b9f811
--- /dev/null
+++ b/tests/es6modules/ES6_ExportAllFrom_Intermediary2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Intermediary2
+ * @flow
+ */
+
+export * from "ES6_ExportAllFrom_Source2";
diff --git a/tests/es6modules/ES6_ExportAllFrom_Source1.js b/tests/es6modules/ES6_ExportAllFrom_Source1.js
new file mode 100644
index 000000000000..4eb8683774cf
--- /dev/null
+++ b/tests/es6modules/ES6_ExportAllFrom_Source1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Source1
+ * @flow
+ */
+
+export var numberValue1 = 1;
diff --git a/tests/es6modules/ES6_ExportAllFrom_Source2.js b/tests/es6modules/ES6_ExportAllFrom_Source2.js
new file mode 100644
index 000000000000..5616a706ecea
--- /dev/null
+++ b/tests/es6modules/ES6_ExportAllFrom_Source2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportAllFrom_Source2
+ * @flow
+ */
+
+export var numberValue2 = 1;
diff --git a/tests/es6modules/ES6_ExportFrom_Intermediary1.js b/tests/es6modules/ES6_ExportFrom_Intermediary1.js
new file mode 100644
index 000000000000..568cf963529e
--- /dev/null
+++ b/tests/es6modules/ES6_ExportFrom_Intermediary1.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule ES6_ExportFrom_Intermediary1
+ * @flow
+ */
+
+export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed
+} from "ES6_ExportFrom_Source1";
diff --git a/tests/es6modules/ES6_ExportFrom_Intermediary2.js b/tests/es6modules/ES6_ExportFrom_Intermediary2.js
new file mode 100644
index 000000000000..f4f62e4821e1
--- /dev/null
+++ b/tests/es6modules/ES6_ExportFrom_Intermediary2.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule ES6_ExportFrom_Intermediary2
+ * @flow
+ */
+
+export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed2
+} from "ES6_ExportFrom_Source2";
diff --git a/tests/es6modules/ES6_ExportFrom_Source1.js b/tests/es6modules/ES6_ExportFrom_Source1.js
new file mode 100644
index 000000000000..f41da3c58823
--- /dev/null
+++ b/tests/es6modules/ES6_ExportFrom_Source1.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportFrom_Source1
+ * @flow
+ */
+
+export var numberValue1 = 1, numberValue2 = 2;
diff --git a/tests/es6modules/ES6_ExportFrom_Source2.js b/tests/es6modules/ES6_ExportFrom_Source2.js
new file mode 100644
index 000000000000..fd7541549551
--- /dev/null
+++ b/tests/es6modules/ES6_ExportFrom_Source2.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule ES6_ExportFrom_Source2
+ * @flow
+ */
+
+export var numberValue1 = 1, numberValue2 = 2;
diff --git a/tests/es6modules/ES6_Named1.js b/tests/es6modules/ES6_Named1.js
new file mode 100644
index 000000000000..2e71f0b72589
--- /dev/null
+++ b/tests/es6modules/ES6_Named1.js
@@ -0,0 +1,22 @@
+/**
+ * @providesModule ES6_Named1
+ * @flow
+ */
+
+var specifierNumber1 = 1;
+var specifierNumber2 = 2;
+var specifierNumber3 = 3;
+var groupedSpecifierNumber1 = 1;
+var groupedSpecifierNumber2 = 2;
+
+export {specifierNumber1};
+export {specifierNumber2 as specifierNumber2Renamed};
+export {specifierNumber3};
+export {groupedSpecifierNumber1, groupedSpecifierNumber2};
+
+export function givesANumber(): number { return 42; };
+export class NumberGenerator { givesANumber(): number { return 42; }};
+
+export var varDeclNumber1 = 1, varDeclNumber2 = 2;
+export var {destructuredObjNumber} = {destructuredObjNumber: 1};
+export var [destructuredArrNumber] = [1]
diff --git a/tests/es6modules/ES6_Named2.js b/tests/es6modules/ES6_Named2.js
new file mode 100644
index 000000000000..4abc37e137ca
--- /dev/null
+++ b/tests/es6modules/ES6_Named2.js
@@ -0,0 +1,20 @@
+/**
+ * @providesModule ES6_Named2
+ * @flow
+ */
+
+var specifierNumber4 = 1;
+var specifierNumber5 = 2;
+var groupedSpecifierNumber3 = 1;
+var groupedSpecifierNumber4 = 2;
+
+export {specifierNumber4};
+export {specifierNumber5 as specifierNumber5Renamed};
+export {groupedSpecifierNumber3, groupedSpecifierNumber4};
+
+export function givesANumber2(): number { return 42; };
+export class NumberGenerator2 { givesANumber(): number { return 42; }};
+
+export var varDeclNumber3 = 1, varDeclNumber4 = 2;
+export var {destructuredObjNumber2} = {destructuredObjNumber2: 1};
+export var [destructuredArrNumber2] = [1]
diff --git a/tests/es6modules/ExportType.js b/tests/es6modules/ExportType.js
new file mode 100644
index 000000000000..3949a39d32bf
--- /dev/null
+++ b/tests/es6modules/ExportType.js
@@ -0,0 +1,3 @@
+// @flow
+
+export type typeAlias = number;
diff --git a/tests/es6modules/ProvidesModuleA.js b/tests/es6modules/ProvidesModuleA.js
new file mode 100644
index 000000000000..f2cbd52ce005
--- /dev/null
+++ b/tests/es6modules/ProvidesModuleA.js
@@ -0,0 +1,10 @@
+/**
+ * @providesModule A
+ * @flow
+ */
+
+exports.numberValue1 = 42;
+exports.numberValue2 = 42;
+exports.numberValue3 = 42;
+exports.numberValue4 = 42;
+exports.stringValue = "str";
diff --git a/tests/es6modules/ProvidesModuleCJSDefault.js b/tests/es6modules/ProvidesModuleCJSDefault.js
new file mode 100644
index 000000000000..a3d9c135a2c1
--- /dev/null
+++ b/tests/es6modules/ProvidesModuleCJSDefault.js
@@ -0,0 +1,8 @@
+/**
+ * @providesModule CJSDefault
+ * @flow
+ */
+
+module.exports = {
+  numberValue: 42
+};
diff --git a/tests/es6modules/ProvidesModuleD.js b/tests/es6modules/ProvidesModuleD.js
new file mode 100644
index 000000000000..a4d5ee842062
--- /dev/null
+++ b/tests/es6modules/ProvidesModuleD.js
@@ -0,0 +1,4 @@
+/**
+ * @providesModule D
+ * @flow
+ */
diff --git a/tests/es6modules/ProvidesModuleES6Default.js b/tests/es6modules/ProvidesModuleES6Default.js
new file mode 100644
index 000000000000..636a1946109c
--- /dev/null
+++ b/tests/es6modules/ProvidesModuleES6Default.js
@@ -0,0 +1,10 @@
+/**
+ * @providesModule ES6Default
+ * @flow
+ */
+
+/*
+export default {
+  numberValue: 42,
+};
+*/
diff --git a/tests/es6modules/SideEffects.js b/tests/es6modules/SideEffects.js
new file mode 100644
index 000000000000..e667c4717b69
--- /dev/null
+++ b/tests/es6modules/SideEffects.js
@@ -0,0 +1 @@
+/* @flow */
diff --git a/tests/es6modules/__snapshots__/jsfmt.spec.js.snap b/tests/es6modules/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7e854f72ac46
--- /dev/null
+++ b/tests/es6modules/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,1297 @@
+exports[`test B.js 1`] = `
+"/* @flow */
+
+exports.numberValue = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+exports.numberValue = 42;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"/* @flow */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test CommonJS_Clobbering_Class.js 1`] = `
+"/**
+ * @providesModule CommonJS_Clobbering_Class
+ * @flow
+ */
+
+class Base {
+  static baseProp: number;
+}
+
+class Test extends Base {
+  static childProp: number;
+
+  static staticNumber1():number { return 1; }
+  static staticNumber2():number { return 2; }
+  static staticNumber3():number { return 3; }
+
+  instNumber1():number { return 1; }
+  instNumber2():number { return 2; }
+};
+
+module.exports = Test;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Clobbering_Class
+ * @flow
+ */
+class Base {
+  static baseProp: number;
+}
+class Test extends Base {
+  static childProp: number;
+  staticNumber1(): number {
+    return 1;
+  }
+  staticNumber2(): number {
+    return 2;
+  }
+  staticNumber3(): number {
+    return 3;
+  }
+  instNumber1(): number {
+    return 1;
+  }
+  instNumber2(): number {
+    return 2;
+  }
+}
+module.exports = Test;
+
+"
+`;
+
+exports[`test CommonJS_Clobbering_Frozen.js 1`] = `
+"/**
+ * @providesModule CommonJS_Clobbering_Frozen
+ * @flow
+ */
+
+module.exports = Object.freeze({
+  numberValue1: 1,
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Clobbering_Frozen
+ * @flow
+ */
+module.exports = Object.freeze({ numberValue1: 1 });
+
+"
+`;
+
+exports[`test CommonJS_Clobbering_Lit.js 1`] = `
+"/**
+ * @providesModule CommonJS_Clobbering_Lit
+ * @flow
+ */
+
+module.exports = {
+  numberValue1: 1,
+  numberValue2: 2,
+  numberValue3: 3,
+  numberValue4: 4,
+  numberValue5: 5
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Clobbering_Lit
+ * @flow
+ */
+module.exports = {
+  numberValue1: 1,
+  numberValue2: 2,
+  numberValue3: 3,
+  numberValue4: 4,
+  numberValue5: 5
+};
+
+"
+`;
+
+exports[`test CommonJS_Named.js 1`] = `
+"/**
+ * @providesModule CommonJS_Named
+ * @flow
+ */
+
+exports.numberValue1 = 1;
+exports.numberValue2 = 2;
+exports.numberValue3 = 3;
+exports.numberValue4 = 4;
+exports.numberValue5 = 5;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CommonJS_Named
+ * @flow
+ */
+exports.numberValue1 = 1;
+exports.numberValue2 = 2;
+exports.numberValue3 = 3;
+exports.numberValue4 = 4;
+exports.numberValue5 = 5;
+
+"
+`;
+
+exports[`test ES6_Default_AnonClass1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_AnonClass1
+ * @flow
+ */
+
+export default class { givesANum(): number { return 42; }};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_AnonClass1
+ * @flow
+ */
+export default class {
+  givesANum(): number {
+    return 42;
+  }
+}
+
+"
+`;
+
+exports[`test ES6_Default_AnonClass2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_AnonClass2
+ * @flow
+ */
+
+export default class { givesANum(): number { return 42; }};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_AnonClass2
+ * @flow
+ */
+export default class {
+  givesANum(): number {
+    return 42;
+  }
+}
+
+"
+`;
+
+exports[`test ES6_Default_AnonFunction1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_AnonFunction1
+ * @flow
+ */
+
+export default function():number { return 42; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_AnonFunction1
+ * @flow
+ */
+export default function(): number {
+  return 42;
+}
+
+"
+`;
+
+exports[`test ES6_Default_AnonFunction2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_AnonFunction2
+ * @flow
+ */
+
+export default function():number { return 42; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_AnonFunction2
+ * @flow
+ */
+export default function(): number {
+  return 42;
+}
+
+"
+`;
+
+exports[`test ES6_Default_NamedClass1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedClass1
+ * @flow
+ */
+
+export default class Foo { givesANum(): number { return 42; }};
+
+// Regression test for https://github.com/facebook/flow/issues/511
+//
+// Default-exported class should also be available in local scope
+new Foo();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_NamedClass1
+ * @flow
+ */
+export default class Foo {
+  givesANum(): number {
+    return 42;
+  }
+}
+// Regression test for https://github.com/facebook/flow/issues/511
+//
+// Default-exported class should also be available in local scope
+new Foo();
+
+"
+`;
+
+exports[`test ES6_Default_NamedClass2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedClass2
+ * @flow
+ */
+
+export default class Foo { givesANum(): number { return 42; }};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_NamedClass2
+ * @flow
+ */
+export default class Foo {
+  givesANum(): number {
+    return 42;
+  }
+}
+
+"
+`;
+
+exports[`test ES6_Default_NamedFunction1.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedFunction1
+ * @flow
+ */
+
+export default function foo():number { return 42; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_NamedFunction1
+ * @flow
+ */
+export default function foo(): number {
+  return 42;
+}
+
+"
+`;
+
+exports[`test ES6_Default_NamedFunction2.js 1`] = `
+"/**
+ * @providesModule ES6_Default_NamedFunction2
+ * @flow
+ */
+
+export default function foo():number { return 42; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_Default_NamedFunction2
+ * @flow
+ */
+export default function foo(): number {
+  return 42;
+}
+
+"
+`;
+
+exports[`test ES6_DefaultAndNamed.js 1`] = `
+"/* @flow */
+
+export default 42;
+export var str = \'asdf\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+export default 42
+export var str = \"asdf\";
+
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Intermediary1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Intermediary1
+ * @flow
+ */
+
+export * from \"ES6_ExportAllFrom_Source1\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_ExportAllFrom_Intermediary1
+ * @flow
+ */
+export * from \"ES6_ExportAllFrom_Source1\"
+
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Intermediary2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Intermediary2
+ * @flow
+ */
+
+export * from \"ES6_ExportAllFrom_Source2\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_ExportAllFrom_Intermediary2
+ * @flow
+ */
+export * from \"ES6_ExportAllFrom_Source2\"
+
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Source1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Source1
+ * @flow
+ */
+
+export var numberValue1 = 1;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_ExportAllFrom_Source1
+ * @flow
+ */
+export var numberValue1 = 1;
+
+"
+`;
+
+exports[`test ES6_ExportAllFrom_Source2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportAllFrom_Source2
+ * @flow
+ */
+
+export var numberValue2 = 1;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_ExportAllFrom_Source2
+ * @flow
+ */
+export var numberValue2 = 1;
+
+"
+`;
+
+exports[`test ES6_ExportAllFromMulti.js 1`] = `
+"// @flow
+
+export * from \"./ES6_ExportAllFrom_Source1\";
+export * from \"./ES6_ExportAllFrom_Source2\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export * from \"./ES6_ExportAllFrom_Source1\"
+export * from \"./ES6_ExportAllFrom_Source2\"
+
+"
+`;
+
+exports[`test ES6_ExportFrom_Intermediary1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Intermediary1
+ * @flow
+ */
+
+export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed
+} from \"ES6_ExportFrom_Source1\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test ES6_ExportFrom_Intermediary2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Intermediary2
+ * @flow
+ */
+
+export {
+  numberValue1,
+  numberValue2 as numberValue2_renamed2
+} from \"ES6_ExportFrom_Source2\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test ES6_ExportFrom_Source1.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Source1
+ * @flow
+ */
+
+export var numberValue1 = 1, numberValue2 = 2;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_ExportFrom_Source1
+ * @flow
+ */
+export var numberValue1 = 1numberValue2 = 2;
+
+"
+`;
+
+exports[`test ES6_ExportFrom_Source2.js 1`] = `
+"/**
+ * @providesModule ES6_ExportFrom_Source2
+ * @flow
+ */
+
+export var numberValue1 = 1, numberValue2 = 2;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule ES6_ExportFrom_Source2
+ * @flow
+ */
+export var numberValue1 = 1numberValue2 = 2;
+
+"
+`;
+
+exports[`test ES6_Named1.js 1`] = `
+"/**
+ * @providesModule ES6_Named1
+ * @flow
+ */
+
+var specifierNumber1 = 1;
+var specifierNumber2 = 2;
+var specifierNumber3 = 3;
+var groupedSpecifierNumber1 = 1;
+var groupedSpecifierNumber2 = 2;
+
+export {specifierNumber1};
+export {specifierNumber2 as specifierNumber2Renamed};
+export {specifierNumber3};
+export {groupedSpecifierNumber1, groupedSpecifierNumber2};
+
+export function givesANumber(): number { return 42; };
+export class NumberGenerator { givesANumber(): number { return 42; }};
+
+export var varDeclNumber1 = 1, varDeclNumber2 = 2;
+export var {destructuredObjNumber} = {destructuredObjNumber: 1};
+export var [destructuredArrNumber] = [1]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test ES6_Named2.js 1`] = `
+"/**
+ * @providesModule ES6_Named2
+ * @flow
+ */
+
+var specifierNumber4 = 1;
+var specifierNumber5 = 2;
+var groupedSpecifierNumber3 = 1;
+var groupedSpecifierNumber4 = 2;
+
+export {specifierNumber4};
+export {specifierNumber5 as specifierNumber5Renamed};
+export {groupedSpecifierNumber3, groupedSpecifierNumber4};
+
+export function givesANumber2(): number { return 42; };
+export class NumberGenerator2 { givesANumber(): number { return 42; }};
+
+export var varDeclNumber3 = 1, varDeclNumber4 = 2;
+export var {destructuredObjNumber2} = {destructuredObjNumber2: 1};
+export var [destructuredArrNumber2] = [1]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test ExportType.js 1`] = `
+"// @flow
+
+export type typeAlias = number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export type typeAlias = number;
+
+"
+`;
+
+exports[`test ProvidesModuleA.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+
+exports.numberValue1 = 42;
+exports.numberValue2 = 42;
+exports.numberValue3 = 42;
+exports.numberValue4 = 42;
+exports.stringValue = \"str\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule A
+ * @flow
+ */
+exports.numberValue1 = 42;
+exports.numberValue2 = 42;
+exports.numberValue3 = 42;
+exports.numberValue4 = 42;
+exports.stringValue = \"str\";
+
+"
+`;
+
+exports[`test ProvidesModuleCJSDefault.js 1`] = `
+"/**
+ * @providesModule CJSDefault
+ * @flow
+ */
+
+module.exports = {
+  numberValue: 42
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule CJSDefault
+ * @flow
+ */
+module.exports = { numberValue: 42 };
+
+"
+`;
+
+exports[`test ProvidesModuleD.js 1`] = `
+"/**
+ * @providesModule D
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test ProvidesModuleES6Default.js 1`] = `
+"/**
+ * @providesModule ES6Default
+ * @flow
+ */
+
+/*
+export default {
+  numberValue: 42,
+};
+*/
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test SideEffects.js 1`] = `
+"/* @flow */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test es6modules.js 1`] = `
+"/* @flow */
+
+// ===================== //
+// == Path Resolution == //
+// ===================== //
+
+// @providesModule
+import * as DefaultA from \"A\";
+var a1: number = DefaultA.numberValue1;
+var a2: string = DefaultA.numberValue1; // Error: number ~> string
+
+// File path
+import * as DefaultB from \"./B\";
+var b1: number = DefaultB.numberValue;
+var b2: string = DefaultB.numberValue; // Error: number ~> string
+
+// C.js exists, but not as a providesModule
+import DefaultC from \"C\"; // Error: No such module
+
+// @providesModule D exists, but not as a filename
+import DefaultD from \"./D\"; // Error: No such module
+
+// ================================================ //
+// == CommonJS Clobbering Literal Exports -> ES6 == //
+// ================================================ //
+
+import {doesntExist1} from \"CommonJS_Clobbering_Lit\"; // Error: Not an exported binding
+
+import {numberValue1} from \"CommonJS_Clobbering_Lit\";
+var c1: number = numberValue1;
+var c2: string = numberValue1; // Error: number ~> string
+
+import {numberValue2 as numVal1} from \"CommonJS_Clobbering_Lit\";
+var d1: number = numVal1;
+var d2: string = numVal1; // Error: number ~> string
+
+import CJS_Clobb_Lit from \"CommonJS_Clobbering_Lit\";
+var e1: number = CJS_Clobb_Lit.numberValue3;
+var e2: string = CJS_Clobb_Lit.numberValue3; // Error: number ~> string
+CJS_Clobb_Lit.doesntExist; // Error: doesntExist isn\'t a property
+
+import * as CJS_Clobb_Lit_NS from \"CommonJS_Clobbering_Lit\";
+var f1: number = CJS_Clobb_Lit_NS.numberValue4;
+var f2: number = CJS_Clobb_Lit_NS.default.numberValue4;
+CJS_Clobb_Lit_NS.default.default; // Error: No \'default\' property on the exported obj
+var f3: string = CJS_Clobb_Lit_NS.numberValue4; // Error: number ~> string
+var f4: string = CJS_Clobb_Lit_NS.default.numberValue5; // Error: number ~> string
+
+// ============================================== //
+// == CommonJS Clobbering Class Exports -> ES6 == //
+// ============================================== //
+
+import {doesntExist2} from \"CommonJS_Clobbering_Class\"; // Error: Not an exported binding
+
+// The following import should error because class statics are not turned into
+// named exports for now. This avoids complexities with polymorphic static
+// members (where the polymophism is defined on the class itself rather than the
+// method).
+import {staticNumber1, baseProp, childProp} from \"CommonJS_Clobbering_Class\"; // Error
+
+import CJS_Clobb_Class from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class();
+new CJS_Clobb_Class().doesntExist; // Error: Class has no \`doesntExist\` property
+var h1: number = CJS_Clobb_Class.staticNumber2();
+var h2: string = CJS_Clobb_Class.staticNumber2(); // Error: number ~> string
+var h3: number = new CJS_Clobb_Class().instNumber1();
+var h4: string = new CJS_Clobb_Class().instNumber1(); // Error: number ~> string
+
+import * as CJS_Clobb_Class_NS from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class_NS(); // Error: Namespace object isn\'t constructable
+var i1: number = CJS_Clobb_Class_NS.staticNumber3(); // Error: Class statics not copied to Namespace object
+var i2: number = new CJS_Clobb_Class_NS.default().instNumber2();
+var i3: string = new CJS_Clobb_Class_NS.default().instNumber2(); // Error: number ~> string
+
+// =================================== //
+// == CommonJS Named Exports -> ES6 == //
+// =================================== //
+
+import {doesntExist3} from \"CommonJS_Named\"; // Error: Not an exported binding
+
+import {numberValue2} from \"CommonJS_Named\";
+var j1: number = numberValue2;
+var j2: string = numberValue2; // Error: number ~> string
+
+import {numberValue3 as numVal3} from \"CommonJS_Named\";
+var k1: number = numVal3;
+var k2: string = numVal3; // Error: number ~> string
+
+import * as CJS_Named from \"CommonJS_Named\";
+var l1: number = CJS_Named.numberValue1;
+var l2: string = CJS_Named.numberValue1; // Error: number ~> string
+CJS_Named.doesntExist; // Error: doesntExist isn\'t a property
+
+import * as CJS_Named_NS from \"CommonJS_Named\";
+var m1: number = CJS_Named_NS.numberValue4;
+var m2: string = CJS_Named_NS.default.numberValue4; // Error: CommonJS_Named has no default export
+var m3: string = CJS_Named_NS.numberValue4; // Error: number ~> string
+
+//////////////////////////////
+// == ES6 Default -> ES6 == //
+//////////////////////////////
+
+import {doesntExist4} from \"ES6_Default_AnonFunction1\"; // Error: Not an exported binding
+
+import ES6_Def_AnonFunc1 from \"ES6_Default_AnonFunction1\";
+var n1: number = ES6_Def_AnonFunc1();
+var n2: string = ES6_Def_AnonFunc1(); // Error: number ~> string
+
+import ES6_Def_NamedFunc1 from \"ES6_Default_NamedFunction1\";
+var o1: number = ES6_Def_NamedFunc1();
+var o2: string = ES6_Def_NamedFunc1(); // Error: number ~> string
+
+import ES6_Def_AnonClass1 from \"ES6_Default_AnonClass1\";
+var p1: number = new ES6_Def_AnonClass1().givesANum();
+var p2: string = new ES6_Def_AnonClass1().givesANum(); // Error: number ~> string
+
+import ES6_Def_NamedClass1 from \"ES6_Default_NamedClass1\";
+var q1: number = new ES6_Def_NamedClass1().givesANum();
+var q2: string = new ES6_Def_NamedClass1().givesANum(); // Error: number ~> string
+
+////////////////////////////
+// == ES6 Named -> ES6 == //
+////////////////////////////
+
+import doesntExist5 from \"ES6_Named1\"; // Error: Not an exported binding
+
+import {specifierNumber1 as specifierNumber1_1} from \"ES6_Named1\";
+var r1: number = specifierNumber1_1;
+var r2: string = specifierNumber1_1; // Error: number ~> string
+
+import {specifierNumber2Renamed} from \"ES6_Named1\";
+var s1: number = specifierNumber2Renamed;
+var s2: string = specifierNumber2Renamed; // Error: number ~> string
+
+import {specifierNumber3 as specifierNumber3Renamed} from \"ES6_Named1\";
+var t1: number = specifierNumber3Renamed;
+var t2: string = specifierNumber3Renamed; // Error: number ~> string
+
+import {groupedSpecifierNumber1, groupedSpecifierNumber2} from \"ES6_Named1\";
+var u1: number = groupedSpecifierNumber1;
+var u2: number = groupedSpecifierNumber2;
+var u3: string = groupedSpecifierNumber1; // Error: number ~> string
+var u4: string = groupedSpecifierNumber2; // Error: number ~> string
+
+import {givesANumber} from \"ES6_Named1\";
+var v1: number = givesANumber();
+var v2: string = givesANumber(); // Error: number ~> string
+
+import {NumberGenerator} from \"ES6_Named1\";
+var w1: number = new NumberGenerator().givesANumber();
+var w2: string = new NumberGenerator().givesANumber(); // Error: number ~> string
+
+import {varDeclNumber1, varDeclNumber2} from \"ES6_Named1\";
+var x1: number = varDeclNumber1;
+var x2: number = varDeclNumber2;
+var x3: string = varDeclNumber1; // Error: number ~> string
+var x4: string = varDeclNumber2; // Error: number ~> string
+
+import {destructuredObjNumber} from \"ES6_Named1\";
+var y1: number = destructuredObjNumber;
+var y2: string = destructuredObjNumber; // Error: number ~> string
+
+import {destructuredArrNumber} from \"ES6_Named1\";
+var z1: number = destructuredArrNumber;
+var z2: string = destructuredArrNumber; // Error: number ~> string
+
+import {numberValue1 as numberValue4} from \"ES6_ExportFrom_Intermediary1\";
+var aa1: number = numberValue4;
+var aa2: string = numberValue4; // Error: number ~> string
+
+import {numberValue2_renamed} from \"ES6_ExportFrom_Intermediary1\";
+var ab1: number = numberValue2_renamed;
+var ab2: string = numberValue2_renamed; // Error: number ~> string
+
+import {numberValue1 as numberValue5} from \"ES6_ExportAllFrom_Intermediary1\";
+var ac1: number = numberValue5;
+var ac2: string = numberValue5; // Error: number ~> string
+
+///////////////////////////////////
+// == ES6 Default -> CommonJS == //
+///////////////////////////////////
+
+require(\'ES6_Default_AnonFunction2\').doesntExist; // Error: \'doesntExist\' isn\'t an export
+
+var ES6_Def_AnonFunc2 = require(\"ES6_Default_AnonFunction2\").default;
+var ad1: number = ES6_Def_AnonFunc2();
+var ad2: string = ES6_Def_AnonFunc2(); // Error: number ~> string
+
+var ES6_Def_NamedFunc2 = require(\"ES6_Default_NamedFunction2\").default;
+var ae1: number = ES6_Def_NamedFunc2();
+var ae2: string = ES6_Def_NamedFunc2(); // Error: number ~> string
+
+var ES6_Def_AnonClass2 = require(\"ES6_Default_AnonClass2\").default;
+var af1: number = new ES6_Def_AnonClass2().givesANum();
+var af2: string = new ES6_Def_AnonClass2().givesANum(); // Error: number ~> string
+
+var ES6_Def_NamedClass2 = require(\"ES6_Default_NamedClass2\").default;
+var ag1: number = new ES6_Def_NamedClass2().givesANum();
+var ag2: string = new ES6_Def_NamedClass2().givesANum(); // Error: number ~> string
+
+/////////////////////////////////
+// == ES6 Named -> CommonJS == //
+/////////////////////////////////
+
+var specifierNumber4 = require(\"ES6_Named2\").specifierNumber4;
+var ah1: number = specifierNumber4;
+var ah2: string = specifierNumber4; // Error: number ~> string
+
+var specifierNumber5Renamed = require(\"ES6_Named2\").specifierNumber5Renamed;
+var ai1: number = specifierNumber5Renamed;
+var ai2: string = specifierNumber5Renamed; // Error: number ~> string
+
+var groupedSpecifierNumber3 = require(\"ES6_Named2\").groupedSpecifierNumber3;
+var groupedSpecifierNumber4 = require(\"ES6_Named2\").groupedSpecifierNumber4;
+var aj1: number = groupedSpecifierNumber3;
+var aj2: number = groupedSpecifierNumber4;
+var aj3: string = groupedSpecifierNumber3; // Error: number ~> string
+var aj4: string = groupedSpecifierNumber4; // Error: number ~> string
+
+var givesANumber2 = require(\"ES6_Named2\").givesANumber2;
+var ak1: number = givesANumber2();
+var ak2: string = givesANumber2(); // Error: number ~> string
+
+var NumberGenerator2 = require(\"ES6_Named2\").NumberGenerator2;
+var al1: number = new NumberGenerator2().givesANumber();
+var al2: string = new NumberGenerator2().givesANumber(); // Error: number ~> string
+
+var varDeclNumber3 = require(\"ES6_Named2\").varDeclNumber3;
+var varDeclNumber4 = require(\"ES6_Named2\").varDeclNumber4;
+var am1: number = varDeclNumber3;
+var am2: number = varDeclNumber4;
+var am3: string = varDeclNumber3; // Error: number ~> string
+var am4: string = varDeclNumber4; // Error: number ~> string
+
+var destructuredObjNumber2 = require(\"ES6_Named2\").destructuredObjNumber2;
+var an1: number = destructuredObjNumber2;
+var an2: string = destructuredObjNumber2; // Error: number ~> string
+
+var destructuredArrNumber2 = require(\"ES6_Named2\").destructuredArrNumber2;
+var ao1: number = destructuredArrNumber2;
+var ao2: string = destructuredArrNumber2; // Error: number ~> string
+
+var numberValue6 = require(\"ES6_ExportFrom_Intermediary2\").numberValue1;
+var ap1: number = numberValue6;
+var ap2: string = numberValue6; // Error: number ~> string
+
+var numberValue2_renamed2 = require(\"ES6_ExportFrom_Intermediary2\").numberValue2_renamed2;
+var aq1: number = numberValue2_renamed2;
+var aq2: string = numberValue2_renamed2; // Error: number ~> string
+
+var numberValue7 = require(\"ES6_ExportAllFrom_Intermediary2\").numberValue2;
+var ar1: number = numberValue7;
+var ar2: string = numberValue7; // Error: number ~> string
+
+////////////////////////////////////////////////////////
+// == ES6 Default+Named -> ES6 import Default+Named== //
+////////////////////////////////////////////////////////
+
+import defaultNum, {str as namedStr} from \"./ES6_DefaultAndNamed\";
+
+var as1: number = defaultNum;
+var as2: string = defaultNum; // Error: number ~> string
+
+var as3: string = namedStr;
+var as4: number = namedStr; // Error: string ~> number
+
+////////////////////////////////////////
+// == Side-effect only ES6 imports == //
+////////////////////////////////////////
+
+import \"./SideEffects\";
+
+//////////////////////////////////////////////
+// == Suggest export name on likely typo == //
+//////////////////////////////////////////////
+import specifierNumber1 from \"ES6_Named1\"; // Error: Did you mean \`import {specifierNumber1} from ...\`?
+import {specifierNumber} from \"ES6_Named1\"; // Error: Did you mean \`specifierNumber1\`?
+
+///////////////////////////////////////////////////
+// == Multi \`export *\` should combine exports == //
+///////////////////////////////////////////////////
+import {
+  numberValue1 as numberValue8,
+  numberValue2 as numberValue9
+} from \"./ES6_ExportAllFromMulti\";
+
+var at1: number = numberValue8;
+var at2: string = numberValue8; // Error: number ~> string
+
+var at3: number = numberValue9;
+var at4: string = numberValue9; // Error: number ~> string
+
+/////////////////////////////////////////////////////////////
+// == Vanilla \`import\` cannot import a type-only export == //
+/////////////////////////////////////////////////////////////
+import {typeAlias} from \"./ExportType\"; // Error: Cannot vanilla-import a type alias!
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// ===================== //
+// == Path Resolution == //
+// ===================== //
+// @providesModule
+import * as DefaultA from \"A\";
+var a1: number = DefaultA.numberValue1;
+var a2: string = DefaultA.numberValue1;// Error: number ~> string
+// File path
+import * as DefaultB from \"./B\";
+var b1: number = DefaultB.numberValue;
+var b2: string = DefaultB.numberValue;// Error: number ~> string
+// C.js exists, but not as a providesModule
+import DefaultC from \"C\";// Error: No such module
+// @providesModule D exists, but not as a filename
+import DefaultD from \"./D\";// Error: No such module
+// ================================================ //
+// == CommonJS Clobbering Literal Exports -> ES6 == //
+// ================================================ //
+import { doesntExist1 } from \"CommonJS_Clobbering_Lit\";// Error: Not an exported binding
+import { numberValue1 } from \"CommonJS_Clobbering_Lit\";
+var c1: number = numberValue1;
+var c2: string = numberValue1;// Error: number ~> string
+import { numberValue2 as numVal1 } from \"CommonJS_Clobbering_Lit\";
+var d1: number = numVal1;
+var d2: string = numVal1;// Error: number ~> string
+import CJS_Clobb_Lit from \"CommonJS_Clobbering_Lit\";
+var e1: number = CJS_Clobb_Lit.numberValue3;
+var e2: string = CJS_Clobb_Lit.numberValue3;// Error: number ~> string
+CJS_Clobb_Lit.doesntExist;// Error: doesntExist isn\'t a property
+import * as CJS_Clobb_Lit_NS from \"CommonJS_Clobbering_Lit\";
+var f1: number = CJS_Clobb_Lit_NS.numberValue4;
+var f2: number = CJS_Clobb_Lit_NS.default.numberValue4;
+CJS_Clobb_Lit_NS.default.default;// Error: No \'default\' property on the exported obj
+var f3: string = CJS_Clobb_Lit_NS.numberValue4;// Error: number ~> string
+var f4: string = CJS_Clobb_Lit_NS.default.numberValue5;// Error: number ~> string
+// ============================================== //
+// == CommonJS Clobbering Class Exports -> ES6 == //
+// ============================================== //
+import { doesntExist2 } from \"CommonJS_Clobbering_Class\";// Error: Not an exported binding
+// The following import should error because class statics are not turned into
+// named exports for now. This avoids complexities with polymorphic static
+// members (where the polymophism is defined on the class itself rather than the
+// method).
+import { staticNumber1, baseProp, childProp } from \"CommonJS_Clobbering_Class\";// Error
+import CJS_Clobb_Class from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class();
+new CJS_Clobb_Class().doesntExist;// Error: Class has no \`doesntExist\` property
+var h1: number = CJS_Clobb_Class.staticNumber2();
+var h2: string = CJS_Clobb_Class.staticNumber2();// Error: number ~> string
+var h3: number = new CJS_Clobb_Class().instNumber1();
+var h4: string = new CJS_Clobb_Class().instNumber1();// Error: number ~> string
+import * as CJS_Clobb_Class_NS from \"CommonJS_Clobbering_Class\";
+new CJS_Clobb_Class_NS();// Error: Namespace object isn\'t constructable
+var i1: number = CJS_Clobb_Class_NS.staticNumber3();// Error: Class statics not copied to Namespace object
+var i2: number = new CJS_Clobb_Class_NS.default().instNumber2();
+var i3: string = new CJS_Clobb_Class_NS.default().instNumber2();// Error: number ~> string
+// =================================== //
+// == CommonJS Named Exports -> ES6 == //
+// =================================== //
+import { doesntExist3 } from \"CommonJS_Named\";// Error: Not an exported binding
+import { numberValue2 } from \"CommonJS_Named\";
+var j1: number = numberValue2;
+var j2: string = numberValue2;// Error: number ~> string
+import { numberValue3 as numVal3 } from \"CommonJS_Named\";
+var k1: number = numVal3;
+var k2: string = numVal3;// Error: number ~> string
+import * as CJS_Named from \"CommonJS_Named\";
+var l1: number = CJS_Named.numberValue1;
+var l2: string = CJS_Named.numberValue1;// Error: number ~> string
+CJS_Named.doesntExist;// Error: doesntExist isn\'t a property
+import * as CJS_Named_NS from \"CommonJS_Named\";
+var m1: number = CJS_Named_NS.numberValue4;
+var m2: string = CJS_Named_NS.default.numberValue4;// Error: CommonJS_Named has no default export
+var m3: string = CJS_Named_NS.numberValue4;// Error: number ~> string
+//////////////////////////////
+// == ES6 Default -> ES6 == //
+//////////////////////////////
+import { doesntExist4 } from \"ES6_Default_AnonFunction1\";// Error: Not an exported binding
+import ES6_Def_AnonFunc1 from \"ES6_Default_AnonFunction1\";
+var n1: number = ES6_Def_AnonFunc1();
+var n2: string = ES6_Def_AnonFunc1();// Error: number ~> string
+import ES6_Def_NamedFunc1 from \"ES6_Default_NamedFunction1\";
+var o1: number = ES6_Def_NamedFunc1();
+var o2: string = ES6_Def_NamedFunc1();// Error: number ~> string
+import ES6_Def_AnonClass1 from \"ES6_Default_AnonClass1\";
+var p1: number = new ES6_Def_AnonClass1().givesANum();
+var p2: string = new ES6_Def_AnonClass1().givesANum();// Error: number ~> string
+import ES6_Def_NamedClass1 from \"ES6_Default_NamedClass1\";
+var q1: number = new ES6_Def_NamedClass1().givesANum();
+var q2: string = new ES6_Def_NamedClass1().givesANum();// Error: number ~> string
+////////////////////////////
+// == ES6 Named -> ES6 == //
+////////////////////////////
+import doesntExist5 from \"ES6_Named1\";// Error: Not an exported binding
+import { specifierNumber1 as specifierNumber1_1 } from \"ES6_Named1\";
+var r1: number = specifierNumber1_1;
+var r2: string = specifierNumber1_1;// Error: number ~> string
+import { specifierNumber2Renamed } from \"ES6_Named1\";
+var s1: number = specifierNumber2Renamed;
+var s2: string = specifierNumber2Renamed;// Error: number ~> string
+import { specifierNumber3 as specifierNumber3Renamed } from \"ES6_Named1\";
+var t1: number = specifierNumber3Renamed;
+var t2: string = specifierNumber3Renamed;// Error: number ~> string
+import { groupedSpecifierNumber1, groupedSpecifierNumber2 } from \"ES6_Named1\";
+var u1: number = groupedSpecifierNumber1;
+var u2: number = groupedSpecifierNumber2;
+var u3: string = groupedSpecifierNumber1;// Error: number ~> string
+var u4: string = groupedSpecifierNumber2;// Error: number ~> string
+import { givesANumber } from \"ES6_Named1\";
+var v1: number = givesANumber();
+var v2: string = givesANumber();// Error: number ~> string
+import { NumberGenerator } from \"ES6_Named1\";
+var w1: number = new NumberGenerator().givesANumber();
+var w2: string = new NumberGenerator().givesANumber();// Error: number ~> string
+import { varDeclNumber1, varDeclNumber2 } from \"ES6_Named1\";
+var x1: number = varDeclNumber1;
+var x2: number = varDeclNumber2;
+var x3: string = varDeclNumber1;// Error: number ~> string
+var x4: string = varDeclNumber2;// Error: number ~> string
+import { destructuredObjNumber } from \"ES6_Named1\";
+var y1: number = destructuredObjNumber;
+var y2: string = destructuredObjNumber;// Error: number ~> string
+import { destructuredArrNumber } from \"ES6_Named1\";
+var z1: number = destructuredArrNumber;
+var z2: string = destructuredArrNumber;// Error: number ~> string
+import { numberValue1 as numberValue4 } from \"ES6_ExportFrom_Intermediary1\";
+var aa1: number = numberValue4;
+var aa2: string = numberValue4;// Error: number ~> string
+import { numberValue2_renamed } from \"ES6_ExportFrom_Intermediary1\";
+var ab1: number = numberValue2_renamed;
+var ab2: string = numberValue2_renamed;// Error: number ~> string
+import { numberValue1 as numberValue5 } from \"ES6_ExportAllFrom_Intermediary1\";
+var ac1: number = numberValue5;
+var ac2: string = numberValue5;// Error: number ~> string
+///////////////////////////////////
+// == ES6 Default -> CommonJS == //
+///////////////////////////////////
+require(
+  \"ES6_Default_AnonFunction2\"
+).doesntExist;// Error: \'doesntExist\' isn\'t an export
+var ES6_Def_AnonFunc2 = require(\"ES6_Default_AnonFunction2\").default;
+var ad1: number = ES6_Def_AnonFunc2();
+var ad2: string = ES6_Def_AnonFunc2();// Error: number ~> string
+var ES6_Def_NamedFunc2 = require(\"ES6_Default_NamedFunction2\").default;
+var ae1: number = ES6_Def_NamedFunc2();
+var ae2: string = ES6_Def_NamedFunc2();// Error: number ~> string
+var ES6_Def_AnonClass2 = require(\"ES6_Default_AnonClass2\").default;
+var af1: number = new ES6_Def_AnonClass2().givesANum();
+var af2: string = new ES6_Def_AnonClass2().givesANum();// Error: number ~> string
+var ES6_Def_NamedClass2 = require(\"ES6_Default_NamedClass2\").default;
+var ag1: number = new ES6_Def_NamedClass2().givesANum();
+var ag2: string = new ES6_Def_NamedClass2().givesANum();// Error: number ~> string
+/////////////////////////////////
+// == ES6 Named -> CommonJS == //
+/////////////////////////////////
+var specifierNumber4 = require(\"ES6_Named2\").specifierNumber4;
+var ah1: number = specifierNumber4;
+var ah2: string = specifierNumber4;// Error: number ~> string
+var specifierNumber5Renamed = require(\"ES6_Named2\").specifierNumber5Renamed;
+var ai1: number = specifierNumber5Renamed;
+var ai2: string = specifierNumber5Renamed;// Error: number ~> string
+var groupedSpecifierNumber3 = require(\"ES6_Named2\").groupedSpecifierNumber3;
+var groupedSpecifierNumber4 = require(\"ES6_Named2\").groupedSpecifierNumber4;
+var aj1: number = groupedSpecifierNumber3;
+var aj2: number = groupedSpecifierNumber4;
+var aj3: string = groupedSpecifierNumber3;// Error: number ~> string
+var aj4: string = groupedSpecifierNumber4;// Error: number ~> string
+var givesANumber2 = require(\"ES6_Named2\").givesANumber2;
+var ak1: number = givesANumber2();
+var ak2: string = givesANumber2();// Error: number ~> string
+var NumberGenerator2 = require(\"ES6_Named2\").NumberGenerator2;
+var al1: number = new NumberGenerator2().givesANumber();
+var al2: string = new NumberGenerator2().givesANumber();// Error: number ~> string
+var varDeclNumber3 = require(\"ES6_Named2\").varDeclNumber3;
+var varDeclNumber4 = require(\"ES6_Named2\").varDeclNumber4;
+var am1: number = varDeclNumber3;
+var am2: number = varDeclNumber4;
+var am3: string = varDeclNumber3;// Error: number ~> string
+var am4: string = varDeclNumber4;// Error: number ~> string
+var destructuredObjNumber2 = require(\"ES6_Named2\").destructuredObjNumber2;
+var an1: number = destructuredObjNumber2;
+var an2: string = destructuredObjNumber2;// Error: number ~> string
+var destructuredArrNumber2 = require(\"ES6_Named2\").destructuredArrNumber2;
+var ao1: number = destructuredArrNumber2;
+var ao2: string = destructuredArrNumber2;// Error: number ~> string
+var numberValue6 = require(\"ES6_ExportFrom_Intermediary2\").numberValue1;
+var ap1: number = numberValue6;
+var ap2: string = numberValue6;// Error: number ~> string
+var numberValue2_renamed2 = require(
+  \"ES6_ExportFrom_Intermediary2\"
+).numberValue2_renamed2;
+var aq1: number = numberValue2_renamed2;
+var aq2: string = numberValue2_renamed2;// Error: number ~> string
+var numberValue7 = require(\"ES6_ExportAllFrom_Intermediary2\").numberValue2;
+var ar1: number = numberValue7;
+var ar2: string = numberValue7;// Error: number ~> string
+////////////////////////////////////////////////////////
+// == ES6 Default+Named -> ES6 import Default+Named== //
+////////////////////////////////////////////////////////
+import defaultNum, { str as namedStr } from \"./ES6_DefaultAndNamed\";
+var as1: number = defaultNum;
+var as2: string = defaultNum;// Error: number ~> string
+var as3: string = namedStr;
+var as4: number = namedStr;// Error: string ~> number
+////////////////////////////////////////
+// == Side-effect only ES6 imports == //
+////////////////////////////////////////
+import \"./SideEffects\";
+//////////////////////////////////////////////
+// == Suggest export name on likely typo == //
+//////////////////////////////////////////////
+import specifierNumber1 from \"ES6_Named1\";// Error: Did you mean \`import {specifierNumber1} from ...\`?
+import { specifierNumber } from \"ES6_Named1\";// Error: Did you mean \`specifierNumber1\`?
+///////////////////////////////////////////////////
+// == Multi \`export *\` should combine exports == //
+///////////////////////////////////////////////////
+import { numberValue1 as numberValue8, numberValue2 as numberValue9 } from \"./ES6_ExportAllFromMulti\";
+var at1: number = numberValue8;
+var at2: string = numberValue8;// Error: number ~> string
+var at3: number = numberValue9;
+var at4: string = numberValue9;// Error: number ~> string
+/////////////////////////////////////////////////////////////
+// == Vanilla \`import\` cannot import a type-only export == //
+/////////////////////////////////////////////////////////////
+import { typeAlias } from \"./ExportType\";// Error: Cannot vanilla-import a type alias!
+
+"
+`;
+
+exports[`test test_imports_are_frozen.js 1`] = `
+"/* @flow */
+
+//
+// Imports
+//
+
+// CommonJS module
+import * as DefaultA from \"A\";
+DefaultA.numberValue1 = 123; // Error: DefaultA is frozen
+
+// ES6 module
+import * as ES6_Named1 from \"ES6_Named1\";
+ES6_Named1.varDeclNumber1 = 123; // Error: ES6_Named1 is frozen
+
+// CommonJS module that clobbers module.exports
+import * as CommonJS_Star from \"CommonJS_Clobbering_Lit\";
+CommonJS_Star.numberValue1 = 123; // Error: frozen
+CommonJS_Star.default.numberValue1 = 123; // ok
+
+import CommonJS_Clobbering_Lit from \"CommonJS_Clobbering_Lit\";
+CommonJS_Clobbering_Lit.numberValue1 = 123; // ok
+
+// CommonJS module that clobbers module.exports with a frozen object
+import * as CommonJS_Frozen_Star from \"CommonJS_Clobbering_Frozen\";
+CommonJS_Frozen_Star.numberValue1 = 123; // Error: frozen
+CommonJS_Frozen_Star.default.numberValue1 = 123; // Error: frozen
+
+import CommonJS_Clobbering_Frozen from \"CommonJS_Clobbering_Frozen\";
+CommonJS_Clobbering_Frozen.numberValue1 = 123; // Error: exports are frozen
+
+
+//
+// Requires
+//
+
+function testRequires() {
+  // CommonJS module
+  var DefaultA = require(\"A\");
+  DefaultA.numberValue1 = 123; // ok, not frozen by default
+
+  // ES6 module
+  var ES6_Named1 = require(\"ES6_Named1\");
+  ES6_Named1.numberValue = 123; // error, es6 exports are frozen
+
+  // CommonJS module that clobbers module.exports
+  var CommonJS_Star = require(\"CommonJS_Clobbering_Lit\");
+  CommonJS_Star.numberValue1 = 123; // ok, not frozen by default
+
+  // CommonJS module that clobbers module.exports with a frozen object
+  var CommonJS_Frozen_Star = require(\"CommonJS_Clobbering_Frozen\");
+  CommonJS_Frozen_Star.numberValue1 = 123; // Error: frozen
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+//
+// Imports
+//
+// CommonJS module
+import * as DefaultA from \"A\";
+DefaultA.numberValue1 = 123;// Error: DefaultA is frozen
+// ES6 module
+import * as ES6_Named1 from \"ES6_Named1\";
+ES6_Named1.varDeclNumber1 = 123;// Error: ES6_Named1 is frozen
+// CommonJS module that clobbers module.exports
+import * as CommonJS_Star from \"CommonJS_Clobbering_Lit\";
+CommonJS_Star.numberValue1 = 123;// Error: frozen
+CommonJS_Star.default.numberValue1 = 123;// ok
+import CommonJS_Clobbering_Lit from \"CommonJS_Clobbering_Lit\";
+CommonJS_Clobbering_Lit.numberValue1 = 123;// ok
+// CommonJS module that clobbers module.exports with a frozen object
+import * as CommonJS_Frozen_Star from \"CommonJS_Clobbering_Frozen\";
+CommonJS_Frozen_Star.numberValue1 = 123;// Error: frozen
+CommonJS_Frozen_Star.default.numberValue1 = 123;// Error: frozen
+import CommonJS_Clobbering_Frozen from \"CommonJS_Clobbering_Frozen\";
+CommonJS_Clobbering_Frozen.numberValue1 = 123;// Error: exports are frozen
+//
+// Requires
+//
+function testRequires() {
+  // CommonJS module
+  var DefaultA = require(\"A\");
+  DefaultA.numberValue1 = 123;// ok, not frozen by default
+  // ES6 module
+  var ES6_Named1 = require(\"ES6_Named1\");
+  ES6_Named1.numberValue = 123;// error, es6 exports are frozen
+  // CommonJS module that clobbers module.exports
+  var CommonJS_Star = require(\"CommonJS_Clobbering_Lit\");
+  CommonJS_Star.numberValue1 = 123;// ok, not frozen by default
+  // CommonJS module that clobbers module.exports with a frozen object
+  var CommonJS_Frozen_Star = require(\"CommonJS_Clobbering_Frozen\");
+  CommonJS_Frozen_Star.numberValue1 = 123;// Error: frozen
+}
+
+"
+`;
diff --git a/tests/es6modules/es6modules.js b/tests/es6modules/es6modules.js
new file mode 100644
index 000000000000..a43f876aa601
--- /dev/null
+++ b/tests/es6modules/es6modules.js
@@ -0,0 +1,296 @@
+/* @flow */
+
+// ===================== //
+// == Path Resolution == //
+// ===================== //
+
+// @providesModule
+import * as DefaultA from "A";
+var a1: number = DefaultA.numberValue1;
+var a2: string = DefaultA.numberValue1; // Error: number ~> string
+
+// File path
+import * as DefaultB from "./B";
+var b1: number = DefaultB.numberValue;
+var b2: string = DefaultB.numberValue; // Error: number ~> string
+
+// C.js exists, but not as a providesModule
+import DefaultC from "C"; // Error: No such module
+
+// @providesModule D exists, but not as a filename
+import DefaultD from "./D"; // Error: No such module
+
+// ================================================ //
+// == CommonJS Clobbering Literal Exports -> ES6 == //
+// ================================================ //
+
+import {doesntExist1} from "CommonJS_Clobbering_Lit"; // Error: Not an exported binding
+
+import {numberValue1} from "CommonJS_Clobbering_Lit";
+var c1: number = numberValue1;
+var c2: string = numberValue1; // Error: number ~> string
+
+import {numberValue2 as numVal1} from "CommonJS_Clobbering_Lit";
+var d1: number = numVal1;
+var d2: string = numVal1; // Error: number ~> string
+
+import CJS_Clobb_Lit from "CommonJS_Clobbering_Lit";
+var e1: number = CJS_Clobb_Lit.numberValue3;
+var e2: string = CJS_Clobb_Lit.numberValue3; // Error: number ~> string
+CJS_Clobb_Lit.doesntExist; // Error: doesntExist isn't a property
+
+import * as CJS_Clobb_Lit_NS from "CommonJS_Clobbering_Lit";
+var f1: number = CJS_Clobb_Lit_NS.numberValue4;
+var f2: number = CJS_Clobb_Lit_NS.default.numberValue4;
+CJS_Clobb_Lit_NS.default.default; // Error: No 'default' property on the exported obj
+var f3: string = CJS_Clobb_Lit_NS.numberValue4; // Error: number ~> string
+var f4: string = CJS_Clobb_Lit_NS.default.numberValue5; // Error: number ~> string
+
+// ============================================== //
+// == CommonJS Clobbering Class Exports -> ES6 == //
+// ============================================== //
+
+import {doesntExist2} from "CommonJS_Clobbering_Class"; // Error: Not an exported binding
+
+// The following import should error because class statics are not turned into
+// named exports for now. This avoids complexities with polymorphic static
+// members (where the polymophism is defined on the class itself rather than the
+// method).
+import {staticNumber1, baseProp, childProp} from "CommonJS_Clobbering_Class"; // Error
+
+import CJS_Clobb_Class from "CommonJS_Clobbering_Class";
+new CJS_Clobb_Class();
+new CJS_Clobb_Class().doesntExist; // Error: Class has no `doesntExist` property
+var h1: number = CJS_Clobb_Class.staticNumber2();
+var h2: string = CJS_Clobb_Class.staticNumber2(); // Error: number ~> string
+var h3: number = new CJS_Clobb_Class().instNumber1();
+var h4: string = new CJS_Clobb_Class().instNumber1(); // Error: number ~> string
+
+import * as CJS_Clobb_Class_NS from "CommonJS_Clobbering_Class";
+new CJS_Clobb_Class_NS(); // Error: Namespace object isn't constructable
+var i1: number = CJS_Clobb_Class_NS.staticNumber3(); // Error: Class statics not copied to Namespace object
+var i2: number = new CJS_Clobb_Class_NS.default().instNumber2();
+var i3: string = new CJS_Clobb_Class_NS.default().instNumber2(); // Error: number ~> string
+
+// =================================== //
+// == CommonJS Named Exports -> ES6 == //
+// =================================== //
+
+import {doesntExist3} from "CommonJS_Named"; // Error: Not an exported binding
+
+import {numberValue2} from "CommonJS_Named";
+var j1: number = numberValue2;
+var j2: string = numberValue2; // Error: number ~> string
+
+import {numberValue3 as numVal3} from "CommonJS_Named";
+var k1: number = numVal3;
+var k2: string = numVal3; // Error: number ~> string
+
+import * as CJS_Named from "CommonJS_Named";
+var l1: number = CJS_Named.numberValue1;
+var l2: string = CJS_Named.numberValue1; // Error: number ~> string
+CJS_Named.doesntExist; // Error: doesntExist isn't a property
+
+import * as CJS_Named_NS from "CommonJS_Named";
+var m1: number = CJS_Named_NS.numberValue4;
+var m2: string = CJS_Named_NS.default.numberValue4; // Error: CommonJS_Named has no default export
+var m3: string = CJS_Named_NS.numberValue4; // Error: number ~> string
+
+//////////////////////////////
+// == ES6 Default -> ES6 == //
+//////////////////////////////
+
+import {doesntExist4} from "ES6_Default_AnonFunction1"; // Error: Not an exported binding
+
+import ES6_Def_AnonFunc1 from "ES6_Default_AnonFunction1";
+var n1: number = ES6_Def_AnonFunc1();
+var n2: string = ES6_Def_AnonFunc1(); // Error: number ~> string
+
+import ES6_Def_NamedFunc1 from "ES6_Default_NamedFunction1";
+var o1: number = ES6_Def_NamedFunc1();
+var o2: string = ES6_Def_NamedFunc1(); // Error: number ~> string
+
+import ES6_Def_AnonClass1 from "ES6_Default_AnonClass1";
+var p1: number = new ES6_Def_AnonClass1().givesANum();
+var p2: string = new ES6_Def_AnonClass1().givesANum(); // Error: number ~> string
+
+import ES6_Def_NamedClass1 from "ES6_Default_NamedClass1";
+var q1: number = new ES6_Def_NamedClass1().givesANum();
+var q2: string = new ES6_Def_NamedClass1().givesANum(); // Error: number ~> string
+
+////////////////////////////
+// == ES6 Named -> ES6 == //
+////////////////////////////
+
+import doesntExist5 from "ES6_Named1"; // Error: Not an exported binding
+
+import {specifierNumber1 as specifierNumber1_1} from "ES6_Named1";
+var r1: number = specifierNumber1_1;
+var r2: string = specifierNumber1_1; // Error: number ~> string
+
+import {specifierNumber2Renamed} from "ES6_Named1";
+var s1: number = specifierNumber2Renamed;
+var s2: string = specifierNumber2Renamed; // Error: number ~> string
+
+import {specifierNumber3 as specifierNumber3Renamed} from "ES6_Named1";
+var t1: number = specifierNumber3Renamed;
+var t2: string = specifierNumber3Renamed; // Error: number ~> string
+
+import {groupedSpecifierNumber1, groupedSpecifierNumber2} from "ES6_Named1";
+var u1: number = groupedSpecifierNumber1;
+var u2: number = groupedSpecifierNumber2;
+var u3: string = groupedSpecifierNumber1; // Error: number ~> string
+var u4: string = groupedSpecifierNumber2; // Error: number ~> string
+
+import {givesANumber} from "ES6_Named1";
+var v1: number = givesANumber();
+var v2: string = givesANumber(); // Error: number ~> string
+
+import {NumberGenerator} from "ES6_Named1";
+var w1: number = new NumberGenerator().givesANumber();
+var w2: string = new NumberGenerator().givesANumber(); // Error: number ~> string
+
+import {varDeclNumber1, varDeclNumber2} from "ES6_Named1";
+var x1: number = varDeclNumber1;
+var x2: number = varDeclNumber2;
+var x3: string = varDeclNumber1; // Error: number ~> string
+var x4: string = varDeclNumber2; // Error: number ~> string
+
+import {destructuredObjNumber} from "ES6_Named1";
+var y1: number = destructuredObjNumber;
+var y2: string = destructuredObjNumber; // Error: number ~> string
+
+import {destructuredArrNumber} from "ES6_Named1";
+var z1: number = destructuredArrNumber;
+var z2: string = destructuredArrNumber; // Error: number ~> string
+
+import {numberValue1 as numberValue4} from "ES6_ExportFrom_Intermediary1";
+var aa1: number = numberValue4;
+var aa2: string = numberValue4; // Error: number ~> string
+
+import {numberValue2_renamed} from "ES6_ExportFrom_Intermediary1";
+var ab1: number = numberValue2_renamed;
+var ab2: string = numberValue2_renamed; // Error: number ~> string
+
+import {numberValue1 as numberValue5} from "ES6_ExportAllFrom_Intermediary1";
+var ac1: number = numberValue5;
+var ac2: string = numberValue5; // Error: number ~> string
+
+///////////////////////////////////
+// == ES6 Default -> CommonJS == //
+///////////////////////////////////
+
+require('ES6_Default_AnonFunction2').doesntExist; // Error: 'doesntExist' isn't an export
+
+var ES6_Def_AnonFunc2 = require("ES6_Default_AnonFunction2").default;
+var ad1: number = ES6_Def_AnonFunc2();
+var ad2: string = ES6_Def_AnonFunc2(); // Error: number ~> string
+
+var ES6_Def_NamedFunc2 = require("ES6_Default_NamedFunction2").default;
+var ae1: number = ES6_Def_NamedFunc2();
+var ae2: string = ES6_Def_NamedFunc2(); // Error: number ~> string
+
+var ES6_Def_AnonClass2 = require("ES6_Default_AnonClass2").default;
+var af1: number = new ES6_Def_AnonClass2().givesANum();
+var af2: string = new ES6_Def_AnonClass2().givesANum(); // Error: number ~> string
+
+var ES6_Def_NamedClass2 = require("ES6_Default_NamedClass2").default;
+var ag1: number = new ES6_Def_NamedClass2().givesANum();
+var ag2: string = new ES6_Def_NamedClass2().givesANum(); // Error: number ~> string
+
+/////////////////////////////////
+// == ES6 Named -> CommonJS == //
+/////////////////////////////////
+
+var specifierNumber4 = require("ES6_Named2").specifierNumber4;
+var ah1: number = specifierNumber4;
+var ah2: string = specifierNumber4; // Error: number ~> string
+
+var specifierNumber5Renamed = require("ES6_Named2").specifierNumber5Renamed;
+var ai1: number = specifierNumber5Renamed;
+var ai2: string = specifierNumber5Renamed; // Error: number ~> string
+
+var groupedSpecifierNumber3 = require("ES6_Named2").groupedSpecifierNumber3;
+var groupedSpecifierNumber4 = require("ES6_Named2").groupedSpecifierNumber4;
+var aj1: number = groupedSpecifierNumber3;
+var aj2: number = groupedSpecifierNumber4;
+var aj3: string = groupedSpecifierNumber3; // Error: number ~> string
+var aj4: string = groupedSpecifierNumber4; // Error: number ~> string
+
+var givesANumber2 = require("ES6_Named2").givesANumber2;
+var ak1: number = givesANumber2();
+var ak2: string = givesANumber2(); // Error: number ~> string
+
+var NumberGenerator2 = require("ES6_Named2").NumberGenerator2;
+var al1: number = new NumberGenerator2().givesANumber();
+var al2: string = new NumberGenerator2().givesANumber(); // Error: number ~> string
+
+var varDeclNumber3 = require("ES6_Named2").varDeclNumber3;
+var varDeclNumber4 = require("ES6_Named2").varDeclNumber4;
+var am1: number = varDeclNumber3;
+var am2: number = varDeclNumber4;
+var am3: string = varDeclNumber3; // Error: number ~> string
+var am4: string = varDeclNumber4; // Error: number ~> string
+
+var destructuredObjNumber2 = require("ES6_Named2").destructuredObjNumber2;
+var an1: number = destructuredObjNumber2;
+var an2: string = destructuredObjNumber2; // Error: number ~> string
+
+var destructuredArrNumber2 = require("ES6_Named2").destructuredArrNumber2;
+var ao1: number = destructuredArrNumber2;
+var ao2: string = destructuredArrNumber2; // Error: number ~> string
+
+var numberValue6 = require("ES6_ExportFrom_Intermediary2").numberValue1;
+var ap1: number = numberValue6;
+var ap2: string = numberValue6; // Error: number ~> string
+
+var numberValue2_renamed2 = require("ES6_ExportFrom_Intermediary2").numberValue2_renamed2;
+var aq1: number = numberValue2_renamed2;
+var aq2: string = numberValue2_renamed2; // Error: number ~> string
+
+var numberValue7 = require("ES6_ExportAllFrom_Intermediary2").numberValue2;
+var ar1: number = numberValue7;
+var ar2: string = numberValue7; // Error: number ~> string
+
+////////////////////////////////////////////////////////
+// == ES6 Default+Named -> ES6 import Default+Named== //
+////////////////////////////////////////////////////////
+
+import defaultNum, {str as namedStr} from "./ES6_DefaultAndNamed";
+
+var as1: number = defaultNum;
+var as2: string = defaultNum; // Error: number ~> string
+
+var as3: string = namedStr;
+var as4: number = namedStr; // Error: string ~> number
+
+////////////////////////////////////////
+// == Side-effect only ES6 imports == //
+////////////////////////////////////////
+
+import "./SideEffects";
+
+//////////////////////////////////////////////
+// == Suggest export name on likely typo == //
+//////////////////////////////////////////////
+import specifierNumber1 from "ES6_Named1"; // Error: Did you mean `import {specifierNumber1} from ...`?
+import {specifierNumber} from "ES6_Named1"; // Error: Did you mean `specifierNumber1`?
+
+///////////////////////////////////////////////////
+// == Multi `export *` should combine exports == //
+///////////////////////////////////////////////////
+import {
+  numberValue1 as numberValue8,
+  numberValue2 as numberValue9
+} from "./ES6_ExportAllFromMulti";
+
+var at1: number = numberValue8;
+var at2: string = numberValue8; // Error: number ~> string
+
+var at3: number = numberValue9;
+var at4: string = numberValue9; // Error: number ~> string
+
+/////////////////////////////////////////////////////////////
+// == Vanilla `import` cannot import a type-only export == //
+/////////////////////////////////////////////////////////////
+import {typeAlias} from "./ExportType"; // Error: Cannot vanilla-import a type alias!
diff --git a/tests/es6modules/jsfmt.spec.js b/tests/es6modules/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/es6modules/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/es6modules/test_imports_are_frozen.js b/tests/es6modules/test_imports_are_frozen.js
new file mode 100644
index 000000000000..7fd1e51490d5
--- /dev/null
+++ b/tests/es6modules/test_imports_are_frozen.js
@@ -0,0 +1,52 @@
+/* @flow */
+
+//
+// Imports
+//
+
+// CommonJS module
+import * as DefaultA from "A";
+DefaultA.numberValue1 = 123; // Error: DefaultA is frozen
+
+// ES6 module
+import * as ES6_Named1 from "ES6_Named1";
+ES6_Named1.varDeclNumber1 = 123; // Error: ES6_Named1 is frozen
+
+// CommonJS module that clobbers module.exports
+import * as CommonJS_Star from "CommonJS_Clobbering_Lit";
+CommonJS_Star.numberValue1 = 123; // Error: frozen
+CommonJS_Star.default.numberValue1 = 123; // ok
+
+import CommonJS_Clobbering_Lit from "CommonJS_Clobbering_Lit";
+CommonJS_Clobbering_Lit.numberValue1 = 123; // ok
+
+// CommonJS module that clobbers module.exports with a frozen object
+import * as CommonJS_Frozen_Star from "CommonJS_Clobbering_Frozen";
+CommonJS_Frozen_Star.numberValue1 = 123; // Error: frozen
+CommonJS_Frozen_Star.default.numberValue1 = 123; // Error: frozen
+
+import CommonJS_Clobbering_Frozen from "CommonJS_Clobbering_Frozen";
+CommonJS_Clobbering_Frozen.numberValue1 = 123; // Error: exports are frozen
+
+
+//
+// Requires
+//
+
+function testRequires() {
+  // CommonJS module
+  var DefaultA = require("A");
+  DefaultA.numberValue1 = 123; // ok, not frozen by default
+
+  // ES6 module
+  var ES6_Named1 = require("ES6_Named1");
+  ES6_Named1.numberValue = 123; // error, es6 exports are frozen
+
+  // CommonJS module that clobbers module.exports
+  var CommonJS_Star = require("CommonJS_Clobbering_Lit");
+  CommonJS_Star.numberValue1 = 123; // ok, not frozen by default
+
+  // CommonJS module that clobbers module.exports with a frozen object
+  var CommonJS_Frozen_Star = require("CommonJS_Clobbering_Frozen");
+  CommonJS_Frozen_Star.numberValue1 = 123; // Error: frozen
+}
diff --git a/tests/es_declare_module/__snapshots__/jsfmt.spec.js.snap b/tests/es_declare_module/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..46041e8518a8
--- /dev/null
+++ b/tests/es_declare_module/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,80 @@
+exports[`test es_declare_module.js 1`] = `
+"// @flow
+
+import {num1, str1} from "CJS_Named";
+import CJS_Named from "CJS_Named";
+(num1: number);
+(num1: string); // Error: number ~> string
+(str1: string);
+(str1: number); // Error: string ~> number
+(CJS_Named: {num1: number, str1: string});
+(CJS_Named: number); // Error: Module ~> number
+
+import {num2} from "CJS_Clobbered"; // Error: No such export!
+import {numExport} from "CJS_Clobbered";
+(numExport: number);
+(numExport: string); // Error: number ~> string
+import type {numType} from "CJS_Clobbered";
+(42: numType);
+('asdf': numType); // Error: string ~> number
+
+import {strHidden} from "ES"; // Error: No such export!
+import {str3} from "ES";
+(str3: string);
+(str3: number); // Error: string ~> number
+
+import {num3} from "ES";
+(num3: number);
+(num3: string); // Error: number ~> string
+
+import {C} from "ES";
+import type {C as CType} from "ES";
+(new C(): C);
+(42: C); // Error: number ~> C
+(new C(): CType);
+(42: CType); // Error: number ~> CType
+
+import {T} from "ES"; // Error: T is a type import, not a value
+import type {T as T2} from "ES";
+(42: T2);
+('asdf': T2); // Error: string ~> number
+
+import {exports as nope} from "ES"; // Error: Not an export
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { num1, str1 } from "CJS_Named";
+import CJS_Named from "CJS_Named";
+(num1: number);
+(num1: string);// Error: number ~> string
+(str1: string);
+(str1: number);// Error: string ~> number
+(CJS_Named: { num1: number, str1: string });
+(CJS_Named: number);// Error: Module ~> number
+import { num2 } from "CJS_Clobbered";// Error: No such export!
+import { numExport } from "CJS_Clobbered";
+(numExport: number);
+(numExport: string);// Error: number ~> string
+import type { numType } from "CJS_Clobbered";
+(42: numType);
+("asdf": numType);// Error: string ~> number
+import { strHidden } from "ES";// Error: No such export!
+import { str3 } from "ES";
+(str3: string);
+(str3: number);// Error: string ~> number
+import { num3 } from "ES";
+(num3: number);
+(num3: string);// Error: number ~> string
+import { C } from "ES";
+import type { C as CType } from "ES";
+(new C(): C);
+(42: C);// Error: number ~> C
+(new C(): CType);
+(42: CType);// Error: number ~> CType
+import { T } from "ES";// Error: T is a type import, not a value
+import type { T as T2 } from "ES";
+(42: T2);
+("asdf": T2);// Error: string ~> number
+import { exports as nope } from "ES";// Error: Not an export
+
+"
+`;
diff --git a/tests/es_declare_module/es_declare_module.js b/tests/es_declare_module/es_declare_module.js
new file mode 100644
index 000000000000..6395bceca7d5
--- /dev/null
+++ b/tests/es_declare_module/es_declare_module.js
@@ -0,0 +1,41 @@
+// @flow
+
+import {num1, str1} from "CJS_Named";
+import CJS_Named from "CJS_Named";
+(num1: number);
+(num1: string); // Error: number ~> string
+(str1: string);
+(str1: number); // Error: string ~> number
+(CJS_Named: {num1: number, str1: string});
+(CJS_Named: number); // Error: Module ~> number
+
+import {num2} from "CJS_Clobbered"; // Error: No such export!
+import {numExport} from "CJS_Clobbered";
+(numExport: number);
+(numExport: string); // Error: number ~> string
+import type {numType} from "CJS_Clobbered";
+(42: numType);
+('asdf': numType); // Error: string ~> number
+
+import {strHidden} from "ES"; // Error: No such export!
+import {str3} from "ES";
+(str3: string);
+(str3: number); // Error: string ~> number
+
+import {num3} from "ES";
+(num3: number);
+(num3: string); // Error: number ~> string
+
+import {C} from "ES";
+import type {C as CType} from "ES";
+(new C(): C);
+(42: C); // Error: number ~> C
+(new C(): CType);
+(42: CType); // Error: number ~> CType
+
+import {T} from "ES"; // Error: T is a type import, not a value
+import type {T as T2} from "ES";
+(42: T2);
+('asdf': T2); // Error: string ~> number
+
+import {exports as nope} from "ES"; // Error: Not an export
diff --git a/tests/es_declare_module/flow-typed/__snapshots__/jsfmt.spec.js.snap b/tests/es_declare_module/flow-typed/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4d0c81b089be
--- /dev/null
+++ b/tests/es_declare_module/flow-typed/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,40 @@
+exports[`test declares.js 1`] = `
+"declare module \"CJS_Named\" {
+  declare var num1: number;
+  declare var str1: string;
+}
+
+declare module \"CJS_Clobbered\" {
+  declare var num2: number;
+  declare type numType = number;
+  declare var exports: {
+    numExport: number,
+  };
+}
+
+declare module \"ES\" {
+  declare var strHidden: string;
+  declare export {strHidden as str3};
+  declare export var num3: number;
+  declare export class C {}
+  declare export type T = number;
+  declare var exports: number;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (16:10)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4490:10)
+    at Parser.pp$7.flowParseDeclareModule (/node_modules/babylon/lib/index.js:4518:20)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4483:19)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
diff --git a/tests/es_declare_module/flow-typed/declares.js b/tests/es_declare_module/flow-typed/declares.js
new file mode 100644
index 000000000000..50198afb76c9
--- /dev/null
+++ b/tests/es_declare_module/flow-typed/declares.js
@@ -0,0 +1,21 @@
+declare module "CJS_Named" {
+  declare var num1: number;
+  declare var str1: string;
+}
+
+declare module "CJS_Clobbered" {
+  declare var num2: number;
+  declare type numType = number;
+  declare var exports: {
+    numExport: number,
+  };
+}
+
+declare module "ES" {
+  declare var strHidden: string;
+  declare export {strHidden as str3};
+  declare export var num3: number;
+  declare export class C {}
+  declare export type T = number;
+  declare var exports: number;
+}
diff --git a/tests/es_declare_module/flow-typed/jsfmt.spec.js b/tests/es_declare_module/flow-typed/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/es_declare_module/flow-typed/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/es_declare_module/jsfmt.spec.js b/tests/es_declare_module/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/es_declare_module/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_class_instance_fields.ignore/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_class_instance_fields.ignore/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1f28115f0d5e
--- /dev/null
+++ b/tests/esproposal_class_instance_fields.ignore/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,20 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+class Foo {
+  annotationOnly: string;
+  initOnly = 'asdf'
+  initWithAnnotation: string = 'asdf';
+  [computed]: string;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class Foo {
+  annotationOnly: string;
+  initOnly = "asdf";
+  initWithAnnotation: string = "asdf";
+  [computed]: string;
+}
+
+"
+`;
diff --git a/tests/esproposal_class_instance_fields.ignore/jsfmt.spec.js b/tests/esproposal_class_instance_fields.ignore/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_class_instance_fields.ignore/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_class_instance_fields.ignore/test.js b/tests/esproposal_class_instance_fields.ignore/test.js
new file mode 100644
index 000000000000..7525cf355c95
--- /dev/null
+++ b/tests/esproposal_class_instance_fields.ignore/test.js
@@ -0,0 +1,8 @@
+/* @flow */
+
+class Foo {
+  annotationOnly: string;
+  initOnly = 'asdf'
+  initWithAnnotation: string = 'asdf';
+  [computed]: string;
+}
diff --git a/tests/esproposal_class_instance_fields.warn/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_class_instance_fields.warn/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c2c53423e3e9
--- /dev/null
+++ b/tests/esproposal_class_instance_fields.warn/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+class Foo {
+  annotationOnly: string;
+  initOnly = 'asdf';
+  initWithAnnotation: string = 'asdf';
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class Foo {
+  annotationOnly: string;
+  initOnly = "asdf";
+  initWithAnnotation: string = "asdf";
+}
+
+"
+`;
diff --git a/tests/esproposal_class_instance_fields.warn/jsfmt.spec.js b/tests/esproposal_class_instance_fields.warn/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_class_instance_fields.warn/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_class_instance_fields.warn/test.js b/tests/esproposal_class_instance_fields.warn/test.js
new file mode 100644
index 000000000000..ac74ba3e8d7f
--- /dev/null
+++ b/tests/esproposal_class_instance_fields.warn/test.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+class Foo {
+  annotationOnly: string;
+  initOnly = 'asdf';
+  initWithAnnotation: string = 'asdf';
+}
diff --git a/tests/esproposal_class_static_fields.ignore/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_class_static_fields.ignore/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1ce10796ca4c
--- /dev/null
+++ b/tests/esproposal_class_static_fields.ignore/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+class Foo {
+  static annotationOnly: string;
+  static initOnly = 'asdf';
+  static initWithAnnotation: string = 'asdf';
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class Foo {
+  static annotationOnly: string;
+  static initOnly = "asdf";
+  static initWithAnnotation: string = "asdf";
+}
+
+"
+`;
diff --git a/tests/esproposal_class_static_fields.ignore/jsfmt.spec.js b/tests/esproposal_class_static_fields.ignore/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_class_static_fields.ignore/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_class_static_fields.ignore/test.js b/tests/esproposal_class_static_fields.ignore/test.js
new file mode 100644
index 000000000000..f47f1b642f4f
--- /dev/null
+++ b/tests/esproposal_class_static_fields.ignore/test.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+class Foo {
+  static annotationOnly: string;
+  static initOnly = 'asdf';
+  static initWithAnnotation: string = 'asdf';
+}
diff --git a/tests/esproposal_class_static_fields.warn/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_class_static_fields.warn/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1ce10796ca4c
--- /dev/null
+++ b/tests/esproposal_class_static_fields.warn/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+class Foo {
+  static annotationOnly: string;
+  static initOnly = 'asdf';
+  static initWithAnnotation: string = 'asdf';
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class Foo {
+  static annotationOnly: string;
+  static initOnly = "asdf";
+  static initWithAnnotation: string = "asdf";
+}
+
+"
+`;
diff --git a/tests/esproposal_class_static_fields.warn/jsfmt.spec.js b/tests/esproposal_class_static_fields.warn/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_class_static_fields.warn/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_class_static_fields.warn/test.js b/tests/esproposal_class_static_fields.warn/test.js
new file mode 100644
index 000000000000..f47f1b642f4f
--- /dev/null
+++ b/tests/esproposal_class_static_fields.warn/test.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+class Foo {
+  static annotationOnly: string;
+  static initOnly = 'asdf';
+  static initWithAnnotation: string = 'asdf';
+}
diff --git a/tests/esproposal_decorators.ignore/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_decorators.ignore/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bc24fea44557
--- /dev/null
+++ b/tests/esproposal_decorators.ignore/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,29 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+@decorator4
+class Foo {
+  @decorator1
+  method1() {}
+
+  @decorator2
+  @decorator3
+  method2() {}
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+@decorator4
+class Foo {
+  @decorator1
+  method1() {
+    
+  }
+  @decorator2
+  @decorator3
+  method2() {
+    
+  }
+}
+
+"
+`;
diff --git a/tests/esproposal_decorators.ignore/jsfmt.spec.js b/tests/esproposal_decorators.ignore/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_decorators.ignore/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_decorators.ignore/test.js b/tests/esproposal_decorators.ignore/test.js
new file mode 100644
index 000000000000..972036955184
--- /dev/null
+++ b/tests/esproposal_decorators.ignore/test.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+@decorator4
+class Foo {
+  @decorator1
+  method1() {}
+
+  @decorator2
+  @decorator3
+  method2() {}
+}
diff --git a/tests/esproposal_decorators.warn/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_decorators.warn/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bc24fea44557
--- /dev/null
+++ b/tests/esproposal_decorators.warn/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,29 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+@decorator4
+class Foo {
+  @decorator1
+  method1() {}
+
+  @decorator2
+  @decorator3
+  method2() {}
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+@decorator4
+class Foo {
+  @decorator1
+  method1() {
+    
+  }
+  @decorator2
+  @decorator3
+  method2() {
+    
+  }
+}
+
+"
+`;
diff --git a/tests/esproposal_decorators.warn/jsfmt.spec.js b/tests/esproposal_decorators.warn/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_decorators.warn/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_decorators.warn/test.js b/tests/esproposal_decorators.warn/test.js
new file mode 100644
index 000000000000..972036955184
--- /dev/null
+++ b/tests/esproposal_decorators.warn/test.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+@decorator4
+class Foo {
+  @decorator1
+  method1() {}
+
+  @decorator2
+  @decorator3
+  method2() {}
+}
diff --git a/tests/esproposal_export_star_as.enable/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_export_star_as.enable/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3b337efbf4b7
--- /dev/null
+++ b/tests/esproposal_export_star_as.enable/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,56 @@
+exports[`test dest.js 1`] = `
+"// @flow
+
+import {source} from \"./test\";
+
+var a: number = source.num;
+var b: string = source.num; // Error: num ~> string
+
+var c: string = source.str;
+var d: number = source.str; // Error: num ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { source } from \"./test\";
+var a: number = source.num;
+var b: string = source.num;// Error: num ~> string
+var c: string = source.str;
+var d: number = source.str;// Error: num ~> string
+
+"
+`;
+
+exports[`test source.js 1`] = `
+"// @flow
+
+export var str = \'asdf\';
+export var num = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export var str = \"asdf\";
+export var num = 42;
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"// @flow
+
+export * as source from \"./source\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
diff --git a/tests/esproposal_export_star_as.enable/dest.js b/tests/esproposal_export_star_as.enable/dest.js
new file mode 100644
index 000000000000..99f558d3bd43
--- /dev/null
+++ b/tests/esproposal_export_star_as.enable/dest.js
@@ -0,0 +1,9 @@
+// @flow
+
+import {source} from "./test";
+
+var a: number = source.num;
+var b: string = source.num; // Error: num ~> string
+
+var c: string = source.str;
+var d: number = source.str; // Error: num ~> string
diff --git a/tests/esproposal_export_star_as.enable/jsfmt.spec.js b/tests/esproposal_export_star_as.enable/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_export_star_as.enable/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_export_star_as.enable/source.js b/tests/esproposal_export_star_as.enable/source.js
new file mode 100644
index 000000000000..98d19df9fad7
--- /dev/null
+++ b/tests/esproposal_export_star_as.enable/source.js
@@ -0,0 +1,4 @@
+// @flow
+
+export var str = 'asdf';
+export var num = 42;
diff --git a/tests/esproposal_export_star_as.enable/test.js b/tests/esproposal_export_star_as.enable/test.js
new file mode 100644
index 000000000000..5fdc1272948f
--- /dev/null
+++ b/tests/esproposal_export_star_as.enable/test.js
@@ -0,0 +1,3 @@
+// @flow
+
+export * as source from "./source";
diff --git a/tests/esproposal_export_star_as.ignore/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_export_star_as.ignore/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5e14073ad095
--- /dev/null
+++ b/tests/esproposal_export_star_as.ignore/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,56 @@
+exports[`test dest.js 1`] = `
+"// @flow
+
+import {source} from \"./test\";
+
+var a: number = source.num;
+var b: string = source.num; // Error: num ~> string
+
+var c: string = source.str;
+var d: number = source.str; // Ignored error: num ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { source } from \"./test\";
+var a: number = source.num;
+var b: string = source.num;// Error: num ~> string
+var c: string = source.str;
+var d: number = source.str;// Ignored error: num ~> string
+
+"
+`;
+
+exports[`test source.js 1`] = `
+"// @flow
+
+export var str = \'asdf\';
+export var num = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export var str = \"asdf\";
+export var num = 42;
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"// @flow
+
+export * as source from \"./source\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
diff --git a/tests/esproposal_export_star_as.ignore/dest.js b/tests/esproposal_export_star_as.ignore/dest.js
new file mode 100644
index 000000000000..fa12f1ad78a9
--- /dev/null
+++ b/tests/esproposal_export_star_as.ignore/dest.js
@@ -0,0 +1,9 @@
+// @flow
+
+import {source} from "./test";
+
+var a: number = source.num;
+var b: string = source.num; // Error: num ~> string
+
+var c: string = source.str;
+var d: number = source.str; // Ignored error: num ~> string
diff --git a/tests/esproposal_export_star_as.ignore/jsfmt.spec.js b/tests/esproposal_export_star_as.ignore/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_export_star_as.ignore/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_export_star_as.ignore/source.js b/tests/esproposal_export_star_as.ignore/source.js
new file mode 100644
index 000000000000..98d19df9fad7
--- /dev/null
+++ b/tests/esproposal_export_star_as.ignore/source.js
@@ -0,0 +1,4 @@
+// @flow
+
+export var str = 'asdf';
+export var num = 42;
diff --git a/tests/esproposal_export_star_as.ignore/test.js b/tests/esproposal_export_star_as.ignore/test.js
new file mode 100644
index 000000000000..5fdc1272948f
--- /dev/null
+++ b/tests/esproposal_export_star_as.ignore/test.js
@@ -0,0 +1,3 @@
+// @flow
+
+export * as source from "./source";
diff --git a/tests/esproposal_export_star_as.warn/__snapshots__/jsfmt.spec.js.snap b/tests/esproposal_export_star_as.warn/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9fc286f9e3a6
--- /dev/null
+++ b/tests/esproposal_export_star_as.warn/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+export * as foo from \"./test\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
diff --git a/tests/esproposal_export_star_as.warn/jsfmt.spec.js b/tests/esproposal_export_star_as.warn/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/esproposal_export_star_as.warn/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/esproposal_export_star_as.warn/test.js b/tests/esproposal_export_star_as.warn/test.js
new file mode 100644
index 000000000000..ee71a9b8482e
--- /dev/null
+++ b/tests/esproposal_export_star_as.warn/test.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+export * as foo from "./test";
diff --git a/tests/export_default/P.js b/tests/export_default/P.js
new file mode 100644
index 000000000000..a0181c306670
--- /dev/null
+++ b/tests/export_default/P.js
@@ -0,0 +1 @@
+module.exports = require('M');
diff --git a/tests/export_default/__snapshots__/jsfmt.spec.js.snap b/tests/export_default/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..74c813571c86
--- /dev/null
+++ b/tests/export_default/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test P.js 1`] = `
+"module.exports = require('M');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = require("M");
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"var M = require('M');
+var N = require('N');
+N.x = M(N.x);
+var P = require('./P'); // implementation of P redirects to module M
+N.y = P(N.y);
+var Q = require('Q'); // declaration of Q redirects to module M
+N.z = Q(N.z);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var M = require("M");
+var N = require("N");
+N.x = M(N.x);
+var P = require("./P");// implementation of P redirects to module M
+N.y = P(N.y);
+var Q = require("Q");// declaration of Q redirects to module M
+N.z = Q(N.z);
+
+"
+`;
diff --git a/tests/export_default/jsfmt.spec.js b/tests/export_default/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/export_default/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/export_default/lib/__snapshots__/jsfmt.spec.js.snap b/tests/export_default/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c474b386925f
--- /dev/null
+++ b/tests/export_default/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,30 @@
+exports[`test lib.js 1`] = `
+"declare module M {
+    declare function exports(x:string): string;
+}
+declare module N {
+    declare var x: number;
+    declare var y: number;
+    declare var z: number;
+}
+declare module Q {
+    declare var exports: $Exports<\'M\'>;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/export_default/lib/jsfmt.spec.js b/tests/export_default/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/export_default/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/export_default/lib/lib.js b/tests/export_default/lib/lib.js
new file mode 100644
index 000000000000..b2d466ba1831
--- /dev/null
+++ b/tests/export_default/lib/lib.js
@@ -0,0 +1,11 @@
+declare module M {
+    declare function exports(x:string): string;
+}
+declare module N {
+    declare var x: number;
+    declare var y: number;
+    declare var z: number;
+}
+declare module Q {
+    declare var exports: $Exports<'M'>;
+}
diff --git a/tests/export_default/test.js b/tests/export_default/test.js
new file mode 100644
index 000000000000..be26514294ab
--- /dev/null
+++ b/tests/export_default/test.js
@@ -0,0 +1,7 @@
+var M = require('M');
+var N = require('N');
+N.x = M(N.x);
+var P = require('./P'); // implementation of P redirects to module M
+N.y = P(N.y);
+var Q = require('Q'); // declaration of Q redirects to module M
+N.z = Q(N.z);
diff --git a/tests/export_type/__snapshots__/jsfmt.spec.js.snap b/tests/export_type/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3e7a1e3fe947
--- /dev/null
+++ b/tests/export_type/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,141 @@
+exports[`test cjs_with_types.js 1`] = `
+"/* @flow */
+
+export type talias4 = number;
+export interface IFoo { prop: number };
+
+module.exports = {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at printExportDeclaration (/src/printer.js:1774:21)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
+
+exports[`test importer.js 1`] = `
+"/* @flow */
+
+import type {
+  inlinedType1,
+  standaloneType1,
+  talias1,
+  talias3,
+} from \"./types_only\";
+
+var a: inlinedType1 = 42;
+var b: inlinedType1 = \'asdf\'; // Error: string ~> number
+
+var c: standaloneType1 = 42;
+var d: standaloneType1 = \'asdf\'; // Error: string ~> number
+
+var e: talias1 = 42;
+var f: talias1 = \'asdf\'; // Error: string ~> number
+
+var g: talias3 = 42;
+var h: talias3 = \'asdf\'; // Error: string ~> number
+
+import type {talias4} from \"./cjs_with_types\";
+var i: talias4 = 42;
+var j: talias4 = \'asdf\'; // Error: string ~> number
+
+import {IFoo, IFoo2} from \"./types_only\";
+
+var k: IFoo = {prop: 42};
+var l: IFoo = {prop: \'asdf\'}; // Error: {prop:string} ~> {prop:number}
+
+var m: IFoo2 = {prop: \'asdf\'};
+var n: IFoo2 = {prop: 42}; // Error: {prop:number} ~> {prop:string}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+import type { inlinedType1, standaloneType1, talias1, talias3 } from \"./types_only\";
+var a: inlinedType1 = 42;
+var b: inlinedType1 = \"asdf\";// Error: string ~> number
+var c: standaloneType1 = 42;
+var d: standaloneType1 = \"asdf\";// Error: string ~> number
+var e: talias1 = 42;
+var f: talias1 = \"asdf\";// Error: string ~> number
+var g: talias3 = 42;
+var h: talias3 = \"asdf\";// Error: string ~> number
+import type { talias4 } from \"./cjs_with_types\";
+var i: talias4 = 42;
+var j: talias4 = \"asdf\";// Error: string ~> number
+import { IFoo, IFoo2 } from \"./types_only\";
+var k: IFoo = { prop: 42 };
+var l: IFoo = { prop: \"asdf\" };// Error: {prop:string} ~> {prop:number}
+var m: IFoo2 = { prop: \"asdf\" };
+var n: IFoo2 = { prop: 42 };// Error: {prop:number} ~> {prop:string}
+
+"
+`;
+
+exports[`test types_only.js 1`] = `
+"/* @flow */
+
+export type inlinedType1 = number;
+var a: inlinedType1 = 42;
+var b: inlinedType1 = \'asdf\'; // Error: string ~> number
+
+type standaloneType1 = number;
+export type {standaloneType1};
+
+type standaloneType2 = number;
+export {standaloneType2}; // Error: Missing \`type\` keyword
+
+export type {talias1, talias2 as talias3, IFoo2} from \"./types_only2\";
+
+export interface IFoo { prop: number };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test types_only2.js 1`] = `
+"/* @flow */
+
+export type talias1 = number;
+export type talias2 = number;
+export interface IFoo2 { prop: string };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at printExportDeclaration (/src/printer.js:1774:21)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
diff --git a/tests/export_type/cjs_with_types.js b/tests/export_type/cjs_with_types.js
new file mode 100644
index 000000000000..1b174f3ca346
--- /dev/null
+++ b/tests/export_type/cjs_with_types.js
@@ -0,0 +1,6 @@
+/* @flow */
+
+export type talias4 = number;
+export interface IFoo { prop: number };
+
+module.exports = {}
diff --git a/tests/export_type/importer.js b/tests/export_type/importer.js
new file mode 100644
index 000000000000..cb35f910304f
--- /dev/null
+++ b/tests/export_type/importer.js
@@ -0,0 +1,32 @@
+/* @flow */
+
+import type {
+  inlinedType1,
+  standaloneType1,
+  talias1,
+  talias3,
+} from "./types_only";
+
+var a: inlinedType1 = 42;
+var b: inlinedType1 = 'asdf'; // Error: string ~> number
+
+var c: standaloneType1 = 42;
+var d: standaloneType1 = 'asdf'; // Error: string ~> number
+
+var e: talias1 = 42;
+var f: talias1 = 'asdf'; // Error: string ~> number
+
+var g: talias3 = 42;
+var h: talias3 = 'asdf'; // Error: string ~> number
+
+import type {talias4} from "./cjs_with_types";
+var i: talias4 = 42;
+var j: talias4 = 'asdf'; // Error: string ~> number
+
+import {IFoo, IFoo2} from "./types_only";
+
+var k: IFoo = {prop: 42};
+var l: IFoo = {prop: 'asdf'}; // Error: {prop:string} ~> {prop:number}
+
+var m: IFoo2 = {prop: 'asdf'};
+var n: IFoo2 = {prop: 42}; // Error: {prop:number} ~> {prop:string}
diff --git a/tests/export_type/jsfmt.spec.js b/tests/export_type/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/export_type/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/export_type/types_only.js b/tests/export_type/types_only.js
new file mode 100644
index 000000000000..315e7b6ff150
--- /dev/null
+++ b/tests/export_type/types_only.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+export type inlinedType1 = number;
+var a: inlinedType1 = 42;
+var b: inlinedType1 = 'asdf'; // Error: string ~> number
+
+type standaloneType1 = number;
+export type {standaloneType1};
+
+type standaloneType2 = number;
+export {standaloneType2}; // Error: Missing `type` keyword
+
+export type {talias1, talias2 as talias3, IFoo2} from "./types_only2";
+
+export interface IFoo { prop: number };
diff --git a/tests/export_type/types_only2.js b/tests/export_type/types_only2.js
new file mode 100644
index 000000000000..4ef72006764c
--- /dev/null
+++ b/tests/export_type/types_only2.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+export type talias1 = number;
+export type talias2 = number;
+export interface IFoo2 { prop: string };
diff --git a/tests/extensions/__snapshots__/jsfmt.spec.js.snap b/tests/extensions/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..27b381d5b26f
--- /dev/null
+++ b/tests/extensions/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var imp = require('./bar');
+imp(1337);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var imp = require("./bar");
+imp(1337);
+
+"
+`;
diff --git a/tests/extensions/foo.js b/tests/extensions/foo.js
new file mode 100644
index 000000000000..66c9fcbe962d
--- /dev/null
+++ b/tests/extensions/foo.js
@@ -0,0 +1,2 @@
+var imp = require('./bar');
+imp(1337);
diff --git a/tests/extensions/jsfmt.spec.js b/tests/extensions/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/extensions/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/facebook_fbt_none/__snapshots__/jsfmt.spec.js.snap b/tests/facebook_fbt_none/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ca33925515bf
--- /dev/null
+++ b/tests/facebook_fbt_none/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,23 @@
+exports[`test main.js 1`] = `
+"// @flow
+var React = require(\'react\');
+(<fbt />: React.Element<*>);
+(<fbt />: number); // Error: ReactElement ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/facebook_fbt_none/jsfmt.spec.js b/tests/facebook_fbt_none/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/facebook_fbt_none/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/facebook_fbt_none/main.js b/tests/facebook_fbt_none/main.js
new file mode 100644
index 000000000000..46a530d2b702
--- /dev/null
+++ b/tests/facebook_fbt_none/main.js
@@ -0,0 +1,4 @@
+// @flow
+var React = require('react');
+(<fbt />: React.Element<*>);
+(<fbt />: number); // Error: ReactElement ~> number
diff --git a/tests/facebook_fbt_some/__snapshots__/jsfmt.spec.js.snap b/tests/facebook_fbt_some/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..72087bf26494
--- /dev/null
+++ b/tests/facebook_fbt_some/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,12 @@
+exports[`test main.js 1`] = `
+"// @flow
+
+(<fbt />: number);
+(<fbt />: string); // Error (the libdef in this test marks fbt as number)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+(<fbt/>: number);
+(<fbt/>: string);// Error (the libdef in this test marks fbt as number)
+
+"
+`;
diff --git a/tests/facebook_fbt_some/flow-typed/__snapshots__/jsfmt.spec.js.snap b/tests/facebook_fbt_some/flow-typed/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..80e8f68130a3
--- /dev/null
+++ b/tests/facebook_fbt_some/flow-typed/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test fbt.js 1`] = `
+"type Fbt = number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+type Fbt = number;
+
+"
+`;
diff --git a/tests/facebook_fbt_some/flow-typed/fbt.js b/tests/facebook_fbt_some/flow-typed/fbt.js
new file mode 100644
index 000000000000..373058cd8684
--- /dev/null
+++ b/tests/facebook_fbt_some/flow-typed/fbt.js
@@ -0,0 +1 @@
+type Fbt = number
diff --git a/tests/facebook_fbt_some/flow-typed/jsfmt.spec.js b/tests/facebook_fbt_some/flow-typed/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/facebook_fbt_some/flow-typed/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/facebook_fbt_some/jsfmt.spec.js b/tests/facebook_fbt_some/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/facebook_fbt_some/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/facebook_fbt_some/main.js b/tests/facebook_fbt_some/main.js
new file mode 100644
index 000000000000..01900f6a68e2
--- /dev/null
+++ b/tests/facebook_fbt_some/main.js
@@ -0,0 +1,4 @@
+// @flow
+
+(<fbt />: number);
+(<fbt />: string); // Error (the libdef in this test marks fbt as number)
diff --git a/tests/facebookisms/Bar.js b/tests/facebookisms/Bar.js
new file mode 100644
index 000000000000..fa9036afc162
--- /dev/null
+++ b/tests/facebookisms/Bar.js
@@ -0,0 +1,2 @@
+var Bar = { x: 0 };
+module.exports = Bar;
diff --git a/tests/facebookisms/__snapshots__/jsfmt.spec.js.snap b/tests/facebookisms/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a92ab7b855eb
--- /dev/null
+++ b/tests/facebookisms/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,242 @@
+exports[`test Bar.js 1`] = `
+"var Bar = { x: 0 };
+module.exports = Bar;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var Bar = { x: 0 };
+module.exports = Bar;
+
+"
+`;
+
+exports[`test copyProperties.js 1`] = `
+"// @flow
+
+let tests = [
+  // global
+  function() {
+    (copyProperties()); // error, unknown global
+  },
+
+  // annotation
+  function(copyProperties: Object$Assign) {
+    let result = {};
+    result.baz = false;
+    (copyProperties(
+      result,
+      { foo: 'a' },
+      { bar: 123 }
+    ): { foo: string, bar: number, baz: boolean });
+  },
+
+  // module from lib
+  function() {
+    const copyProperties = require('copyProperties');
+    let x = { foo: 'a' };
+    let y = { bar: 123 };
+    (copyProperties({}, x, y): { foo: string, bar: number });
+  },
+
+  // too few args
+  function(copyProperties: Object$Assign) {
+    copyProperties();
+    (copyProperties({ foo: 'a' }): { foo: number }); // err, num !~> string
+  },
+
+  // passed as a function
+  function(copyProperties: Object$Assign) {
+    function x(cb: Function) {}
+    x(copyProperties);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // global
+  function() {
+    copyProperties();// error, unknown global
+  },
+  // annotation
+  function(copyProperties: Object$Assign) {
+    let result = {};
+    result.baz = false;
+    (copyProperties(result, { foo: "a" }, { bar: 123 }): {
+      foo: string,
+      bar: number,
+      baz: boolean
+    });
+  },
+  // module from lib
+  function() {
+    const copyProperties = require("copyProperties");
+    let x = { foo: "a" };
+    let y = { bar: 123 };
+    (copyProperties({}, x, y): { foo: string, bar: number });
+  },
+  // too few args
+  function(copyProperties: Object$Assign) {
+    copyProperties();
+    (copyProperties({ foo: "a" }): { foo: number });// err, num !~> string
+  },
+  // passed as a function
+  function(copyProperties: Object$Assign) {
+    function x(cb: Function) {
+      
+    }
+    x(copyProperties);
+  }
+];
+
+"
+`;
+
+exports[`test invariant.js 1`] = `
+"/* @flow */
+
+let tests = [
+  function() {
+    let x: ?string = null;
+    invariant(x, 'truthy only'); // error, forgot to require invariant
+  },
+
+  function(invariant: Function) {
+    let x: ?string = null;
+    invariant(x);
+    (x: string);
+  }
+]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+let tests = [
+  function() {
+    let x: ?string = null;
+    invariant(x, "truthy only");// error, forgot to require invariant
+  },
+  function(invariant: Function) {
+    let x: ?string = null;
+    invariant(x);
+    (x: string);
+  }
+];
+
+"
+`;
+
+exports[`test lib.js 1`] = `
+"declare module "copyProperties" {
+  declare var exports: Object$Assign;
+}
+
+declare module "mergeInto" {
+  declare var exports: $Facebookism$MergeInto;
+}
+
+declare module "mixin" {
+  declare var exports: $Facebookism$Mixin;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare module "copyProperties" {
+  declare var exports: Object$Assign;
+}
+declare module "mergeInto" {
+  declare var exports: $Facebookism$MergeInto;
+}
+declare module "mixin" {
+  declare var exports: $Facebookism$Mixin;
+}
+
+"
+`;
+
+exports[`test mergeInto.js 1`] = `
+"// @flow
+
+let tests = [
+  // global
+  function() {
+    (mergeInto()); // error, unknown global
+  },
+
+  // annotation
+  function(mergeInto: $Facebookism$MergeInto) {
+    let result = {};
+    result.baz = false;
+    (mergeInto(result, { foo: 'a' }, { bar: 123 }): void);
+    (result: { foo: string, bar: number, baz: boolean });
+  },
+
+  // module from lib
+  function() {
+    const mergeInto = require('mergeInto');
+    let result: { foo?: string, bar?: number, baz: boolean } = { baz: false };
+    (mergeInto(result, { foo: 'a' }, { bar: 123 }): void);
+  },
+
+  // too few args
+  function(mergeInto: $Facebookism$MergeInto) {
+    mergeInto();
+  },
+
+  // passed as a function
+  function(mergeInto: $Facebookism$MergeInto) {
+    function x(cb: Function) {}
+    x(mergeInto);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  // global
+  function() {
+    mergeInto();// error, unknown global
+  },
+  // annotation
+  function(mergeInto: $Facebookism$MergeInto) {
+    let result = {};
+    result.baz = false;
+    (mergeInto(result, { foo: "a" }, { bar: 123 }): void);
+    (result: { foo: string, bar: number, baz: boolean });
+  },
+  // module from lib
+  function() {
+    const mergeInto = require("mergeInto");
+    let result: { foo?: string, bar?: number, baz: boolean } = { baz: false };
+    (mergeInto(result, { foo: "a" }, { bar: 123 }): void);
+  },
+  // too few args
+  function(mergeInto: $Facebookism$MergeInto) {
+    mergeInto();
+  },
+  // passed as a function
+  function(mergeInto: $Facebookism$MergeInto) {
+    function x(cb: Function) {
+      
+    }
+    x(mergeInto);
+  }
+];
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"var Bar = require('./Bar');
+var mixin = require('mixin');
+
+class Foo extends mixin(Bar) {
+  m() {
+    var x: string = this.x;
+    this.y = "";
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var Bar = require("./Bar");
+var mixin = require("mixin");
+class Foo extends mixin(Bar) {
+  m() {
+    var x: string = this.x;
+    this.y = "";
+  }
+}
+
+"
+`;
diff --git a/tests/facebookisms/copyProperties.js b/tests/facebookisms/copyProperties.js
new file mode 100644
index 000000000000..0f20e91b630e
--- /dev/null
+++ b/tests/facebookisms/copyProperties.js
@@ -0,0 +1,39 @@
+// @flow
+
+let tests = [
+  // global
+  function() {
+    (copyProperties()); // error, unknown global
+  },
+
+  // annotation
+  function(copyProperties: Object$Assign) {
+    let result = {};
+    result.baz = false;
+    (copyProperties(
+      result,
+      { foo: 'a' },
+      { bar: 123 }
+    ): { foo: string, bar: number, baz: boolean });
+  },
+
+  // module from lib
+  function() {
+    const copyProperties = require('copyProperties');
+    let x = { foo: 'a' };
+    let y = { bar: 123 };
+    (copyProperties({}, x, y): { foo: string, bar: number });
+  },
+
+  // too few args
+  function(copyProperties: Object$Assign) {
+    copyProperties();
+    (copyProperties({ foo: 'a' }): { foo: number }); // err, num !~> string
+  },
+
+  // passed as a function
+  function(copyProperties: Object$Assign) {
+    function x(cb: Function) {}
+    x(copyProperties);
+  }
+];
diff --git a/tests/facebookisms/invariant.js b/tests/facebookisms/invariant.js
new file mode 100644
index 000000000000..7474dd69d35f
--- /dev/null
+++ b/tests/facebookisms/invariant.js
@@ -0,0 +1,14 @@
+/* @flow */
+
+let tests = [
+  function() {
+    let x: ?string = null;
+    invariant(x, 'truthy only'); // error, forgot to require invariant
+  },
+
+  function(invariant: Function) {
+    let x: ?string = null;
+    invariant(x);
+    (x: string);
+  }
+]
diff --git a/tests/facebookisms/jsfmt.spec.js b/tests/facebookisms/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/facebookisms/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/facebookisms/lib.js b/tests/facebookisms/lib.js
new file mode 100644
index 000000000000..bc96320ec47d
--- /dev/null
+++ b/tests/facebookisms/lib.js
@@ -0,0 +1,11 @@
+declare module "copyProperties" {
+  declare var exports: Object$Assign;
+}
+
+declare module "mergeInto" {
+  declare var exports: $Facebookism$MergeInto;
+}
+
+declare module "mixin" {
+  declare var exports: $Facebookism$Mixin;
+}
diff --git a/tests/facebookisms/mergeInto.js b/tests/facebookisms/mergeInto.js
new file mode 100644
index 000000000000..9b1d08df751a
--- /dev/null
+++ b/tests/facebookisms/mergeInto.js
@@ -0,0 +1,34 @@
+// @flow
+
+let tests = [
+  // global
+  function() {
+    (mergeInto()); // error, unknown global
+  },
+
+  // annotation
+  function(mergeInto: $Facebookism$MergeInto) {
+    let result = {};
+    result.baz = false;
+    (mergeInto(result, { foo: 'a' }, { bar: 123 }): void);
+    (result: { foo: string, bar: number, baz: boolean });
+  },
+
+  // module from lib
+  function() {
+    const mergeInto = require('mergeInto');
+    let result: { foo?: string, bar?: number, baz: boolean } = { baz: false };
+    (mergeInto(result, { foo: 'a' }, { bar: 123 }): void);
+  },
+
+  // too few args
+  function(mergeInto: $Facebookism$MergeInto) {
+    mergeInto();
+  },
+
+  // passed as a function
+  function(mergeInto: $Facebookism$MergeInto) {
+    function x(cb: Function) {}
+    x(mergeInto);
+  }
+];
diff --git a/tests/facebookisms/test.js b/tests/facebookisms/test.js
new file mode 100644
index 000000000000..5d484ac096fa
--- /dev/null
+++ b/tests/facebookisms/test.js
@@ -0,0 +1,9 @@
+var Bar = require('./Bar');
+var mixin = require('mixin');
+
+class Foo extends mixin(Bar) {
+  m() {
+    var x: string = this.x;
+    this.y = "";
+  }
+}
diff --git a/tests/fetch/__snapshots__/jsfmt.spec.js.snap b/tests/fetch/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6c8225a8ddec
--- /dev/null
+++ b/tests/fetch/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,329 @@
+exports[`test fetch.js 1`] = `
+"/* @flow */
+
+// most of the details are tested in the separate file
+// here I test the basic usage
+
+const myRequest = new Request(\'http://google.com\');
+
+const a: Promise<string> =
+  fetch(myRequest)
+  .then(response => response.text());
+
+const b: Promise<string> = fetch(myRequest); // incorrect
+
+var myInit = { method: \'GET\',
+               headers: {
+                   \'Content-Type\': \'image/jpeg\'
+               },
+               mode: \'cors\',
+               cache: \'default\' };
+
+const c: Promise<Blob> =
+  fetch(\'image.png\')
+  .then(response => response.blob()); // correct
+
+const d: Promise<Blob> = fetch(\'image.png\'); // incorrect
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test headers.js 1`] = `
+"/* @flow */
+
+const a = new Headers(\"\'Content-Type\': \'image/jpeg\'\"); // not correct
+const b = new Headers([\'Content-Type\', \'image/jpeg\']); // not correct
+const c = new Headers({\'Content-Type\', \'image/jpeg\'}); // correct
+const d = new Headers(c); // correct
+const e: Headers = new Headers(); // correct
+e.append(\'Content-Type\', \'image/jpeg\'); // correct
+e.append(\'Content-Type\'); // not correct
+e.append({\'Content-Type\', \'image/jpeg\'}); // not correct
+e.set(\'Content-Type\', \'image/jpeg\'); // correct
+e.set(\'Content-Type\'); // not correct
+e.set({\'Content-Type\', \'image/jpeg\'}); // not correct
+
+const f: Headers = e.append(\'Content-Type\', \'image/jpeg\'); // not correct
+
+const g: string = e.get(\'Content-Type\'); // correct
+const h: number = e.get(\'Content-Type\'); // not correct
+
+for (let v of e) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+for (let v of e.entries()) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+e.getAll(\'content-type\').forEach((v: string) => {}); // correct
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:37)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseObjPropValue (/node_modules/babylon/lib/index.js:3940:8)
+    at Parser.parseObjPropValue (/node_modules/babylon/lib/index.js:5537:13)
+    at Parser.pp$3.parseObj (/node_modules/babylon/lib/index.js:3871:10)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3561:19)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+"
+`;
+
+exports[`test request.js 1`] = `
+"/* @flow */
+const a: Request = new Request(); // incorrect
+const b: Request = new Request(\'http://example.org\'); // correct
+const c: Request = new Request(b); // correct
+const d: Request = new Request(c.clone()); // correct (doesn\'t make much sense though)
+const e: Request = new Request(b, c); // incorrect
+
+const f: Request = new Request({}) // incorrect
+const g: Request = new Request(\'http://example.org\', {}) // correct
+
+const h: Request = new Request(\'http://example.org\', {
+  method: \'GET\',
+  headers: {
+    \'Content-Type\': \'image/jpeg\'
+  },
+  mode: \'cors\',
+  cache: \'default\'
+}) // correct
+
+const i: Request = new Request(\'http://example.org\', {
+  method: \'POST\',
+  headers: {
+    \'Content-Type\': \'image/jpeg\'
+  },
+  body: new URLSearchParams(\"key=value\"),
+  mode: \'cors\',
+  cache: \'default\'
+}) // correct
+
+const j: Request = new Request(\'http://example.org\', {
+  method: \'GET\',
+  headers: \'Content-Type: image/jpeg\',
+  mode: \'cors\',
+  cache: \'default\'
+}) // incorrect - headers is string
+
+const k: Request = new Request(\'http://example.org\', {
+  method: \'CONNECT\',
+  headers: {
+    \'Content-Type\': \'image/jpeg\'
+  },
+  mode: \'cors\',
+  cache: \'default\'
+}) // incorrect - CONNECT is forbidden
+
+var l: boolean = h.bodyUsed;
+
+h.text().then((t: string) => t); // correct
+h.text().then((t: Buffer) => t); // incorrect
+h.arrayBuffer().then((ab: ArrayBuffer) => ab); // correct
+h.arrayBuffer().then((ab: Buffer) => ab); // incorrect
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+const a: Request = new Request();// incorrect
+const b: Request = new Request(\"http://example.org\");// correct
+const c: Request = new Request(b);// correct
+const d: Request = new Request(
+  c.clone()
+);// correct (doesn\'t make much sense though)
+const e: Request = new Request(b, c);// incorrect
+const f: Request = new Request({});// incorrect
+const g: Request = new Request(\"http://example.org\", {});// correct
+const h: Request = new Request(
+  \"http://example.org\",
+  {
+    method: \"GET\",
+    headers: { \"Content-Type\": \"image/jpeg\" },
+    mode: \"cors\",
+    cache: \"default\"
+  }
+);// correct
+const i: Request = new Request(
+  \"http://example.org\",
+  {
+    method: \"POST\",
+    headers: { \"Content-Type\": \"image/jpeg\" },
+    body: new URLSearchParams(\"key=value\"),
+    mode: \"cors\",
+    cache: \"default\"
+  }
+);// correct
+const j: Request = new Request(
+  \"http://example.org\",
+  {
+    method: \"GET\",
+    headers: \"Content-Type: image/jpeg\",
+    mode: \"cors\",
+    cache: \"default\"
+  }
+);// incorrect - headers is string
+const k: Request = new Request(
+  \"http://example.org\",
+  {
+    method: \"CONNECT\",
+    headers: { \"Content-Type\": \"image/jpeg\" },
+    mode: \"cors\",
+    cache: \"default\"
+  }
+);// incorrect - CONNECT is forbidden
+var l: boolean = h.bodyUsed;
+h.text().then((t: string) => t);// correct
+h.text().then((t: Buffer) => t);// incorrect
+h.arrayBuffer().then((ab: ArrayBuffer) => ab);// correct
+h.arrayBuffer().then((ab: Buffer) => ab);// incorrect
+
+"
+`;
+
+exports[`test response.js 1`] = `
+"/* @flow */
+const a: Response = new Response(); // correct
+const b: Response = new Response(new Blob()); // correct
+const c: Response = new Response(new FormData()); // correct
+
+const d: Response = new Response(new FormData(), {
+    status: 404
+}); // correct
+
+const e: Response = new Response(\"responsebody\", {
+    status: \"404\"
+}); // incorrect
+
+const f: Response = new Response(\"responsebody\", {
+    status: 404,
+    headers: \"\'Content-Type\': \'image/jpeg\'\"
+}); // incorrect
+
+const g: Response = new Response(\"responsebody\", {
+    status: 404,
+    headers: {
+        \'Content-Type\': \'image/jpeg\'
+    }
+}); // correct
+
+const h: Response = new Response(\"responsebody\", {
+    status: 404,
+    headers: new Headers({
+        \'Content-Type\': \'image/jpeg\'
+    })
+}); // correct, if verbose
+
+const i: Response = new Response({
+    status: 404,
+    headers: new Headers({
+        \'Content-Type\': \'image/jpeg\'
+    })
+}); // incorrect
+
+const ok: boolean = h.ok;
+const status: number = h.status;
+
+h.text().then((t: string) => t); // correct
+h.text().then((t: Buffer) => t); // incorrect
+h.arrayBuffer().then((ab: ArrayBuffer) => ab); // correct
+h.arrayBuffer().then((ab: Buffer) => ab); // incorrect
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+const a: Response = new Response();// correct
+const b: Response = new Response(new Blob());// correct
+const c: Response = new Response(new FormData());// correct
+const d: Response = new Response(new FormData(), { status: 404 });// correct
+const e: Response = new Response(\"responsebody\", { status: \"404\" });// incorrect
+const f: Response = new Response(
+  \"responsebody\",
+  { status: 404, headers: \"\'Content-Type\': \'image/jpeg\'\" }
+);// incorrect
+const g: Response = new Response(
+  \"responsebody\",
+  { status: 404, headers: { \"Content-Type\": \"image/jpeg\" } }
+);// correct
+const h: Response = new Response(
+  \"responsebody\",
+  { status: 404, headers: new Headers({ \"Content-Type\": \"image/jpeg\" }) }
+);// correct, if verbose
+const i: Response = new Response({
+  status: 404,
+  headers: new Headers({ \"Content-Type\": \"image/jpeg\" })
+});// incorrect
+const ok: boolean = h.ok;
+const status: number = h.status;
+h.text().then((t: string) => t);// correct
+h.text().then((t: Buffer) => t);// incorrect
+h.arrayBuffer().then((ab: ArrayBuffer) => ab);// correct
+h.arrayBuffer().then((ab: Buffer) => ab);// incorrect
+
+"
+`;
+
+exports[`test urlsearchparams.js 1`] = `
+"/* @flow */
+
+const a = new URLSearchParams(\"key1=value1\"); // correct
+const b = new URLSearchParams([\'key1\', \'value1\']); // not correct
+const c = new URLSearchParams({\'key1\', \'value1\'}); // not correct
+const d = new URLSearchParams(c); // correct
+const e: URLSearchParams = new URLSearchParams(); // correct
+e.append(\'key1\', \'value1\'); // correct
+e.append(\'key1\'); // not correct
+e.append({\'key1\', \'value1\'}); // not correct
+e.set(\'key1\', \'value1\'); // correct
+e.set(\'key1\'); // not correct
+e.set({\'key1\', \'value1\'}); // not correct
+
+const f: URLSearchParams = e.append(\'key1\', \'value1\'); // not correct
+
+const g: string = e.get(\'key1\'); // correct
+const h: number = e.get(\'key1\'); // not correct
+
+for (let v of e) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+for (let v of e.entries()) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+e.getAll(\'key1\').forEach((v: string) => {}); // correct
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:37)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseObjPropValue (/node_modules/babylon/lib/index.js:3940:8)
+    at Parser.parseObjPropValue (/node_modules/babylon/lib/index.js:5537:13)
+    at Parser.pp$3.parseObj (/node_modules/babylon/lib/index.js:3871:10)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3561:19)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+"
+`;
diff --git a/tests/fetch/fetch.js b/tests/fetch/fetch.js
new file mode 100644
index 000000000000..bd1f44a84333
--- /dev/null
+++ b/tests/fetch/fetch.js
@@ -0,0 +1,25 @@
+/* @flow */
+
+// most of the details are tested in the separate file
+// here I test the basic usage
+
+const myRequest = new Request('http://google.com');
+
+const a: Promise<string> =
+  fetch(myRequest)
+  .then(response => response.text());
+
+const b: Promise<string> = fetch(myRequest); // incorrect
+
+var myInit = { method: 'GET',
+               headers: {
+                   'Content-Type': 'image/jpeg'
+               },
+               mode: 'cors',
+               cache: 'default' };
+
+const c: Promise<Blob> =
+  fetch('image.png')
+  .then(response => response.blob()); // correct
+
+const d: Promise<Blob> = fetch('image.png'); // incorrect
diff --git a/tests/fetch/headers.js b/tests/fetch/headers.js
new file mode 100644
index 000000000000..9eab0d99635b
--- /dev/null
+++ b/tests/fetch/headers.js
@@ -0,0 +1,28 @@
+/* @flow */
+
+const a = new Headers("'Content-Type': 'image/jpeg'"); // not correct
+const b = new Headers(['Content-Type', 'image/jpeg']); // not correct
+const c = new Headers({'Content-Type', 'image/jpeg'}); // correct
+const d = new Headers(c); // correct
+const e: Headers = new Headers(); // correct
+e.append('Content-Type', 'image/jpeg'); // correct
+e.append('Content-Type'); // not correct
+e.append({'Content-Type', 'image/jpeg'}); // not correct
+e.set('Content-Type', 'image/jpeg'); // correct
+e.set('Content-Type'); // not correct
+e.set({'Content-Type', 'image/jpeg'}); // not correct
+
+const f: Headers = e.append('Content-Type', 'image/jpeg'); // not correct
+
+const g: string = e.get('Content-Type'); // correct
+const h: number = e.get('Content-Type'); // not correct
+
+for (let v of e) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+for (let v of e.entries()) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+e.getAll('content-type').forEach((v: string) => {}); // correct
diff --git a/tests/fetch/jsfmt.spec.js b/tests/fetch/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/fetch/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/fetch/request.js b/tests/fetch/request.js
new file mode 100644
index 000000000000..1f8981e91f28
--- /dev/null
+++ b/tests/fetch/request.js
@@ -0,0 +1,51 @@
+/* @flow */
+const a: Request = new Request(); // incorrect
+const b: Request = new Request('http://example.org'); // correct
+const c: Request = new Request(b); // correct
+const d: Request = new Request(c.clone()); // correct (doesn't make much sense though)
+const e: Request = new Request(b, c); // incorrect
+
+const f: Request = new Request({}) // incorrect
+const g: Request = new Request('http://example.org', {}) // correct
+
+const h: Request = new Request('http://example.org', {
+  method: 'GET',
+  headers: {
+    'Content-Type': 'image/jpeg'
+  },
+  mode: 'cors',
+  cache: 'default'
+}) // correct
+
+const i: Request = new Request('http://example.org', {
+  method: 'POST',
+  headers: {
+    'Content-Type': 'image/jpeg'
+  },
+  body: new URLSearchParams("key=value"),
+  mode: 'cors',
+  cache: 'default'
+}) // correct
+
+const j: Request = new Request('http://example.org', {
+  method: 'GET',
+  headers: 'Content-Type: image/jpeg',
+  mode: 'cors',
+  cache: 'default'
+}) // incorrect - headers is string
+
+const k: Request = new Request('http://example.org', {
+  method: 'CONNECT',
+  headers: {
+    'Content-Type': 'image/jpeg'
+  },
+  mode: 'cors',
+  cache: 'default'
+}) // incorrect - CONNECT is forbidden
+
+var l: boolean = h.bodyUsed;
+
+h.text().then((t: string) => t); // correct
+h.text().then((t: Buffer) => t); // incorrect
+h.arrayBuffer().then((ab: ArrayBuffer) => ab); // correct
+h.arrayBuffer().then((ab: Buffer) => ab); // incorrect
diff --git a/tests/fetch/response.js b/tests/fetch/response.js
new file mode 100644
index 000000000000..f68b4d8b3493
--- /dev/null
+++ b/tests/fetch/response.js
@@ -0,0 +1,46 @@
+/* @flow */
+const a: Response = new Response(); // correct
+const b: Response = new Response(new Blob()); // correct
+const c: Response = new Response(new FormData()); // correct
+
+const d: Response = new Response(new FormData(), {
+    status: 404
+}); // correct
+
+const e: Response = new Response("responsebody", {
+    status: "404"
+}); // incorrect
+
+const f: Response = new Response("responsebody", {
+    status: 404,
+    headers: "'Content-Type': 'image/jpeg'"
+}); // incorrect
+
+const g: Response = new Response("responsebody", {
+    status: 404,
+    headers: {
+        'Content-Type': 'image/jpeg'
+    }
+}); // correct
+
+const h: Response = new Response("responsebody", {
+    status: 404,
+    headers: new Headers({
+        'Content-Type': 'image/jpeg'
+    })
+}); // correct, if verbose
+
+const i: Response = new Response({
+    status: 404,
+    headers: new Headers({
+        'Content-Type': 'image/jpeg'
+    })
+}); // incorrect
+
+const ok: boolean = h.ok;
+const status: number = h.status;
+
+h.text().then((t: string) => t); // correct
+h.text().then((t: Buffer) => t); // incorrect
+h.arrayBuffer().then((ab: ArrayBuffer) => ab); // correct
+h.arrayBuffer().then((ab: Buffer) => ab); // incorrect
diff --git a/tests/fetch/urlsearchparams.js b/tests/fetch/urlsearchparams.js
new file mode 100644
index 000000000000..f40aae313f36
--- /dev/null
+++ b/tests/fetch/urlsearchparams.js
@@ -0,0 +1,28 @@
+/* @flow */
+
+const a = new URLSearchParams("key1=value1"); // correct
+const b = new URLSearchParams(['key1', 'value1']); // not correct
+const c = new URLSearchParams({'key1', 'value1'}); // not correct
+const d = new URLSearchParams(c); // correct
+const e: URLSearchParams = new URLSearchParams(); // correct
+e.append('key1', 'value1'); // correct
+e.append('key1'); // not correct
+e.append({'key1', 'value1'}); // not correct
+e.set('key1', 'value1'); // correct
+e.set('key1'); // not correct
+e.set({'key1', 'value1'}); // not correct
+
+const f: URLSearchParams = e.append('key1', 'value1'); // not correct
+
+const g: string = e.get('key1'); // correct
+const h: number = e.get('key1'); // not correct
+
+for (let v of e) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+for (let v of e.entries()) {
+  const [i, j]: [string, string] = v; // correct
+}
+
+e.getAll('key1').forEach((v: string) => {}); // correct
diff --git a/tests/find-module/__snapshots__/jsfmt.spec.js.snap b/tests/find-module/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2855edc03840
--- /dev/null
+++ b/tests/find-module/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,20 @@
+exports[`test req.js 1`] = `
+"module.exports = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = 0;
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"var x = require('./req');
+(x: string);
+
+import x from './req';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("./req");
+(x: string);
+import x from "./req";
+
+"
+`;
diff --git a/tests/find-module/jsfmt.spec.js b/tests/find-module/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/find-module/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/find-module/req.js b/tests/find-module/req.js
new file mode 100644
index 000000000000..d5b2e8bb3efb
--- /dev/null
+++ b/tests/find-module/req.js
@@ -0,0 +1 @@
+module.exports = 0;
diff --git a/tests/find-module/test.js b/tests/find-module/test.js
new file mode 100644
index 000000000000..79de263f6960
--- /dev/null
+++ b/tests/find-module/test.js
@@ -0,0 +1,4 @@
+var x = require('./req');
+(x: string);
+
+import x from './req';
diff --git a/tests/find-refs/__snapshots__/jsfmt.spec.js.snap b/tests/find-refs/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bd0b87986865
--- /dev/null
+++ b/tests/find-refs/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,77 @@
+exports[`test locals.js 1`] = `
+"// @flow
+
+// Variable defs and uses
+var foo = function() { };
+foo();
+foo = null;
+foo();
+
+// Nested functions
+function bar() {
+  function bar() {
+  }
+  bar();
+}
+bar();
+
+// Classes
+class C { }
+new C;
+class D extends C { }
+
+// Type aliases
+type T = number;
+type S = T;
+((_: T) => {});
+
+// Refinements
+let nullable: ?string = \"\";
+if (nullable != null) {
+  console.log(nullable.length);
+  nullable = null;
+}
+(nullable: null);
+
+// Destructuring
+let { x, y } = { x: 0, y: 0 };
+let { x: _x, y: _y } = { x, y };
+({ x: _x, y: _y });
+
+// Not in scope
+wut1;
+wut1 = wut2;
+wut2;
+
+// JSX
+var React = require(\'react\');
+class Fancy extends React.Component {
+  props: { x: number };
+}
+<Fancy x=0/>;
+
+// Imports
+import { wut3 } from \'wutland\';
+import type { wut4 } from \'wutland\';
+(wut3: wut4);
+
+// Qualified types
+(null: React.Component);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:5687
+          throw jsxError || err;
+          ^
+
+SyntaxError: JSX value should be either an expression or a quoted JSX text (50:9)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp$8.jsxParseAttributeValue (/node_modules/babylon/lib/index.js:6255:12)
+    at Parser.pp$8.jsxParseAttribute (/node_modules/babylon/lib/index.js:6306:42)
+    at Parser.pp$8.jsxParseOpeningElementAt (/node_modules/babylon/lib/index.js:6317:31)
+    at Parser.pp$8.jsxParseElementAt (/node_modules/babylon/lib/index.js:6339:29)
+    at Parser.pp$8.jsxParseElement (/node_modules/babylon/lib/index.js:6394:15)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6406:21)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+"
+`;
diff --git a/tests/find-refs/jsfmt.spec.js b/tests/find-refs/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/find-refs/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/find-refs/locals.js b/tests/find-refs/locals.js
new file mode 100644
index 000000000000..5651166c1f62
--- /dev/null
+++ b/tests/find-refs/locals.js
@@ -0,0 +1,58 @@
+// @flow
+
+// Variable defs and uses
+var foo = function() { };
+foo();
+foo = null;
+foo();
+
+// Nested functions
+function bar() {
+  function bar() {
+  }
+  bar();
+}
+bar();
+
+// Classes
+class C { }
+new C;
+class D extends C { }
+
+// Type aliases
+type T = number;
+type S = T;
+((_: T) => {});
+
+// Refinements
+let nullable: ?string = "";
+if (nullable != null) {
+  console.log(nullable.length);
+  nullable = null;
+}
+(nullable: null);
+
+// Destructuring
+let { x, y } = { x: 0, y: 0 };
+let { x: _x, y: _y } = { x, y };
+({ x: _x, y: _y });
+
+// Not in scope
+wut1;
+wut1 = wut2;
+wut2;
+
+// JSX
+var React = require('react');
+class Fancy extends React.Component {
+  props: { x: number };
+}
+<Fancy x=0/>;
+
+// Imports
+import { wut3 } from 'wutland';
+import type { wut4 } from 'wutland';
+(wut3: wut4);
+
+// Qualified types
+(null: React.Component);
diff --git a/tests/fixpoint/Fun.js b/tests/fixpoint/Fun.js
new file mode 100644
index 000000000000..944a780d1260
--- /dev/null
+++ b/tests/fixpoint/Fun.js
@@ -0,0 +1,30 @@
+
+/* @providesModule Fun */
+
+function eq(x:number,y:number) { return true };
+function sub(x:number,y:number) { return 0; }
+function mul(x:number,y:number) { return 0; }
+
+function fix(fold) {
+  var delta = function(delta) {
+    return fold(
+      function(x) { var eta = delta(delta); return eta(x); }
+    );
+  };
+  return delta(delta);
+}
+
+function mk_factorial() {
+  return fix(function(factorial) {
+    return function(n) {
+      if (eq (n, 1)) { return 1; }
+      return mul (factorial (sub (n, 1)), n);
+    };
+  });
+}
+
+
+var factorial = mk_factorial();
+factorial("...");
+
+module.exports = {fn: fix};
diff --git a/tests/fixpoint/Ycombinator.js b/tests/fixpoint/Ycombinator.js
new file mode 100644
index 000000000000..d433603e5ca0
--- /dev/null
+++ b/tests/fixpoint/Ycombinator.js
@@ -0,0 +1,21 @@
+
+/* @providesModule Ycombinator */
+
+function Y(f) {
+  function g(x) { return f(x(x)); }
+  g(g);
+}
+
+function func1(f) {
+  function fix_f(x:number):number { return f(x); }
+  return fix_f;
+}
+function func2(f) {
+  function fix_f(x:string):string { return f(x); }
+  return fix_f;
+}
+
+Y(func1);
+Y(func2);
+
+module.exports = Y;
diff --git a/tests/fixpoint/__snapshots__/jsfmt.spec.js.snap b/tests/fixpoint/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b397dc2a755f
--- /dev/null
+++ b/tests/fixpoint/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,120 @@
+exports[`test Fun.js 1`] = `
+"
+/* @providesModule Fun */
+
+function eq(x:number,y:number) { return true };
+function sub(x:number,y:number) { return 0; }
+function mul(x:number,y:number) { return 0; }
+
+function fix(fold) {
+  var delta = function(delta) {
+    return fold(
+      function(x) { var eta = delta(delta); return eta(x); }
+    );
+  };
+  return delta(delta);
+}
+
+function mk_factorial() {
+  return fix(function(factorial) {
+    return function(n) {
+      if (eq (n, 1)) { return 1; }
+      return mul (factorial (sub (n, 1)), n);
+    };
+  });
+}
+
+
+var factorial = mk_factorial();
+factorial("...");
+
+module.exports = {fn: fix};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Fun */
+function eq(x: number, y: number) {
+  return true;
+}
+function sub(x: number, y: number) {
+  return 0;
+}
+function mul(x: number, y: number) {
+  return 0;
+}
+function fix(fold) {
+  var delta = function(delta) {
+    return fold(
+      function(x) {
+        var eta = delta(delta);
+        return eta(x);
+      }
+    );
+  };
+  return delta(delta);
+}
+function mk_factorial() {
+  return fix(
+    function(factorial) {
+      return function(n) {
+        if (eq(n, 1)) {
+          return 1;
+        }
+        return mul(factorial(sub(n, 1)), n);
+      };
+    }
+  );
+}
+var factorial = mk_factorial();
+factorial("...");
+module.exports = { fn: fix };
+
+"
+`;
+
+exports[`test Ycombinator.js 1`] = `
+"
+/* @providesModule Ycombinator */
+
+function Y(f) {
+  function g(x) { return f(x(x)); }
+  g(g);
+}
+
+function func1(f) {
+  function fix_f(x:number):number { return f(x); }
+  return fix_f;
+}
+function func2(f) {
+  function fix_f(x:string):string { return f(x); }
+  return fix_f;
+}
+
+Y(func1);
+Y(func2);
+
+module.exports = Y;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Ycombinator */
+function Y(f) {
+  function g(x) {
+    return f(x(x));
+  }
+  g(g);
+}
+function func1(f) {
+  function fix_f(x: number): number {
+    return f(x);
+  }
+  return fix_f;
+}
+function func2(f) {
+  function fix_f(x: string): string {
+    return f(x);
+  }
+  return fix_f;
+}
+Y(func1);
+Y(func2);
+module.exports = Y;
+
+"
+`;
diff --git a/tests/fixpoint/jsfmt.spec.js b/tests/fixpoint/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/fixpoint/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/flow_ast.template_strings/__snapshots__/jsfmt.spec.js.snap b/tests/flow_ast.template_strings/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f3ef97d9d279
--- /dev/null
+++ b/tests/flow_ast.template_strings/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test foo.js 1`] = `
+"a\`foo \${bar} baz\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+a\`foo \${bar} baz\`;
+
+"
+`;
diff --git a/tests/flow_ast.template_strings/foo.js b/tests/flow_ast.template_strings/foo.js
new file mode 100644
index 000000000000..201691617f58
--- /dev/null
+++ b/tests/flow_ast.template_strings/foo.js
@@ -0,0 +1 @@
+a`foo ${bar} baz`
diff --git a/tests/flow_ast.template_strings/jsfmt.spec.js b/tests/flow_ast.template_strings/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/flow_ast.template_strings/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/for/__snapshots__/jsfmt.spec.js.snap b/tests/for/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..84356a0db27e
--- /dev/null
+++ b/tests/for/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,272 @@
+exports[`test abnormal.js 1`] = `
+"/* @flow */
+
+function foo(x: boolean) {
+  var max = 10;
+  for (var ii = 0; ii < max; ii++) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function baz(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    continue;
+  }
+  console.log('this is still reachable');
+}
+
+function bliffl(x: boolean) {
+  var max = 10;
+  loop1: for (var ii = 0; ii < max; ii++) {
+    loop2: for (var jj = 0; jj < max; jj++) {
+      break loop1;
+    }
+    console.log('this is still reachable');
+  }
+  console.log('this is still reachable');
+}
+
+function corge(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    break;
+  }
+  console.log('this is still reachable');
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo(x: boolean) {
+  var max = 10;
+  for (var ii = 0; ii < max; ii++) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log("this is still reachable");
+}
+function bar(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    return;
+  }
+  console.log("this is still reachable");
+}
+function baz(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    continue;
+  }
+  console.log("this is still reachable");
+}
+function bliffl(x: boolean) {
+  var max = 10;
+  loop1:
+for (var ii = 0; ii < max; ii++) {
+    loop2:
+for (var jj = 0; jj < max; jj++) {
+      break loop1;
+    }
+    console.log("this is still reachable");
+  }
+  console.log("this is still reachable");
+}
+function corge(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    break;
+  }
+  console.log("this is still reachable");
+}
+
+"
+`;
+
+exports[`test abnormal_for_in.js 1`] = `
+"function foo(x: boolean) {
+  var obj = { a: 1, b: 2};
+  for (var prop in obj) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  for (var prop in {}) {
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function baz(x: boolean) {
+  for (var prop in {}) {
+    continue;
+  }
+  console.log('this is still reachable');
+}
+
+function bliffl(x: boolean) {
+  var obj = { a: 1, b: 2};
+  loop1: for (var prop1 in obj) {
+    loop2: for (var prop2 in obj) {
+      break loop1;
+    }
+    console.log('this is still reachable');
+  }
+  console.log('this is still reachable');
+}
+
+function corge(x: boolean) {
+  for (var prop in {}) {
+    break;
+  }
+  console.log('this is still reachable');
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(x: boolean) {
+  var obj = { a: 1, b: 2 };
+  for (var prop in obj) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log("this is still reachable");
+}
+function bar(x: boolean) {
+  for (var prop in {}) {
+    return;
+  }
+  console.log("this is still reachable");
+}
+function baz(x: boolean) {
+  for (var prop in {}) {
+    continue;
+  }
+  console.log("this is still reachable");
+}
+function bliffl(x: boolean) {
+  var obj = { a: 1, b: 2 };
+  loop1:
+for (var prop1 in obj) {
+    loop2:
+for (var prop2 in obj) {
+      break loop1;
+    }
+    console.log("this is still reachable");
+  }
+  console.log("this is still reachable");
+}
+function corge(x: boolean) {
+  for (var prop in {}) {
+    break;
+  }
+  console.log("this is still reachable");
+}
+
+"
+`;
+
+exports[`test abnormal_for_of.js 1`] = `
+"function foo(x: boolean) {
+  var arr = [1, 2, 3];
+  for (var elem of arr) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  for (var elem of []) {
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function baz(x: boolean) {
+  for (var elem of []) {
+    continue;
+  }
+  console.log('this is still reachable');
+}
+
+function bliffl(x: boolean) {
+  var arr = [1, 2, 3];
+  loop1: for (var elem of arr) {
+    loop2: for (var elem of arr) {
+      break loop1;
+    }
+    console.log('this is still reachable');
+  }
+  console.log('this is still reachable');
+}
+
+function corge(x: boolean) {
+  for (var elem of []) {
+    break;
+  }
+  console.log('this is still reachable');
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(x: boolean) {
+  var arr = [ 1, 2, 3 ];
+  for (var elem of arr) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log("this is still reachable");
+}
+function bar(x: boolean) {
+  for (var elem of [  ]) {
+    return;
+  }
+  console.log("this is still reachable");
+}
+function baz(x: boolean) {
+  for (var elem of [  ]) {
+    continue;
+  }
+  console.log("this is still reachable");
+}
+function bliffl(x: boolean) {
+  var arr = [ 1, 2, 3 ];
+  loop1:
+for (var elem of arr) {
+    loop2:
+for (var elem of arr) {
+      break loop1;
+    }
+    console.log("this is still reachable");
+  }
+  console.log("this is still reachable");
+}
+function corge(x: boolean) {
+  for (var elem of [  ]) {
+    break;
+  }
+  console.log("this is still reachable");
+}
+
+"
+`;
diff --git a/tests/for/abnormal.js b/tests/for/abnormal.js
new file mode 100644
index 000000000000..cc588841c2d6
--- /dev/null
+++ b/tests/for/abnormal.js
@@ -0,0 +1,47 @@
+/* @flow */
+
+function foo(x: boolean) {
+  var max = 10;
+  for (var ii = 0; ii < max; ii++) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function baz(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    continue;
+  }
+  console.log('this is still reachable');
+}
+
+function bliffl(x: boolean) {
+  var max = 10;
+  loop1: for (var ii = 0; ii < max; ii++) {
+    loop2: for (var jj = 0; jj < max; jj++) {
+      break loop1;
+    }
+    console.log('this is still reachable');
+  }
+  console.log('this is still reachable');
+}
+
+function corge(x: boolean) {
+  var max = 0;
+  for (var ii = 0; ii < max; ii++) {
+    break;
+  }
+  console.log('this is still reachable');
+}
diff --git a/tests/for/abnormal_for_in.js b/tests/for/abnormal_for_in.js
new file mode 100644
index 000000000000..add7d98c52b2
--- /dev/null
+++ b/tests/for/abnormal_for_in.js
@@ -0,0 +1,42 @@
+function foo(x: boolean) {
+  var obj = { a: 1, b: 2};
+  for (var prop in obj) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  for (var prop in {}) {
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function baz(x: boolean) {
+  for (var prop in {}) {
+    continue;
+  }
+  console.log('this is still reachable');
+}
+
+function bliffl(x: boolean) {
+  var obj = { a: 1, b: 2};
+  loop1: for (var prop1 in obj) {
+    loop2: for (var prop2 in obj) {
+      break loop1;
+    }
+    console.log('this is still reachable');
+  }
+  console.log('this is still reachable');
+}
+
+function corge(x: boolean) {
+  for (var prop in {}) {
+    break;
+  }
+  console.log('this is still reachable');
+}
diff --git a/tests/for/abnormal_for_of.js b/tests/for/abnormal_for_of.js
new file mode 100644
index 000000000000..f6724018ed55
--- /dev/null
+++ b/tests/for/abnormal_for_of.js
@@ -0,0 +1,42 @@
+function foo(x: boolean) {
+  var arr = [1, 2, 3];
+  for (var elem of arr) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  for (var elem of []) {
+    return;
+  }
+  console.log('this is still reachable');
+}
+
+function baz(x: boolean) {
+  for (var elem of []) {
+    continue;
+  }
+  console.log('this is still reachable');
+}
+
+function bliffl(x: boolean) {
+  var arr = [1, 2, 3];
+  loop1: for (var elem of arr) {
+    loop2: for (var elem of arr) {
+      break loop1;
+    }
+    console.log('this is still reachable');
+  }
+  console.log('this is still reachable');
+}
+
+function corge(x: boolean) {
+  for (var elem of []) {
+    break;
+  }
+  console.log('this is still reachable');
+}
diff --git a/tests/for/jsfmt.spec.js b/tests/for/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/for/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/forof/__snapshots__/jsfmt.spec.js.snap b/tests/forof/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c772d3d905fc
--- /dev/null
+++ b/tests/forof/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,72 @@
+exports[`test forof.js 1`] = `
+"/**
+ * @flow
+ */
+
+function testArray(arr: Array<number>): void {
+  for (var x of arr) {
+    (x: string); // Error - number ~> string
+  }
+}
+
+function testIterable1(iterable: Iterable<number>): void {
+  for (var x of iterable) {
+    (x: string); // Error - number ~> string
+  }
+}
+
+function testIterable2(iterable: Iterable<*>): void {
+  for (var x of iterable) {
+    (x: string);
+  }
+}
+
+function testString(str: string): void {
+  for (var x of str) {
+    (x: number); // Error - string ~> number
+  }
+}
+
+function testMap1(map: Map<string, number>): void {
+  for (var elem of map) {
+    (elem: [string, number]);
+    (elem: number); // Error - tuple ~> number
+  }
+}
+
+function testMap2(map: Map<*, *>): void {
+  for (var elem of map) {
+    (elem: [number, string]); // Any tuple is fine
+    (elem: number); // Error - tuple ~> number
+  }
+}
+
+function testSet1(set: Set<string>): void {
+  for (var x of set) {
+    (x: number); // Error - string ~> number
+  }
+}
+
+function testSet2(set: Set<*>): void {
+  for (var x of set) {
+    (x: number); // Anything goes
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/forof/forof.js b/tests/forof/forof.js
new file mode 100644
index 000000000000..ffcece1b14a0
--- /dev/null
+++ b/tests/forof/forof.js
@@ -0,0 +1,53 @@
+/**
+ * @flow
+ */
+
+function testArray(arr: Array<number>): void {
+  for (var x of arr) {
+    (x: string); // Error - number ~> string
+  }
+}
+
+function testIterable1(iterable: Iterable<number>): void {
+  for (var x of iterable) {
+    (x: string); // Error - number ~> string
+  }
+}
+
+function testIterable2(iterable: Iterable<*>): void {
+  for (var x of iterable) {
+    (x: string);
+  }
+}
+
+function testString(str: string): void {
+  for (var x of str) {
+    (x: number); // Error - string ~> number
+  }
+}
+
+function testMap1(map: Map<string, number>): void {
+  for (var elem of map) {
+    (elem: [string, number]);
+    (elem: number); // Error - tuple ~> number
+  }
+}
+
+function testMap2(map: Map<*, *>): void {
+  for (var elem of map) {
+    (elem: [number, string]); // Any tuple is fine
+    (elem: number); // Error - tuple ~> number
+  }
+}
+
+function testSet1(set: Set<string>): void {
+  for (var x of set) {
+    (x: number); // Error - string ~> number
+  }
+}
+
+function testSet2(set: Set<*>): void {
+  for (var x of set) {
+    (x: number); // Anything goes
+  }
+}
diff --git a/tests/forof/jsfmt.spec.js b/tests/forof/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/forof/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/function/__snapshots__/jsfmt.spec.js.snap b/tests/function/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..668c46396d01
--- /dev/null
+++ b/tests/function/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,287 @@
+exports[`test apply.js 1`] = `
+"function test(a: string, b: number): number {
+  return this.length; // expect []/\"\" this
+}
+
+// tuples flow correctly into params
+test.apply(\"\", [\"\", 0]);
+
+// wrong this is an error
+test.apply(0, [\"\", 0]); // error: lookup \`length\` on Number
+
+// not enough arguments is an error (via incompatible RestT)
+test.apply(\"\", [\"\"]); // error: string ~> number
+
+// mistyped arguments is an error
+test.apply(\"\", [\"\", \"\"]); // error: string ~> number (2nd arg)
+test.apply(\"\", [0, 0]); // error: number ~> string (1st arg)
+
+// resolve args array from tvar
+function f(args) { test.apply(\"\", args) }
+f([\"\", 0]); // OK
+f([\"\", \"\"]); // error: string ~> number (2nd arg)
+f([0, 0]); // error: number ~> string (1st arg)
+
+// expect array
+test.apply(\"\", \"not array\"); // error: expect array of args
+
+// expect 4 errors:
+// - lookup length on Number (because 0 is used as \`this\`)
+// - 123 is not a string
+// - \'foo\' is not a number
+// - return type (number) is not void
+(test.call.apply(test, [0, 123, \'foo\']): void);
+
+// expect 2 errors:
+// - lookup length on number (0 is used as \`this\`)
+// - 123 is not a string
+(test.bind.apply(test, [0, 123]): (b: number) => number);
+
+// args are optional
+function test2(): number { return 0; }
+(test2.apply(): number);
+(test2.apply(\"\"): number);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test bind.js 1`] = `
+"// @flow
+
+let tests = [
+  function(x: (a: string, b: string) => void) {
+    let y = x.bind(x, \'foo\');
+    y(\'bar\'); // ok
+    y(123); // error, number !~> string
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test call.js 1`] = `
+"// @flow
+
+function test(a: string, b: number): number {
+  return this.length; // expect []/\"\" this
+}
+
+// args flow correctly into params
+test.call(\"\", \"\", 0);
+
+// wrong this is an error
+test.call(0, \"\", 0); // error: lookup \`length\` on Number
+
+// not enough arguments is an error (via incompatible RestT)
+test.call(\"\", \"\"); // error: string ~> number
+
+// mistyped arguments is an error
+test.call(\"\", \"\", \"\"); // error: string ~> number (2nd arg)
+test.call(\"\", 0, 0); // error: number ~> string (1st arg)
+
+// resolve args array from tvar
+function f(args) { test.call(\"\", args[0], args[1]) }
+f([\"\", 0]); // OK
+f([\"\", \"\"]); // error: string ~> number (2nd arg)
+f([0, 0]); // error: number ~> string (1st arg)
+
+// expect 3 errors:
+// - lookup length on Number (0 used as \`this\`)
+// - number !~> string (param a)
+// - string !~> number (param b)
+(test.apply.call(test, 0, [0, \'foo\']): number);
+
+// args are optional
+function test2(): number { return 0; }
+(test2.call(): number);
+(test2.call(\"\"): number);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function test(a: string, b: number): number {
+  return this.length;// expect []/\"\" this
+}
+// args flow correctly into params
+test.call(\"\", \"\", 0);
+// wrong this is an error
+test.call(0, \"\", 0);// error: lookup \`length\` on Number
+// not enough arguments is an error (via incompatible RestT)
+test.call(\"\", \"\");// error: string ~> number
+// mistyped arguments is an error
+test.call(\"\", \"\", \"\");// error: string ~> number (2nd arg)
+test.call(\"\", 0, 0);// error: number ~> string (1st arg)
+// resolve args array from tvar
+function f(args) {
+  test.call(\"\", args[0], args[1]);
+}
+f([ \"\", 0 ]);// OK
+f([ \"\", \"\" ]);// error: string ~> number (2nd arg)
+f([ 0, 0 ]);// error: number ~> string (1st arg)
+// expect 3 errors:
+// - lookup length on Number (0 used as \`this\`)
+// - number !~> string (param a)
+// - string !~> number (param b)
+(test.apply.call(test, 0, [ 0, \"foo\" ]): number);
+// args are optional
+function test2(): number {
+  return 0;
+}
+(test2.call(): number);
+(test2.call(\"\"): number);
+
+"
+`;
+
+exports[`test function.js 1`] = `
+"/**
+ * @flow
+ */
+
+// Previously we represented Function as (...rest: any) => any
+// This means the following wouldn\'t pass, because that arrow function
+// can only be called with 3 arguments.
+var a: Function = (a, b, c) => 123;
+
+var b: Function = function(a: number, b: number): number { return a + b; };
+
+class C {}
+
+var c: Function = C;
+
+function good(x: Function, MyThing: Function): number {
+  var o: Object = x; // Function is an Object
+  x.foo = 123;
+  x[\'foo\'] = 456;
+  x();
+  <MyThing />;
+  var {...something} = x;
+  Object.assign(x, {hi: \'there\'});
+  Object.keys(x);
+  return x.bar + x[\'bar\'] + x.lala();
+}
+
+function bad(x: Function, y: Object): void {
+  var a: number = x; // Error
+  var b: string = x; // Error
+  var c: Function = y; // Object is not a Function
+}
+
+let tests = [
+  function(y: () => void, z: Function) {
+    function x() {}
+    (x.length: void); // error, it\'s a number
+    (y.length: void); // error, it\'s a number
+    (z.length: void); // error, it\'s a number
+
+    (x.name: void); // error, it\'s a string
+    (y.name: void); // error, it\'s a string
+    (z.name: void); // error, it\'s a string
+  },
+
+  function(y: () => void, z: Function) {
+    function x() {}
+    x.length = \'foo\'; // error, it\'s a number
+    y.length = \'foo\'; // error, it\'s a number
+    z.length = \'foo\'; // error, it\'s a number
+
+    x.name = 123; // error, it\'s a string
+    y.name = 123; // error, it\'s a string
+    z.name = 123; // error, it\'s a string
+
+    // Non-(Function.prototype) properties on a \`Function\` type should be \`any\`
+    (z.foo: number);
+    (z.foo: string);
+  },
+];
+
+// \`Function\` types can be bound (resulting in a \`Function\` type)
+var d: Function = () => 1;
+var e = (d.bind(1): Function)();
+(e: number);
+(e: string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test rest.js 1`] = `
+"/* regression tests */
+
+function rest_array<T>(...xs: Array<T>): T {
+  return xs[0];
+}
+
+// Warn, singleton tuple types don\'t represent rest params
+function rest_tuple<T>(...xs: [T]): T {
+  return xs[0];
+}
+
+function rest_any(...xs: any): any {
+  return xs[0];
+}
+
+// Warn, arbitrary subtypes of an array type don\'t represent rest params
+function rest_t<U, T: Array<U>>(...xs: T): U {
+  return xs[0];
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/function/apply.js b/tests/function/apply.js
new file mode 100644
index 000000000000..527839d334c1
--- /dev/null
+++ b/tests/function/apply.js
@@ -0,0 +1,42 @@
+function test(a: string, b: number): number {
+  return this.length; // expect []/"" this
+}
+
+// tuples flow correctly into params
+test.apply("", ["", 0]);
+
+// wrong this is an error
+test.apply(0, ["", 0]); // error: lookup `length` on Number
+
+// not enough arguments is an error (via incompatible RestT)
+test.apply("", [""]); // error: string ~> number
+
+// mistyped arguments is an error
+test.apply("", ["", ""]); // error: string ~> number (2nd arg)
+test.apply("", [0, 0]); // error: number ~> string (1st arg)
+
+// resolve args array from tvar
+function f(args) { test.apply("", args) }
+f(["", 0]); // OK
+f(["", ""]); // error: string ~> number (2nd arg)
+f([0, 0]); // error: number ~> string (1st arg)
+
+// expect array
+test.apply("", "not array"); // error: expect array of args
+
+// expect 4 errors:
+// - lookup length on Number (because 0 is used as `this`)
+// - 123 is not a string
+// - 'foo' is not a number
+// - return type (number) is not void
+(test.call.apply(test, [0, 123, 'foo']): void);
+
+// expect 2 errors:
+// - lookup length on number (0 is used as `this`)
+// - 123 is not a string
+(test.bind.apply(test, [0, 123]): (b: number) => number);
+
+// args are optional
+function test2(): number { return 0; }
+(test2.apply(): number);
+(test2.apply(""): number);
diff --git a/tests/function/bind.js b/tests/function/bind.js
new file mode 100644
index 000000000000..1e29e8ee60eb
--- /dev/null
+++ b/tests/function/bind.js
@@ -0,0 +1,9 @@
+// @flow
+
+let tests = [
+  function(x: (a: string, b: string) => void) {
+    let y = x.bind(x, 'foo');
+    y('bar'); // ok
+    y(123); // error, number !~> string
+  },
+];
diff --git a/tests/function/call.js b/tests/function/call.js
new file mode 100644
index 000000000000..ebb6acd2e8a3
--- /dev/null
+++ b/tests/function/call.js
@@ -0,0 +1,35 @@
+// @flow
+
+function test(a: string, b: number): number {
+  return this.length; // expect []/"" this
+}
+
+// args flow correctly into params
+test.call("", "", 0);
+
+// wrong this is an error
+test.call(0, "", 0); // error: lookup `length` on Number
+
+// not enough arguments is an error (via incompatible RestT)
+test.call("", ""); // error: string ~> number
+
+// mistyped arguments is an error
+test.call("", "", ""); // error: string ~> number (2nd arg)
+test.call("", 0, 0); // error: number ~> string (1st arg)
+
+// resolve args array from tvar
+function f(args) { test.call("", args[0], args[1]) }
+f(["", 0]); // OK
+f(["", ""]); // error: string ~> number (2nd arg)
+f([0, 0]); // error: number ~> string (1st arg)
+
+// expect 3 errors:
+// - lookup length on Number (0 used as `this`)
+// - number !~> string (param a)
+// - string !~> number (param b)
+(test.apply.call(test, 0, [0, 'foo']): number);
+
+// args are optional
+function test2(): number { return 0; }
+(test2.call(): number);
+(test2.call(""): number);
diff --git a/tests/function/function.js b/tests/function/function.js
new file mode 100644
index 000000000000..496b3031d645
--- /dev/null
+++ b/tests/function/function.js
@@ -0,0 +1,66 @@
+/**
+ * @flow
+ */
+
+// Previously we represented Function as (...rest: any) => any
+// This means the following wouldn't pass, because that arrow function
+// can only be called with 3 arguments.
+var a: Function = (a, b, c) => 123;
+
+var b: Function = function(a: number, b: number): number { return a + b; };
+
+class C {}
+
+var c: Function = C;
+
+function good(x: Function, MyThing: Function): number {
+  var o: Object = x; // Function is an Object
+  x.foo = 123;
+  x['foo'] = 456;
+  x();
+  <MyThing />;
+  var {...something} = x;
+  Object.assign(x, {hi: 'there'});
+  Object.keys(x);
+  return x.bar + x['bar'] + x.lala();
+}
+
+function bad(x: Function, y: Object): void {
+  var a: number = x; // Error
+  var b: string = x; // Error
+  var c: Function = y; // Object is not a Function
+}
+
+let tests = [
+  function(y: () => void, z: Function) {
+    function x() {}
+    (x.length: void); // error, it's a number
+    (y.length: void); // error, it's a number
+    (z.length: void); // error, it's a number
+
+    (x.name: void); // error, it's a string
+    (y.name: void); // error, it's a string
+    (z.name: void); // error, it's a string
+  },
+
+  function(y: () => void, z: Function) {
+    function x() {}
+    x.length = 'foo'; // error, it's a number
+    y.length = 'foo'; // error, it's a number
+    z.length = 'foo'; // error, it's a number
+
+    x.name = 123; // error, it's a string
+    y.name = 123; // error, it's a string
+    z.name = 123; // error, it's a string
+
+    // Non-(Function.prototype) properties on a `Function` type should be `any`
+    (z.foo: number);
+    (z.foo: string);
+  },
+];
+
+// `Function` types can be bound (resulting in a `Function` type)
+var d: Function = () => 1;
+var e = (d.bind(1): Function)();
+(e: number);
+(e: string);
diff --git a/tests/function/jsfmt.spec.js b/tests/function/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/function/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/function/rest.js b/tests/function/rest.js
new file mode 100644
index 000000000000..78f52926f951
--- /dev/null
+++ b/tests/function/rest.js
@@ -0,0 +1,19 @@
+/* regression tests */
+
+function rest_array<T>(...xs: Array<T>): T {
+  return xs[0];
+}
+
+// Warn, singleton tuple types don't represent rest params
+function rest_tuple<T>(...xs: [T]): T {
+  return xs[0];
+}
+
+function rest_any(...xs: any): any {
+  return xs[0];
+}
+
+// Warn, arbitrary subtypes of an array type don't represent rest params
+function rest_t<U, T: Array<U>>(...xs: T): U {
+  return xs[0];
+}
diff --git a/tests/funrec/__snapshots__/jsfmt.spec.js.snap b/tests/funrec/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..945fe504c59b
--- /dev/null
+++ b/tests/funrec/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,19 @@
+exports[`test funrec.js 1`] = `
+"function bar(x) { return x; }
+function foo() {
+    return function bound() {
+        return bar(bound);
+    };
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function bar(x) {
+  return x;
+}
+function foo() {
+  return function bound() {
+    return bar(bound);
+  };
+}
+
+"
+`;
diff --git a/tests/funrec/funrec.js b/tests/funrec/funrec.js
new file mode 100644
index 000000000000..4f597e22d574
--- /dev/null
+++ b/tests/funrec/funrec.js
@@ -0,0 +1,6 @@
+function bar(x) { return x; }
+function foo() {
+    return function bound() {
+        return bar(bound);
+    };
+}
diff --git a/tests/funrec/jsfmt.spec.js b/tests/funrec/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/funrec/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/generators/__snapshots__/jsfmt.spec.js.snap b/tests/generators/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..67db9796bc48
--- /dev/null
+++ b/tests/generators/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,454 @@
+exports[`test class.js 1`] = `
+"class GeneratorExamples {
+  *stmt_yield(): Generator<number, void, void> {
+    yield 0; // ok
+    yield \"\"; // error: string ~> number
+  }
+
+  *stmt_next(): Generator<void, void, number> {
+    var a = yield;
+    if (a) {
+      (a : number); // ok
+    }
+
+    var b = yield;
+    if (b) {
+      (b : string); // error: number ~> string
+    }
+  }
+
+  *stmt_return_ok(): Generator<void, number, void> {
+    return 0; // ok
+  }
+
+  *stmt_return_err(): Generator<void, number, void> {
+    return \"\"; // error: string ~> number
+  }
+
+  *infer_stmt() {
+    var x: boolean = yield 0; // error: number ~> boolean
+    return \"\";
+  }
+
+  *widen_next() {
+    var x = yield 0;
+    if (typeof x === \"number\") {
+    } else if (typeof x === \"boolean\") {
+    } else {
+      (x : string) // ok, sherlock
+    }
+  }
+
+  *widen_yield() {
+    yield 0;
+    yield \"\";
+    yield true;
+  }
+
+  *delegate_next_generator() {
+    function *inner() {
+      var x: number = yield; // error: string ~> number
+    }
+    yield *inner();
+  }
+
+  *delegate_yield_generator() {
+    function *inner() {
+      yield \"\";
+    }
+
+    yield *inner();
+  }
+
+  *delegate_return_generator() {
+    function *inner() {
+      return \"\";
+    }
+
+    var x: number = yield *inner(); // error: string ~> number
+  }
+
+  // only generators can make use of a value passed to next
+  *delegate_next_iterable(xs: Array<number>) {
+    yield *xs;
+  }
+
+  *delegate_yield_iterable(xs: Array<number>) {
+    yield *xs;
+  }
+
+  *delegate_return_iterable(xs: Array<number>) {
+    var x: void = yield *xs // ok: Iterator has no yield value
+  }
+
+  *generic_yield<Y>(y: Y): Generator<Y,void,void> {
+    yield y;
+  }
+
+  *generic_return<R>(r: R): Generator<void,R,void> {
+    return r;
+  }
+
+  *generic_next<N>(): Generator<void,N,N> {
+    return yield undefined;
+  }
+}
+
+var examples = new GeneratorExamples();
+
+for (var x of examples.infer_stmt()) { (x : string) } // error: number ~> string
+
+var infer_stmt_next = examples.infer_stmt().next(0).value; // error: number ~> boolean
+if (typeof infer_stmt_next === \"undefined\") {
+} else if (typeof infer_stmt_next === \"number\") {
+} else {
+  (infer_stmt_next : boolean) // error: string ~> boolean
+}
+
+examples.widen_next().next(0)
+examples.widen_next().next(\"\")
+examples.widen_next().next(true)
+
+for (var x of examples.widen_yield()) {
+  if (typeof x === \"number\") {
+  } else if (typeof x === \"boolean\") {
+  } else {
+    (x : string) // ok, sherlock
+  }
+}
+
+examples.delegate_next_generator().next(\"\");
+
+for (var x of examples.delegate_yield_generator()) {
+  (x : number) // error: string ~> number
+}
+
+examples.delegate_next_iterable([]).next(\"\"); // error: Iterator has no next value
+
+for (var x of examples.delegate_yield_iterable([])) {
+  (x : string) // error: number ~> string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test class_failure.js 1`] = `
+"// generalization of failure in class.js
+
+class GeneratorExamples<X> {
+  *infer_stmt() {
+    var x: boolean = yield 0; // error: number ~> boolean
+    return \"\";
+  }
+}
+
+var examples = new GeneratorExamples();
+
+for (var x of examples.infer_stmt()) { (x : string) } // error: number ~> string
+
+var infer_stmt_next = examples.infer_stmt().next(0).value; // error: number ~> boolean
+
+if (typeof infer_stmt_next === \"undefined\") {
+} else if (typeof infer_stmt_next === \"number\") {
+} else {
+  (infer_stmt_next : boolean) // error: string ~> boolean
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test generators.js 1`] = `
+"function *stmt_yield(): Generator<number, void, void> {
+  yield 0; // ok
+  yield \"\"; // error: string ~> number
+}
+
+function *stmt_next(): Generator<void, void, number> {
+  var a = yield;
+  if (a) {
+    (a : number); // ok
+  }
+
+  var b = yield;
+  if (b) {
+    (b : string); // error: number ~> string
+  }
+}
+
+function *stmt_return_ok(): Generator<void, number, void> {
+  return 0; // ok
+}
+
+function *stmt_return_err(): Generator<void, number, void> {
+  return \"\"; // error: string ~> number
+}
+
+function *infer_stmt() {
+  var x: boolean = yield 0;
+  return \"\";
+}
+for (var x of infer_stmt()) { (x : string) } // error: number ~> string
+var infer_stmt_next = infer_stmt().next(0).value; // error: number ~> boolean
+if (typeof infer_stmt_next === \"undefined\") {
+} else if (typeof infer_stmt_next === \"number\") {
+} else {
+  (infer_stmt_next : boolean) // error: string ~> boolean
+}
+
+function *widen_next() {
+  var x = yield 0;
+  if (typeof x === \"number\") {
+  } else if (typeof x === \"boolean\") {
+  } else {
+    (x : string) // ok, sherlock
+  }
+}
+widen_next().next(0)
+widen_next().next(\"\")
+widen_next().next(true)
+
+function *widen_yield() {
+  yield 0;
+  yield \"\";
+  yield true;
+}
+for (var x of widen_yield()) {
+  if (typeof x === \"number\") {
+  } else if (typeof x === \"boolean\") {
+  } else {
+    (x : string) // ok, sherlock
+  }
+}
+
+function *delegate_next_generator() {
+  function *inner() {
+    var x: number = yield; // error: string ~> number
+  }
+  yield *inner();
+}
+delegate_next_generator().next(\"\");
+
+function *delegate_yield_generator() {
+  function *inner() {
+    yield \"\";
+  }
+
+  yield *inner();
+}
+for (var x of delegate_yield_generator()) {
+  (x : number) // error: string ~> number
+}
+
+function *delegate_return_generator() {
+  function *inner() {
+    return \"\";
+  }
+
+  var x: number = yield *inner(); // error: string ~> number
+}
+
+// only generators can make use of a value passed to next
+function *delegate_next_iterable(xs: Array<number>) {
+  yield *xs;
+}
+delegate_next_iterable([]).next(\"\"); // error: Iterator has no next value
+
+function *delegate_yield_iterable(xs: Array<number>) {
+  yield *xs;
+}
+for (var x of delegate_yield_iterable([])) {
+  (x : string) // error: number ~> string
+}
+
+function *delegate_return_iterable(xs: Array<number>) {
+  var x: void = yield *xs // ok: Iterator has no yield value
+}
+
+function *generic_yield<Y>(y: Y): Generator<Y,void,void> {
+  yield y;
+}
+
+function *generic_return<R>(r: R): Generator<void,R,void> {
+  return r;
+}
+
+function *generic_next<N>(): Generator<void,N,N> {
+  return yield undefined;
+}
+
+function *multiple_return(b) {
+  if (b) {
+    return 0;
+  } else {
+    return \"foo\";
+  }
+}
+let multiple_return_result = multiple_return().next();
+if (multiple_return_result.done) {
+  (multiple_return_result.value: void); // error: number|string ~> void
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test return.js 1`] = `
+"function test1(gen: Generator<void, string, void>) {
+  // You can pass whatever you like to return, it doesn\'t need to be related to
+  // the Generator\'s return type
+  var ret = gen.return(0);
+  (ret.value: void); // error: string | number ~> void
+}
+
+// However, a generator can \"refuse\" the return by catching an exception and
+// yielding or returning internally.
+function *refuse_return() {
+  try {
+    yield 1;
+  } finally {
+    return 0;
+  }
+}
+var refuse_return_gen = refuse_return();
+var refuse_return_result = refuse_return_gen.return(\"string\");
+if (refuse_return_result.done) {
+  (refuse_return_result.value: string); // error: number | void ~> string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test throw.js 1`] = `
+"function *catch_return() {
+  try {
+    yield 0;
+  } catch (e) {
+    return e;
+  }
+}
+
+var catch_return_value = catch_return().throw(\"\").value;
+if (catch_return_value !== undefined) {
+  (catch_return_value : string); // error: number ~> string
+}
+
+function *yield_return() {
+  try {
+    yield 0;
+    return;
+  } catch (e) {
+    yield e;
+  }
+}
+var yield_return_value = yield_return().throw(\"\").value;
+if (yield_return_value !== undefined) {
+  (yield_return_value: string); // error: number ~> string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function* catch_return() {
+  try {
+    yield 0;
+  } catch (e) {
+    return e;
+  }
+}
+var catch_return_value = catch_return().throw(\"\").value;
+if (catch_return_value !== undefined) {
+  (catch_return_value: string);// error: number ~> string
+}
+function* yield_return() {
+  try {
+    yield 0;
+    return;
+  } catch (e) {
+    yield e;
+  }
+}
+var yield_return_value = yield_return().throw(\"\").value;
+if (yield_return_value !== undefined) {
+  (yield_return_value: string);// error: number ~> string
+}
+
+"
+`;
+
+exports[`test variance.js 1`] = `
+"declare var g1: Generator<string, string, ?string>;
+var g2: Generator<?string, ?string, string> = g1;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/generators/class.js b/tests/generators/class.js
new file mode 100644
index 000000000000..8e88486f3831
--- /dev/null
+++ b/tests/generators/class.js
@@ -0,0 +1,129 @@
+class GeneratorExamples {
+  *stmt_yield(): Generator<number, void, void> {
+    yield 0; // ok
+    yield ""; // error: string ~> number
+  }
+
+  *stmt_next(): Generator<void, void, number> {
+    var a = yield;
+    if (a) {
+      (a : number); // ok
+    }
+
+    var b = yield;
+    if (b) {
+      (b : string); // error: number ~> string
+    }
+  }
+
+  *stmt_return_ok(): Generator<void, number, void> {
+    return 0; // ok
+  }
+
+  *stmt_return_err(): Generator<void, number, void> {
+    return ""; // error: string ~> number
+  }
+
+  *infer_stmt() {
+    var x: boolean = yield 0; // error: number ~> boolean
+    return "";
+  }
+
+  *widen_next() {
+    var x = yield 0;
+    if (typeof x === "number") {
+    } else if (typeof x === "boolean") {
+    } else {
+      (x : string) // ok, sherlock
+    }
+  }
+
+  *widen_yield() {
+    yield 0;
+    yield "";
+    yield true;
+  }
+
+  *delegate_next_generator() {
+    function *inner() {
+      var x: number = yield; // error: string ~> number
+    }
+    yield *inner();
+  }
+
+  *delegate_yield_generator() {
+    function *inner() {
+      yield "";
+    }
+
+    yield *inner();
+  }
+
+  *delegate_return_generator() {
+    function *inner() {
+      return "";
+    }
+
+    var x: number = yield *inner(); // error: string ~> number
+  }
+
+  // only generators can make use of a value passed to next
+  *delegate_next_iterable(xs: Array<number>) {
+    yield *xs;
+  }
+
+  *delegate_yield_iterable(xs: Array<number>) {
+    yield *xs;
+  }
+
+  *delegate_return_iterable(xs: Array<number>) {
+    var x: void = yield *xs // ok: Iterator has no yield value
+  }
+
+  *generic_yield<Y>(y: Y): Generator<Y,void,void> {
+    yield y;
+  }
+
+  *generic_return<R>(r: R): Generator<void,R,void> {
+    return r;
+  }
+
+  *generic_next<N>(): Generator<void,N,N> {
+    return yield undefined;
+  }
+}
+
+var examples = new GeneratorExamples();
+
+for (var x of examples.infer_stmt()) { (x : string) } // error: number ~> string
+
+var infer_stmt_next = examples.infer_stmt().next(0).value; // error: number ~> boolean
+if (typeof infer_stmt_next === "undefined") {
+} else if (typeof infer_stmt_next === "number") {
+} else {
+  (infer_stmt_next : boolean) // error: string ~> boolean
+}
+
+examples.widen_next().next(0)
+examples.widen_next().next("")
+examples.widen_next().next(true)
+
+for (var x of examples.widen_yield()) {
+  if (typeof x === "number") {
+  } else if (typeof x === "boolean") {
+  } else {
+    (x : string) // ok, sherlock
+  }
+}
+
+examples.delegate_next_generator().next("");
+
+for (var x of examples.delegate_yield_generator()) {
+  (x : number) // error: string ~> number
+}
+
+examples.delegate_next_iterable([]).next(""); // error: Iterator has no next value
+
+for (var x of examples.delegate_yield_iterable([])) {
+  (x : string) // error: number ~> string
+}
diff --git a/tests/generators/class_failure.js b/tests/generators/class_failure.js
new file mode 100644
index 000000000000..42697f5de7ff
--- /dev/null
+++ b/tests/generators/class_failure.js
@@ -0,0 +1,20 @@
+// generalization of failure in class.js
+
+class GeneratorExamples<X> {
+  *infer_stmt() {
+    var x: boolean = yield 0; // error: number ~> boolean
+    return "";
+  }
+}
+
+var examples = new GeneratorExamples();
+
+for (var x of examples.infer_stmt()) { (x : string) } // error: number ~> string
+
+var infer_stmt_next = examples.infer_stmt().next(0).value; // error: number ~> boolean
+
+if (typeof infer_stmt_next === "undefined") {
+} else if (typeof infer_stmt_next === "number") {
+} else {
+  (infer_stmt_next : boolean) // error: string ~> boolean
+}
diff --git a/tests/generators/generators.js b/tests/generators/generators.js
new file mode 100644
index 000000000000..c59630bae767
--- /dev/null
+++ b/tests/generators/generators.js
@@ -0,0 +1,129 @@
+function *stmt_yield(): Generator<number, void, void> {
+  yield 0; // ok
+  yield ""; // error: string ~> number
+}
+
+function *stmt_next(): Generator<void, void, number> {
+  var a = yield;
+  if (a) {
+    (a : number); // ok
+  }
+
+  var b = yield;
+  if (b) {
+    (b : string); // error: number ~> string
+  }
+}
+
+function *stmt_return_ok(): Generator<void, number, void> {
+  return 0; // ok
+}
+
+function *stmt_return_err(): Generator<void, number, void> {
+  return ""; // error: string ~> number
+}
+
+function *infer_stmt() {
+  var x: boolean = yield 0;
+  return "";
+}
+for (var x of infer_stmt()) { (x : string) } // error: number ~> string
+var infer_stmt_next = infer_stmt().next(0).value; // error: number ~> boolean
+if (typeof infer_stmt_next === "undefined") {
+} else if (typeof infer_stmt_next === "number") {
+} else {
+  (infer_stmt_next : boolean) // error: string ~> boolean
+}
+
+function *widen_next() {
+  var x = yield 0;
+  if (typeof x === "number") {
+  } else if (typeof x === "boolean") {
+  } else {
+    (x : string) // ok, sherlock
+  }
+}
+widen_next().next(0)
+widen_next().next("")
+widen_next().next(true)
+
+function *widen_yield() {
+  yield 0;
+  yield "";
+  yield true;
+}
+for (var x of widen_yield()) {
+  if (typeof x === "number") {
+  } else if (typeof x === "boolean") {
+  } else {
+    (x : string) // ok, sherlock
+  }
+}
+
+function *delegate_next_generator() {
+  function *inner() {
+    var x: number = yield; // error: string ~> number
+  }
+  yield *inner();
+}
+delegate_next_generator().next("");
+
+function *delegate_yield_generator() {
+  function *inner() {
+    yield "";
+  }
+
+  yield *inner();
+}
+for (var x of delegate_yield_generator()) {
+  (x : number) // error: string ~> number
+}
+
+function *delegate_return_generator() {
+  function *inner() {
+    return "";
+  }
+
+  var x: number = yield *inner(); // error: string ~> number
+}
+
+// only generators can make use of a value passed to next
+function *delegate_next_iterable(xs: Array<number>) {
+  yield *xs;
+}
+delegate_next_iterable([]).next(""); // error: Iterator has no next value
+
+function *delegate_yield_iterable(xs: Array<number>) {
+  yield *xs;
+}
+for (var x of delegate_yield_iterable([])) {
+  (x : string) // error: number ~> string
+}
+
+function *delegate_return_iterable(xs: Array<number>) {
+  var x: void = yield *xs // ok: Iterator has no yield value
+}
+
+function *generic_yield<Y>(y: Y): Generator<Y,void,void> {
+  yield y;
+}
+
+function *generic_return<R>(r: R): Generator<void,R,void> {
+  return r;
+}
+
+function *generic_next<N>(): Generator<void,N,N> {
+  return yield undefined;
+}
+
+function *multiple_return(b) {
+  if (b) {
+    return 0;
+  } else {
+    return "foo";
+  }
+}
+let multiple_return_result = multiple_return().next();
+if (multiple_return_result.done) {
+  (multiple_return_result.value: void); // error: number|string ~> void
+}
diff --git a/tests/generators/jsfmt.spec.js b/tests/generators/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/generators/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/generators/return.js b/tests/generators/return.js
new file mode 100644
index 000000000000..411d5ec17de0
--- /dev/null
+++ b/tests/generators/return.js
@@ -0,0 +1,21 @@
+function test1(gen: Generator<void, string, void>) {
+  // You can pass whatever you like to return, it doesn't need to be related to
+  // the Generator's return type
+  var ret = gen.return(0);
+  (ret.value: void); // error: string | number ~> void
+}
+
+// However, a generator can "refuse" the return by catching an exception and
+// yielding or returning internally.
+function *refuse_return() {
+  try {
+    yield 1;
+  } finally {
+    return 0;
+  }
+}
+var refuse_return_gen = refuse_return();
+var refuse_return_result = refuse_return_gen.return("string");
+if (refuse_return_result.done) {
+  (refuse_return_result.value: string); // error: number | void ~> string
+}
diff --git a/tests/generators/throw.js b/tests/generators/throw.js
new file mode 100644
index 000000000000..de4ae94883d3
--- /dev/null
+++ b/tests/generators/throw.js
@@ -0,0 +1,25 @@
+function *catch_return() {
+  try {
+    yield 0;
+  } catch (e) {
+    return e;
+  }
+}
+
+var catch_return_value = catch_return().throw("").value;
+if (catch_return_value !== undefined) {
+  (catch_return_value : string); // error: number ~> string
+}
+
+function *yield_return() {
+  try {
+    yield 0;
+    return;
+  } catch (e) {
+    yield e;
+  }
+}
+var yield_return_value = yield_return().throw("").value;
+if (yield_return_value !== undefined) {
+  (yield_return_value: string); // error: number ~> string
+}
diff --git a/tests/generators/variance.js b/tests/generators/variance.js
new file mode 100644
index 000000000000..021c3eddef17
--- /dev/null
+++ b/tests/generators/variance.js
@@ -0,0 +1,2 @@
+declare var g1: Generator<string, string, ?string>;
+var g2: Generator<?string, ?string, string> = g1;
diff --git a/tests/generics/__snapshots__/jsfmt.spec.js.snap b/tests/generics/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0edf6ac3fab0
--- /dev/null
+++ b/tests/generics/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,62 @@
+exports[`test generics.js 1`] = `
+"class C<X> {
+  x:X;
+  constructor(x:X) { this.x = x; }
+  get():X { return this.x; }
+}
+
+class D<T> {
+  x:T;
+  m<S>(z:S,u:T,v):S {
+    this.x = u;
+    v.u = u;
+    return z;
+  }
+}
+
+var d = new D();
+var o = {};
+var b = d.m(true,0,o);
+var s:string = d.x;
+var n:number = o.u;
+
+class E<X> extends C<X> {
+    //x:X;
+    set(x:X):X { /*return x;*/ this.x = x; return /*this.x; */this.get(); }
+}
+
+var e = new E(); // error: too few arguments to inherited constructor
+var x:string = e.set(0);
+
+class F<X> { }
+class G<Y> extends F<Array<Y>> {}
+class H<Z> extends G<Array<Z>> {
+    x:Z;
+    foo(x:Z) { this.x = x; }
+}
+
+var h1 = new H();
+h1.foo([\"...\"]);
+var h2:F<Array<Array<Array<number>>>> = h1;
+
+var obj : Object<string, string> = {} // error, arity 0
+var fn : Function<string> = function() { return \'foo\'; } // error, arity 0
+var fn : function<string> = function() { return \'foo\'; } // error, arity 0
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (43:9)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
diff --git a/tests/generics/generics.js b/tests/generics/generics.js
new file mode 100644
index 000000000000..603f3aebb836
--- /dev/null
+++ b/tests/generics/generics.js
@@ -0,0 +1,43 @@
+class C<X> {
+  x:X;
+  constructor(x:X) { this.x = x; }
+  get():X { return this.x; }
+}
+
+class D<T> {
+  x:T;
+  m<S>(z:S,u:T,v):S {
+    this.x = u;
+    v.u = u;
+    return z;
+  }
+}
+
+var d = new D();
+var o = {};
+var b = d.m(true,0,o);
+var s:string = d.x;
+var n:number = o.u;
+
+class E<X> extends C<X> {
+    //x:X;
+    set(x:X):X { /*return x;*/ this.x = x; return /*this.x; */this.get(); }
+}
+
+var e = new E(); // error: too few arguments to inherited constructor
+var x:string = e.set(0);
+
+class F<X> { }
+class G<Y> extends F<Array<Y>> {}
+class H<Z> extends G<Array<Z>> {
+    x:Z;
+    foo(x:Z) { this.x = x; }
+}
+
+var h1 = new H();
+h1.foo(["..."]);
+var h2:F<Array<Array<Array<number>>>> = h1;
+
+var obj : Object<string, string> = {} // error, arity 0
+var fn : Function<string> = function() { return 'foo'; } // error, arity 0
+var fn : function<string> = function() { return 'foo'; } // error, arity 0
diff --git a/tests/generics/jsfmt.spec.js b/tests/generics/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/generics/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/geolocation/__snapshots__/jsfmt.spec.js.snap b/tests/geolocation/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..989969569252
--- /dev/null
+++ b/tests/geolocation/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,39 @@
+exports[`test a.js 1`] = `
+"/* @flow */
+
+var geolocation = new Geolocation();
+var id = geolocation.watchPosition(
+  position => {
+    var coords: Coordinates = position.coords;
+    var accuracy: number = coords.accuracy;
+  },
+  e => {
+    var message: string = e.message;
+    switch (e.code) {
+      case e.PERMISSION_DENIED:
+      case e.POSITION_UNAVAILABLE:
+      case e.TIMEOUT:
+      default:
+        break;
+    }
+  }
+);
+geolocation.clearWatch(id);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/geolocation/a.js b/tests/geolocation/a.js
new file mode 100644
index 000000000000..21090c0c43b2
--- /dev/null
+++ b/tests/geolocation/a.js
@@ -0,0 +1,20 @@
+/* @flow */
+
+var geolocation = new Geolocation();
+var id = geolocation.watchPosition(
+  position => {
+    var coords: Coordinates = position.coords;
+    var accuracy: number = coords.accuracy;
+  },
+  e => {
+    var message: string = e.message;
+    switch (e.code) {
+      case e.PERMISSION_DENIED:
+      case e.POSITION_UNAVAILABLE:
+      case e.TIMEOUT:
+      default:
+        break;
+    }
+  }
+);
+geolocation.clearWatch(id);
diff --git a/tests/geolocation/jsfmt.spec.js b/tests/geolocation/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/geolocation/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/get-def/__snapshots__/jsfmt.spec.js.snap b/tests/get-def/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..11081a6e424b
--- /dev/null
+++ b/tests/get-def/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,83 @@
+exports[`test example.js 1`] = `
+"/* @flow */
+
+var lib = require('./library');
+
+function add(a: number, b: number): number {
+  return a + b;
+}
+
+var re = /^keynote (talk){2} (lightning){3,5} (talk){2} closing partytime!!!/
+
+// t123456
+add(lib.iTakeAString(42), 7);
+
+// D123456
+lib.bar();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var lib = require("./library");
+function add(a: number, b: number): number {
+  return a + b;
+}
+var re = /^keynote (talk){2} (lightning){3,5} (talk){2} closing partytime!!!/;
+// t123456
+add(lib.iTakeAString(42), 7);
+// D123456
+lib.bar();
+
+"
+`;
+
+exports[`test imports.js 1`] = `
+"// @flow
+
+import thing from "./helpers/exports_default.js";
+thing;
+
+import {foo, bar as baz} from "./helpers/exports_named.js";
+foo;
+baz;
+
+import * as things from "./helpers/exports_named.js";
+things;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import thing from "./helpers/exports_default.js";
+thing;
+import { foo, bar as baz } from "./helpers/exports_named.js";
+foo;
+baz;
+import * as things from "./helpers/exports_named.js";
+things;
+
+"
+`;
+
+exports[`test library.js 1`] = `
+"/* @flow */
+
+module.exports = {
+
+  iTakeAString: function(name: string): number {
+    return 42;
+  },
+
+  bar: function(): number {
+    return 42;
+  },
+
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports = {
+  iTakeAString: function(name: string): number {
+    return 42;
+  },
+  bar: function(): number {
+    return 42;
+  }
+};
+
+"
+`;
diff --git a/tests/get-def/example.js b/tests/get-def/example.js
new file mode 100644
index 000000000000..430af4dddd06
--- /dev/null
+++ b/tests/get-def/example.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+var lib = require('./library');
+
+function add(a: number, b: number): number {
+  return a + b;
+}
+
+var re = /^keynote (talk){2} (lightning){3,5} (talk){2} closing partytime!!!/
+
+// t123456
+add(lib.iTakeAString(42), 7);
+
+// D123456
+lib.bar();
diff --git a/tests/get-def/helpers/__snapshots__/jsfmt.spec.js.snap b/tests/get-def/helpers/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..45914a5abd03
--- /dev/null
+++ b/tests/get-def/helpers/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test exports_default.js 1`] = `
+"// @flow
+
+const x = "foo";
+
+export default x;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+const x = "foo";
+export default x
+
+"
+`;
+
+exports[`test exports_named.js 1`] = `
+"// @flow
+
+export const foo = "foo";
+export const bar = "bar";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export const foo = "foo";
+export const bar = "bar";
+
+"
+`;
diff --git a/tests/get-def/helpers/exports_default.js b/tests/get-def/helpers/exports_default.js
new file mode 100644
index 000000000000..35d13ab4a63c
--- /dev/null
+++ b/tests/get-def/helpers/exports_default.js
@@ -0,0 +1,5 @@
+// @flow
+
+const x = "foo";
+
+export default x;
diff --git a/tests/get-def/helpers/exports_named.js b/tests/get-def/helpers/exports_named.js
new file mode 100644
index 000000000000..1d89d4eb161c
--- /dev/null
+++ b/tests/get-def/helpers/exports_named.js
@@ -0,0 +1,4 @@
+// @flow
+
+export const foo = "foo";
+export const bar = "bar";
diff --git a/tests/get-def/helpers/jsfmt.spec.js b/tests/get-def/helpers/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/get-def/helpers/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/get-def/imports.js b/tests/get-def/imports.js
new file mode 100644
index 000000000000..34cf5bc9c3c6
--- /dev/null
+++ b/tests/get-def/imports.js
@@ -0,0 +1,11 @@
+// @flow
+
+import thing from "./helpers/exports_default.js";
+thing;
+
+import {foo, bar as baz} from "./helpers/exports_named.js";
+foo;
+baz;
+
+import * as things from "./helpers/exports_named.js";
+things;
diff --git a/tests/get-def/jsfmt.spec.js b/tests/get-def/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/get-def/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/get-def/library.js b/tests/get-def/library.js
new file mode 100644
index 000000000000..fae7b9fc3770
--- /dev/null
+++ b/tests/get-def/library.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+module.exports = {
+
+  iTakeAString: function(name: string): number {
+    return 42;
+  },
+
+  bar: function(): number {
+    return 42;
+  },
+
+};
diff --git a/tests/get-def2/Parent.js b/tests/get-def2/Parent.js
new file mode 100644
index 000000000000..830a1cd31ed6
--- /dev/null
+++ b/tests/get-def2/Parent.js
@@ -0,0 +1,4 @@
+// @flow
+
+var ParentFoo = {foo: 'bar'};
+module.exports = {ParentFoo};
diff --git a/tests/get-def2/__snapshots__/jsfmt.spec.js.snap b/tests/get-def2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bad7c5acd016
--- /dev/null
+++ b/tests/get-def2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,127 @@
+exports[`test Parent.js 1`] = `
+"// @flow
+
+var ParentFoo = {foo: 'bar'};
+module.exports = {ParentFoo};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var ParentFoo = { foo: "bar" };
+module.exports = { ParentFoo };
+
+"
+`;
+
+exports[`test main.js 1`] = `
+"// @flow
+
+var Parent = require('./Parent');
+
+// Hops through destructuring
+let ParentFoo;
+({ParentFoo} = Parent);
+ParentFoo; // Points to lval in line above this
+
+// Follows assignment on simple/"non-destructuring" patterns
+let ParentFoo2;
+ParentFoo2 = Parent;
+ParentFoo2; // Points to LHS of line above this
+
+// Follows assignment with declaration
+let ParentFoo3 = Parent;
+ParentFoo3; // Points to LHS of line above this
+
+// Follows non-destructured property access of \`require('Parent')\`
+let foo = require('./Parent').ParentFoo.foo;
+foo;
+
+import type {Foo} from './types';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var Parent = require("./Parent");
+// Hops through destructuring
+let ParentFoo;
+{ ParentFoo } = Parent;
+ParentFoo;// Points to lval in line above this
+// Follows assignment on simple/"non-destructuring" patterns
+let ParentFoo2;
+ParentFoo2 = Parent;
+ParentFoo2;// Points to LHS of line above this
+// Follows assignment with declaration
+let ParentFoo3 = Parent;
+ParentFoo3;// Points to LHS of line above this
+// Follows non-destructured property access of \`require('Parent')\`
+let foo = require("./Parent").ParentFoo.foo;
+foo;
+import type { Foo } from "./types";
+
+"
+`;
+
+exports[`test override.js 1`] = `
+"// @flow
+
+class C {
+  override() { }
+}
+
+class D extends C {
+  foo() { this.override() }
+  bar() { this.override }
+  override() { }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class C {
+  override() {
+    
+  }
+}
+class D extends C {
+  foo() {
+    this.override();
+  }
+  bar() {
+    this.override;
+  }
+  override() {
+    
+  }
+}
+
+"
+`;
+
+exports[`test react.js 1`] = `
+"var React = require('react');
+
+class C extends React.Component {
+  props: { x: string };
+}
+
+let msg = "hello";
+
+(<C x={msg}/>);
+
+(<div id={msg}/>);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require("react");
+class C extends React.Component {
+  props: { x: string };
+}
+let msg = "hello";
+<C x={msg}/>;
+<div id={msg}/>;
+
+"
+`;
+
+exports[`test types.js 1`] = `
+"// @flow
+
+export type Foo = {};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export type Foo = {};
+
+"
+`;
diff --git a/tests/get-def2/jsfmt.spec.js b/tests/get-def2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/get-def2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/get-def2/lib/__snapshots__/jsfmt.spec.js.snap b/tests/get-def2/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1c2c02375402
--- /dev/null
+++ b/tests/get-def2/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test jsx.js 1`] = `
+"declare var $React: $Exports<\'react\'>; // fake import
+type $JSXIntrinsic<T> = Class<$React.Component<void,T,mixed>>;
+
+type $JSXIntrinsics = {
+  div: $JSXIntrinsic<{id: string}>,
+  span: $JSXIntrinsic<{id: string, class: string}>,
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/get-def2/lib/jsfmt.spec.js b/tests/get-def2/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/get-def2/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/get-def2/lib/jsx.js b/tests/get-def2/lib/jsx.js
new file mode 100644
index 000000000000..7de8608bc649
--- /dev/null
+++ b/tests/get-def2/lib/jsx.js
@@ -0,0 +1,7 @@
+declare var $React: $Exports<'react'>; // fake import
+type $JSXIntrinsic<T> = Class<$React.Component<void,T,mixed>>;
+
+type $JSXIntrinsics = {
+  div: $JSXIntrinsic<{id: string}>,
+  span: $JSXIntrinsic<{id: string, class: string}>,
+};
diff --git a/tests/get-def2/main.js b/tests/get-def2/main.js
new file mode 100644
index 000000000000..63064a345a05
--- /dev/null
+++ b/tests/get-def2/main.js
@@ -0,0 +1,23 @@
+// @flow
+
+var Parent = require('./Parent');
+
+// Hops through destructuring
+let ParentFoo;
+({ParentFoo} = Parent);
+ParentFoo; // Points to lval in line above this
+
+// Follows assignment on simple/"non-destructuring" patterns
+let ParentFoo2;
+ParentFoo2 = Parent;
+ParentFoo2; // Points to LHS of line above this
+
+// Follows assignment with declaration
+let ParentFoo3 = Parent;
+ParentFoo3; // Points to LHS of line above this
+
+// Follows non-destructured property access of `require('Parent')`
+let foo = require('./Parent').ParentFoo.foo;
+foo;
+
+import type {Foo} from './types';
diff --git a/tests/get-def2/override.js b/tests/get-def2/override.js
new file mode 100644
index 000000000000..50de748aeb9c
--- /dev/null
+++ b/tests/get-def2/override.js
@@ -0,0 +1,11 @@
+// @flow
+
+class C {
+  override() { }
+}
+
+class D extends C {
+  foo() { this.override() }
+  bar() { this.override }
+  override() { }
+}
diff --git a/tests/get-def2/react.js b/tests/get-def2/react.js
new file mode 100644
index 000000000000..1c633ef60d61
--- /dev/null
+++ b/tests/get-def2/react.js
@@ -0,0 +1,11 @@
+var React = require('react');
+
+class C extends React.Component {
+  props: { x: string };
+}
+
+let msg = "hello";
+
+(<C x={msg}/>);
+
+(<div id={msg}/>);
diff --git a/tests/get-def2/types.js b/tests/get-def2/types.js
new file mode 100644
index 000000000000..2778d2acab1c
--- /dev/null
+++ b/tests/get-def2/types.js
@@ -0,0 +1,3 @@
+// @flow
+
+export type Foo = {};
diff --git a/tests/get-imports-and-importers/__snapshots__/jsfmt.spec.js.snap b/tests/get-imports-and-importers/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3a4850bffce2
--- /dev/null
+++ b/tests/get-imports-and-importers/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,35 @@
+exports[`test a.js 1`] = `
+"// @flow
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test b.js 1`] = `
+"/**
+ * @flow
+ * @providesModule b
+ */
+require('./a');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ * @providesModule b
+ */
+require("./a");
+
+"
+`;
+
+exports[`test c.js 1`] = `
+"// @flow
+require('./a.js');
+require('b');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+require("./a.js");
+require("b");
+
+"
+`;
diff --git a/tests/get-imports-and-importers/a.js b/tests/get-imports-and-importers/a.js
new file mode 100644
index 000000000000..46e7f7c04567
--- /dev/null
+++ b/tests/get-imports-and-importers/a.js
@@ -0,0 +1 @@
+// @flow
diff --git a/tests/get-imports-and-importers/b.js b/tests/get-imports-and-importers/b.js
new file mode 100644
index 000000000000..6f8b57f3965d
--- /dev/null
+++ b/tests/get-imports-and-importers/b.js
@@ -0,0 +1,5 @@
+/**
+ * @flow
+ * @providesModule b
+ */
+require('./a');
diff --git a/tests/get-imports-and-importers/c.js b/tests/get-imports-and-importers/c.js
new file mode 100644
index 000000000000..31d5ef9657f4
--- /dev/null
+++ b/tests/get-imports-and-importers/c.js
@@ -0,0 +1,3 @@
+// @flow
+require('./a.js');
+require('b');
diff --git a/tests/get-imports-and-importers/jsfmt.spec.js b/tests/get-imports-and-importers/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/get-imports-and-importers/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/getters_and_setters_disabled/__snapshots__/jsfmt.spec.js.snap b/tests/getters_and_setters_disabled/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1c785f6ffd3c
--- /dev/null
+++ b/tests/getters_and_setters_disabled/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test getters_and_setters.js 1`] = `
+"/**
+ * @flow
+ */
+
+var f = {
+  get a() { return 4; },
+  set b(x: number) { this.c = b; },
+  c: 10,
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+var f = {
+  get a() {
+    return 4;
+  },
+  set b(x: number) {
+    this.c = b;
+  },
+  c: 10
+};
+
+"
+`;
diff --git a/tests/getters_and_setters_disabled/getters_and_setters.js b/tests/getters_and_setters_disabled/getters_and_setters.js
new file mode 100644
index 000000000000..f20bb4867a5a
--- /dev/null
+++ b/tests/getters_and_setters_disabled/getters_and_setters.js
@@ -0,0 +1,9 @@
+/**
+ * @flow
+ */
+
+var f = {
+  get a() { return 4; },
+  set b(x: number) { this.c = b; },
+  c: 10,
+};
diff --git a/tests/getters_and_setters_disabled/jsfmt.spec.js b/tests/getters_and_setters_disabled/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/getters_and_setters_disabled/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/getters_and_setters_enabled/__snapshots__/jsfmt.spec.js.snap b/tests/getters_and_setters_enabled/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7bb852a92f5d
--- /dev/null
+++ b/tests/getters_and_setters_enabled/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,451 @@
+exports[`test class.js 1`] = `
+"/**
+ * @flow
+ */
+
+var z: number = 123;
+
+class Foo {
+  get goodGetterNoAnnotation() { return 4; }
+  get goodGetterWithAnnotation(): number { return 4; }
+
+  set goodSetterNoAnnotation(x) { z = x; }
+  set goodSetterWithAnnotation(x: number) { z = x; }
+
+  get propWithMatchingGetterAndSetter(): number { return 4; }
+  set propWithMatchingGetterAndSetter(x: number) { }
+
+  // The getter and setter need not have the same type - no error
+  get propWithSubtypingGetterAndSetter(): ?number { return 4; }
+  set propWithSubtypingGetterAndSetter(x: number) { }
+
+  // The getter and setter need not have the same type - no error
+  set propWithSubtypingGetterAndSetterReordered(x: number) { }
+  get propWithSubtypingGetterAndSetterReordered(): ?number { return 4; }
+
+  get propWithMismatchingGetterAndSetter(): number { return 4; }
+  set propWithMismatchingGetterAndSetter(x: string) { } // doesn't match getter (OK)
+
+  propOverriddenWithGetter: number;
+  get propOverriddenWithGetter() { return "hello"; }
+
+  propOverriddenWithSetter: number;
+  set propOverriddenWithSetter(x: string) { }
+};
+
+var foo = new Foo();
+
+// Test getting properties with getters
+var testGetterNoError1: number = foo.goodGetterNoAnnotation;
+var testGetterNoError2: number = foo.goodGetterWithAnnotation;
+
+var testGetterWithError1: string = foo.goodGetterNoAnnotation; // Error number ~> string
+var testGetterWithError2: string = foo.goodGetterWithAnnotation; // Error number ~> string
+
+// Test setting properties with getters
+foo.goodSetterNoAnnotation = 123;
+foo.goodSetterWithAnnotation = 123;
+
+// TODO: Why does no annotation mean no error?
+foo.goodSetterNoAnnotation = "hello"; // Error string ~> number
+foo.goodSetterWithAnnotation = "hello"; // Error string ~> number
+
+var testSubtypingGetterAndSetter: number = foo.propWithSubtypingGetterAndSetter; // Error ?number ~> number
+
+var testPropOverridenWithGetter: number = foo.propOverriddenWithGetter; // Error string ~> number
+foo.propOverriddenWithSetter = 123; // Error number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+var z: number = 123;
+class Foo {
+  get goodGetterNoAnnotation() {
+    return 4;
+  }
+  get goodGetterWithAnnotation(): number {
+    return 4;
+  }
+  set goodSetterNoAnnotation(x) {
+    z = x;
+  }
+  set goodSetterWithAnnotation(x: number) {
+    z = x;
+  }
+  get propWithMatchingGetterAndSetter(): number {
+    return 4;
+  }
+  set propWithMatchingGetterAndSetter(x: number) {
+    
+  }
+  // The getter and setter need not have the same type - no error
+  get propWithSubtypingGetterAndSetter(): ?number {
+    return 4;
+  }
+  set propWithSubtypingGetterAndSetter(x: number) {
+    
+  }
+  // The getter and setter need not have the same type - no error
+  set propWithSubtypingGetterAndSetterReordered(x: number) {
+    
+  }
+  get propWithSubtypingGetterAndSetterReordered(): ?number {
+    return 4;
+  }
+  get propWithMismatchingGetterAndSetter(): number {
+    return 4;
+  }
+  set propWithMismatchingGetterAndSetter(x: string) {
+    
+  }// doesn't match getter (OK)
+  propOverriddenWithGetter: number;
+  get propOverriddenWithGetter() {
+    return "hello";
+  }
+  propOverriddenWithSetter: number;
+  set propOverriddenWithSetter(x: string) {
+    
+  }
+}
+var foo = new Foo();
+// Test getting properties with getters
+var testGetterNoError1: number = foo.goodGetterNoAnnotation;
+var testGetterNoError2: number = foo.goodGetterWithAnnotation;
+var testGetterWithError1: string = foo.goodGetterNoAnnotation;// Error number ~> string
+var testGetterWithError2: string = foo.goodGetterWithAnnotation;// Error number ~> string
+// Test setting properties with getters
+foo.goodSetterNoAnnotation = 123;
+foo.goodSetterWithAnnotation = 123;
+// TODO: Why does no annotation mean no error?
+foo.goodSetterNoAnnotation = "hello";// Error string ~> number
+foo.goodSetterWithAnnotation = "hello";// Error string ~> number
+var testSubtypingGetterAndSetter: number = foo.propWithSubtypingGetterAndSetter;// Error ?number ~> number
+var testPropOverridenWithGetter: number = foo.propOverriddenWithGetter;// Error string ~> number
+foo.propOverriddenWithSetter = 123;// Error number ~> string
+
+"
+`;
+
+exports[`test object.js 1`] = `
+"/**
+ * @flow
+ */
+
+var z: number = 123;
+
+class A {}
+class B extends A {}
+class C extends A {}
+
+var obj = {
+  get goodGetterNoAnnotation() { return 4; },
+  get goodGetterWithAnnotation(): number { return 4; },
+
+  set goodSetterNoAnnotation(x) { z = x; },
+  set goodSetterWithAnnotation(x: number) { z = x; },
+
+  get propWithMatchingGetterAndSetter(): number { return 4; },
+  set propWithMatchingGetterAndSetter(x: number) { },
+
+  // The getter and setter need not have the same type
+  get propWithSubtypingGetterAndSetter(): ?number { return 4; }, // OK
+  set propWithSubtypingGetterAndSetter(x: number) { },
+
+  set propWithSubtypingGetterAndSetterReordered(x: number) { }, // OK
+  get propWithSubtypingGetterAndSetterReordered(): ?number { return 4; },
+
+  get exampleOfOrderOfGetterAndSetter(): A { return new A(); },
+  set exampleOfOrderOfGetterAndSetter(x: B) {},
+
+  set exampleOfOrderOfGetterAndSetterReordered(x: B) {},
+  get exampleOfOrderOfGetterAndSetterReordered(): A { return new A(); },
+};
+
+
+
+// Test getting properties with getters
+var testGetterNoError1: number = obj.goodGetterNoAnnotation;
+var testGetterNoError2: number = obj.goodGetterWithAnnotation;
+
+var testGetterWithError1: string = obj.goodGetterNoAnnotation; // Error number ~> string
+var testGetterWithError2: string = obj.goodGetterWithAnnotation; // Error number ~> string
+
+// Test setting properties with getters
+obj.goodSetterNoAnnotation = 123;
+obj.goodSetterWithAnnotation = 123;
+
+obj.goodSetterNoAnnotation = "hello"; // Error string ~> number
+obj.goodSetterWithAnnotation = "hello"; // Error string ~> number
+
+var testSubtypingGetterAndSetter: number = obj.propWithSubtypingGetterAndSetter; // Error ?number ~> number
+
+// When building this feature, it was tempting to flow the setter into the
+// getter and then use either the getter or setter as the type of the property.
+// This example shows the danger of using the getter's type
+obj.exampleOfOrderOfGetterAndSetter = new C(); // Error C ~> B
+
+// And this example shows the danger of using the setter's type.
+var testExampleOrOrderOfGetterAndSetterReordered: number =
+  obj.exampleOfOrderOfGetterAndSetterReordered; // Error A ~> B
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+var z: number = 123;
+class A {}
+class B extends A {}
+class C extends A {}
+var obj = {
+  get goodGetterNoAnnotation() {
+    return 4;
+  },
+  get goodGetterWithAnnotation(): number {
+    return 4;
+  },
+  set goodSetterNoAnnotation(x) {
+    z = x;
+  },
+  set goodSetterWithAnnotation(x: number) {
+    z = x;
+  },
+  get propWithMatchingGetterAndSetter(): number {
+    return 4;
+  },
+  set propWithMatchingGetterAndSetter(x: number) {
+    
+  },
+  // The getter and setter need not have the same type
+  // OK
+  get propWithSubtypingGetterAndSetter(): ?number {
+    return 4;
+  },
+  set propWithSubtypingGetterAndSetter(x: number) {
+    
+  },
+  // OK set propWithSubtypingGetterAndSetterReordered(x: number) {
+    
+  },
+  get propWithSubtypingGetterAndSetterReordered(): ?number {
+    return 4;
+  },
+  get exampleOfOrderOfGetterAndSetter(): A {
+    return new A();
+  },
+  set exampleOfOrderOfGetterAndSetter(x: B) {
+    
+  },
+  set exampleOfOrderOfGetterAndSetterReordered(x: B) {
+    
+  },
+  get exampleOfOrderOfGetterAndSetterReordered(): A {
+    return new A();
+  }
+};
+// Test getting properties with getters
+var testGetterNoError1: number = obj.goodGetterNoAnnotation;
+var testGetterNoError2: number = obj.goodGetterWithAnnotation;
+var testGetterWithError1: string = obj.goodGetterNoAnnotation;// Error number ~> string
+var testGetterWithError2: string = obj.goodGetterWithAnnotation;// Error number ~> string
+// Test setting properties with getters
+obj.goodSetterNoAnnotation = 123;
+obj.goodSetterWithAnnotation = 123;
+obj.goodSetterNoAnnotation = "hello";// Error string ~> number
+obj.goodSetterWithAnnotation = "hello";// Error string ~> number
+var testSubtypingGetterAndSetter: number = obj.propWithSubtypingGetterAndSetter;// Error ?number ~> number
+// When building this feature, it was tempting to flow the setter into the
+// getter and then use either the getter or setter as the type of the property.
+// This example shows the danger of using the getter's type
+obj.exampleOfOrderOfGetterAndSetter = new C();// Error C ~> B
+// And this example shows the danger of using the setter's type.
+var testExampleOrOrderOfGetterAndSetterReordered: number = obj.exampleOfOrderOfGetterAndSetterReordered;// Error A ~> B
+
+"
+`;
+
+exports[`test react.js 1`] = `
+"/**
+ * @flow
+ */
+
+React.createClass({
+  propTypes: {
+    get a() { return 4; },
+    set b(x: number) { this.c = x; },
+    c: 10,
+  }
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+React.createClass({
+  propTypes: {
+    get a() {
+      return 4;
+    },
+    set b(x: number) {
+      this.c = x;
+    },
+    c: 10
+  }
+});
+
+"
+`;
+
+exports[`test variance.js 1`] = `
+"/* @flow */
+
+class A {}
+class B extends A {}
+class C extends B {}
+
+declare var a: A;
+declare var b: B;
+declare var c: C;
+
+class Base {
+  x: B;
+  +pos: B;
+  -neg: B;
+  get get(): B { return this.x };
+  set set(value: B): void { this.x = value };
+  get getset(): B { return this.x };
+  set getset(value: B): void { this.x = value };
+}
+
+(class extends Base {
+  // error: getter incompatible with read/write property
+  get x(): B { return b }
+});
+
+(class extends Base {
+  // error: setter incompatible with read/write property
+  set x(value: B): void {}
+});
+
+(class extends Base {
+  // ok: get/set co/contra with read/write property, resp.
+  get x(): C { return c }
+  set x(value: A): void {}
+});
+
+(class extends Base {
+  // error: setter incompatible with read-only property
+  set pos(value: B): void {}
+});
+
+(class extends Base {
+  // ok: getter covariant with read-only property
+  get pos(): C { return c }
+});
+
+(class extends Base {
+  // error: getter incompatible with write-only property
+  get neg(): B { return b }
+});
+
+(class extends Base {
+  // ok: setter contravariant with write-only property
+  set neg(value: A): void {}
+});
+
+(class extends Base {
+  // ok: read/write covariant with getter
+  get: C;
+});
+
+(class extends Base {
+  // ok: read/write contravariant with setter
+  set: A;
+});
+
+(class extends Base {
+  // ok: read/write invariant with get/set
+  getset: B;
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class A {}
+class B extends A {}
+class C extends B {}
+declare var a: A;
+declare var b: B;
+declare var c: C;
+class Base {
+  x: B;
+  +pos: B;
+  -neg: B;
+  get get(): B {
+    return this.x;
+  }
+  set set(value: B): void {
+    this.x = value;
+  }
+  get getset(): B {
+    return this.x;
+  }
+  set getset(value: B): void {
+    this.x = value;
+  }
+}
+class extends Base {
+  // error: getter incompatible with read/write property
+  get x(): B {
+    return b;
+  }
+};
+class extends Base {
+  // error: setter incompatible with read/write property
+  set x(value: B): void {
+    
+  }
+};
+class extends Base {
+  // ok: get/set co/contra with read/write property, resp.
+  get x(): C {
+    return c;
+  }
+  set x(value: A): void {
+    
+  }
+};
+class extends Base {
+  // error: setter incompatible with read-only property
+  set pos(value: B): void {
+    
+  }
+};
+class extends Base {
+  // ok: getter covariant with read-only property
+  get pos(): C {
+    return c;
+  }
+};
+class extends Base {
+  // error: getter incompatible with write-only property
+  get neg(): B {
+    return b;
+  }
+};
+class extends Base {
+  // ok: setter contravariant with write-only property
+  set neg(value: A): void {
+    
+  }
+};
+class extends Base {
+  // ok: read/write covariant with getter
+  get: C;
+};
+class extends Base {
+  // ok: read/write contravariant with setter
+  set: A;
+};
+class extends Base {
+  // ok: read/write invariant with get/set
+  getset: B;
+};
+
+"
+`;
diff --git a/tests/getters_and_setters_enabled/class.js b/tests/getters_and_setters_enabled/class.js
new file mode 100644
index 000000000000..c9a3707e28df
--- /dev/null
+++ b/tests/getters_and_setters_enabled/class.js
@@ -0,0 +1,55 @@
+/**
+ * @flow
+ */
+
+var z: number = 123;
+
+class Foo {
+  get goodGetterNoAnnotation() { return 4; }
+  get goodGetterWithAnnotation(): number { return 4; }
+
+  set goodSetterNoAnnotation(x) { z = x; }
+  set goodSetterWithAnnotation(x: number) { z = x; }
+
+  get propWithMatchingGetterAndSetter(): number { return 4; }
+  set propWithMatchingGetterAndSetter(x: number) { }
+
+  // The getter and setter need not have the same type - no error
+  get propWithSubtypingGetterAndSetter(): ?number { return 4; }
+  set propWithSubtypingGetterAndSetter(x: number) { }
+
+  // The getter and setter need not have the same type - no error
+  set propWithSubtypingGetterAndSetterReordered(x: number) { }
+  get propWithSubtypingGetterAndSetterReordered(): ?number { return 4; }
+
+  get propWithMismatchingGetterAndSetter(): number { return 4; }
+  set propWithMismatchingGetterAndSetter(x: string) { } // doesn't match getter (OK)
+
+  propOverriddenWithGetter: number;
+  get propOverriddenWithGetter() { return "hello"; }
+
+  propOverriddenWithSetter: number;
+  set propOverriddenWithSetter(x: string) { }
+};
+
+var foo = new Foo();
+
+// Test getting properties with getters
+var testGetterNoError1: number = foo.goodGetterNoAnnotation;
+var testGetterNoError2: number = foo.goodGetterWithAnnotation;
+
+var testGetterWithError1: string = foo.goodGetterNoAnnotation; // Error number ~> string
+var testGetterWithError2: string = foo.goodGetterWithAnnotation; // Error number ~> string
+
+// Test setting properties with getters
+foo.goodSetterNoAnnotation = 123;
+foo.goodSetterWithAnnotation = 123;
+
+// TODO: Why does no annotation mean no error?
+foo.goodSetterNoAnnotation = "hello"; // Error string ~> number
+foo.goodSetterWithAnnotation = "hello"; // Error string ~> number
+
+var testSubtypingGetterAndSetter: number = foo.propWithSubtypingGetterAndSetter; // Error ?number ~> number
+
+var testPropOverridenWithGetter: number = foo.propOverriddenWithGetter; // Error string ~> number
+foo.propOverriddenWithSetter = 123; // Error number ~> string
diff --git a/tests/getters_and_setters_enabled/jsfmt.spec.js b/tests/getters_and_setters_enabled/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/getters_and_setters_enabled/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/getters_and_setters_enabled/object.js b/tests/getters_and_setters_enabled/object.js
new file mode 100644
index 000000000000..5e54f25f40dc
--- /dev/null
+++ b/tests/getters_and_setters_enabled/object.js
@@ -0,0 +1,60 @@
+/**
+ * @flow
+ */
+
+var z: number = 123;
+
+class A {}
+class B extends A {}
+class C extends A {}
+
+var obj = {
+  get goodGetterNoAnnotation() { return 4; },
+  get goodGetterWithAnnotation(): number { return 4; },
+
+  set goodSetterNoAnnotation(x) { z = x; },
+  set goodSetterWithAnnotation(x: number) { z = x; },
+
+  get propWithMatchingGetterAndSetter(): number { return 4; },
+  set propWithMatchingGetterAndSetter(x: number) { },
+
+  // The getter and setter need not have the same type
+  get propWithSubtypingGetterAndSetter(): ?number { return 4; }, // OK
+  set propWithSubtypingGetterAndSetter(x: number) { },
+
+  set propWithSubtypingGetterAndSetterReordered(x: number) { }, // OK
+  get propWithSubtypingGetterAndSetterReordered(): ?number { return 4; },
+
+  get exampleOfOrderOfGetterAndSetter(): A { return new A(); },
+  set exampleOfOrderOfGetterAndSetter(x: B) {},
+
+  set exampleOfOrderOfGetterAndSetterReordered(x: B) {},
+  get exampleOfOrderOfGetterAndSetterReordered(): A { return new A(); },
+};
+
+
+
+// Test getting properties with getters
+var testGetterNoError1: number = obj.goodGetterNoAnnotation;
+var testGetterNoError2: number = obj.goodGetterWithAnnotation;
+
+var testGetterWithError1: string = obj.goodGetterNoAnnotation; // Error number ~> string
+var testGetterWithError2: string = obj.goodGetterWithAnnotation; // Error number ~> string
+
+// Test setting properties with getters
+obj.goodSetterNoAnnotation = 123;
+obj.goodSetterWithAnnotation = 123;
+
+obj.goodSetterNoAnnotation = "hello"; // Error string ~> number
+obj.goodSetterWithAnnotation = "hello"; // Error string ~> number
+
+var testSubtypingGetterAndSetter: number = obj.propWithSubtypingGetterAndSetter; // Error ?number ~> number
+
+// When building this feature, it was tempting to flow the setter into the
+// getter and then use either the getter or setter as the type of the property.
+// This example shows the danger of using the getter's type
+obj.exampleOfOrderOfGetterAndSetter = new C(); // Error C ~> B
+
+// And this example shows the danger of using the setter's type.
+var testExampleOrOrderOfGetterAndSetterReordered: number =
+  obj.exampleOfOrderOfGetterAndSetterReordered; // Error A ~> B
diff --git a/tests/getters_and_setters_enabled/react.js b/tests/getters_and_setters_enabled/react.js
new file mode 100644
index 000000000000..811acd9ec376
--- /dev/null
+++ b/tests/getters_and_setters_enabled/react.js
@@ -0,0 +1,11 @@
+/**
+ * @flow
+ */
+
+React.createClass({
+  propTypes: {
+    get a() { return 4; },
+    set b(x: number) { this.c = x; },
+    c: 10,
+  }
+});
diff --git a/tests/getters_and_setters_enabled/variance.js b/tests/getters_and_setters_enabled/variance.js
new file mode 100644
index 000000000000..8337453d57d9
--- /dev/null
+++ b/tests/getters_and_setters_enabled/variance.js
@@ -0,0 +1,70 @@
+/* @flow */
+
+class A {}
+class B extends A {}
+class C extends B {}
+
+declare var a: A;
+declare var b: B;
+declare var c: C;
+
+class Base {
+  x: B;
+  +pos: B;
+  -neg: B;
+  get get(): B { return this.x };
+  set set(value: B): void { this.x = value };
+  get getset(): B { return this.x };
+  set getset(value: B): void { this.x = value };
+}
+
+(class extends Base {
+  // error: getter incompatible with read/write property
+  get x(): B { return b }
+});
+
+(class extends Base {
+  // error: setter incompatible with read/write property
+  set x(value: B): void {}
+});
+
+(class extends Base {
+  // ok: get/set co/contra with read/write property, resp.
+  get x(): C { return c }
+  set x(value: A): void {}
+});
+
+(class extends Base {
+  // error: setter incompatible with read-only property
+  set pos(value: B): void {}
+});
+
+(class extends Base {
+  // ok: getter covariant with read-only property
+  get pos(): C { return c }
+});
+
+(class extends Base {
+  // error: getter incompatible with write-only property
+  get neg(): B { return b }
+});
+
+(class extends Base {
+  // ok: setter contravariant with write-only property
+  set neg(value: A): void {}
+});
+
+(class extends Base {
+  // ok: read/write covariant with getter
+  get: C;
+});
+
+(class extends Base {
+  // ok: read/write contravariant with setter
+  set: A;
+});
+
+(class extends Base {
+  // ok: read/write invariant with get/set
+  getset: B;
+});
diff --git a/tests/haste_cycle/API.js b/tests/haste_cycle/API.js
new file mode 100644
index 000000000000..9224269fc476
--- /dev/null
+++ b/tests/haste_cycle/API.js
@@ -0,0 +1,3 @@
+// @flow
+
+var OpenGraphObject = require('./models/OpenGraphObject.js');
diff --git a/tests/haste_cycle/__snapshots__/jsfmt.spec.js.snap b/tests/haste_cycle/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a6433431534f
--- /dev/null
+++ b/tests/haste_cycle/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test API.js 1`] = `
+"// @flow
+
+var OpenGraphObject = require('./models/OpenGraphObject.js');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var OpenGraphObject = require("./models/OpenGraphObject.js");
+
+"
+`;
diff --git a/tests/haste_cycle/jsfmt.spec.js b/tests/haste_cycle/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/haste_cycle/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/haste_cycle/models/OpenGraphAction.js b/tests/haste_cycle/models/OpenGraphAction.js
new file mode 100644
index 000000000000..364e413bb22f
--- /dev/null
+++ b/tests/haste_cycle/models/OpenGraphAction.js
@@ -0,0 +1,3 @@
+// @flow
+
+var OpenGraphValueContainer = require('./OpenGraphValueContainer.js');
diff --git a/tests/haste_cycle/models/OpenGraphObject.js b/tests/haste_cycle/models/OpenGraphObject.js
new file mode 100644
index 000000000000..364e413bb22f
--- /dev/null
+++ b/tests/haste_cycle/models/OpenGraphObject.js
@@ -0,0 +1,3 @@
+// @flow
+
+var OpenGraphValueContainer = require('./OpenGraphValueContainer.js');
diff --git a/tests/haste_cycle/models/OpenGraphValueContainer.js b/tests/haste_cycle/models/OpenGraphValueContainer.js
new file mode 100644
index 000000000000..24d28abd4d28
--- /dev/null
+++ b/tests/haste_cycle/models/OpenGraphValueContainer.js
@@ -0,0 +1,3 @@
+// @flow
+
+var OpenGraphObject = require('./OpenGraphObject.js');
diff --git a/tests/haste_cycle/models/__snapshots__/jsfmt.spec.js.snap b/tests/haste_cycle/models/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9b3493adb074
--- /dev/null
+++ b/tests/haste_cycle/models/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,32 @@
+exports[`test OpenGraphAction.js 1`] = `
+"// @flow
+
+var OpenGraphValueContainer = require('./OpenGraphValueContainer.js');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var OpenGraphValueContainer = require("./OpenGraphValueContainer.js");
+
+"
+`;
+
+exports[`test OpenGraphObject.js 1`] = `
+"// @flow
+
+var OpenGraphValueContainer = require('./OpenGraphValueContainer.js');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var OpenGraphValueContainer = require("./OpenGraphValueContainer.js");
+
+"
+`;
+
+exports[`test OpenGraphValueContainer.js 1`] = `
+"// @flow
+
+var OpenGraphObject = require('./OpenGraphObject.js');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var OpenGraphObject = require("./OpenGraphObject.js");
+
+"
+`;
diff --git a/tests/haste_cycle/models/jsfmt.spec.js b/tests/haste_cycle/models/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/haste_cycle/models/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/haste_dupe/__snapshots__/jsfmt.spec.js.snap b/tests/haste_dupe/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..88db0d310415
--- /dev/null
+++ b/tests/haste_dupe/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,51 @@
+exports[`test dupe1.js 1`] = `
+"/**
+ * Dupe provider 1/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe1";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Dupe provider 1/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe1";
+
+"
+`;
+
+exports[`test dupe2.js 1`] = `
+"/**
+ * Dupe provider 2/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe2";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Dupe provider 2/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe2";
+
+"
+`;
+
+exports[`test requires_dupe.js 1`] = `
+"/**
+ * depends on doubly-provided module
+ * @flow
+ */
+var dupe = require('Dupe');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * depends on doubly-provided module
+ * @flow
+ */
+var dupe = require("Dupe");
+
+"
+`;
diff --git a/tests/haste_dupe/dupe1.js b/tests/haste_dupe/dupe1.js
new file mode 100644
index 000000000000..1a298b67eae7
--- /dev/null
+++ b/tests/haste_dupe/dupe1.js
@@ -0,0 +1,6 @@
+/**
+ * Dupe provider 1/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe1";
diff --git a/tests/haste_dupe/dupe2.js b/tests/haste_dupe/dupe2.js
new file mode 100644
index 000000000000..aa64ae687dd8
--- /dev/null
+++ b/tests/haste_dupe/dupe2.js
@@ -0,0 +1,6 @@
+/**
+ * Dupe provider 2/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe2";
diff --git a/tests/haste_dupe/jsfmt.spec.js b/tests/haste_dupe/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/haste_dupe/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/haste_dupe/requires_dupe.js b/tests/haste_dupe/requires_dupe.js
new file mode 100644
index 000000000000..129992b7ab05
--- /dev/null
+++ b/tests/haste_dupe/requires_dupe.js
@@ -0,0 +1,5 @@
+/**
+ * depends on doubly-provided module
+ * @flow
+ */
+var dupe = require('Dupe');
diff --git a/tests/ignore_package/__snapshots__/jsfmt.spec.js.snap b/tests/ignore_package/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..365defe04de3
--- /dev/null
+++ b/tests/ignore_package/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,31 @@
+exports[`test foo.js 1`] = `
+"/** @flow */
+/* this require routes to nothing, because
+   our node_modules/underscore directory
+   has been excluded. If package.json files
+   are being excluded properly, we'll get
+   'Required module not found'.
+ */
+var _ = require('underscore');
+
+function foo(): string {
+  return _.foo();
+}
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/** @flow */
+/* this require routes to nothing, because
+   our node_modules/underscore directory
+   has been excluded. If package.json files
+   are being excluded properly, we'll get
+   'Required module not found'.
+ */
+var _ = require("underscore");
+function foo(): string {
+  return _.foo();
+}
+module.exports = foo;
+
+"
+`;
diff --git a/tests/ignore_package/foo.js b/tests/ignore_package/foo.js
new file mode 100644
index 000000000000..ff3a3366ac03
--- /dev/null
+++ b/tests/ignore_package/foo.js
@@ -0,0 +1,14 @@
+/** @flow */
+/* this require routes to nothing, because
+   our node_modules/underscore directory
+   has been excluded. If package.json files
+   are being excluded properly, we'll get
+   'Required module not found'.
+ */
+var _ = require('underscore');
+
+function foo(): string {
+  return _.foo();
+}
+
+module.exports = foo;
diff --git a/tests/ignore_package/jsfmt.spec.js b/tests/ignore_package/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/ignore_package/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/immutable_methods/__snapshots__/jsfmt.spec.js.snap b/tests/immutable_methods/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7365d8ee4758
--- /dev/null
+++ b/tests/immutable_methods/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,29 @@
+exports[`test test.js 1`] = `
+"class A {
+    foo(): A { return this; }
+}
+class B extends A {
+    foo(): B { return this; }
+}
+class C extends A {}
+var a: A = new B();
+a.foo = function(): C { return new C(); }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {
+  foo(): A {
+    return this;
+  }
+}
+class B extends A {
+  foo(): B {
+    return this;
+  }
+}
+class C extends A {}
+var a: A = new B();
+a.foo = function(): C {
+  return new C();
+};
+
+"
+`;
diff --git a/tests/immutable_methods/jsfmt.spec.js b/tests/immutable_methods/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/immutable_methods/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/immutable_methods/test.js b/tests/immutable_methods/test.js
new file mode 100644
index 000000000000..2278239a27d9
--- /dev/null
+++ b/tests/immutable_methods/test.js
@@ -0,0 +1,9 @@
+class A {
+    foo(): A { return this; }
+}
+class B extends A {
+    foo(): B { return this; }
+}
+class C extends A {}
+var a: A = new B();
+a.foo = function(): C { return new C(); }
diff --git a/tests/import_type/ExportCJSDefault_Class.js b/tests/import_type/ExportCJSDefault_Class.js
new file mode 100644
index 000000000000..dbbb5594a550
--- /dev/null
+++ b/tests/import_type/ExportCJSDefault_Class.js
@@ -0,0 +1,12 @@
+/**
+ * @flow
+ */
+
+class ClassFoo3 {
+  givesANum(): number { return 42; }
+  static givesAFoo3(): ClassFoo3 {
+    return new ClassFoo3();
+  }
+}
+
+module.exports = ClassFoo3;
diff --git a/tests/import_type/ExportCJSNamed_Class.js b/tests/import_type/ExportCJSNamed_Class.js
new file mode 100644
index 000000000000..5a6ff405708a
--- /dev/null
+++ b/tests/import_type/ExportCJSNamed_Class.js
@@ -0,0 +1,22 @@
+/**
+ * @flow
+ */
+
+class ClassFoo4 {
+  returnsANumber(): number { return 42; }
+}
+
+class ClassFoo5 {}
+
+function givesAFoo4(): ClassFoo4 {
+  return new ClassFoo4();
+}
+
+function givesAFoo5(): ClassFoo5 {
+  return new ClassFoo5();
+}
+
+exports.ClassFoo4 = ClassFoo4;
+exports.ClassFoo5 = ClassFoo5
+exports.foo4Inst = new ClassFoo4();
+exports.foo5Inst = new ClassFoo5();
diff --git a/tests/import_type/ExportDefault_Class.js b/tests/import_type/ExportDefault_Class.js
new file mode 100644
index 000000000000..9fe9fb3dc2e7
--- /dev/null
+++ b/tests/import_type/ExportDefault_Class.js
@@ -0,0 +1,10 @@
+/**
+ * @flow
+ */
+
+class ClassFoo1 {
+  returnsANumber(): number { return 42; }
+}
+
+export default ClassFoo1;
+export var foo1Inst = new ClassFoo1();
diff --git a/tests/import_type/ExportNamed_Alias.js b/tests/import_type/ExportNamed_Alias.js
new file mode 100644
index 000000000000..0f8c0f810195
--- /dev/null
+++ b/tests/import_type/ExportNamed_Alias.js
@@ -0,0 +1,12 @@
+/**
+ * @flow
+ */
+
+export type AliasFoo3  = {
+  givesANum(): number
+};
+export function givesAFoo3Obj(): AliasFoo3 {
+  return {
+    givesANum(): number { return 42; }
+  };
+};
diff --git a/tests/import_type/ExportNamed_Class.js b/tests/import_type/ExportNamed_Class.js
new file mode 100644
index 000000000000..e5486eec5430
--- /dev/null
+++ b/tests/import_type/ExportNamed_Class.js
@@ -0,0 +1,10 @@
+/**
+ * @flow
+ */
+
+class ClassFoo2 {
+  returnsANumber(): number { return 42; }
+}
+
+export {ClassFoo2};
+export var foo2Inst = new ClassFoo2();
diff --git a/tests/import_type/ExportsANumber.js b/tests/import_type/ExportsANumber.js
new file mode 100644
index 000000000000..bd4ab83a20e3
--- /dev/null
+++ b/tests/import_type/ExportsANumber.js
@@ -0,0 +1,3 @@
+/* @ flow */
+
+export var numValue = 42;
diff --git a/tests/import_type/__snapshots__/jsfmt.spec.js.snap b/tests/import_type/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..86121979ecbe
--- /dev/null
+++ b/tests/import_type/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,340 @@
+exports[`test ExportCJSDefault_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo3 {
+  givesANum(): number { return 42; }
+  static givesAFoo3(): ClassFoo3 {
+    return new ClassFoo3();
+  }
+}
+
+module.exports = ClassFoo3;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class ClassFoo3 {
+  givesANum(): number {
+    return 42;
+  }
+  givesAFoo3(): ClassFoo3 {
+    return new ClassFoo3();
+  }
+}
+module.exports = ClassFoo3;
+
+"
+`;
+
+exports[`test ExportCJSNamed_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo4 {
+  returnsANumber(): number { return 42; }
+}
+
+class ClassFoo5 {}
+
+function givesAFoo4(): ClassFoo4 {
+  return new ClassFoo4();
+}
+
+function givesAFoo5(): ClassFoo5 {
+  return new ClassFoo5();
+}
+
+exports.ClassFoo4 = ClassFoo4;
+exports.ClassFoo5 = ClassFoo5
+exports.foo4Inst = new ClassFoo4();
+exports.foo5Inst = new ClassFoo5();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class ClassFoo4 {
+  returnsANumber(): number {
+    return 42;
+  }
+}
+class ClassFoo5 {}
+function givesAFoo4(): ClassFoo4 {
+  return new ClassFoo4();
+}
+function givesAFoo5(): ClassFoo5 {
+  return new ClassFoo5();
+}
+exports.ClassFoo4 = ClassFoo4;
+exports.ClassFoo5 = ClassFoo5;
+exports.foo4Inst = new ClassFoo4();
+exports.foo5Inst = new ClassFoo5();
+
+"
+`;
+
+exports[`test ExportDefault_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo1 {
+  returnsANumber(): number { return 42; }
+}
+
+export default ClassFoo1;
+export var foo1Inst = new ClassFoo1();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class ClassFoo1 {
+  returnsANumber(): number {
+    return 42;
+  }
+}
+export default ClassFoo1
+export var foo1Inst = new ClassFoo1();
+
+"
+`;
+
+exports[`test ExportNamed_Alias.js 1`] = `
+"/**
+ * @flow
+ */
+
+export type AliasFoo3  = {
+  givesANum(): number
+};
+export function givesAFoo3Obj(): AliasFoo3 {
+  return {
+    givesANum(): number { return 42; }
+  };
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test ExportNamed_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo2 {
+  returnsANumber(): number { return 42; }
+}
+
+export {ClassFoo2};
+export var foo2Inst = new ClassFoo2();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test ExportsANumber.js 1`] = `
+"/* @ flow */
+
+export var numValue = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @ flow */
+export var numValue = 42;
+
+"
+`;
+
+exports[`test import_type.js 1`] = `
+"/**
+ * @flow
+ */
+
+/////////////////////////////////////////////////
+// == Importing Class Type (Default Export) == //
+/////////////////////////////////////////////////
+
+import type ClassFoo1 from \"./ExportDefault_Class\";
+import {foo1Inst} from \"./ExportDefault_Class\";
+
+var a1: ClassFoo1 = foo1Inst;
+var a2: number = foo1Inst; // Error: ClassFoo1 ~> number
+new ClassFoo1(); // Error: ClassFoo1 is not a value-identifier
+
+///////////////////////////////////////////////
+// == Importing Class Type (Named Export) == //
+///////////////////////////////////////////////
+
+import type {ClassFoo2} from \"./ExportNamed_Class\";
+import {foo2Inst} from \"./ExportNamed_Class\";
+
+var b1: ClassFoo2 = foo2Inst;
+var b2: number = foo2Inst; // Error: ClassFoo2 ~> number
+new ClassFoo2(); // Error: ClassFoo2 is not a value-identifier
+
+/////////////////////////////////////////////////////
+// == Importing Class Type (CJS Default Export) == //
+/////////////////////////////////////////////////////
+
+import type ClassFoo3T from \"./ExportCJSDefault_Class\";
+import ClassFoo3 from \"./ExportCJSDefault_Class\";
+var c1: ClassFoo3T = new ClassFoo3();
+new ClassFoo3T(); // Error: ClassFoo3 is not a value-identifier
+
+///////////////////////////////////////////////////
+// == Importing Class Type (CJS Named Export) == //
+///////////////////////////////////////////////////
+
+import type {ClassFoo4, ClassFoo5} from \"./ExportCJSNamed_Class\";
+import {foo4Inst, foo5Inst} from \"./ExportCJSNamed_Class\";
+
+var d1: ClassFoo4 = foo4Inst;
+var d2: number = foo4Inst; // Error: ClassFoo4 ~> number
+new ClassFoo4(); // Error: ClassFoo4 is not a value-identifier
+// TODO: this errors correctly, but the message is just \'can\'t resolve name\'
+var d3: typeof ClassFoo5 = foo5Inst; // Error: Can\'t typeof a type alias
+
+////////////////////////////////////////////
+// == Import Type Alias (Named Export) == //
+////////////////////////////////////////////
+
+import type {AliasFoo3} from \"./ExportNamed_Alias\";
+import {givesAFoo3Obj} from \"./ExportNamed_Alias\";
+var e1: AliasFoo3 = givesAFoo3Obj();
+var e2: number = givesAFoo3Obj(); // Error: AliasFoo3 ~> number
+var e3: typeof AliasFoo3 = givesAFoo3Obj(); // Error: Can\'t typeof a type alias
+
+//////////////////////////////////////////////
+// == Import Type Alias (Default Export) == //
+//////////////////////////////////////////////
+
+// TODO: No support for this right now. It\'s most likely possible, but it\'s
+//       unclear how useful it is at the moment and it entails a little
+//       more work than named type exports, so I\'m punting on it for now.
+
+///////////////////////////////////////////////////////
+// == Import Type With Non-Alias Compatible Value == //
+///////////////////////////////////////////////////////
+
+import type {numValue} from \"./ExportsANumber\"; // Error: Cannot import-type a number value
+
+////////////////////////////////////////////////////////////////////////
+// == Regression Test: https://github.com/facebook/flow/issues/359 == //
+// Ensure that type bindings stay type bindings across function body  //
+// env contexts.                                                      //
+////////////////////////////////////////////////////////////////////////
+
+import type ClassFoo6 from \"./issue-359\";
+function foo() {
+  ClassFoo6; // Error: Not a value binding
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+/////////////////////////////////////////////////
+// == Importing Class Type (Default Export) == //
+/////////////////////////////////////////////////
+import type ClassFoo1 from \"./ExportDefault_Class\";
+import { foo1Inst } from \"./ExportDefault_Class\";
+var a1: ClassFoo1 = foo1Inst;
+var a2: number = foo1Inst;// Error: ClassFoo1 ~> number
+new ClassFoo1();// Error: ClassFoo1 is not a value-identifier
+///////////////////////////////////////////////
+// == Importing Class Type (Named Export) == //
+///////////////////////////////////////////////
+import type { ClassFoo2 } from \"./ExportNamed_Class\";
+import { foo2Inst } from \"./ExportNamed_Class\";
+var b1: ClassFoo2 = foo2Inst;
+var b2: number = foo2Inst;// Error: ClassFoo2 ~> number
+new ClassFoo2();// Error: ClassFoo2 is not a value-identifier
+/////////////////////////////////////////////////////
+// == Importing Class Type (CJS Default Export) == //
+/////////////////////////////////////////////////////
+import type ClassFoo3T from \"./ExportCJSDefault_Class\";
+import ClassFoo3 from \"./ExportCJSDefault_Class\";
+var c1: ClassFoo3T = new ClassFoo3();
+new ClassFoo3T();// Error: ClassFoo3 is not a value-identifier
+///////////////////////////////////////////////////
+// == Importing Class Type (CJS Named Export) == //
+///////////////////////////////////////////////////
+import type { ClassFoo4, ClassFoo5 } from \"./ExportCJSNamed_Class\";
+import { foo4Inst, foo5Inst } from \"./ExportCJSNamed_Class\";
+var d1: ClassFoo4 = foo4Inst;
+var d2: number = foo4Inst;// Error: ClassFoo4 ~> number
+new ClassFoo4();// Error: ClassFoo4 is not a value-identifier
+// TODO: this errors correctly, but the message is just \'can\'t resolve name\'
+var d3: typeof ClassFoo5 = foo5Inst;// Error: Can\'t typeof a type alias
+////////////////////////////////////////////
+// == Import Type Alias (Named Export) == //
+////////////////////////////////////////////
+import type { AliasFoo3 } from \"./ExportNamed_Alias\";
+import { givesAFoo3Obj } from \"./ExportNamed_Alias\";
+var e1: AliasFoo3 = givesAFoo3Obj();
+var e2: number = givesAFoo3Obj();// Error: AliasFoo3 ~> number
+var e3: typeof AliasFoo3 = givesAFoo3Obj();// Error: Can\'t typeof a type alias
+//////////////////////////////////////////////
+// == Import Type Alias (Default Export) == //
+//////////////////////////////////////////////
+// TODO: No support for this right now. It\'s most likely possible, but it\'s
+//       unclear how useful it is at the moment and it entails a little
+//       more work than named type exports, so I\'m punting on it for now.
+///////////////////////////////////////////////////////
+// == Import Type With Non-Alias Compatible Value == //
+///////////////////////////////////////////////////////
+import type { numValue } from \"./ExportsANumber\";// Error: Cannot import-type a number value
+////////////////////////////////////////////////////////////////////////
+// == Regression Test: https://github.com/facebook/flow/issues/359 == //
+// Ensure that type bindings stay type bindings across function body  //
+// env contexts.                                                      //
+////////////////////////////////////////////////////////////////////////
+import type ClassFoo6 from \"./issue-359\";
+function foo() {
+  ClassFoo6;// Error: Not a value binding
+}
+
+"
+`;
+
+exports[`test issue-359.js 1`] = `
+"/* @flow */
+
+class ClassFoo6 {};
+
+export default ClassFoo6;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class ClassFoo6 {}
+export default ClassFoo6
+
+"
+`;
diff --git a/tests/import_type/import_type.js b/tests/import_type/import_type.js
new file mode 100644
index 000000000000..96ec2be84ea4
--- /dev/null
+++ b/tests/import_type/import_type.js
@@ -0,0 +1,82 @@
+/**
+ * @flow
+ */
+
+/////////////////////////////////////////////////
+// == Importing Class Type (Default Export) == //
+/////////////////////////////////////////////////
+
+import type ClassFoo1 from "./ExportDefault_Class";
+import {foo1Inst} from "./ExportDefault_Class";
+
+var a1: ClassFoo1 = foo1Inst;
+var a2: number = foo1Inst; // Error: ClassFoo1 ~> number
+new ClassFoo1(); // Error: ClassFoo1 is not a value-identifier
+
+///////////////////////////////////////////////
+// == Importing Class Type (Named Export) == //
+///////////////////////////////////////////////
+
+import type {ClassFoo2} from "./ExportNamed_Class";
+import {foo2Inst} from "./ExportNamed_Class";
+
+var b1: ClassFoo2 = foo2Inst;
+var b2: number = foo2Inst; // Error: ClassFoo2 ~> number
+new ClassFoo2(); // Error: ClassFoo2 is not a value-identifier
+
+/////////////////////////////////////////////////////
+// == Importing Class Type (CJS Default Export) == //
+/////////////////////////////////////////////////////
+
+import type ClassFoo3T from "./ExportCJSDefault_Class";
+import ClassFoo3 from "./ExportCJSDefault_Class";
+var c1: ClassFoo3T = new ClassFoo3();
+new ClassFoo3T(); // Error: ClassFoo3 is not a value-identifier
+
+///////////////////////////////////////////////////
+// == Importing Class Type (CJS Named Export) == //
+///////////////////////////////////////////////////
+
+import type {ClassFoo4, ClassFoo5} from "./ExportCJSNamed_Class";
+import {foo4Inst, foo5Inst} from "./ExportCJSNamed_Class";
+
+var d1: ClassFoo4 = foo4Inst;
+var d2: number = foo4Inst; // Error: ClassFoo4 ~> number
+new ClassFoo4(); // Error: ClassFoo4 is not a value-identifier
+// TODO: this errors correctly, but the message is just 'can't resolve name'
+var d3: typeof ClassFoo5 = foo5Inst; // Error: Can't typeof a type alias
+
+////////////////////////////////////////////
+// == Import Type Alias (Named Export) == //
+////////////////////////////////////////////
+
+import type {AliasFoo3} from "./ExportNamed_Alias";
+import {givesAFoo3Obj} from "./ExportNamed_Alias";
+var e1: AliasFoo3 = givesAFoo3Obj();
+var e2: number = givesAFoo3Obj(); // Error: AliasFoo3 ~> number
+var e3: typeof AliasFoo3 = givesAFoo3Obj(); // Error: Can't typeof a type alias
+
+//////////////////////////////////////////////
+// == Import Type Alias (Default Export) == //
+//////////////////////////////////////////////
+
+// TODO: No support for this right now. It's most likely possible, but it's
+//       unclear how useful it is at the moment and it entails a little
+//       more work than named type exports, so I'm punting on it for now.
+
+///////////////////////////////////////////////////////
+// == Import Type With Non-Alias Compatible Value == //
+///////////////////////////////////////////////////////
+
+import type {numValue} from "./ExportsANumber"; // Error: Cannot import-type a number value
+
+////////////////////////////////////////////////////////////////////////
+// == Regression Test: https://github.com/facebook/flow/issues/359 == //
+// Ensure that type bindings stay type bindings across function body  //
+// env contexts.                                                      //
+////////////////////////////////////////////////////////////////////////
+
+import type ClassFoo6 from "./issue-359";
+function foo() {
+  ClassFoo6; // Error: Not a value binding
+}
diff --git a/tests/import_type/issue-359.js b/tests/import_type/issue-359.js
new file mode 100644
index 000000000000..ee16df3468f4
--- /dev/null
+++ b/tests/import_type/issue-359.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+class ClassFoo6 {};
+
+export default ClassFoo6;
diff --git a/tests/import_type/jsfmt.spec.js b/tests/import_type/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/import_type/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/import_typeof/ExportCJSDefault_Class.js b/tests/import_typeof/ExportCJSDefault_Class.js
new file mode 100644
index 000000000000..dbbb5594a550
--- /dev/null
+++ b/tests/import_typeof/ExportCJSDefault_Class.js
@@ -0,0 +1,12 @@
+/**
+ * @flow
+ */
+
+class ClassFoo3 {
+  givesANum(): number { return 42; }
+  static givesAFoo3(): ClassFoo3 {
+    return new ClassFoo3();
+  }
+}
+
+module.exports = ClassFoo3;
diff --git a/tests/import_typeof/ExportCJSDefault_Number.js b/tests/import_typeof/ExportCJSDefault_Number.js
new file mode 100644
index 000000000000..a659089f56f5
--- /dev/null
+++ b/tests/import_typeof/ExportCJSDefault_Number.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+module.exports = 42;
diff --git a/tests/import_typeof/ExportCJSNamed_Class.js b/tests/import_typeof/ExportCJSNamed_Class.js
new file mode 100644
index 000000000000..d62df9161ea5
--- /dev/null
+++ b/tests/import_typeof/ExportCJSNamed_Class.js
@@ -0,0 +1,7 @@
+/**
+ * @flow
+ */
+
+class ClassFoo4 {}
+
+exports.ClassFoo4 = ClassFoo4;
diff --git a/tests/import_typeof/ExportCJSNamed_Number.js b/tests/import_typeof/ExportCJSNamed_Number.js
new file mode 100644
index 000000000000..9341801928fd
--- /dev/null
+++ b/tests/import_typeof/ExportCJSNamed_Number.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+exports.num = 42;
diff --git a/tests/import_typeof/ExportDefault_Class.js b/tests/import_typeof/ExportDefault_Class.js
new file mode 100644
index 000000000000..04777aa3fa28
--- /dev/null
+++ b/tests/import_typeof/ExportDefault_Class.js
@@ -0,0 +1,9 @@
+/**
+ * @flow
+ */
+
+class ClassFoo1 {
+  returnsANumber(): number { return 42; }
+}
+
+export default ClassFoo1;
diff --git a/tests/import_typeof/ExportDefault_Number.js b/tests/import_typeof/ExportDefault_Number.js
new file mode 100644
index 000000000000..4f63aba00b99
--- /dev/null
+++ b/tests/import_typeof/ExportDefault_Number.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+export default 42;
diff --git a/tests/import_typeof/ExportNamed_Alias.js b/tests/import_typeof/ExportNamed_Alias.js
new file mode 100644
index 000000000000..0f8c0f810195
--- /dev/null
+++ b/tests/import_typeof/ExportNamed_Alias.js
@@ -0,0 +1,12 @@
+/**
+ * @flow
+ */
+
+export type AliasFoo3  = {
+  givesANum(): number
+};
+export function givesAFoo3Obj(): AliasFoo3 {
+  return {
+    givesANum(): number { return 42; }
+  };
+};
diff --git a/tests/import_typeof/ExportNamed_Class.js b/tests/import_typeof/ExportNamed_Class.js
new file mode 100644
index 000000000000..90ee78a0b440
--- /dev/null
+++ b/tests/import_typeof/ExportNamed_Class.js
@@ -0,0 +1,9 @@
+/**
+ * @flow
+ */
+
+class ClassFoo2 {
+  returnsANumber(): number { return 42; }
+}
+
+export {ClassFoo2};
diff --git a/tests/import_typeof/ExportNamed_Multi.js b/tests/import_typeof/ExportNamed_Multi.js
new file mode 100644
index 000000000000..91f96c936d6f
--- /dev/null
+++ b/tests/import_typeof/ExportNamed_Multi.js
@@ -0,0 +1,4 @@
+// @flow
+
+export var num = 42;
+export var str = 'asdf';
diff --git a/tests/import_typeof/ExportNamed_Number.js b/tests/import_typeof/ExportNamed_Number.js
new file mode 100644
index 000000000000..dc4b2ec97d0d
--- /dev/null
+++ b/tests/import_typeof/ExportNamed_Number.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+export var num = 42;
diff --git a/tests/import_typeof/__snapshots__/jsfmt.spec.js.snap b/tests/import_typeof/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5eade817f7a9
--- /dev/null
+++ b/tests/import_typeof/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,371 @@
+exports[`test ExportCJSDefault_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo3 {
+  givesANum(): number { return 42; }
+  static givesAFoo3(): ClassFoo3 {
+    return new ClassFoo3();
+  }
+}
+
+module.exports = ClassFoo3;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class ClassFoo3 {
+  givesANum(): number {
+    return 42;
+  }
+  givesAFoo3(): ClassFoo3 {
+    return new ClassFoo3();
+  }
+}
+module.exports = ClassFoo3;
+
+"
+`;
+
+exports[`test ExportCJSDefault_Number.js 1`] = `
+"/* @flow */
+
+module.exports = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports = 42;
+
+"
+`;
+
+exports[`test ExportCJSNamed_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo4 {}
+
+exports.ClassFoo4 = ClassFoo4;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class ClassFoo4 {}
+exports.ClassFoo4 = ClassFoo4;
+
+"
+`;
+
+exports[`test ExportCJSNamed_Number.js 1`] = `
+"/* @flow */
+
+exports.num = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+exports.num = 42;
+
+"
+`;
+
+exports[`test ExportDefault_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo1 {
+  returnsANumber(): number { return 42; }
+}
+
+export default ClassFoo1;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class ClassFoo1 {
+  returnsANumber(): number {
+    return 42;
+  }
+}
+export default ClassFoo1
+
+"
+`;
+
+exports[`test ExportDefault_Number.js 1`] = `
+"/* @flow */
+
+export default 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+export default 42
+
+"
+`;
+
+exports[`test ExportNamed_Alias.js 1`] = `
+"/**
+ * @flow
+ */
+
+export type AliasFoo3  = {
+  givesANum(): number
+};
+export function givesAFoo3Obj(): AliasFoo3 {
+  return {
+    givesANum(): number { return 42; }
+  };
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test ExportNamed_Class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassFoo2 {
+  returnsANumber(): number { return 42; }
+}
+
+export {ClassFoo2};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1785
+        fromString(\", \").join(path.map(print, \"specifiers\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at printExportDeclaration (/src/printer.js:1785:26)
+    at genericPrintNoParens (/src/printer.js:488:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+"
+`;
+
+exports[`test ExportNamed_Multi.js 1`] = `
+"// @flow
+
+export var num = 42;
+export var str = \'asdf\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export var num = 42;
+export var str = \"asdf\";
+
+"
+`;
+
+exports[`test ExportNamed_Number.js 1`] = `
+"/* @flow */
+
+export var num = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+export var num = 42;
+
+"
+`;
+
+exports[`test import_typeof.js 1`] = `
+"/**
+ * @flow
+ */
+
+///////////////////////////////////////////////////
+// == Importing Class Typeof (Default Export) == //
+///////////////////////////////////////////////////
+
+import typeof ClassFoo1T from \"./ExportDefault_Class\";
+import ClassFoo1 from \"./ExportDefault_Class\";
+
+var a1: ClassFoo1T = ClassFoo1;
+var a2: ClassFoo1T = new ClassFoo1(); // Error: ClassFoo1 (inst) ~> ClassFoo1 (class)
+new ClassFoo1T(); // Error: ClassFoo1T is not bound to a value
+
+/////////////////////////////////////////////////
+// == Importing Class Typeof (Named Export) == //
+/////////////////////////////////////////////////
+
+import typeof {ClassFoo2 as ClassFoo2T} from \"./ExportNamed_Class\";
+import {ClassFoo2} from \"./ExportNamed_Class\";
+
+var b1: ClassFoo2T = ClassFoo2;
+var b2: ClassFoo2T = new ClassFoo2(); // Error: ClassFoo2 (inst) ~> ClassFoo2 (class)
+new ClassFoo2T(); // Error: ClassFoo2T is not bound to a value
+
+///////////////////////////////////////////////////////
+// == Importing Class Typeof (CJS Default Export) == //
+///////////////////////////////////////////////////////
+
+import typeof ClassFoo3T from \"./ExportCJSDefault_Class\";
+import ClassFoo3 from \"./ExportCJSDefault_Class\";
+
+var c1: ClassFoo3T = ClassFoo3;
+var c2: ClassFoo3T = new ClassFoo3(); // Error: ClassFoo3 (inst) ~> ClassFoo3 (class)
+
+/////////////////////////////////////////////////////
+// == Importing Class Typeof (CJS Named Export) == //
+/////////////////////////////////////////////////////
+
+import typeof {ClassFoo4 as ClassFoo4T} from \"./ExportCJSNamed_Class\";
+import {ClassFoo4} from \"./ExportCJSNamed_Class\";
+
+var d1: ClassFoo4T = ClassFoo4;
+var d2: ClassFoo4T = new ClassFoo4(); // Error: ClassFoo4 (inst) ~> ClassFoo4 (class)
+
+//////////////////////////////////////////////
+// == Import Typeof Alias (Named Export) == //
+//////////////////////////////////////////////
+
+import typeof {AliasFoo3} from \"./ExportNamed_Alias\"; // Error: Can\'t \`import typeof\` type aliases!
+
+////////////////////////////////////////////////
+// == Import Typeof Alias (Default Export) == //
+////////////////////////////////////////////////
+
+// TODO: No support for this right now. It\'s most likely possible, but it\'s
+//       unclear how useful it is at the moment and it entails a little
+//       more work than named type exports, so I\'m punting on it for now.
+
+///////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (Default Export) == //
+///////////////////////////////////////////////////////////////
+
+import typeof num_default from \"./ExportDefault_Number\";
+
+var f1: num_default = 42;
+var f2: num_default = \'asdf\'; // Error: string ~> number
+
+/////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (Named Export) == //
+/////////////////////////////////////////////////////////////
+
+import typeof {num as num_named} from \"./ExportNamed_Number\";
+
+var g1: num_named = 42;
+var g2: num_named = \'asdf\'; // Error: string ~> number
+
+///////////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (CJS Default Export) == //
+///////////////////////////////////////////////////////////////////
+
+import typeof num_cjs_default from \"./ExportCJSDefault_Number\";
+
+var h1: num_cjs_default = 42;
+var h2: num_cjs_default = \'asdf\'; // Error: string ~> number
+
+/////////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (CJS Named Export) == //
+/////////////////////////////////////////////////////////////////
+
+import typeof {num as num_cjs_named} from \"./ExportCJSNamed_Number\";
+
+var i1: num_cjs_named = 42;
+var i2: num_cjs_named = \'asdf\'; // Error: string ~> number
+
+///////////////////////////////////////////////
+// == Import Typeof ModuleNamespaceObject == //
+///////////////////////////////////////////////
+
+import typeof * as ModuleNSObjT from \"./ExportNamed_Multi\";
+var j1: ModuleNSObjT = {num: 42, str: \'asdf\'};
+var j2: ModuleNSObjT = {num: 42, str: 42}; // Error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+///////////////////////////////////////////////////
+// == Importing Class Typeof (Default Export) == //
+///////////////////////////////////////////////////
+import typeof ClassFoo1T from \"./ExportDefault_Class\";
+import ClassFoo1 from \"./ExportDefault_Class\";
+var a1: ClassFoo1T = ClassFoo1;
+var a2: ClassFoo1T = new ClassFoo1();// Error: ClassFoo1 (inst) ~> ClassFoo1 (class)
+new ClassFoo1T();// Error: ClassFoo1T is not bound to a value
+/////////////////////////////////////////////////
+// == Importing Class Typeof (Named Export) == //
+/////////////////////////////////////////////////
+import typeof { ClassFoo2 as ClassFoo2T } from \"./ExportNamed_Class\";
+import { ClassFoo2 } from \"./ExportNamed_Class\";
+var b1: ClassFoo2T = ClassFoo2;
+var b2: ClassFoo2T = new ClassFoo2();// Error: ClassFoo2 (inst) ~> ClassFoo2 (class)
+new ClassFoo2T();// Error: ClassFoo2T is not bound to a value
+///////////////////////////////////////////////////////
+// == Importing Class Typeof (CJS Default Export) == //
+///////////////////////////////////////////////////////
+import typeof ClassFoo3T from \"./ExportCJSDefault_Class\";
+import ClassFoo3 from \"./ExportCJSDefault_Class\";
+var c1: ClassFoo3T = ClassFoo3;
+var c2: ClassFoo3T = new ClassFoo3();// Error: ClassFoo3 (inst) ~> ClassFoo3 (class)
+/////////////////////////////////////////////////////
+// == Importing Class Typeof (CJS Named Export) == //
+/////////////////////////////////////////////////////
+import typeof { ClassFoo4 as ClassFoo4T } from \"./ExportCJSNamed_Class\";
+import { ClassFoo4 } from \"./ExportCJSNamed_Class\";
+var d1: ClassFoo4T = ClassFoo4;
+var d2: ClassFoo4T = new ClassFoo4();// Error: ClassFoo4 (inst) ~> ClassFoo4 (class)
+//////////////////////////////////////////////
+// == Import Typeof Alias (Named Export) == //
+//////////////////////////////////////////////
+import typeof { AliasFoo3 } from \"./ExportNamed_Alias\";// Error: Can\'t \`import typeof\` type aliases!
+////////////////////////////////////////////////
+// == Import Typeof Alias (Default Export) == //
+////////////////////////////////////////////////
+// TODO: No support for this right now. It\'s most likely possible, but it\'s
+//       unclear how useful it is at the moment and it entails a little
+//       more work than named type exports, so I\'m punting on it for now.
+///////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (Default Export) == //
+///////////////////////////////////////////////////////////////
+import typeof num_default from \"./ExportDefault_Number\";
+var f1: num_default = 42;
+var f2: num_default = \"asdf\";// Error: string ~> number
+/////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (Named Export) == //
+/////////////////////////////////////////////////////////////
+import typeof { num as num_named } from \"./ExportNamed_Number\";
+var g1: num_named = 42;
+var g2: num_named = \"asdf\";// Error: string ~> number
+///////////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (CJS Default Export) == //
+///////////////////////////////////////////////////////////////////
+import typeof num_cjs_default from \"./ExportCJSDefault_Number\";
+var h1: num_cjs_default = 42;
+var h2: num_cjs_default = \"asdf\";// Error: string ~> number
+/////////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (CJS Named Export) == //
+/////////////////////////////////////////////////////////////////
+import typeof { num as num_cjs_named } from \"./ExportCJSNamed_Number\";
+var i1: num_cjs_named = 42;
+var i2: num_cjs_named = \"asdf\";// Error: string ~> number
+///////////////////////////////////////////////
+// == Import Typeof ModuleNamespaceObject == //
+///////////////////////////////////////////////
+import typeof * as ModuleNSObjT from \"./ExportNamed_Multi\";
+var j1: ModuleNSObjT = { num: 42, str: \"asdf\" };
+var j2: ModuleNSObjT = { num: 42, str: 42 };// Error: number ~> string
+
+"
+`;
diff --git a/tests/import_typeof/import_typeof.js b/tests/import_typeof/import_typeof.js
new file mode 100644
index 000000000000..6916f800420c
--- /dev/null
+++ b/tests/import_typeof/import_typeof.js
@@ -0,0 +1,103 @@
+/**
+ * @flow
+ */
+
+///////////////////////////////////////////////////
+// == Importing Class Typeof (Default Export) == //
+///////////////////////////////////////////////////
+
+import typeof ClassFoo1T from "./ExportDefault_Class";
+import ClassFoo1 from "./ExportDefault_Class";
+
+var a1: ClassFoo1T = ClassFoo1;
+var a2: ClassFoo1T = new ClassFoo1(); // Error: ClassFoo1 (inst) ~> ClassFoo1 (class)
+new ClassFoo1T(); // Error: ClassFoo1T is not bound to a value
+
+/////////////////////////////////////////////////
+// == Importing Class Typeof (Named Export) == //
+/////////////////////////////////////////////////
+
+import typeof {ClassFoo2 as ClassFoo2T} from "./ExportNamed_Class";
+import {ClassFoo2} from "./ExportNamed_Class";
+
+var b1: ClassFoo2T = ClassFoo2;
+var b2: ClassFoo2T = new ClassFoo2(); // Error: ClassFoo2 (inst) ~> ClassFoo2 (class)
+new ClassFoo2T(); // Error: ClassFoo2T is not bound to a value
+
+///////////////////////////////////////////////////////
+// == Importing Class Typeof (CJS Default Export) == //
+///////////////////////////////////////////////////////
+
+import typeof ClassFoo3T from "./ExportCJSDefault_Class";
+import ClassFoo3 from "./ExportCJSDefault_Class";
+
+var c1: ClassFoo3T = ClassFoo3;
+var c2: ClassFoo3T = new ClassFoo3(); // Error: ClassFoo3 (inst) ~> ClassFoo3 (class)
+
+/////////////////////////////////////////////////////
+// == Importing Class Typeof (CJS Named Export) == //
+/////////////////////////////////////////////////////
+
+import typeof {ClassFoo4 as ClassFoo4T} from "./ExportCJSNamed_Class";
+import {ClassFoo4} from "./ExportCJSNamed_Class";
+
+var d1: ClassFoo4T = ClassFoo4;
+var d2: ClassFoo4T = new ClassFoo4(); // Error: ClassFoo4 (inst) ~> ClassFoo4 (class)
+
+//////////////////////////////////////////////
+// == Import Typeof Alias (Named Export) == //
+//////////////////////////////////////////////
+
+import typeof {AliasFoo3} from "./ExportNamed_Alias"; // Error: Can't `import typeof` type aliases!
+
+////////////////////////////////////////////////
+// == Import Typeof Alias (Default Export) == //
+////////////////////////////////////////////////
+
+// TODO: No support for this right now. It's most likely possible, but it's
+//       unclear how useful it is at the moment and it entails a little
+//       more work than named type exports, so I'm punting on it for now.
+
+///////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (Default Export) == //
+///////////////////////////////////////////////////////////////
+
+import typeof num_default from "./ExportDefault_Number";
+
+var f1: num_default = 42;
+var f2: num_default = 'asdf'; // Error: string ~> number
+
+/////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (Named Export) == //
+/////////////////////////////////////////////////////////////
+
+import typeof {num as num_named} from "./ExportNamed_Number";
+
+var g1: num_named = 42;
+var g2: num_named = 'asdf'; // Error: string ~> number
+
+///////////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (CJS Default Export) == //
+///////////////////////////////////////////////////////////////////
+
+import typeof num_cjs_default from "./ExportCJSDefault_Number";
+
+var h1: num_cjs_default = 42;
+var h2: num_cjs_default = 'asdf'; // Error: string ~> number
+
+/////////////////////////////////////////////////////////////////
+// == Import Typeof With Non-Class Value (CJS Named Export) == //
+/////////////////////////////////////////////////////////////////
+
+import typeof {num as num_cjs_named} from "./ExportCJSNamed_Number";
+
+var i1: num_cjs_named = 42;
+var i2: num_cjs_named = 'asdf'; // Error: string ~> number
+
+///////////////////////////////////////////////
+// == Import Typeof ModuleNamespaceObject == //
+///////////////////////////////////////////////
+
+import typeof * as ModuleNSObjT from "./ExportNamed_Multi";
+var j1: ModuleNSObjT = {num: 42, str: 'asdf'};
+var j2: ModuleNSObjT = {num: 42, str: 42}; // Error: number ~> string
diff --git a/tests/import_typeof/jsfmt.spec.js b/tests/import_typeof/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/import_typeof/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/include/foo/batman/__snapshots__/jsfmt.spec.js.snap b/tests/include/foo/batman/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0716adec34e2
--- /dev/null
+++ b/tests/include/foo/batman/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test baz.js 1`] = `
+"/* @flow */
+
+var x: number = "not a number" // Error string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var x: number = "not a number";// Error string ~> number
+
+"
+`;
diff --git a/tests/include/foo/batman/baz.js b/tests/include/foo/batman/baz.js
new file mode 100644
index 000000000000..d6b2eca30b2a
--- /dev/null
+++ b/tests/include/foo/batman/baz.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+var x: number = "not a number" // Error string ~> number
diff --git a/tests/include/foo/batman/jsfmt.spec.js b/tests/include/foo/batman/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/include/foo/batman/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/include/included/__snapshots__/jsfmt.spec.js.snap b/tests/include/included/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0e05f7235a80
--- /dev/null
+++ b/tests/include/included/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test test.js 1`] = `
+"(123: string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+(123: string);
+
+"
+`;
diff --git a/tests/include/included/jsfmt.spec.js b/tests/include/included/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/include/included/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/include/included/test.js b/tests/include/included/test.js
new file mode 100644
index 000000000000..c41afeed67c2
--- /dev/null
+++ b/tests/include/included/test.js
@@ -0,0 +1 @@
+(123: string);
diff --git a/tests/incremental/__snapshots__/jsfmt.spec.js.snap b/tests/incremental/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..51fa6eb132d4
--- /dev/null
+++ b/tests/incremental/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,33 @@
+exports[`test a.js 1`] = `
+"/* @providesModule IncrModuleA */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test b.js 1`] = `
+"/* @providesModule IncrModuleB
+   @flow
+*/
+
+var A = require('IncrModuleA');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule IncrModuleB
+   @flow
+*/
+var A = require("IncrModuleA");
+
+"
+`;
+
+exports[`test dup_a.js 1`] = `
+"/* @providesModule IncrModuleA */
+
+var x:string = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule IncrModuleA */
+var x: string = 0;
+
+"
+`;
diff --git a/tests/incremental/a.js b/tests/incremental/a.js
new file mode 100644
index 000000000000..02ef81a82995
--- /dev/null
+++ b/tests/incremental/a.js
@@ -0,0 +1 @@
+/* @providesModule IncrModuleA */
diff --git a/tests/incremental/b.js b/tests/incremental/b.js
new file mode 100644
index 000000000000..221ffef4467a
--- /dev/null
+++ b/tests/incremental/b.js
@@ -0,0 +1,5 @@
+/* @providesModule IncrModuleB
+   @flow
+*/
+
+var A = require('IncrModuleA');
diff --git a/tests/incremental/dup_a.js b/tests/incremental/dup_a.js
new file mode 100644
index 000000000000..b996546f23a1
--- /dev/null
+++ b/tests/incremental/dup_a.js
@@ -0,0 +1,3 @@
+/* @providesModule IncrModuleA */
+
+var x:string = 0;
diff --git a/tests/incremental/jsfmt.spec.js b/tests/incremental/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_basic/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_basic/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c90d4376220c
--- /dev/null
+++ b/tests/incremental_basic/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,39 @@
+exports[`test a.js 1`] = `
+"// @flow
+var a: string = 0;
+module.exports = a;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a: string = 0;
+module.exports = a;
+
+"
+`;
+
+exports[`test b.js 1`] = `
+"// @flow
+var a = require('./a');
+var b: number = a;
+module.exports = b;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a = require("./a");
+var b: number = a;
+module.exports = b;
+
+"
+`;
+
+exports[`test c.js 1`] = `
+"// @flow
+var b = require('./b');
+var c: string = b;
+module.exports = c;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var b = require("./b");
+var c: string = b;
+module.exports = c;
+
+"
+`;
diff --git a/tests/incremental_basic/a.js b/tests/incremental_basic/a.js
new file mode 100644
index 000000000000..f863b77254c3
--- /dev/null
+++ b/tests/incremental_basic/a.js
@@ -0,0 +1,3 @@
+// @flow
+var a: string = 0;
+module.exports = a;
diff --git a/tests/incremental_basic/b.js b/tests/incremental_basic/b.js
new file mode 100644
index 000000000000..8f3560a45c53
--- /dev/null
+++ b/tests/incremental_basic/b.js
@@ -0,0 +1,4 @@
+// @flow
+var a = require('./a');
+var b: number = a;
+module.exports = b;
diff --git a/tests/incremental_basic/c.js b/tests/incremental_basic/c.js
new file mode 100644
index 000000000000..3c6b3f56fe5d
--- /dev/null
+++ b/tests/incremental_basic/c.js
@@ -0,0 +1,4 @@
+// @flow
+var b = require('./b');
+var c: string = b;
+module.exports = c;
diff --git a/tests/incremental_basic/jsfmt.spec.js b/tests/incremental_basic/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_basic/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_basic/tmp1/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_basic/tmp1/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..53f45bfe5ffa
--- /dev/null
+++ b/tests/incremental_basic/tmp1/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,13 @@
+exports[`test b.js 1`] = `
+"// @flow
+var a = require('./a');
+var b = a;
+module.exports = b;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a = require("./a");
+var b = a;
+module.exports = b;
+
+"
+`;
diff --git a/tests/incremental_basic/tmp1/b.js b/tests/incremental_basic/tmp1/b.js
new file mode 100644
index 000000000000..14c1a8efab19
--- /dev/null
+++ b/tests/incremental_basic/tmp1/b.js
@@ -0,0 +1,4 @@
+// @flow
+var a = require('./a');
+var b = a;
+module.exports = b;
diff --git a/tests/incremental_basic/tmp1/jsfmt.spec.js b/tests/incremental_basic/tmp1/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_basic/tmp1/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_basic/tmp2/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_basic/tmp2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2f9e0b72c72f
--- /dev/null
+++ b/tests/incremental_basic/tmp2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,11 @@
+exports[`test a.js 1`] = `
+"// @flow
+var a = 0;
+module.exports = a;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a = 0;
+module.exports = a;
+
+"
+`;
diff --git a/tests/incremental_basic/tmp2/a.js b/tests/incremental_basic/tmp2/a.js
new file mode 100644
index 000000000000..6c8a55571b7a
--- /dev/null
+++ b/tests/incremental_basic/tmp2/a.js
@@ -0,0 +1,3 @@
+// @flow
+var a = 0;
+module.exports = a;
diff --git a/tests/incremental_basic/tmp2/jsfmt.spec.js b/tests/incremental_basic/tmp2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_basic/tmp2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_basic/tmp3/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_basic/tmp3/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9fc637bf3218
--- /dev/null
+++ b/tests/incremental_basic/tmp3/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,13 @@
+exports[`test b.js 1`] = `
+"// @flow
+var a = require('./a');
+var b: number = a;
+module.exports = b;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a = require("./a");
+var b: number = a;
+module.exports = b;
+
+"
+`;
diff --git a/tests/incremental_basic/tmp3/b.js b/tests/incremental_basic/tmp3/b.js
new file mode 100644
index 000000000000..8f3560a45c53
--- /dev/null
+++ b/tests/incremental_basic/tmp3/b.js
@@ -0,0 +1,4 @@
+// @flow
+var a = require('./a');
+var b: number = a;
+module.exports = b;
diff --git a/tests/incremental_basic/tmp3/jsfmt.spec.js b/tests/incremental_basic/tmp3/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_basic/tmp3/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_cycle/A.js b/tests/incremental_cycle/A.js
new file mode 100644
index 000000000000..d745347242b6
--- /dev/null
+++ b/tests/incremental_cycle/A.js
@@ -0,0 +1,8 @@
+// @flow
+
+class A {
+  b: number;
+  c: string;
+}
+
+module.exports = A;
diff --git a/tests/incremental_cycle/B.js b/tests/incremental_cycle/B.js
new file mode 100644
index 000000000000..2aebd1fc0cb8
--- /dev/null
+++ b/tests/incremental_cycle/B.js
@@ -0,0 +1,9 @@
+// @flow
+var A = require ('./A');
+import type C from './C';
+
+class B extends A {
+  c: C;
+}
+
+module.exports = B;
diff --git a/tests/incremental_cycle/C.js b/tests/incremental_cycle/C.js
new file mode 100644
index 000000000000..3b7aed9f91d3
--- /dev/null
+++ b/tests/incremental_cycle/C.js
@@ -0,0 +1,9 @@
+// @flow
+var A = require ('./A');
+import type B from './B';
+
+class C extends A {
+  b: B;
+}
+
+module.exports = C;
diff --git a/tests/incremental_cycle/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_cycle/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..48806a659072
--- /dev/null
+++ b/tests/incremental_cycle/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,63 @@
+exports[`test A.js 1`] = `
+"// @flow
+
+class A {
+  b: number;
+  c: string;
+}
+
+module.exports = A;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class A {
+  b: number;
+  c: string;
+}
+module.exports = A;
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"// @flow
+var A = require ('./A');
+import type C from './C';
+
+class B extends A {
+  c: C;
+}
+
+module.exports = B;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var A = require("./A");
+import type C from "./C";
+class B extends A {
+  c: C;
+}
+module.exports = B;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"// @flow
+var A = require ('./A');
+import type B from './B';
+
+class C extends A {
+  b: B;
+}
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var A = require("./A");
+import type B from "./B";
+class C extends A {
+  b: B;
+}
+module.exports = C;
+
+"
+`;
diff --git a/tests/incremental_cycle/jsfmt.spec.js b/tests/incremental_cycle/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_cycle/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_cycle/tmp1/B.js b/tests/incremental_cycle/tmp1/B.js
new file mode 100644
index 000000000000..0beb2ae1ee93
--- /dev/null
+++ b/tests/incremental_cycle/tmp1/B.js
@@ -0,0 +1,5 @@
+// @flow
+var A = require ('./A');
+import type C from './C';
+
+export type B = string;
diff --git a/tests/incremental_cycle/tmp1/C.js b/tests/incremental_cycle/tmp1/C.js
new file mode 100644
index 000000000000..6e957cdd46d1
--- /dev/null
+++ b/tests/incremental_cycle/tmp1/C.js
@@ -0,0 +1,9 @@
+// @flow
+var A = require ('./A');
+import type { B } from './B'
+
+class C extends A {
+  b: B;
+}
+
+module.exports = C;
diff --git a/tests/incremental_cycle/tmp1/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_cycle/tmp1/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2712efe33fbd
--- /dev/null
+++ b/tests/incremental_cycle/tmp1/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,36 @@
+exports[`test B.js 1`] = `
+"// @flow
+var A = require ('./A');
+import type C from './C';
+
+export type B = string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var A = require("./A");
+import type C from "./C";
+export type B = string;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"// @flow
+var A = require ('./A');
+import type { B } from './B'
+
+class C extends A {
+  b: B;
+}
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var A = require("./A");
+import type { B } from "./B";
+class C extends A {
+  b: B;
+}
+module.exports = C;
+
+"
+`;
diff --git a/tests/incremental_cycle/tmp1/jsfmt.spec.js b/tests/incremental_cycle/tmp1/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_cycle/tmp1/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_cycle/tmp2/B.js b/tests/incremental_cycle/tmp2/B.js
new file mode 100644
index 000000000000..b9f7dd32dc37
--- /dev/null
+++ b/tests/incremental_cycle/tmp2/B.js
@@ -0,0 +1,5 @@
+// @flow
+var A = require ('./A');
+//import type C from './C';
+
+export type B = string;
diff --git a/tests/incremental_cycle/tmp2/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_cycle/tmp2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6781d9af80b0
--- /dev/null
+++ b/tests/incremental_cycle/tmp2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,14 @@
+exports[`test B.js 1`] = `
+"// @flow
+var A = require ('./A');
+//import type C from './C';
+
+export type B = string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var A = require("./A");
+//import type C from './C';
+export type B = string;
+
+"
+`;
diff --git a/tests/incremental_cycle/tmp2/jsfmt.spec.js b/tests/incremental_cycle/tmp2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_cycle/tmp2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_cycle/tmp3/B.js b/tests/incremental_cycle/tmp3/B.js
new file mode 100644
index 000000000000..748fd837e9f8
--- /dev/null
+++ b/tests/incremental_cycle/tmp3/B.js
@@ -0,0 +1,6 @@
+// @flow
+var A = require ('./A');
+import type C from './C';
+
+
+export type B = string;
diff --git a/tests/incremental_cycle/tmp3/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_cycle/tmp3/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3e2ea4f503ac
--- /dev/null
+++ b/tests/incremental_cycle/tmp3/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test B.js 1`] = `
+"// @flow
+var A = require ('./A');
+import type C from './C';
+
+
+export type B = string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var A = require("./A");
+import type C from "./C";
+export type B = string;
+
+"
+`;
diff --git a/tests/incremental_cycle/tmp3/jsfmt.spec.js b/tests/incremental_cycle/tmp3/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_cycle/tmp3/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_delete/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_delete/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..90424706cea3
--- /dev/null
+++ b/tests/incremental_delete/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,123 @@
+exports[`test a.js 1`] = `
+"// @flow
+var a: string = 0;
+module.exports = a;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a: string = 0;
+module.exports = a;
+
+"
+`;
+
+exports[`test b.js 1`] = `
+"// @flow
+var a = require('./a');
+var b: number = a;
+module.exports = b;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var a = require("./a");
+var b: number = a;
+module.exports = b;
+
+"
+`;
+
+exports[`test c.js 1`] = `
+"// @flow
+var b = require('./b');
+var c: string = b;
+module.exports = c;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var b = require("./b");
+var c: string = b;
+module.exports = c;
+
+"
+`;
+
+exports[`test dupe1.js 1`] = `
+"/**
+ * Dupe provider 1/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe1";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Dupe provider 1/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe1";
+
+"
+`;
+
+exports[`test dupe2.js 1`] = `
+"/**
+ * Dupe provider 2/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe2";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Dupe provider 2/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe2";
+
+"
+`;
+
+exports[`test requires_dupe.js 1`] = `
+"/**
+ * depends on doubly-provided module
+ * @flow
+ */
+var dupe = require('Dupe');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * depends on doubly-provided module
+ * @flow
+ */
+var dupe = require("Dupe");
+
+"
+`;
+
+exports[`test requires_unchecked.js 1`] = `
+"/**
+ * depends on an unchecked module, which will be deleted
+ * @flow
+ */
+var unchecked = require('Unchecked');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * depends on an unchecked module, which will be deleted
+ * @flow
+ */
+var unchecked = require("Unchecked");
+
+"
+`;
+
+exports[`test unchecked.js 1`] = `
+"/**
+ * Not a flow module.
+ * @providesModule Unchecked
+ */
+module.exports = "unchecked";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Not a flow module.
+ * @providesModule Unchecked
+ */
+module.exports = "unchecked";
+
+"
+`;
diff --git a/tests/incremental_delete/a.js b/tests/incremental_delete/a.js
new file mode 100644
index 000000000000..f863b77254c3
--- /dev/null
+++ b/tests/incremental_delete/a.js
@@ -0,0 +1,3 @@
+// @flow
+var a: string = 0;
+module.exports = a;
diff --git a/tests/incremental_delete/b.js b/tests/incremental_delete/b.js
new file mode 100644
index 000000000000..8f3560a45c53
--- /dev/null
+++ b/tests/incremental_delete/b.js
@@ -0,0 +1,4 @@
+// @flow
+var a = require('./a');
+var b: number = a;
+module.exports = b;
diff --git a/tests/incremental_delete/c.js b/tests/incremental_delete/c.js
new file mode 100644
index 000000000000..3c6b3f56fe5d
--- /dev/null
+++ b/tests/incremental_delete/c.js
@@ -0,0 +1,4 @@
+// @flow
+var b = require('./b');
+var c: string = b;
+module.exports = c;
diff --git a/tests/incremental_delete/dupe1.js b/tests/incremental_delete/dupe1.js
new file mode 100644
index 000000000000..1a298b67eae7
--- /dev/null
+++ b/tests/incremental_delete/dupe1.js
@@ -0,0 +1,6 @@
+/**
+ * Dupe provider 1/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe1";
diff --git a/tests/incremental_delete/dupe2.js b/tests/incremental_delete/dupe2.js
new file mode 100644
index 000000000000..aa64ae687dd8
--- /dev/null
+++ b/tests/incremental_delete/dupe2.js
@@ -0,0 +1,6 @@
+/**
+ * Dupe provider 2/2
+ * @providesModule Dupe
+ * @flow
+ */
+module.exports = "dupe2";
diff --git a/tests/incremental_delete/jsfmt.spec.js b/tests/incremental_delete/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_delete/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_delete/requires_dupe.js b/tests/incremental_delete/requires_dupe.js
new file mode 100644
index 000000000000..129992b7ab05
--- /dev/null
+++ b/tests/incremental_delete/requires_dupe.js
@@ -0,0 +1,5 @@
+/**
+ * depends on doubly-provided module
+ * @flow
+ */
+var dupe = require('Dupe');
diff --git a/tests/incremental_delete/requires_unchecked.js b/tests/incremental_delete/requires_unchecked.js
new file mode 100644
index 000000000000..1db1b9bc6a4c
--- /dev/null
+++ b/tests/incremental_delete/requires_unchecked.js
@@ -0,0 +1,5 @@
+/**
+ * depends on an unchecked module, which will be deleted
+ * @flow
+ */
+var unchecked = require('Unchecked');
diff --git a/tests/incremental_delete/unchecked.js b/tests/incremental_delete/unchecked.js
new file mode 100644
index 000000000000..96d63429283f
--- /dev/null
+++ b/tests/incremental_delete/unchecked.js
@@ -0,0 +1,5 @@
+/**
+ * Not a flow module.
+ * @providesModule Unchecked
+ */
+module.exports = "unchecked";
diff --git a/tests/incremental_duplicate_delete/A.js b/tests/incremental_duplicate_delete/A.js
new file mode 100644
index 000000000000..638d95f80d1d
--- /dev/null
+++ b/tests/incremental_duplicate_delete/A.js
@@ -0,0 +1,4 @@
+/**
+ * @providesModule A
+ * @flow
+ */
diff --git a/tests/incremental_duplicate_delete/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_duplicate_delete/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..519ef51f35cb
--- /dev/null
+++ b/tests/incremental_duplicate_delete/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test A.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/incremental_duplicate_delete/jsfmt.spec.js b/tests/incremental_duplicate_delete/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_duplicate_delete/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_json/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_json/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..435a7ef63301
--- /dev/null
+++ b/tests/incremental_json/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test test.js 1`] = `
+"/**
+ * @flow
+ */
+var data = require('./data');
+var x: number = data.x;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+var data = require("./data");
+var x: number = data.x;
+
+"
+`;
diff --git a/tests/incremental_json/jsfmt.spec.js b/tests/incremental_json/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_json/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_json/test.js b/tests/incremental_json/test.js
new file mode 100644
index 000000000000..3eb8f377fcbe
--- /dev/null
+++ b/tests/incremental_json/test.js
@@ -0,0 +1,5 @@
+/**
+ * @flow
+ */
+var data = require('./data');
+var x: number = data.x;
diff --git a/tests/incremental_mixed_naming_cycle/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_mixed_naming_cycle/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6b272ab92e10
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,102 @@
+exports[`test a.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+
+(require('./b'): void);
+(require('C'): void);
+
+module.exports = 'A';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule A
+ * @flow
+ */
+(require("./b"): void);
+(require("C"): void);
+module.exports = "A";
+
+"
+`;
+
+exports[`test b.js 1`] = `
+"/**
+ * @providesModule B
+ * @flow
+ */
+
+(require('A'): void);
+(require('D'): void);
+
+module.exports = 'B';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule B
+ * @flow
+ */
+(require("A"): void);
+(require("D"): void);
+module.exports = "B";
+
+"
+`;
+
+exports[`test c.js 1`] = `
+"/**
+ * @providesModule C
+ * @flow
+ */
+
+require('Root');
+(require('./b'): void);
+
+module.exports = 'C';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule C
+ * @flow
+ */
+require("Root");
+(require("./b"): void);
+module.exports = "C";
+
+"
+`;
+
+exports[`test d.js 1`] = `
+"/**
+ * @providesModule D
+ * @flow
+ */
+
+(require('./b'): void);
+
+module.exports = 'D';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule D
+ * @flow
+ */
+(require("./b"): void);
+module.exports = "D";
+
+"
+`;
+
+exports[`test root.js 1`] = `
+"/**
+ * @providesModule Root
+ * @flow
+ */
+
+module.exports = 'Root';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule Root
+ * @flow
+ */
+module.exports = "Root";
+
+"
+`;
diff --git a/tests/incremental_mixed_naming_cycle/a.js b/tests/incremental_mixed_naming_cycle/a.js
new file mode 100644
index 000000000000..e5effdb2d447
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/a.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule A
+ * @flow
+ */
+
+(require('./b'): void);
+(require('C'): void);
+
+module.exports = 'A';
diff --git a/tests/incremental_mixed_naming_cycle/b.js b/tests/incremental_mixed_naming_cycle/b.js
new file mode 100644
index 000000000000..be1f28147565
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/b.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule B
+ * @flow
+ */
+
+(require('A'): void);
+(require('D'): void);
+
+module.exports = 'B';
diff --git a/tests/incremental_mixed_naming_cycle/c.js b/tests/incremental_mixed_naming_cycle/c.js
new file mode 100644
index 000000000000..a9cf3abb6f6a
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/c.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule C
+ * @flow
+ */
+
+require('Root');
+(require('./b'): void);
+
+module.exports = 'C';
diff --git a/tests/incremental_mixed_naming_cycle/d.js b/tests/incremental_mixed_naming_cycle/d.js
new file mode 100644
index 000000000000..b95edb89b908
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/d.js
@@ -0,0 +1,8 @@
+/**
+ * @providesModule D
+ * @flow
+ */
+
+(require('./b'): void);
+
+module.exports = 'D';
diff --git a/tests/incremental_mixed_naming_cycle/jsfmt.spec.js b/tests/incremental_mixed_naming_cycle/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_mixed_naming_cycle/root.js b/tests/incremental_mixed_naming_cycle/root.js
new file mode 100644
index 000000000000..890d205a10e3
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/root.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule Root
+ * @flow
+ */
+
+module.exports = 'Root';
diff --git a/tests/incremental_mixed_naming_cycle/tmp1/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_mixed_naming_cycle/tmp1/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e441192b8fbe
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/tmp1/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test root.js 1`] = `
+"/**
+ * @providesModule Root
+ * @flow
+ */
+
+// trivial edit (adding this comment)
+module.exports = 'Root';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule Root
+ * @flow
+ */
+// trivial edit (adding this comment)
+module.exports = "Root";
+
+"
+`;
diff --git a/tests/incremental_mixed_naming_cycle/tmp1/jsfmt.spec.js b/tests/incremental_mixed_naming_cycle/tmp1/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/tmp1/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_mixed_naming_cycle/tmp1/root.js b/tests/incremental_mixed_naming_cycle/tmp1/root.js
new file mode 100644
index 000000000000..d5d42fa36245
--- /dev/null
+++ b/tests/incremental_mixed_naming_cycle/tmp1/root.js
@@ -0,0 +1,7 @@
+/**
+ * @providesModule Root
+ * @flow
+ */
+
+// trivial edit (adding this comment)
+module.exports = 'Root';
diff --git a/tests/incremental_non_flow_move/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_non_flow_move/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..51bc01bd2485
--- /dev/null
+++ b/tests/incremental_non_flow_move/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,24 @@
+exports[`test foo.js 1`] = `
+"/*
+ * @providesModule Foo
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"/**
+ * @flow
+ */
+
+require('Foo');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+require("Foo");
+
+"
+`;
diff --git a/tests/incremental_non_flow_move/foo.js b/tests/incremental_non_flow_move/foo.js
new file mode 100644
index 000000000000..ddb85456b207
--- /dev/null
+++ b/tests/incremental_non_flow_move/foo.js
@@ -0,0 +1,3 @@
+/*
+ * @providesModule Foo
+ */
diff --git a/tests/incremental_non_flow_move/jsfmt.spec.js b/tests/incremental_non_flow_move/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_non_flow_move/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/incremental_non_flow_move/test.js b/tests/incremental_non_flow_move/test.js
new file mode 100644
index 000000000000..98297b3fb64b
--- /dev/null
+++ b/tests/incremental_non_flow_move/test.js
@@ -0,0 +1,5 @@
+/**
+ * @flow
+ */
+
+require('Foo');
diff --git a/tests/incremental_path/dir/__snapshots__/jsfmt.spec.js.snap b/tests/incremental_path/dir/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4631bc37ffb5
--- /dev/null
+++ b/tests/incremental_path/dir/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test a.js 1`] = `
+"// @flow
+(require('b'): boolean);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+(require("b"): boolean);
+
+"
+`;
diff --git a/tests/incremental_path/dir/a.js b/tests/incremental_path/dir/a.js
new file mode 100644
index 000000000000..cb2264c959c3
--- /dev/null
+++ b/tests/incremental_path/dir/a.js
@@ -0,0 +1,2 @@
+// @flow
+(require('b'): boolean);
diff --git a/tests/incremental_path/dir/jsfmt.spec.js b/tests/incremental_path/dir/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/incremental_path/dir/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/indexer/A.js b/tests/indexer/A.js
new file mode 100644
index 000000000000..3f14aa36f4fc
--- /dev/null
+++ b/tests/indexer/A.js
@@ -0,0 +1,39 @@
+// No indexer should be fine
+function foo0(): {} {
+  return { foo: "bar" }
+}
+
+// Matching indexer should be fine
+function foo1(): {[key: string]: string} {
+  return { foo: "bar" }
+}
+
+// Indexer with different key type is an error when it matches
+function foo2(): {[key: number]: string} {
+  return { foo: "bar" }
+}
+
+// Matching indexer with different value type is an error
+function foo3(): {[key: string]: number} {
+  return { foo: "bar" }
+}
+
+// Indexer with different key type and different value type is twice an error
+function foo4(): {[key: number]: number} {
+  return { foo: "bar" }
+}
+
+// If key exists in object type then indexer is not matched
+function foo5(): {[key: string]: number; foo: string} {
+  return { foo: "bar" }
+}
+
+// If key exists in object type then indexer is not matched
+function foo6(): {[key: number]: number; foo: string} {
+  return { foo: "bar" }
+}
+
+// Should still complain about mistyped properties
+function foo7(): {[key: string]: number; foo: number} {
+  return { foo: "bar" }
+}
diff --git a/tests/indexer/__snapshots__/jsfmt.spec.js.snap b/tests/indexer/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..205a700b09df
--- /dev/null
+++ b/tests/indexer/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,101 @@
+exports[`test A.js 1`] = `
+"// No indexer should be fine
+function foo0(): {} {
+  return { foo: "bar" }
+}
+
+// Matching indexer should be fine
+function foo1(): {[key: string]: string} {
+  return { foo: "bar" }
+}
+
+// Indexer with different key type is an error when it matches
+function foo2(): {[key: number]: string} {
+  return { foo: "bar" }
+}
+
+// Matching indexer with different value type is an error
+function foo3(): {[key: string]: number} {
+  return { foo: "bar" }
+}
+
+// Indexer with different key type and different value type is twice an error
+function foo4(): {[key: number]: number} {
+  return { foo: "bar" }
+}
+
+// If key exists in object type then indexer is not matched
+function foo5(): {[key: string]: number; foo: string} {
+  return { foo: "bar" }
+}
+
+// If key exists in object type then indexer is not matched
+function foo6(): {[key: number]: number; foo: string} {
+  return { foo: "bar" }
+}
+
+// Should still complain about mistyped properties
+function foo7(): {[key: string]: number; foo: number} {
+  return { foo: "bar" }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// No indexer should be fine
+function foo0(): {} {
+  return { foo: "bar" };
+}
+// Matching indexer should be fine
+function foo1(): { [key: string]: string } {
+  return { foo: "bar" };
+}
+// Indexer with different key type is an error when it matches
+function foo2(): { [key: number]: string } {
+  return { foo: "bar" };
+}
+// Matching indexer with different value type is an error
+function foo3(): { [key: string]: number } {
+  return { foo: "bar" };
+}
+// Indexer with different key type and different value type is twice an error
+function foo4(): { [key: number]: number } {
+  return { foo: "bar" };
+}
+// If key exists in object type then indexer is not matched
+function foo5(): { [key: string]: number, foo: string } {
+  return { foo: "bar" };
+}
+// If key exists in object type then indexer is not matched
+function foo6(): { [key: number]: number, foo: string } {
+  return { foo: "bar" };
+}
+// Should still complain about mistyped properties
+function foo7(): { [key: string]: number, foo: number } {
+  return { foo: "bar" };
+}
+
+"
+`;
+
+exports[`test multiple.js 1`] = `
+"// @flow
+
+let tests = [
+  function() {
+    ({}: {
+      [k1: string]: string,
+      [k2: number]: number, // error: not supported (yet)
+    });
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  function() {
+    ({}: {
+      [k1: string]: string,
+      // error: not supported (yet) [k2: number]: number
+    });
+  }
+];
+
+"
+`;
diff --git a/tests/indexer/jsfmt.spec.js b/tests/indexer/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/indexer/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/indexer/multiple.js b/tests/indexer/multiple.js
new file mode 100644
index 000000000000..2d6e931c9420
--- /dev/null
+++ b/tests/indexer/multiple.js
@@ -0,0 +1,10 @@
+// @flow
+
+let tests = [
+  function() {
+    ({}: {
+      [k1: string]: string,
+      [k2: number]: number, // error: not supported (yet)
+    });
+  }
+];
diff --git a/tests/init/__snapshots__/jsfmt.spec.js.snap b/tests/init/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..460df9006972
--- /dev/null
+++ b/tests/init/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,552 @@
+exports[`test hoisted.js 1`] = `
+"/**
+ * test initialization tracking in the presence of hoisting
+ * @flow
+ */
+
+function _if(b: () => boolean) {
+  if (b()) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _while(b: () => boolean) {
+  while (b()) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _do_while(b: () => boolean) {
+  do {
+    var f = function () {};
+  } while (b());
+  f(); // ok
+}
+
+function _for(n: number) {
+  for (var i = 0; i < n; i++) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _for_in(obj: Object) {
+  for (var p in obj) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _for_of(arr: Array<number>) {
+  for (var x of arr) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test hoisted2.js 1`] = `
+"/**
+ * test initialization tracking for vars
+ * note: for try/catch/finally, see tests/try/init.js
+ * @flow
+ */
+
+// deferred init on annotated vars is ok
+function linear_deferred_init() {
+  var x:number;
+  x = 0;
+  var y:number = x;
+}
+
+// ...but use of var before init gives undefined
+function linear_pre_init() {
+  var x:number;
+  var y:number = x; // error
+}
+
+// local use of annotated vars in an if is ok
+function if_scoped_init(b) {
+  if (b) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// but not across if/else
+function if_else_partial_init(b) {
+  if (b) {
+    var x:number = 0;
+  } else {
+    var y:number = x; // error
+  }
+}
+
+// use of var before if gives undefined
+function if_pre_init(b) {
+  var y:number = x; // error
+  if (b) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function if_partial_post_init(b) {
+  if (b) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// ...unless both branches have initialized
+function if_post_init(b) {
+  if (b) {
+    var x:number = 0;
+  } else {
+    var x:number = 1;
+  }
+  var y:number = x;
+}
+
+// use of var after partial init (non-exhaustive if) gives undefined
+function if_partial_post_init(b) {
+  var x:number;
+  if (b) {
+    x = 0;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of var after guaranteed init (exhaustive if) is ok
+function if_post_init(b) {
+  var x:number;
+  if (b) {
+    x = 0;
+  } else {
+    x = 1;
+  }
+  var y:number = x;
+}
+
+// use of var after partial init (non-exhaustive switch) gives undefined
+function switch_partial_post_init(i) {
+  var x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of var after guaranteed init (exhaustive switch) is ok
+function switch_post_init(i) {
+  var x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+    default:
+      x = 2;
+  }
+  var y:number = x; // no error, all cases covered
+}
+
+// local use of annotated var in switch is ok
+function switch_scoped_init_1(i) {
+  switch (i) {
+    case 0:
+      var x:number = 0;
+      var y:number = x;
+  }
+}
+
+// ...but use of var before switch gives undefined
+function switch_scoped_init_2(i) {
+  var y:number = x; // error
+  switch (i) {
+    case 0:
+      var x:number = 0;
+  }
+}
+
+// ...and after
+function switch_scoped_init_3(i) {
+  switch (i) {
+    case 0:
+      var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// ...and in a fallthrough case without initialization
+function switch_scoped_init_4(i) {
+  switch (i) {
+    case 0:
+      var x:number = 0;
+    case 1:
+      var y:number = x; // error
+  }
+}
+
+// local use of annotated var in while is ok
+function while_scoped_init(b) {
+  while (b) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use of var before while gives undefined
+function while_pre_init(b) {
+  var y:number = x; // error
+  while (b) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function while_post_init(b) {
+   while (b) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// local use of annotated var in do-while is ok
+function do_while_scoped_init(b) {
+  do {
+    var x:number = 0;
+    var y:number = x;
+  } while (b);
+}
+
+// ...but use before do-while gives undefined
+function do_while_pre_init(b) {
+  var y:number = x; // error
+  do {
+    var x:number = 0;
+  } while (b);
+}
+
+// after is ok, because loop is guaranteed to run
+function do_while_post_init(b) {
+  do {
+    var x:number = 0;
+  } while (b);
+  var y:number = x;
+}
+
+// local use of annotated var in for is ok
+function for_scoped_init(b) {
+  for (;b;) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use before for gives undefined
+function for_pre_init(b) {
+  var y:number = x; // error
+  for (;b;) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function for_post_init(b) {
+   for (;b;) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// local use of annotated var in for-in is ok
+function for_in_scoped_init() {
+  for (var p in { a:1, b: 2 }) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use before while gives undefined
+function for_in_pre_init() {
+  var y:number = x; // error
+  for (var p in { a:1, b: 2 }) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function for_in_post_init() {
+  for (var p in { a:1, b: 2 }) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// local use of annotated var in for-of is ok
+function for_of_scoped_init() {
+  for (var x of [1, 2, 3]) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use before while gives undefined
+function for_in_pre_init() {
+  var y:number = x; // error
+  for (var x of [1, 2, 3]) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function for_in_post_init() {
+  for (var x of [1, 2, 3]) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test let.js 1`] = `
+"/**
+ * test initialization tracking for lets
+ * @flow
+ */
+
+// deferred init on annotated lets is ok
+function linear_deferred_init() {
+  let x:number;
+  x = 0;
+  let y:number = x;
+}
+
+// use of let before init gives undefined
+function linear_pre_init() {
+  let x:number;
+  let y:?number = x;  // ok
+  let z:number = x;   // error
+  x = 0;
+  let w:number = x;   // ok
+}
+
+// self-references in let bindings are not ok
+function self_init() {
+  let x = x;  // \'x\' not initialized!
+}
+
+// use of let after partial init (non-exhaustive if) gives undefined
+function if_partial_post_init(b) {
+  let x:number;
+  if (b) {
+    x = 0;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of let after guaranteed init (exhaustive if) is ok
+function if_post_init(b) {
+  let x:number;
+  if (b) {
+    x = 0;
+  } else {
+    x = 1;
+  }
+  var y:number = x;
+}
+
+// use of let after partial init (non-exhaustive switch) gives undefined
+function switch_partial_post_init(i) {
+  let x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of let after guaranteed init (exhaustive switch) is ok
+function switch_post_init(i) {
+  let x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+    default:
+      x = 2;
+  }
+  var y:number = x; // no error, all cases covered
+}
+
+// use in a switch after a skipped decl is an error
+function switch_scoped_init_2(i) {
+  switch (i) {
+    case 0:
+      let x:number;
+    case 1:
+      let y:number = x; // error, skipped declaration
+  }
+}
+
+// while leaves it possibly uninitialized
+function while_post_init(b) {
+  let x:number;
+  while (b) {
+    x = 0;
+  }
+  var y:number = x; // error
+}
+
+// do-while is ok, because loop is guaranteed to run at least once
+function do_while_post_init(b) {
+  let x:number;
+  do {
+    x = 0;
+  } while (b);
+  var y:number = x; // ok
+}
+
+// for-in leaves it possibly uninitialized
+function for_in_post_init() {
+  var x:number;
+  for (var p in {}) {
+    x = 0;
+  }
+  var y:number = x; // error
+}
+
+// for-of leaves it possibly uninitialized
+function for_of_post_init() {
+  var x:number;
+  for (var x of []) {
+    x = 0;
+  }
+  var y:number = x; // error
+}
+
+// use of let after guaranteed init (exhaustive switch + throw) is ok
+function switch_post_init2(i): number {
+  let bar;
+  switch (i) {
+    case 1:
+      bar = 3;
+      break;
+    default:
+      throw new Error(\'Invalid state\');
+  }
+  return bar; // ok, definitely initialized
+}
+
+// use of let after guaranteed init (exhaustive switch + throw) is ok
+function switch_post_init2(i): number {
+  let bar;
+  switch (i) {
+    case 1:
+      bar = 3;
+      break;
+    default:
+      throw new Error(\'Invalid state\');
+  }
+  return bar; // ok, definitely initialized
+}
+
+// reference of a let-binding is permitted in a sub-closure within the init expr
+function sub_closure_init_reference() {
+  let x = function() { return x; };
+  const y = function() { return y; };
+
+  // var-bindings can reference each other cyclically since they do not incur a
+  // TDZ (...even though this is weird...)
+  var z = z;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test nullable-init.js 1`] = `
+"var o: {x: ?number} = { x: null };
+var a: Array<?number> = [null,null];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/init/hoisted.js b/tests/init/hoisted.js
new file mode 100644
index 000000000000..0a5458712f18
--- /dev/null
+++ b/tests/init/hoisted.js
@@ -0,0 +1,46 @@
+/**
+ * test initialization tracking in the presence of hoisting
+ * @flow
+ */
+
+function _if(b: () => boolean) {
+  if (b()) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _while(b: () => boolean) {
+  while (b()) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _do_while(b: () => boolean) {
+  do {
+    var f = function () {};
+  } while (b());
+  f(); // ok
+}
+
+function _for(n: number) {
+  for (var i = 0; i < n; i++) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _for_in(obj: Object) {
+  for (var p in obj) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
+
+function _for_of(arr: Array<number>) {
+  for (var x of arr) {
+    var f = function () {};
+  }
+  f(); // error, possibly undefined
+}
diff --git a/tests/init/hoisted2.js b/tests/init/hoisted2.js
new file mode 100644
index 000000000000..4258e0e46082
--- /dev/null
+++ b/tests/init/hoisted2.js
@@ -0,0 +1,268 @@
+/**
+ * test initialization tracking for vars
+ * note: for try/catch/finally, see tests/try/init.js
+ * @flow
+ */
+
+// deferred init on annotated vars is ok
+function linear_deferred_init() {
+  var x:number;
+  x = 0;
+  var y:number = x;
+}
+
+// ...but use of var before init gives undefined
+function linear_pre_init() {
+  var x:number;
+  var y:number = x; // error
+}
+
+// local use of annotated vars in an if is ok
+function if_scoped_init(b) {
+  if (b) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// but not across if/else
+function if_else_partial_init(b) {
+  if (b) {
+    var x:number = 0;
+  } else {
+    var y:number = x; // error
+  }
+}
+
+// use of var before if gives undefined
+function if_pre_init(b) {
+  var y:number = x; // error
+  if (b) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function if_partial_post_init(b) {
+  if (b) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// ...unless both branches have initialized
+function if_post_init(b) {
+  if (b) {
+    var x:number = 0;
+  } else {
+    var x:number = 1;
+  }
+  var y:number = x;
+}
+
+// use of var after partial init (non-exhaustive if) gives undefined
+function if_partial_post_init(b) {
+  var x:number;
+  if (b) {
+    x = 0;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of var after guaranteed init (exhaustive if) is ok
+function if_post_init(b) {
+  var x:number;
+  if (b) {
+    x = 0;
+  } else {
+    x = 1;
+  }
+  var y:number = x;
+}
+
+// use of var after partial init (non-exhaustive switch) gives undefined
+function switch_partial_post_init(i) {
+  var x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of var after guaranteed init (exhaustive switch) is ok
+function switch_post_init(i) {
+  var x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+    default:
+      x = 2;
+  }
+  var y:number = x; // no error, all cases covered
+}
+
+// local use of annotated var in switch is ok
+function switch_scoped_init_1(i) {
+  switch (i) {
+    case 0:
+      var x:number = 0;
+      var y:number = x;
+  }
+}
+
+// ...but use of var before switch gives undefined
+function switch_scoped_init_2(i) {
+  var y:number = x; // error
+  switch (i) {
+    case 0:
+      var x:number = 0;
+  }
+}
+
+// ...and after
+function switch_scoped_init_3(i) {
+  switch (i) {
+    case 0:
+      var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// ...and in a fallthrough case without initialization
+function switch_scoped_init_4(i) {
+  switch (i) {
+    case 0:
+      var x:number = 0;
+    case 1:
+      var y:number = x; // error
+  }
+}
+
+// local use of annotated var in while is ok
+function while_scoped_init(b) {
+  while (b) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use of var before while gives undefined
+function while_pre_init(b) {
+  var y:number = x; // error
+  while (b) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function while_post_init(b) {
+   while (b) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// local use of annotated var in do-while is ok
+function do_while_scoped_init(b) {
+  do {
+    var x:number = 0;
+    var y:number = x;
+  } while (b);
+}
+
+// ...but use before do-while gives undefined
+function do_while_pre_init(b) {
+  var y:number = x; // error
+  do {
+    var x:number = 0;
+  } while (b);
+}
+
+// after is ok, because loop is guaranteed to run
+function do_while_post_init(b) {
+  do {
+    var x:number = 0;
+  } while (b);
+  var y:number = x;
+}
+
+// local use of annotated var in for is ok
+function for_scoped_init(b) {
+  for (;b;) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use before for gives undefined
+function for_pre_init(b) {
+  var y:number = x; // error
+  for (;b;) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function for_post_init(b) {
+   for (;b;) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// local use of annotated var in for-in is ok
+function for_in_scoped_init() {
+  for (var p in { a:1, b: 2 }) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use before while gives undefined
+function for_in_pre_init() {
+  var y:number = x; // error
+  for (var p in { a:1, b: 2 }) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function for_in_post_init() {
+  for (var p in { a:1, b: 2 }) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// local use of annotated var in for-of is ok
+function for_of_scoped_init() {
+  for (var x of [1, 2, 3]) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// ...but use before while gives undefined
+function for_in_pre_init() {
+  var y:number = x; // error
+  for (var x of [1, 2, 3]) {
+    var x:number = 0;
+  }
+}
+
+// ...and after
+function for_in_post_init() {
+  for (var x of [1, 2, 3]) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
diff --git a/tests/init/jsfmt.spec.js b/tests/init/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/init/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/init/let.js b/tests/init/let.js
new file mode 100644
index 000000000000..f35e25f95fe9
--- /dev/null
+++ b/tests/init/let.js
@@ -0,0 +1,157 @@
+/**
+ * test initialization tracking for lets
+ * @flow
+ */
+
+// deferred init on annotated lets is ok
+function linear_deferred_init() {
+  let x:number;
+  x = 0;
+  let y:number = x;
+}
+
+// use of let before init gives undefined
+function linear_pre_init() {
+  let x:number;
+  let y:?number = x;  // ok
+  let z:number = x;   // error
+  x = 0;
+  let w:number = x;   // ok
+}
+
+// self-references in let bindings are not ok
+function self_init() {
+  let x = x;  // 'x' not initialized!
+}
+
+// use of let after partial init (non-exhaustive if) gives undefined
+function if_partial_post_init(b) {
+  let x:number;
+  if (b) {
+    x = 0;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of let after guaranteed init (exhaustive if) is ok
+function if_post_init(b) {
+  let x:number;
+  if (b) {
+    x = 0;
+  } else {
+    x = 1;
+  }
+  var y:number = x;
+}
+
+// use of let after partial init (non-exhaustive switch) gives undefined
+function switch_partial_post_init(i) {
+  let x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+  }
+  var y:number = x; // error, possibly uninitialized
+}
+
+// use of let after guaranteed init (exhaustive switch) is ok
+function switch_post_init(i) {
+  let x:number;
+  switch (i) {
+    case 0:
+      x = 0;
+      break;
+    case 1:
+      x = 1;
+      break;
+    default:
+      x = 2;
+  }
+  var y:number = x; // no error, all cases covered
+}
+
+// use in a switch after a skipped decl is an error
+function switch_scoped_init_2(i) {
+  switch (i) {
+    case 0:
+      let x:number;
+    case 1:
+      let y:number = x; // error, skipped declaration
+  }
+}
+
+// while leaves it possibly uninitialized
+function while_post_init(b) {
+  let x:number;
+  while (b) {
+    x = 0;
+  }
+  var y:number = x; // error
+}
+
+// do-while is ok, because loop is guaranteed to run at least once
+function do_while_post_init(b) {
+  let x:number;
+  do {
+    x = 0;
+  } while (b);
+  var y:number = x; // ok
+}
+
+// for-in leaves it possibly uninitialized
+function for_in_post_init() {
+  var x:number;
+  for (var p in {}) {
+    x = 0;
+  }
+  var y:number = x; // error
+}
+
+// for-of leaves it possibly uninitialized
+function for_of_post_init() {
+  var x:number;
+  for (var x of []) {
+    x = 0;
+  }
+  var y:number = x; // error
+}
+
+// use of let after guaranteed init (exhaustive switch + throw) is ok
+function switch_post_init2(i): number {
+  let bar;
+  switch (i) {
+    case 1:
+      bar = 3;
+      break;
+    default:
+      throw new Error('Invalid state');
+  }
+  return bar; // ok, definitely initialized
+}
+
+// use of let after guaranteed init (exhaustive switch + throw) is ok
+function switch_post_init2(i): number {
+  let bar;
+  switch (i) {
+    case 1:
+      bar = 3;
+      break;
+    default:
+      throw new Error('Invalid state');
+  }
+  return bar; // ok, definitely initialized
+}
+
+// reference of a let-binding is permitted in a sub-closure within the init expr
+function sub_closure_init_reference() {
+  let x = function() { return x; };
+  const y = function() { return y; };
+
+  // var-bindings can reference each other cyclically since they do not incur a
+  // TDZ (...even though this is weird...)
+  var z = z;
+}
diff --git a/tests/init/nullable-init.js b/tests/init/nullable-init.js
new file mode 100644
index 000000000000..c5d32d0138a1
--- /dev/null
+++ b/tests/init/nullable-init.js
@@ -0,0 +1,2 @@
+var o: {x: ?number} = { x: null };
+var a: Array<?number> = [null,null];
diff --git a/tests/instanceof/__snapshots__/jsfmt.spec.js.snap b/tests/instanceof/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..48d9d5f61ccc
--- /dev/null
+++ b/tests/instanceof/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,106 @@
+exports[`test instanceof.js 1`] = `
+"/* @flow */
+
+// x instancof t
+class X1 { foo: number; };
+class X2 { foo: string; };
+
+function x(b) { return b ? new X1 : new X2; }
+
+function consumer1(b) {
+    var g = x(b);
+    if (g instanceof X2) g.foo = \'1337\';
+    else g.foo = 1337;
+}
+
+function consumer2(b) {
+    var g = x(b);
+    if (g instanceof X1) g.foo = \'1337\';  // oops
+}
+
+// x.y instanceof t
+class Y1 { bar: X1; };
+class Y2 { bar: X2; };
+
+function y(b) { return b ? new Y1 : new Y2; }
+
+function consumer3(b) {
+    var g = y(b);
+    if (g.bar instanceof X2) g.bar.foo = \'1337\';
+    else g.bar.foo = 1337;
+}
+
+function consumer4(b) {
+    var g = y(b);
+    if (g.bar instanceof X1) g.bar.foo = \'1337\';  // oops
+}
+
+// x.y.z instance of t
+class Z1 { baz: Y1; };
+class Z2 { baz: Y2; };
+
+function z(b) { return b ? new Z1 : new Z2; }
+
+function consumer5(b) {
+    var g = z(b);
+    if (g.baz.bar instanceof X2) g.baz.bar.foo = \'1337\';
+    else g.baz.bar.foo = 1337;
+}
+
+function consumer6(b) {
+    var g = z(b);
+    if (g.baz.bar instanceof X1) g.baz.bar.foo = \'1337\';  // oops
+}
+
+// this instanceof t
+class C {
+  m() {
+    if (this instanceof D)
+      alert(this.s);
+    else
+      alert(\"nope\");
+  }
+}
+
+class D extends C {
+  s: string;
+  constructor() {
+    super();
+    this.s = \"yup\";
+  }
+}
+
+
+function foo0(x: Array<number> | number) {
+  if (x instanceof Array) {
+    x[0] = 123;
+  } else {
+    x++;
+  }
+}
+
+function foo1(x: Array<number> | number) {
+  if (x instanceof Array) {
+    x++; // error
+  } else {
+    x[0] = 123; // error
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/instanceof/instanceof.js b/tests/instanceof/instanceof.js
new file mode 100644
index 000000000000..bcbe7f6b8dc8
--- /dev/null
+++ b/tests/instanceof/instanceof.js
@@ -0,0 +1,87 @@
+/* @flow */
+
+// x instancof t
+class X1 { foo: number; };
+class X2 { foo: string; };
+
+function x(b) { return b ? new X1 : new X2; }
+
+function consumer1(b) {
+    var g = x(b);
+    if (g instanceof X2) g.foo = '1337';
+    else g.foo = 1337;
+}
+
+function consumer2(b) {
+    var g = x(b);
+    if (g instanceof X1) g.foo = '1337';  // oops
+}
+
+// x.y instanceof t
+class Y1 { bar: X1; };
+class Y2 { bar: X2; };
+
+function y(b) { return b ? new Y1 : new Y2; }
+
+function consumer3(b) {
+    var g = y(b);
+    if (g.bar instanceof X2) g.bar.foo = '1337';
+    else g.bar.foo = 1337;
+}
+
+function consumer4(b) {
+    var g = y(b);
+    if (g.bar instanceof X1) g.bar.foo = '1337';  // oops
+}
+
+// x.y.z instance of t
+class Z1 { baz: Y1; };
+class Z2 { baz: Y2; };
+
+function z(b) { return b ? new Z1 : new Z2; }
+
+function consumer5(b) {
+    var g = z(b);
+    if (g.baz.bar instanceof X2) g.baz.bar.foo = '1337';
+    else g.baz.bar.foo = 1337;
+}
+
+function consumer6(b) {
+    var g = z(b);
+    if (g.baz.bar instanceof X1) g.baz.bar.foo = '1337';  // oops
+}
+
+// this instanceof t
+class C {
+  m() {
+    if (this instanceof D)
+      alert(this.s);
+    else
+      alert("nope");
+  }
+}
+
+class D extends C {
+  s: string;
+  constructor() {
+    super();
+    this.s = "yup";
+  }
+}
+
+
+function foo0(x: Array<number> | number) {
+  if (x instanceof Array) {
+    x[0] = 123;
+  } else {
+    x++;
+  }
+}
+
+function foo1(x: Array<number> | number) {
+  if (x instanceof Array) {
+    x++; // error
+  } else {
+    x[0] = 123; // error
+  }
+}
diff --git a/tests/instanceof/jsfmt.spec.js b/tests/instanceof/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/instanceof/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/integration/__snapshots__/jsfmt.spec.js.snap b/tests/integration/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4ca888585bc7
--- /dev/null
+++ b/tests/integration/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test bar.js 1`] = `
+"// @flow
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test foo.js 1`] = `
+"// @flow
+require('./bar');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+require("./bar");
+
+"
+`;
diff --git a/tests/integration/bar.js b/tests/integration/bar.js
new file mode 100644
index 000000000000..46e7f7c04567
--- /dev/null
+++ b/tests/integration/bar.js
@@ -0,0 +1 @@
+// @flow
diff --git a/tests/integration/foo.js b/tests/integration/foo.js
new file mode 100644
index 000000000000..69089d4e9298
--- /dev/null
+++ b/tests/integration/foo.js
@@ -0,0 +1,2 @@
+// @flow
+require('./bar');
diff --git a/tests/integration/jsfmt.spec.js b/tests/integration/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/integration/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/interface/__snapshots__/jsfmt.spec.js.snap b/tests/interface/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b612ebc1a585
--- /dev/null
+++ b/tests/interface/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,211 @@
+exports[`test import.js 1`] = `
+"interface I { x: number }
+export type J = I; // workaround for export interface
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test indexer.js 1`] = `
+"// @flow
+
+interface Ok {
+  [key: string]: string;
+}
+
+interface Bad {
+  [k1: string]: string;
+  [k2: number]: number; // error: not supported (yet)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test interface.js 1`] = `
+"declare class C { x: number; }
+
+var x: string = new C().x;
+
+interface I { x: number; }
+
+var i = new I(); // error
+
+function testInterfaceName(o: I) {
+  (o.name: string); // error, name is static
+  (o.constructor.name: string); // ok
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test test.js 1`] = `
+"interface I { y: string }
+interface I_ { x: number }
+interface J extends I, I_ { }
+interface K extends J { }
+
+var k: K = { x: \"\", y: \"\" }; // error: x should be number
+(k.x: string); // error: x is number
+(k.y: string);
+
+declare class C { x: number }
+declare class D extends C, Other { } // error: multiple extends
+//declare class E implements I { } // parse error
+
+interface A<Y> { y: Y }
+interface A_<X> { x: X }
+interface B<Z> extends A<string>, A_<Z> { z: Z }
+interface E<Z> extends B<Z> { }
+
+var e: E<number> = { x: \"\", y: \"\", z: \"\" }; // error: x and z should be numbers
+(e.x: string); // error: x is number
+(e.y: string);
+(e.z: string); // error: z is number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"import type { J } from \'./import\';
+interface K { }
+interface L extends J, K { y: string }
+
+function foo(l: L) { l.x; l.y; l.z; } // error: z not found in L
+
+// interface + multiple inheritance is similar to object type + intersection
+type M = { y: string } & J & { z: boolean }
+
+function bar(m: M) { m.x; m.y; m.z; } // OK
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test test3.js 1`] = `
+"interface I { x: number, y : string }
+interface J { y : number }
+interface K extends I, J { x: string } // error: x is number in I
+function foo(k: K) {
+  (k.x: number); // error: x is string in K
+  (k.y: number); // error: y is string in I
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test test4.js 1`] = `
+"interface I { foo(x: number): void; }
+(function foo(x: number) { }: I); // error, property \`foo\` not found function
+
+declare class C {
+  bar(i: I): void;
+  bar(f: (x: number) => void): void;
+}
+
+new C().bar((x: string) => { }); // error, number ~/~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
diff --git a/tests/interface/import.js b/tests/interface/import.js
new file mode 100644
index 000000000000..1eba66eac7cb
--- /dev/null
+++ b/tests/interface/import.js
@@ -0,0 +1,2 @@
+interface I { x: number }
+export type J = I; // workaround for export interface
diff --git a/tests/interface/indexer.js b/tests/interface/indexer.js
new file mode 100644
index 000000000000..57d9204eabc5
--- /dev/null
+++ b/tests/interface/indexer.js
@@ -0,0 +1,10 @@
+// @flow
+
+interface Ok {
+  [key: string]: string;
+}
+
+interface Bad {
+  [k1: string]: string;
+  [k2: number]: number; // error: not supported (yet)
+}
diff --git a/tests/interface/interface.js b/tests/interface/interface.js
new file mode 100644
index 000000000000..40a01e3d02bd
--- /dev/null
+++ b/tests/interface/interface.js
@@ -0,0 +1,12 @@
+declare class C { x: number; }
+
+var x: string = new C().x;
+
+interface I { x: number; }
+
+var i = new I(); // error
+
+function testInterfaceName(o: I) {
+  (o.name: string); // error, name is static
+  (o.constructor.name: string); // ok
+}
diff --git a/tests/interface/jsfmt.spec.js b/tests/interface/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/interface/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/interface/test.js b/tests/interface/test.js
new file mode 100644
index 000000000000..1b071ece569f
--- /dev/null
+++ b/tests/interface/test.js
@@ -0,0 +1,22 @@
+interface I { y: string }
+interface I_ { x: number }
+interface J extends I, I_ { }
+interface K extends J { }
+
+var k: K = { x: "", y: "" }; // error: x should be number
+(k.x: string); // error: x is number
+(k.y: string);
+
+declare class C { x: number }
+declare class D extends C, Other { } // error: multiple extends
+//declare class E implements I { } // parse error
+
+interface A<Y> { y: Y }
+interface A_<X> { x: X }
+interface B<Z> extends A<string>, A_<Z> { z: Z }
+interface E<Z> extends B<Z> { }
+
+var e: E<number> = { x: "", y: "", z: "" }; // error: x and z should be numbers
+(e.x: string); // error: x is number
+(e.y: string);
+(e.z: string); // error: z is number
diff --git a/tests/interface/test2.js b/tests/interface/test2.js
new file mode 100644
index 000000000000..0ef83b294e2e
--- /dev/null
+++ b/tests/interface/test2.js
@@ -0,0 +1,10 @@
+import type { J } from './import';
+interface K { }
+interface L extends J, K { y: string }
+
+function foo(l: L) { l.x; l.y; l.z; } // error: z not found in L
+
+// interface + multiple inheritance is similar to object type + intersection
+type M = { y: string } & J & { z: boolean }
+
+function bar(m: M) { m.x; m.y; m.z; } // OK
diff --git a/tests/interface/test3.js b/tests/interface/test3.js
new file mode 100644
index 000000000000..a06a374a1dd9
--- /dev/null
+++ b/tests/interface/test3.js
@@ -0,0 +1,7 @@
+interface I { x: number, y : string }
+interface J { y : number }
+interface K extends I, J { x: string } // error: x is number in I
+function foo(k: K) {
+  (k.x: number); // error: x is string in K
+  (k.y: number); // error: y is string in I
+}
diff --git a/tests/interface/test4.js b/tests/interface/test4.js
new file mode 100644
index 000000000000..91246524d72a
--- /dev/null
+++ b/tests/interface/test4.js
@@ -0,0 +1,9 @@
+interface I { foo(x: number): void; }
+(function foo(x: number) { }: I); // error, property `foo` not found function
+
+declare class C {
+  bar(i: I): void;
+  bar(f: (x: number) => void): void;
+}
+
+new C().bar((x: string) => { }); // error, number ~/~> string
diff --git a/tests/intersection/__snapshots__/jsfmt.spec.js.snap b/tests/intersection/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..97de30df4f01
--- /dev/null
+++ b/tests/intersection/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,207 @@
+exports[`test intersection.js 1`] = `
+"function foo(x: $All<Error,{type:number}>): number {
+    return x.type;
+}
+
+function bar(x: Error & {type:number}): number {
+    return x.type;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test objassign.js 1`] = `
+"/**
+ * Test intersection of objects flowing to spread assignment.
+ *
+ * Definitions in lib/lib.js
+ *
+ * @noflow
+ */
+
+declare var x: ObjAssignT;
+
+let y: ObjAssignT = { ...x }; // should be fine
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Test intersection of objects flowing to spread assignment.
+ *
+ * Definitions in lib/lib.js
+ *
+ * @noflow
+ */
+declare var x: ObjAssignT;
+let y: ObjAssignT = { ...x };// should be fine
+
+"
+`;
+
+exports[`test pred.js 1`] = `
+"/**
+ * Test interaction of object intersections and predicates.
+ * Definitions in lib/lib.js
+ *
+ * @flow
+ */
+
+type DuplexStreamOptions = ReadableStreamOptions & WritableStreamOptions & {
+  allowHalfOpen? : boolean,
+  readableObjectMode? : boolean,
+  writableObjectMode? : boolean
+};
+
+function hasObjectMode_bad(options: DuplexStreamOptions): boolean {
+  return options.objectMode
+    || options.readableObjectMode
+    || options.writableObjectMode; // error, undefined ~> boolean
+}
+
+function hasObjectMode_ok(options: DuplexStreamOptions): boolean {
+  return !!(options.objectMode
+    || options.readableObjectMode
+    || options.writableObjectMode);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test_fun.js 1`] = `
+"/**
+ * Tests for intersections of function types.
+ *
+ * Note: Flow abuses intersection types to model
+ * function overloading, which precludes using a
+ * correct intersection of return types in the result.
+ *
+ * Here we test the special case where return types
+ * are equal. Tests of the overloading behavior can
+ * be found in tests/overload
+ *
+ * Definitions lin lib/lib.js
+ *
+ * @noflow
+ */
+
+// intersection of function types satisfies union of param types
+
+type F = (_: ObjA) => void;
+type G = (_: ObjB) => void;
+type FG = (_: ObjA | ObjB) => void;
+
+declare var fun1 : F & G;
+
+(fun1 : FG);
+
+var fun2 : FG = fun1;
+
+// simpler variation
+declare var f : ((_: number) => void) & ((_: string) => void);
+var g: (_: number | string) => void = f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test_obj.js 1`] = `
+"/**
+ * Tests for intersections of object types
+ *
+ * @noflow
+ */
+
+// TODO we should give explicit errors for incompatibilities
+// which make an intersection uninhabitable:
+// - shared mutable properties with different types
+// - different dictionary types
+//
+// Currently we give no such errors. Instead, we rely on
+// the impossibility of providing a value for such a type
+// to produce errors on value inflows. This is clearly
+// suboptimal, since eg declared vars require no explicit
+// provision of values. This leaves the impossible types
+// free to flow downstream and satisfy impossible constraints.
+
+// intersection of object types satisfies union of properties
+declare var a: A;
+var b: B = a;
+
+// intersection of dictionary types:
+declare var c: C;
+var d: D = c; // ok
+
+// dict type mismatch
+type E = { [key: string]: string };
+var e: E = c; // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Tests for intersections of object types
+ *
+ * @noflow
+ */
+// TODO we should give explicit errors for incompatibilities
+// which make an intersection uninhabitable:
+// - shared mutable properties with different types
+// - different dictionary types
+//
+// Currently we give no such errors. Instead, we rely on
+// the impossibility of providing a value for such a type
+// to produce errors on value inflows. This is clearly
+// suboptimal, since eg declared vars require no explicit
+// provision of values. This leaves the impossible types
+// free to flow downstream and satisfy impossible constraints.
+// intersection of object types satisfies union of properties
+declare var a: A;
+var b: B = a;
+// intersection of dictionary types:
+declare var c: C;
+var d: D = c;// ok
+// dict type mismatch
+type E = { [key: string]: string };
+var e: E = c;// error
+
+"
+`;
diff --git a/tests/intersection/intersection.js b/tests/intersection/intersection.js
new file mode 100644
index 000000000000..7508926e5902
--- /dev/null
+++ b/tests/intersection/intersection.js
@@ -0,0 +1,7 @@
+function foo(x: $All<Error,{type:number}>): number {
+    return x.type;
+}
+
+function bar(x: Error & {type:number}): number {
+    return x.type;
+}
diff --git a/tests/intersection/jsfmt.spec.js b/tests/intersection/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/intersection/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/intersection/lib/__snapshots__/jsfmt.spec.js.snap b/tests/intersection/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..17c299687982
--- /dev/null
+++ b/tests/intersection/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,53 @@
+exports[`test lib.js 1`] = `
+"// @flow
+
+// defs used in tests, here to stress tvar machinery
+
+// used in ObjAssign.js
+//
+type ObjAssignT = { foo: string } & { bar: string };
+
+// used in pred.js
+//
+type ReadableStreamOptions = {
+  highWaterMark? : number,
+  encoding? : ?string,
+  objectMode? : boolean
+};
+
+type WritableStreamOptions = {
+  highWaterMark? : number,
+  decodeString? : boolean,
+  objectMode? : boolean
+};
+
+// used in test_fun.js
+//
+type ObjA = { foo: number, bar: string };
+type ObjB = { baz: bool };
+
+// used in test_obj.js
+//
+type A = { a: string } & { b: string };
+type B = { a: string, b: string };
+
+type C = { [key: string]: number } & { [key: string]: number };
+type D = { [key: string]: number };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/intersection/lib/jsfmt.spec.js b/tests/intersection/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/intersection/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/intersection/lib/lib.js b/tests/intersection/lib/lib.js
new file mode 100644
index 000000000000..df9d7d3f207e
--- /dev/null
+++ b/tests/intersection/lib/lib.js
@@ -0,0 +1,34 @@
+// @flow
+
+// defs used in tests, here to stress tvar machinery
+
+// used in ObjAssign.js
+//
+type ObjAssignT = { foo: string } & { bar: string };
+
+// used in pred.js
+//
+type ReadableStreamOptions = {
+  highWaterMark? : number,
+  encoding? : ?string,
+  objectMode? : boolean
+};
+
+type WritableStreamOptions = {
+  highWaterMark? : number,
+  decodeString? : boolean,
+  objectMode? : boolean
+};
+
+// used in test_fun.js
+//
+type ObjA = { foo: number, bar: string };
+type ObjB = { baz: bool };
+
+// used in test_obj.js
+//
+type A = { a: string } & { b: string };
+type B = { a: string, b: string };
+
+type C = { [key: string]: number } & { [key: string]: number };
+type D = { [key: string]: number };
diff --git a/tests/intersection/objassign.js b/tests/intersection/objassign.js
new file mode 100644
index 000000000000..fc0436123c65
--- /dev/null
+++ b/tests/intersection/objassign.js
@@ -0,0 +1,11 @@
+/**
+ * Test intersection of objects flowing to spread assignment.
+ *
+ * Definitions in lib/lib.js
+ *
+ * @noflow
+ */
+
+declare var x: ObjAssignT;
+
+let y: ObjAssignT = { ...x }; // should be fine
diff --git a/tests/intersection/pred.js b/tests/intersection/pred.js
new file mode 100644
index 000000000000..37a0d13beadf
--- /dev/null
+++ b/tests/intersection/pred.js
@@ -0,0 +1,24 @@
+/**
+ * Test interaction of object intersections and predicates.
+ * Definitions in lib/lib.js
+ *
+ * @flow
+ */
+
+type DuplexStreamOptions = ReadableStreamOptions & WritableStreamOptions & {
+  allowHalfOpen? : boolean,
+  readableObjectMode? : boolean,
+  writableObjectMode? : boolean
+};
+
+function hasObjectMode_bad(options: DuplexStreamOptions): boolean {
+  return options.objectMode
+    || options.readableObjectMode
+    || options.writableObjectMode; // error, undefined ~> boolean
+}
+
+function hasObjectMode_ok(options: DuplexStreamOptions): boolean {
+  return !!(options.objectMode
+    || options.readableObjectMode
+    || options.writableObjectMode);
+}
diff --git a/tests/intersection/test_fun.js b/tests/intersection/test_fun.js
new file mode 100644
index 000000000000..b9b2f81074bb
--- /dev/null
+++ b/tests/intersection/test_fun.js
@@ -0,0 +1,31 @@
+/**
+ * Tests for intersections of function types.
+ *
+ * Note: Flow abuses intersection types to model
+ * function overloading, which precludes using a
+ * correct intersection of return types in the result.
+ *
+ * Here we test the special case where return types
+ * are equal. Tests of the overloading behavior can
+ * be found in tests/overload
+ *
+ * Definitions lin lib/lib.js
+ *
+ * @noflow
+ */
+
+// intersection of function types satisfies union of param types
+
+type F = (_: ObjA) => void;
+type G = (_: ObjB) => void;
+type FG = (_: ObjA | ObjB) => void;
+
+declare var fun1 : F & G;
+
+(fun1 : FG);
+
+var fun2 : FG = fun1;
+
+// simpler variation
+declare var f : ((_: number) => void) & ((_: string) => void);
+var g: (_: number | string) => void = f;
diff --git a/tests/intersection/test_obj.js b/tests/intersection/test_obj.js
new file mode 100644
index 000000000000..6817584708ab
--- /dev/null
+++ b/tests/intersection/test_obj.js
@@ -0,0 +1,29 @@
+/**
+ * Tests for intersections of object types
+ *
+ * @noflow
+ */
+
+// TODO we should give explicit errors for incompatibilities
+// which make an intersection uninhabitable:
+// - shared mutable properties with different types
+// - different dictionary types
+//
+// Currently we give no such errors. Instead, we rely on
+// the impossibility of providing a value for such a type
+// to produce errors on value inflows. This is clearly
+// suboptimal, since eg declared vars require no explicit
+// provision of values. This leaves the impossible types
+// free to flow downstream and satisfy impossible constraints.
+
+// intersection of object types satisfies union of properties
+declare var a: A;
+var b: B = a;
+
+// intersection of dictionary types:
+declare var c: C;
+var d: D = c; // ok
+
+// dict type mismatch
+type E = { [key: string]: string };
+var e: E = c; // error
diff --git a/tests/issues-11/__snapshots__/jsfmt.spec.js.snap b/tests/issues-11/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b9b2b0a3fefb
--- /dev/null
+++ b/tests/issues-11/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test export.js 1`] = `
+"/* @flow */
+exports.x = 1;
+exports.y = "";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+exports.x = 1;
+exports.y = "";
+
+"
+`;
+
+exports[`test import.js 1`] = `
+"/* @flow */
+var e = require('./export');
+var x: string = e.x;
+var y: number = e.y;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var e = require("./export");
+var x: string = e.x;
+var y: number = e.y;
+
+"
+`;
diff --git a/tests/issues-11/export.js b/tests/issues-11/export.js
new file mode 100644
index 000000000000..0fe9283762c9
--- /dev/null
+++ b/tests/issues-11/export.js
@@ -0,0 +1,3 @@
+/* @flow */
+exports.x = 1;
+exports.y = "";
diff --git a/tests/issues-11/import.js b/tests/issues-11/import.js
new file mode 100644
index 000000000000..11d913911e42
--- /dev/null
+++ b/tests/issues-11/import.js
@@ -0,0 +1,4 @@
+/* @flow */
+var e = require('./export');
+var x: string = e.x;
+var y: number = e.y;
diff --git a/tests/issues-11/jsfmt.spec.js b/tests/issues-11/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/issues-11/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/iter/__snapshots__/jsfmt.spec.js.snap b/tests/iter/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0695d0d737bb
--- /dev/null
+++ b/tests/iter/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,73 @@
+exports[`test iter.js 1`] = `
+"var a = [true,false];
+function foo(x) { }
+
+for (var i=0;i<3;i++) {
+    foo(a[i]);
+}
+for (var k in a) {
+    foo(a[k]); // k is a string, which shouldn't be used for array access
+}
+
+var b = (null : ?{[key: string]: string});
+for (var j in b) {
+    foo(b[j]);
+}
+
+var c;
+for (var m in (c = b)) {
+    foo(c[m]);
+}
+
+var d;
+for (var n in (d = a)) {
+    foo(d[n]); // d is a string, which shouldn't be used for array access
+}
+
+for (var x in undefined) {
+    foo(x); // unreachable
+}
+
+for (var x in null) {
+    foo(x); // unreachable
+}
+
+for (var y in this) {
+    // regression test to make sure \`in this\` doesn't fatal. it's currently
+    // allowed, even though we can't actually enumerate all the keys on \`this\`.
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var a = [ true, false ];
+function foo(x) {
+  
+}
+for (var i = 0; i < 3; i++) {
+  foo(a[i]);
+}
+for (var k in a) {
+  foo(a[k]);// k is a string, which shouldn't be used for array access
+}
+var b = (null: ?{ [key: string]: string });
+for (var j in b) {
+  foo(b[j]);
+}
+var c;
+for (var m in c = b) {
+  foo(c[m]);
+}
+var d;
+for (var n in d = a) {
+  foo(d[n]);// d is a string, which shouldn't be used for array access
+}
+for (var x in undefined) {
+  foo(x);// unreachable
+}
+for (var x in null) {
+  foo(x);// unreachable
+}
+for (var y in this) {
+  
+}
+
+"
+`;
diff --git a/tests/iter/iter.js b/tests/iter/iter.js
new file mode 100644
index 000000000000..62241fd8edcc
--- /dev/null
+++ b/tests/iter/iter.js
@@ -0,0 +1,37 @@
+var a = [true,false];
+function foo(x) { }
+
+for (var i=0;i<3;i++) {
+    foo(a[i]);
+}
+for (var k in a) {
+    foo(a[k]); // k is a string, which shouldn't be used for array access
+}
+
+var b = (null : ?{[key: string]: string});
+for (var j in b) {
+    foo(b[j]);
+}
+
+var c;
+for (var m in (c = b)) {
+    foo(c[m]);
+}
+
+var d;
+for (var n in (d = a)) {
+    foo(d[n]); // d is a string, which shouldn't be used for array access
+}
+
+for (var x in undefined) {
+    foo(x); // unreachable
+}
+
+for (var x in null) {
+    foo(x); // unreachable
+}
+
+for (var y in this) {
+    // regression test to make sure `in this` doesn't fatal. it's currently
+    // allowed, even though we can't actually enumerate all the keys on `this`.
+}
diff --git a/tests/iter/jsfmt.spec.js b/tests/iter/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/iter/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/iterable/__snapshots__/jsfmt.spec.js.snap b/tests/iterable/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c0ec883c959b
--- /dev/null
+++ b/tests/iterable/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,270 @@
+exports[`test array.js 1`] = `
+"/* @flow */
+
+var arrayTest1: Iterable<number> = ([1, 2]: Array<number>);
+var arrayTest2: Iterable<number | string> = [1,2,\"hi\"];
+var arrayTest3: Iterable<*> = [1,2,3];
+
+// Error string ~> number
+var arrayTest4: Iterable<number> = [\"hi\"];
+// Error string ~> number
+var arrayTest5: Iterable<string> = [\"hi\", 1];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test caching_bug.js 1`] = `
+"/* @flow */
+
+/**
+ * I\'ve hit a bug with the caching in flow_js.ml. Avik is removing that caching
+ * so it should be fixed soon. The basic idea is I flow something like
+ *
+ * Array<any | any> ~> Iterable<string>
+ *
+ * then Flow won\'t notice when I try to flow
+ *
+ * Array<string | number> ~> Iterable<string>
+ *
+ * We shouldn\'t hit the cache because the union types are different, but we do
+ * anyway. I\'ve fixed this temporarily by bumping the \"meaningful\" param to
+ * Hashtbl.hash_param
+ */
+
+function fill_the_cache(x: Array<any | any>): Iterable<string> { return x; }
+
+// Error: number ~> string
+function miss_the_cache(x: Array<string | number>): Iterable<string> { return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test iter.js 1`] = `
+"/* @flow */
+
+function foo(strs: Iterable<string>): void {
+  for (var s: string of strs) {
+    console.log(s);
+  }
+}
+
+var m: Map<string, number> = new Map();
+
+foo(m.keys());
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test iterator_result.js 1`] = `
+"/* @flow */
+
+function makeIterator(coin_flip: () => boolean ): Iterator<string> {
+  return {
+    \"@@iterator\"() { return makeIterator(coin_flip); },
+    next(): IteratorResult<string, void> {
+      var done = coin_flip();
+      if (!done) {
+        return { done, value: \"still going...\" };
+      } else {
+        return { done };
+      }
+    }
+  }
+}
+
+function makeIterator(coin_flip: () => boolean ): Iterator<string> {
+  return {
+    \"@@iterator\"() { return makeIterator(coin_flip); },
+    next(): IteratorResult<string, void> {
+      var done = coin_flip();
+      if (done) { // Whoops, made a mistake and forgot to negate done
+        return { done, value: \"still going...\" }; // Error string ~> void
+      } else {
+        return { done }; // Error void ~> string
+      }
+    }
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test map.js 1`] = `
+"/* @flow */
+
+function mapTest1(map: Map<string, number>): Iterable<[string, number]> {
+  return map;
+}
+function mapTest2<K, V>(map: Map<K, V>): Iterable<[K, V]> {
+  return map;
+};
+function mapTest3(map: Map<string, number>): Iterable<*> {
+  return map;
+}
+// Error - Map is an Iterable<[K, V]>
+function mapTest4(map: Map<number, string>): Iterable<string> {
+  return map;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test set.js 1`] = `
+"/* @flow */
+
+function setTest1(set: Set<string>): Iterable<string> {
+  return set;
+}
+function setTest2<T>(set: Set<T>): Iterable<T> {
+  return set;
+};
+function setTest3(set: Set<string>): Iterable<*> {
+  return set;
+}
+// Error string ~> number
+function setTest4(set: Set<string>): Iterable<number> {
+  return set;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test string.js 1`] = `
+"/* @flow */
+
+var stringTest1: Iterable<string> = \"hi\";
+var stringTest3: Iterable<*> = \"hi\";
+var stringTest3: Iterable<number> = \"hi\"; // Error - string is a Iterable<string>
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test variance.js 1`] = `
+"/* @flow */
+
+(([]: Array<string>): Iterable<?string>); // ok, Iterable<+T>
+
+(([]: Array<string>).values(): Iterable<?string>); // ok, Iterator<+T>
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/iterable/array.js b/tests/iterable/array.js
new file mode 100644
index 000000000000..c50c20f9352e
--- /dev/null
+++ b/tests/iterable/array.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+var arrayTest1: Iterable<number> = ([1, 2]: Array<number>);
+var arrayTest2: Iterable<number | string> = [1,2,"hi"];
+var arrayTest3: Iterable<*> = [1,2,3];
+
+// Error string ~> number
+var arrayTest4: Iterable<number> = ["hi"];
+// Error string ~> number
+var arrayTest5: Iterable<string> = ["hi", 1];
diff --git a/tests/iterable/caching_bug.js b/tests/iterable/caching_bug.js
new file mode 100644
index 000000000000..6fffea9f95bb
--- /dev/null
+++ b/tests/iterable/caching_bug.js
@@ -0,0 +1,21 @@
+/* @flow */
+
+/**
+ * I've hit a bug with the caching in flow_js.ml. Avik is removing that caching
+ * so it should be fixed soon. The basic idea is I flow something like
+ *
+ * Array<any | any> ~> Iterable<string>
+ *
+ * then Flow won't notice when I try to flow
+ *
+ * Array<string | number> ~> Iterable<string>
+ *
+ * We shouldn't hit the cache because the union types are different, but we do
+ * anyway. I've fixed this temporarily by bumping the "meaningful" param to
+ * Hashtbl.hash_param
+ */
+
+function fill_the_cache(x: Array<any | any>): Iterable<string> { return x; }
+
+// Error: number ~> string
+function miss_the_cache(x: Array<string | number>): Iterable<string> { return x; }
diff --git a/tests/iterable/iter.js b/tests/iterable/iter.js
new file mode 100644
index 000000000000..b8c3d9cf1d9d
--- /dev/null
+++ b/tests/iterable/iter.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+function foo(strs: Iterable<string>): void {
+  for (var s: string of strs) {
+    console.log(s);
+  }
+}
+
+var m: Map<string, number> = new Map();
+
+foo(m.keys());
diff --git a/tests/iterable/iterator_result.js b/tests/iterable/iterator_result.js
new file mode 100644
index 000000000000..cb0b0b162c21
--- /dev/null
+++ b/tests/iterable/iterator_result.js
@@ -0,0 +1,29 @@
+/* @flow */
+
+function makeIterator(coin_flip: () => boolean ): Iterator<string> {
+  return {
+    "@@iterator"() { return makeIterator(coin_flip); },
+    next(): IteratorResult<string, void> {
+      var done = coin_flip();
+      if (!done) {
+        return { done, value: "still going..." };
+      } else {
+        return { done };
+      }
+    }
+  }
+}
+
+function makeIterator(coin_flip: () => boolean ): Iterator<string> {
+  return {
+    "@@iterator"() { return makeIterator(coin_flip); },
+    next(): IteratorResult<string, void> {
+      var done = coin_flip();
+      if (done) { // Whoops, made a mistake and forgot to negate done
+        return { done, value: "still going..." }; // Error string ~> void
+      } else {
+        return { done }; // Error void ~> string
+      }
+    }
+  }
+}
diff --git a/tests/iterable/jsfmt.spec.js b/tests/iterable/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/iterable/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/iterable/map.js b/tests/iterable/map.js
new file mode 100644
index 000000000000..8125f7abf5c3
--- /dev/null
+++ b/tests/iterable/map.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+function mapTest1(map: Map<string, number>): Iterable<[string, number]> {
+  return map;
+}
+function mapTest2<K, V>(map: Map<K, V>): Iterable<[K, V]> {
+  return map;
+};
+function mapTest3(map: Map<string, number>): Iterable<*> {
+  return map;
+}
+// Error - Map is an Iterable<[K, V]>
+function mapTest4(map: Map<number, string>): Iterable<string> {
+  return map;
+}
diff --git a/tests/iterable/set.js b/tests/iterable/set.js
new file mode 100644
index 000000000000..2251e52924e7
--- /dev/null
+++ b/tests/iterable/set.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+function setTest1(set: Set<string>): Iterable<string> {
+  return set;
+}
+function setTest2<T>(set: Set<T>): Iterable<T> {
+  return set;
+};
+function setTest3(set: Set<string>): Iterable<*> {
+  return set;
+}
+// Error string ~> number
+function setTest4(set: Set<string>): Iterable<number> {
+  return set;
+}
diff --git a/tests/iterable/string.js b/tests/iterable/string.js
new file mode 100644
index 000000000000..bae6cec8e657
--- /dev/null
+++ b/tests/iterable/string.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+var stringTest1: Iterable<string> = "hi";
+var stringTest3: Iterable<*> = "hi";
+var stringTest3: Iterable<number> = "hi"; // Error - string is a Iterable<string>
diff --git a/tests/iterable/variance.js b/tests/iterable/variance.js
new file mode 100644
index 000000000000..634c41db3c9f
--- /dev/null
+++ b/tests/iterable/variance.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+(([]: Array<string>): Iterable<?string>); // ok, Iterable<+T>
+
+(([]: Array<string>).values(): Iterable<?string>); // ok, Iterator<+T>
diff --git a/tests/jsx_intrinsics.builtin/__snapshots__/jsfmt.spec.js.snap b/tests/jsx_intrinsics.builtin/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..28d087d9ab26
--- /dev/null
+++ b/tests/jsx_intrinsics.builtin/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,76 @@
+exports[`test main.js 1`] = `
+"// @flow
+
+var React = require(\'react\');
+
+class CustomComponent extends React.Component {
+  props: {
+    prop: string
+  };
+}
+
+var a: React.Element<{prop: string}> = <CustomComponent prop=\"asdf\" />;
+var b: React.Element<{prop1: string}> = <CustomComponent prop=\"asdf\" />; // Error: Props<{prop}> ~> Props<{prop1}>
+
+// Since intrinsics are typed as \`any\` out of the box, we can pass any
+// attributes to intrinsics!
+var c: React.Element<any> = <div not_a_real_attr=\"asdf\" />;
+// However, we don\'t allow such elements to be viewed as React elements with
+// different attributes.
+var d: React.Element<{doesntmatch: string}> = <div not_a_real_attr=\"asdf\" />;
+// No error as long as expectations are consistent, though.
+var e: React.Element<{not_a_real_attr: string}> = <div not_a_real_attr=\"asdf\" />;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test strings.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+
+// The builtin $JSXIntrinsics should allow any string
+
+var Div = \'div\';
+var Bad = \'bad\';
+var Str: string = \'str\';
+
+<Div />; // This is fine
+<Bad />; // This is fine
+<Str />; // This is fine
+
+React.createElement(\'div\', {}); // This is fine
+React.createElement(\'bad\', {}); // This is fine
+
+<Div id={42} />; // This is fine
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+// The builtin $JSXIntrinsics should allow any string
+var Div = \"div\";
+var Bad = \"bad\";
+var Str: string = \"str\";
+<Div/>;// This is fine
+<Bad/>;// This is fine
+<Str/>;// This is fine
+React.createElement(\"div\", {});// This is fine
+React.createElement(\"bad\", {});// This is fine
+<Div id={42}/>;// This is fine
+
+"
+`;
diff --git a/tests/jsx_intrinsics.builtin/jsfmt.spec.js b/tests/jsx_intrinsics.builtin/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/jsx_intrinsics.builtin/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/jsx_intrinsics.builtin/main.js b/tests/jsx_intrinsics.builtin/main.js
new file mode 100644
index 000000000000..4b7ee5a28510
--- /dev/null
+++ b/tests/jsx_intrinsics.builtin/main.js
@@ -0,0 +1,21 @@
+// @flow
+
+var React = require('react');
+
+class CustomComponent extends React.Component {
+  props: {
+    prop: string
+  };
+}
+
+var a: React.Element<{prop: string}> = <CustomComponent prop="asdf" />;
+var b: React.Element<{prop1: string}> = <CustomComponent prop="asdf" />; // Error: Props<{prop}> ~> Props<{prop1}>
+
+// Since intrinsics are typed as `any` out of the box, we can pass any
+// attributes to intrinsics!
+var c: React.Element<any> = <div not_a_real_attr="asdf" />;
+// However, we don't allow such elements to be viewed as React elements with
+// different attributes.
+var d: React.Element<{doesntmatch: string}> = <div not_a_real_attr="asdf" />;
+// No error as long as expectations are consistent, though.
+var e: React.Element<{not_a_real_attr: string}> = <div not_a_real_attr="asdf" />;
diff --git a/tests/jsx_intrinsics.builtin/strings.js b/tests/jsx_intrinsics.builtin/strings.js
new file mode 100644
index 000000000000..f63649cec5f7
--- /dev/null
+++ b/tests/jsx_intrinsics.builtin/strings.js
@@ -0,0 +1,18 @@
+/* @flow */
+
+var React = require('react');
+
+// The builtin $JSXIntrinsics should allow any string
+
+var Div = 'div';
+var Bad = 'bad';
+var Str: string = 'str';
+
+<Div />; // This is fine
+<Bad />; // This is fine
+<Str />; // This is fine
+
+React.createElement('div', {}); // This is fine
+React.createElement('bad', {}); // This is fine
+
+<Div id={42} />; // This is fine
diff --git a/tests/jsx_intrinsics.custom/__snapshots__/jsfmt.spec.js.snap b/tests/jsx_intrinsics.custom/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5034c898429f
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,73 @@
+exports[`test main.js 1`] = `
+"// @flow
+
+var React = require(\'react\');
+
+class CustomComponent extends React.Component {
+  props: {
+    prop: string
+  };
+}
+
+var a: React.Element<{prop: string}> = <CustomComponent prop=\"asdf\" />;
+var b: React.Element<{prop1: string}> = <CustomComponent prop=\"asdf\" />; // Error: Props<{prop}> ~> Props<{prop1}>
+
+<div id=\"asdf\" />;
+<div id={42} />; // Error: (\`id\` prop) number ~> string
+var c: React.Element<{id: string}> = <div id=\"asdf\" />;
+var d: React.Element<{id: number}> = <div id=\"asdf\" />; // Error: Props<{id:string}> ~> Props<{id:number}>
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test strings.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+
+var Div = \'div\';
+var Bad = \'bad\';
+var Str: string = \'str\';
+
+<Div />; // This is fine
+<Bad />; // Error: \'bad\' not in JSXIntrinsics
+<Str />; // Error: string ~> keys of JSXIntrinsics
+
+React.createElement(\'div\', {}); // This is fine
+React.createElement(\'bad\', {}); // Error: \'bad\' not in JSXIntrinsics
+React.createElement(Str, {}); // Error: string ~> keys of JSXIntrinsics
+
+// TODO: Make this an error
+<Div id={42} />; // Not an error but should be eventually
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Div = \"div\";
+var Bad = \"bad\";
+var Str: string = \"str\";
+<Div/>;// This is fine
+<Bad/>;// Error: \'bad\' not in JSXIntrinsics
+<Str/>;// Error: string ~> keys of JSXIntrinsics
+React.createElement(\"div\", {});// This is fine
+React.createElement(\"bad\", {});// Error: \'bad\' not in JSXIntrinsics
+React.createElement(Str, {});// Error: string ~> keys of JSXIntrinsics
+// TODO: Make this an error
+<Div id={42}/>;// Not an error but should be eventually
+
+"
+`;
diff --git a/tests/jsx_intrinsics.custom/jsfmt.spec.js b/tests/jsx_intrinsics.custom/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/jsx_intrinsics.custom/lib/__snapshots__/jsfmt.spec.js.snap b/tests/jsx_intrinsics.custom/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1c2c02375402
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test jsx.js 1`] = `
+"declare var $React: $Exports<\'react\'>; // fake import
+type $JSXIntrinsic<T> = Class<$React.Component<void,T,mixed>>;
+
+type $JSXIntrinsics = {
+  div: $JSXIntrinsic<{id: string}>,
+  span: $JSXIntrinsic<{id: string, class: string}>,
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/jsx_intrinsics.custom/lib/jsfmt.spec.js b/tests/jsx_intrinsics.custom/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/jsx_intrinsics.custom/lib/jsx.js b/tests/jsx_intrinsics.custom/lib/jsx.js
new file mode 100644
index 000000000000..7de8608bc649
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/lib/jsx.js
@@ -0,0 +1,7 @@
+declare var $React: $Exports<'react'>; // fake import
+type $JSXIntrinsic<T> = Class<$React.Component<void,T,mixed>>;
+
+type $JSXIntrinsics = {
+  div: $JSXIntrinsic<{id: string}>,
+  span: $JSXIntrinsic<{id: string, class: string}>,
+};
diff --git a/tests/jsx_intrinsics.custom/main.js b/tests/jsx_intrinsics.custom/main.js
new file mode 100644
index 000000000000..b1f753a4c5c3
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/main.js
@@ -0,0 +1,17 @@
+// @flow
+
+var React = require('react');
+
+class CustomComponent extends React.Component {
+  props: {
+    prop: string
+  };
+}
+
+var a: React.Element<{prop: string}> = <CustomComponent prop="asdf" />;
+var b: React.Element<{prop1: string}> = <CustomComponent prop="asdf" />; // Error: Props<{prop}> ~> Props<{prop1}>
+
+<div id="asdf" />;
+<div id={42} />; // Error: (`id` prop) number ~> string
+var c: React.Element<{id: string}> = <div id="asdf" />;
+var d: React.Element<{id: number}> = <div id="asdf" />; // Error: Props<{id:string}> ~> Props<{id:number}>
diff --git a/tests/jsx_intrinsics.custom/strings.js b/tests/jsx_intrinsics.custom/strings.js
new file mode 100644
index 000000000000..b11fb78d66a3
--- /dev/null
+++ b/tests/jsx_intrinsics.custom/strings.js
@@ -0,0 +1,18 @@
+/* @flow */
+
+var React = require('react');
+
+var Div = 'div';
+var Bad = 'bad';
+var Str: string = 'str';
+
+<Div />; // This is fine
+<Bad />; // Error: 'bad' not in JSXIntrinsics
+<Str />; // Error: string ~> keys of JSXIntrinsics
+
+React.createElement('div', {}); // This is fine
+React.createElement('bad', {}); // Error: 'bad' not in JSXIntrinsics
+React.createElement(Str, {}); // Error: string ~> keys of JSXIntrinsics
+
+// TODO: Make this an error
+<Div id={42} />; // Not an error but should be eventually
diff --git a/tests/keys/__snapshots__/jsfmt.spec.js.snap b/tests/keys/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7e35a42698d3
--- /dev/null
+++ b/tests/keys/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,64 @@
+exports[`test keys.js 1`] = `
+"/* @flow */
+
+function testKeysOfObject(str: string, lit: \'hi\') {
+  (str: $Keys<Object>); // Any string should be fine
+  if (str) {
+    (str: $Keys<Object>); // No error, truthy string should be fine
+  }
+  (\'hi\': $Keys<Object>); // String literal should be fine
+
+  (123: $Keys<Object>); // Error: number -> keys of Object
+}
+
+type StrDict = {[key: string]: mixed};
+function testKeysOfStrDict(str: string, lit: \'hi\') {
+  (str: $Keys<StrDict>); // Any string should be fine
+  if (str) {
+    (str: $Keys<StrDict>); // No error, truthy string should be fine
+  }
+  (\'hi\': $Keys<StrDict>); // String literal should be fine
+
+  (123: $Keys<StrDict>); // Error: number -> keys of StrDict
+}
+
+type StrLitDict = {[key: \'hi\']: mixed};
+function testKeysOfStrLitDict(str: string, lit: \'hi\') {
+  (str: $Keys<StrLitDict>); // Error: Not all strings are allowed
+  if (str) {
+    (str: $Keys<StrLitDict>); // Error: Not all truthy strings are allowed
+  }
+  (\'hi\': $Keys<StrLitDict>); // The right string literal is allowed
+  (\'bye\': $Keys<StrLitDict>); // Error: The wrong string literal is not allowed
+
+  (123: $Keys<StrLitDict>); // Error: number -> keys of StrLitDict
+}
+
+type ObjLit = {hi: mixed};
+function testKeysOfOtherObj(str: string, lit: \'hi\') {
+  (str: $Keys<ObjLit>); // Error: string -> keys of ObjLit
+  if (str) {
+    (str: $Keys<ObjLit>); // Error: truthy string -> keys of ObjLit
+  }
+  (\'hi\': $Keys<ObjLit>); // String literal should be fine
+
+  (123: $Keys<ObjLit>); // Error: number -> keys of ObjLit
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/keys/jsfmt.spec.js b/tests/keys/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/keys/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/keys/keys.js b/tests/keys/keys.js
new file mode 100644
index 000000000000..902bc52594ee
--- /dev/null
+++ b/tests/keys/keys.js
@@ -0,0 +1,45 @@
+/* @flow */
+
+function testKeysOfObject(str: string, lit: 'hi') {
+  (str: $Keys<Object>); // Any string should be fine
+  if (str) {
+    (str: $Keys<Object>); // No error, truthy string should be fine
+  }
+  ('hi': $Keys<Object>); // String literal should be fine
+
+  (123: $Keys<Object>); // Error: number -> keys of Object
+}
+
+type StrDict = {[key: string]: mixed};
+function testKeysOfStrDict(str: string, lit: 'hi') {
+  (str: $Keys<StrDict>); // Any string should be fine
+  if (str) {
+    (str: $Keys<StrDict>); // No error, truthy string should be fine
+  }
+  ('hi': $Keys<StrDict>); // String literal should be fine
+
+  (123: $Keys<StrDict>); // Error: number -> keys of StrDict
+}
+
+type StrLitDict = {[key: 'hi']: mixed};
+function testKeysOfStrLitDict(str: string, lit: 'hi') {
+  (str: $Keys<StrLitDict>); // Error: Not all strings are allowed
+  if (str) {
+    (str: $Keys<StrLitDict>); // Error: Not all truthy strings are allowed
+  }
+  ('hi': $Keys<StrLitDict>); // The right string literal is allowed
+  ('bye': $Keys<StrLitDict>); // Error: The wrong string literal is not allowed
+
+  (123: $Keys<StrLitDict>); // Error: number -> keys of StrLitDict
+}
+
+type ObjLit = {hi: mixed};
+function testKeysOfOtherObj(str: string, lit: 'hi') {
+  (str: $Keys<ObjLit>); // Error: string -> keys of ObjLit
+  if (str) {
+    (str: $Keys<ObjLit>); // Error: truthy string -> keys of ObjLit
+  }
+  ('hi': $Keys<ObjLit>); // String literal should be fine
+
+  (123: $Keys<ObjLit>); // Error: number -> keys of ObjLit
+}
diff --git a/tests/keyvalue/__snapshots__/jsfmt.spec.js.snap b/tests/keyvalue/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8505dac94a90
--- /dev/null
+++ b/tests/keyvalue/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test keyvalue.js 1`] = `
+"// @flow
+
+let tests = [
+  function(x: { [key: number]: string }) {
+    (x[""]: number);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  function(x: { [key: number]: string }) {
+    (x[""]: number);
+  }
+];
+
+"
+`;
diff --git a/tests/keyvalue/jsfmt.spec.js b/tests/keyvalue/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/keyvalue/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/keyvalue/keyvalue.js b/tests/keyvalue/keyvalue.js
new file mode 100644
index 000000000000..469501633e2c
--- /dev/null
+++ b/tests/keyvalue/keyvalue.js
@@ -0,0 +1,7 @@
+// @flow
+
+let tests = [
+  function(x: { [key: number]: string }) {
+    (x[""]: number);
+  }
+];
diff --git a/tests/last_duplicate_property_wins/__snapshots__/jsfmt.spec.js.snap b/tests/last_duplicate_property_wins/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4e569974d5d3
--- /dev/null
+++ b/tests/last_duplicate_property_wins/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,95 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+// Classes
+
+class C {
+  foo(): number { return 0; }
+  foo(): string { return "hello" } // last wins
+  x: number;
+  x: string; // last wins
+  bar(): number { return 0; }
+  bar: string; // field wins over method
+  qux: number;
+  qux(): string { return "hello" } // method loses to field!
+}
+
+// check
+
+((new C).foo(): boolean); // last wins
+((new C).x: boolean); // last wins
+((new C).bar: boolean); // last wins
+((new C).qux: boolean); // weird outlier where last doesn't win in classes
+
+// Objects
+
+const o = {
+  foo(): number { return 0; },
+  foo(): string { return "hello" }, // last wins
+  x: 42,
+  x: "hello", // last wins
+  bar(): number { return 0; },
+  bar: "hello", // last wins
+  qux: 42,
+  qux(): string { return "hello" }, // last wins
+};
+
+// check
+
+(o.foo(): boolean); // last wins
+(o.x: boolean); // last wins
+(o.bar: boolean); // last wins
+(o.qux(): boolean); // last wins
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// Classes
+class C {
+  foo(): number {
+    return 0;
+  }
+  foo(): string {
+    return "hello";
+  }// last wins
+  x: number;
+  x: string;// last wins
+  bar(): number {
+    return 0;
+  }
+  bar: string;// field wins over method
+  qux: number;
+  qux(): string {
+    return "hello";
+  }// method loses to field!
+}
+// check
+(new C().foo(): boolean);// last wins
+(new C().x: boolean);// last wins
+(new C().bar: boolean);// last wins
+(new C().qux: boolean);// weird outlier where last doesn't win in classes
+// Objects
+const o = {
+  foo(): number {
+    return 0;
+  },
+  // last wins foo(): string {
+    return "hello";
+  },
+  x: 42,
+  // last wins x: "hello",
+  bar(): number {
+    return 0;
+  },
+  // last wins bar: "hello",
+  qux: 42,
+  // last wins qux(): string {
+    return "hello";
+  }
+};
+// check
+(o.foo(): boolean);// last wins
+(o.x: boolean);// last wins
+(o.bar: boolean);// last wins
+(o.qux(): boolean);// last wins
+
+"
+`;
diff --git a/tests/last_duplicate_property_wins/jsfmt.spec.js b/tests/last_duplicate_property_wins/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/last_duplicate_property_wins/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/last_duplicate_property_wins/test.js b/tests/last_duplicate_property_wins/test.js
new file mode 100644
index 000000000000..8468262e3d2b
--- /dev/null
+++ b/tests/last_duplicate_property_wins/test.js
@@ -0,0 +1,41 @@
+// @flow
+
+// Classes
+
+class C {
+  foo(): number { return 0; }
+  foo(): string { return "hello" } // last wins
+  x: number;
+  x: string; // last wins
+  bar(): number { return 0; }
+  bar: string; // field wins over method
+  qux: number;
+  qux(): string { return "hello" } // method loses to field!
+}
+
+// check
+
+((new C).foo(): boolean); // last wins
+((new C).x: boolean); // last wins
+((new C).bar: boolean); // last wins
+((new C).qux: boolean); // weird outlier where last doesn't win in classes
+
+// Objects
+
+const o = {
+  foo(): number { return 0; },
+  foo(): string { return "hello" }, // last wins
+  x: 42,
+  x: "hello", // last wins
+  bar(): number { return 0; },
+  bar: "hello", // last wins
+  qux: 42,
+  qux(): string { return "hello" }, // last wins
+};
+
+// check
+
+(o.foo(): boolean); // last wins
+(o.x: boolean); // last wins
+(o.bar: boolean); // last wins
+(o.qux(): boolean); // last wins
diff --git a/tests/lib/__snapshots__/jsfmt.spec.js.snap b/tests/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..173f38aad2ce
--- /dev/null
+++ b/tests/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test libtest.js 1`] = `
+"var x:string = NaN
+var y:string = Number.MAX_VALUE;
+var z:number = new TypeError().name;
+var w:string = parseInt("...");
+
+var a = new Map();
+a.delete('foobar');
+
+var b = undefined;
+if (undefined) {
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: string = NaN;
+var y: string = Number.MAX_VALUE;
+var z: number = new TypeError().name;
+var w: string = parseInt("...");
+var a = new Map();
+a.delete("foobar");
+var b = undefined;
+if (undefined) {
+  
+}
+
+"
+`;
diff --git a/tests/lib/jsfmt.spec.js b/tests/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/lib/libtest.js b/tests/lib/libtest.js
new file mode 100644
index 000000000000..567ac09d40f4
--- /dev/null
+++ b/tests/lib/libtest.js
@@ -0,0 +1,11 @@
+var x:string = NaN
+var y:string = Number.MAX_VALUE;
+var z:number = new TypeError().name;
+var w:string = parseInt("...");
+
+var a = new Map();
+a.delete('foobar');
+
+var b = undefined;
+if (undefined) {
+}
diff --git a/tests/lib_interfaces/declarations/__snapshots__/jsfmt.spec.js.snap b/tests/lib_interfaces/declarations/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..07222343166a
--- /dev/null
+++ b/tests/lib_interfaces/declarations/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test underscore.js 1`] = `
+"interface C<T> {
+  foo(): CArrays<T>;
+  bar(): C<any>;
+}
+interface CArrays<T> extends C<Array<T>> {
+  bar(): C<any>;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1384:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/lib_interfaces/declarations/jsfmt.spec.js b/tests/lib_interfaces/declarations/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/lib_interfaces/declarations/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/lib_interfaces/declarations/underscore.js b/tests/lib_interfaces/declarations/underscore.js
new file mode 100644
index 000000000000..305116bacbec
--- /dev/null
+++ b/tests/lib_interfaces/declarations/underscore.js
@@ -0,0 +1,7 @@
+interface C<T> {
+  foo(): CArrays<T>;
+  bar(): C<any>;
+}
+interface CArrays<T> extends C<Array<T>> {
+  bar(): C<any>;
+}
diff --git a/tests/libconfig/__snapshots__/jsfmt.spec.js.snap b/tests/libconfig/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b941f86bc364
--- /dev/null
+++ b/tests/libconfig/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,51 @@
+exports[`test libA.js 1`] = `
+"declare function foo(x: number): void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test libB.js 1`] = `
+"declare function bar(x: string): void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test libtest.js 1`] = `
+"foo(123);
+bar(123);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+foo(123);
+bar(123);
+
+"
+`;
diff --git a/tests/libconfig/jsfmt.spec.js b/tests/libconfig/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/libconfig/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/libconfig/libA.js b/tests/libconfig/libA.js
new file mode 100644
index 000000000000..304501d2cc6f
--- /dev/null
+++ b/tests/libconfig/libA.js
@@ -0,0 +1 @@
+declare function foo(x: number): void;
diff --git a/tests/libconfig/libB.js b/tests/libconfig/libB.js
new file mode 100644
index 000000000000..218601f8fa85
--- /dev/null
+++ b/tests/libconfig/libB.js
@@ -0,0 +1 @@
+declare function bar(x: string): void;
diff --git a/tests/libconfig/libtest.js b/tests/libconfig/libtest.js
new file mode 100644
index 000000000000..d78728d487b9
--- /dev/null
+++ b/tests/libconfig/libtest.js
@@ -0,0 +1,2 @@
+foo(123);
+bar(123);
diff --git a/tests/libdef_ignored_module/__snapshots__/jsfmt.spec.js.snap b/tests/libdef_ignored_module/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8499e56a2b51
--- /dev/null
+++ b/tests/libdef_ignored_module/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,13 @@
+exports[`test test.js 1`] = `
+"/* @flow */
+
+import foo from "foo";
+
+(foo.bar : string); // error number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+import foo from "foo";
+(foo.bar: string);// error number ~> string
+
+"
+`;
diff --git a/tests/libdef_ignored_module/jsfmt.spec.js b/tests/libdef_ignored_module/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/libdef_ignored_module/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/libdef_ignored_module/lib/__snapshots__/jsfmt.spec.js.snap b/tests/libdef_ignored_module/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5984291f7dc8
--- /dev/null
+++ b/tests/libdef_ignored_module/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,11 @@
+exports[`test foo.js 1`] = `
+"declare module foo {
+  declare var bar: number;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare module foo {
+  declare var bar: number;
+}
+
+"
+`;
diff --git a/tests/libdef_ignored_module/lib/foo.js b/tests/libdef_ignored_module/lib/foo.js
new file mode 100644
index 000000000000..955a7d7f6a79
--- /dev/null
+++ b/tests/libdef_ignored_module/lib/foo.js
@@ -0,0 +1,3 @@
+declare module foo {
+  declare var bar: number;
+}
diff --git a/tests/libdef_ignored_module/lib/jsfmt.spec.js b/tests/libdef_ignored_module/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/libdef_ignored_module/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/libdef_ignored_module/test.js b/tests/libdef_ignored_module/test.js
new file mode 100644
index 000000000000..334e7e8c21bd
--- /dev/null
+++ b/tests/libdef_ignored_module/test.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+import foo from "foo";
+
+(foo.bar : string); // error number ~> string
diff --git a/tests/liberr/__snapshots__/jsfmt.spec.js.snap b/tests/liberr/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fb842df9ee45
--- /dev/null
+++ b/tests/liberr/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test a.js 1`] = `
+"/**
+ * @flow
+ */
+// one error here, to verify lib errors sort to top.
+var x: string = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+// one error here, to verify lib errors sort to top.
+var x: string = 0;
+
+"
+`;
diff --git a/tests/liberr/a.js b/tests/liberr/a.js
new file mode 100644
index 000000000000..f444c23835cd
--- /dev/null
+++ b/tests/liberr/a.js
@@ -0,0 +1,5 @@
+/**
+ * @flow
+ */
+// one error here, to verify lib errors sort to top.
+var x: string = 0;
diff --git a/tests/liberr/jsfmt.spec.js b/tests/liberr/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/liberr/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/liberr/libs/__snapshots__/jsfmt.spec.js.snap b/tests/liberr/libs/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8c596e46cf84
--- /dev/null
+++ b/tests/liberr/libs/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,51 @@
+exports[`test parse_error.js 1`] = `
+"/**
+ * @flow
+ */
+declare class ExampleClass {
+
+  methodA: () => any // parse error, missing comma
+
+  methodB: () => any
+
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (8:2)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowObjectTypeSemicolon (/node_modules/babylon/lib/index.js:4832:10)
+    at Parser.pp$7.flowParseObjectType (/node_modules/babylon/lib/index.js:4813:14)
+    at Parser.pp$7.flowParseInterfaceish (/node_modules/babylon/lib/index.js:4575:20)
+    at Parser.pp$7.flowParseDeclareClass (/node_modules/babylon/lib/index.js:4437:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4474:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+"
+`;
+
+exports[`test type_error.js 1`] = `
+"// @flow
+declare function foo(x: number): Array;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/liberr/libs/jsfmt.spec.js b/tests/liberr/libs/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/liberr/libs/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/liberr/libs/parse_error.js b/tests/liberr/libs/parse_error.js
new file mode 100644
index 000000000000..08cd2a15d3c0
--- /dev/null
+++ b/tests/liberr/libs/parse_error.js
@@ -0,0 +1,10 @@
+/**
+ * @flow
+ */
+declare class ExampleClass {
+
+  methodA: () => any // parse error, missing comma
+
+  methodB: () => any
+
+}
diff --git a/tests/liberr/libs/type_error.js b/tests/liberr/libs/type_error.js
new file mode 100644
index 000000000000..1c36d039ecc4
--- /dev/null
+++ b/tests/liberr/libs/type_error.js
@@ -0,0 +1,2 @@
+// @flow
+declare function foo(x: number): Array;
diff --git a/tests/libflow-typed/__snapshots__/jsfmt.spec.js.snap b/tests/libflow-typed/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5a2c84cb0777
--- /dev/null
+++ b/tests/libflow-typed/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test libtest.js 1`] = `
+"/* @flow */
+const dino : Dinosaur = "Stegosaurus"
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+const dino: Dinosaur = "Stegosaurus";
+
+"
+`;
diff --git a/tests/libflow-typed/flow-typed/__snapshots__/jsfmt.spec.js.snap b/tests/libflow-typed/flow-typed/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fcc919445fd6
--- /dev/null
+++ b/tests/libflow-typed/flow-typed/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,20 @@
+exports[`test dino.js 1`] = `
+"declare type Dinosaur = \"T-Rex\" | \"Apatosaurus\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/libflow-typed/flow-typed/dino.js b/tests/libflow-typed/flow-typed/dino.js
new file mode 100644
index 000000000000..283429db6f73
--- /dev/null
+++ b/tests/libflow-typed/flow-typed/dino.js
@@ -0,0 +1 @@
+declare type Dinosaur = "T-Rex" | "Apatosaurus";
diff --git a/tests/libflow-typed/flow-typed/jsfmt.spec.js b/tests/libflow-typed/flow-typed/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/libflow-typed/flow-typed/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/libflow-typed/jsfmt.spec.js b/tests/libflow-typed/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/libflow-typed/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/libflow-typed/libtest.js b/tests/libflow-typed/libtest.js
new file mode 100644
index 000000000000..8d4b83401678
--- /dev/null
+++ b/tests/libflow-typed/libtest.js
@@ -0,0 +1,2 @@
+/* @flow */
+const dino : Dinosaur = "Stegosaurus"
diff --git a/tests/librec/__snapshots__/jsfmt.spec.js.snap b/tests/librec/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2921149267ff
--- /dev/null
+++ b/tests/librec/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test libtest.js 1`] = `
+"foo(123);
+bar(123);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+foo(123);
+bar(123);
+
+"
+`;
diff --git a/tests/librec/jsfmt.spec.js b/tests/librec/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/librec/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/librec/lib/A/__snapshots__/jsfmt.spec.js.snap b/tests/librec/lib/A/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b1e15472a048
--- /dev/null
+++ b/tests/librec/lib/A/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,20 @@
+exports[`test libA.js 1`] = `
+"declare function foo(x: number): void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/librec/lib/A/jsfmt.spec.js b/tests/librec/lib/A/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/librec/lib/A/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/librec/lib/A/libA.js b/tests/librec/lib/A/libA.js
new file mode 100644
index 000000000000..304501d2cc6f
--- /dev/null
+++ b/tests/librec/lib/A/libA.js
@@ -0,0 +1 @@
+declare function foo(x: number): void;
diff --git a/tests/librec/lib/B/__snapshots__/jsfmt.spec.js.snap b/tests/librec/lib/B/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..09b44d83467e
--- /dev/null
+++ b/tests/librec/lib/B/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,20 @@
+exports[`test libB.js 1`] = `
+"declare function bar(x: string): void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/librec/lib/B/jsfmt.spec.js b/tests/librec/lib/B/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/librec/lib/B/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/librec/lib/B/libB.js b/tests/librec/lib/B/libB.js
new file mode 100644
index 000000000000..218601f8fa85
--- /dev/null
+++ b/tests/librec/lib/B/libB.js
@@ -0,0 +1 @@
+declare function bar(x: string): void;
diff --git a/tests/librec/libtest.js b/tests/librec/libtest.js
new file mode 100644
index 000000000000..d78728d487b9
--- /dev/null
+++ b/tests/librec/libtest.js
@@ -0,0 +1,2 @@
+foo(123);
+bar(123);
diff --git a/tests/literal/__snapshots__/jsfmt.spec.js.snap b/tests/literal/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..09237dbc394c
--- /dev/null
+++ b/tests/literal/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,104 @@
+exports[`test enum.js 1`] = `
+"var APIKeys = {
+    AGE: \'age\',
+    NAME: \'name\',
+};
+
+module.exports = APIKeys;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var APIKeys = { AGE: \"age\", NAME: \"name\" };
+module.exports = APIKeys;
+
+"
+`;
+
+exports[`test enum_client.js 1`] = `
+"var APIKeys = require(\'./enum\');
+// object that maps \"AGE\" to \"age\", \"NAME\" to \"name\"
+
+function foo(x: $Keys<typeof APIKeys>) { }
+foo(\"AGE\");
+foo(\"LOCATION\"); // error
+
+function bar(x: $Keys<{age: number}>) { }
+bar(APIKeys.AGE); // not an error: APIKeys.AGE = \"age\"
+bar(APIKeys.NAME); // error: since \"NAME\" is not in the smaller enum
+
+var object = {};
+object[APIKeys.AGE] = 123; // i.e., object.age = 123
+object[APIKeys.NAME] = \"FOO\"; // i.e., object.name = \"FOO\"
+
+var age:number = object[APIKeys.AGE];
+var name:number = object[APIKeys.NAME]; // error: object.name is a string
+
+var indices = { red: 0, green: 1, blue: 2 };
+var tuple = [42, \"hello\", false];
+var red:string = tuple[indices.red]; // error: tuple[0] is a number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test number.js 1`] = `
+"function test1(x: number): number {
+  return -x;
+}
+
+function test2(x: string): number {
+  return -x;
+}
+
+// sanity checks to make sure merging envs doesn\'t keep creating new NumT\'s
+// because of the UnaryMinusT\'s, causing nontermination
+function test3(x: number, flip_times: number): number {
+  for (var i = 0; i < flip_times; i++) {
+    x = -x;
+  }
+  return x;
+}
+function test4(flip_times: number): number {
+  var x = 1;
+  for (var i = 0; i < flip_times; i++) {
+    x = -x;
+  }
+  return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function test1(x: number): number {
+  return -x;
+}
+function test2(x: string): number {
+  return -x;
+}
+// sanity checks to make sure merging envs doesn\'t keep creating new NumT\'s
+// because of the UnaryMinusT\'s, causing nontermination
+function test3(x: number, flip_times: number): number {
+  for (var i = 0; i < flip_times; i++) {
+    x = -x;
+  }
+  return x;
+}
+function test4(flip_times: number): number {
+  var x = 1;
+  for (var i = 0; i < flip_times; i++) {
+    x = -x;
+  }
+  return x;
+}
+
+"
+`;
diff --git a/tests/literal/enum.js b/tests/literal/enum.js
new file mode 100644
index 000000000000..6449c41bd82c
--- /dev/null
+++ b/tests/literal/enum.js
@@ -0,0 +1,6 @@
+var APIKeys = {
+    AGE: 'age',
+    NAME: 'name',
+};
+
+module.exports = APIKeys;
diff --git a/tests/literal/enum_client.js b/tests/literal/enum_client.js
new file mode 100644
index 000000000000..2259290ad4ef
--- /dev/null
+++ b/tests/literal/enum_client.js
@@ -0,0 +1,21 @@
+var APIKeys = require('./enum');
+// object that maps "AGE" to "age", "NAME" to "name"
+
+function foo(x: $Keys<typeof APIKeys>) { }
+foo("AGE");
+foo("LOCATION"); // error
+
+function bar(x: $Keys<{age: number}>) { }
+bar(APIKeys.AGE); // not an error: APIKeys.AGE = "age"
+bar(APIKeys.NAME); // error: since "NAME" is not in the smaller enum
+
+var object = {};
+object[APIKeys.AGE] = 123; // i.e., object.age = 123
+object[APIKeys.NAME] = "FOO"; // i.e., object.name = "FOO"
+
+var age:number = object[APIKeys.AGE];
+var name:number = object[APIKeys.NAME]; // error: object.name is a string
+
+var indices = { red: 0, green: 1, blue: 2 };
+var tuple = [42, "hello", false];
+var red:string = tuple[indices.red]; // error: tuple[0] is a number
diff --git a/tests/literal/jsfmt.spec.js b/tests/literal/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/literal/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/literal/number.js b/tests/literal/number.js
new file mode 100644
index 000000000000..1ec5299191b5
--- /dev/null
+++ b/tests/literal/number.js
@@ -0,0 +1,23 @@
+function test1(x: number): number {
+  return -x;
+}
+
+function test2(x: string): number {
+  return -x;
+}
+
+// sanity checks to make sure merging envs doesn't keep creating new NumT's
+// because of the UnaryMinusT's, causing nontermination
+function test3(x: number, flip_times: number): number {
+  for (var i = 0; i < flip_times; i++) {
+    x = -x;
+  }
+  return x;
+}
+function test4(flip_times: number): number {
+  var x = 1;
+  for (var i = 0; i < flip_times; i++) {
+    x = -x;
+  }
+  return x;
+}
diff --git a/tests/locals/__snapshots__/jsfmt.spec.js.snap b/tests/locals/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6ed1110ebc93
--- /dev/null
+++ b/tests/locals/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,122 @@
+exports[`test lex.js 1`] = `
+"function switch_scope(x: mixed) {
+  let a = \"\";
+  let b = \"\";
+  switch (x) {
+    case \"foo\":
+      let a;
+      a = 0; // doesn\'t add lower bound to outer a
+      b = 0;
+  }
+  (a : string); // OK
+  (b : string); // error: number ~> string
+}
+
+function try_scope_finally() {
+  let a;
+  let b;
+  try {
+    a = \"\";
+    b = \"\";
+  } finally {
+    let a;
+    a = 0; // doesn\'t add lower bound to outer a
+    b = 0;
+  }
+  (a : string); // ok
+  (b : string); // error: number ~> string
+}
+
+function for_scope() {
+  let a = \"\";
+  let b = \"\";
+  for (let a;;) {
+    a = 0; // doesn\'t add lower bound to outer a
+    b = 0;
+  }
+  (a : string);
+  (b : string); // error: number ~> string
+}
+
+function for_in_scope(o: Object) {
+  let a = 0;
+  let b = 0;
+  for (let a in o) {
+    a = \"\"; // doesn\'t add lower bound to outer a
+    b = \"\";
+  }
+  (a : number);
+  (b : number); // error: string ~> number
+}
+
+function for_of_scope(xs: number[]) {
+  let a = \"\";
+  let b = \"\";
+  for (let a of xs) {
+    a = 0; // doesn\'t add lower bound to outer a
+    b = 0;
+  }
+  (a : string);
+  (b : string); // error: number ~> string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test locals.js 1`] = `
+"var x:string = 0;
+var x:number = 1;
+
+//declare var T: $Type<number | Array<T>>;
+
+function foo(p: bool) {}
+
+function sorry(really: bool) {
+    if (really) {
+        var x: number | string = 1337;
+    } else {
+        var x: bool = true;
+    }
+    foo(x);
+}
+
+function foo0(b: bool): number {
+  var x = 0;
+  if (b) {
+    var x = \"\"; // error: string ~> number
+  }
+  return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/locals/jsfmt.spec.js b/tests/locals/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/locals/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/locals/lex.js b/tests/locals/lex.js
new file mode 100644
index 000000000000..a97bd4604439
--- /dev/null
+++ b/tests/locals/lex.js
@@ -0,0 +1,60 @@
+function switch_scope(x: mixed) {
+  let a = "";
+  let b = "";
+  switch (x) {
+    case "foo":
+      let a;
+      a = 0; // doesn't add lower bound to outer a
+      b = 0;
+  }
+  (a : string); // OK
+  (b : string); // error: number ~> string
+}
+
+function try_scope_finally() {
+  let a;
+  let b;
+  try {
+    a = "";
+    b = "";
+  } finally {
+    let a;
+    a = 0; // doesn't add lower bound to outer a
+    b = 0;
+  }
+  (a : string); // ok
+  (b : string); // error: number ~> string
+}
+
+function for_scope() {
+  let a = "";
+  let b = "";
+  for (let a;;) {
+    a = 0; // doesn't add lower bound to outer a
+    b = 0;
+  }
+  (a : string);
+  (b : string); // error: number ~> string
+}
+
+function for_in_scope(o: Object) {
+  let a = 0;
+  let b = 0;
+  for (let a in o) {
+    a = ""; // doesn't add lower bound to outer a
+    b = "";
+  }
+  (a : number);
+  (b : number); // error: string ~> number
+}
+
+function for_of_scope(xs: number[]) {
+  let a = "";
+  let b = "";
+  for (let a of xs) {
+    a = 0; // doesn't add lower bound to outer a
+    b = 0;
+  }
+  (a : string);
+  (b : string); // error: number ~> string
+}
diff --git a/tests/locals/locals.js b/tests/locals/locals.js
new file mode 100644
index 000000000000..ebb8167bc4dd
--- /dev/null
+++ b/tests/locals/locals.js
@@ -0,0 +1,23 @@
+var x:string = 0;
+var x:number = 1;
+
+//declare var T: $Type<number | Array<T>>;
+
+function foo(p: bool) {}
+
+function sorry(really: bool) {
+    if (really) {
+        var x: number | string = 1337;
+    } else {
+        var x: bool = true;
+    }
+    foo(x);
+}
+
+function foo0(b: bool): number {
+  var x = 0;
+  if (b) {
+    var x = ""; // error: string ~> number
+  }
+  return x;
+}
diff --git a/tests/logical/__snapshots__/jsfmt.spec.js.snap b/tests/logical/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3970bd284909
--- /dev/null
+++ b/tests/logical/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,533 @@
+exports[`test logical.js 1`] = `
+"/* @flow */
+
+/**
+ * A falsy variable on the left side of &&
+ */
+function logical1a(): number { // expected \`: boolean\`
+    var x = false;
+    return x && \'123\';
+}
+
+/**
+ * A truthy variable on the left side of &&
+ */
+function logical1b(): string {
+    var x = true;
+    return x && \'123\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2a(): number { // expected \`: boolean\`
+    return false && \'123\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2b(): number {
+    return 0 && \'123\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2c(): string {
+    return \"\" && 123;
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2d(): string {
+    return true && \'123\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2e(): number {
+    return \'foo\' && 123;
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2f(): string {
+    return 123 && \'foo\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2g(): string {
+    return [1,2,3] && \'foo\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2h(x: {a: number}): string {
+    return x && \'foo\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2i(x: Object): string {
+    return x && \'foo\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2j(x: (a: number) => number): string {
+    return x && \'foo\';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2k(x: Function): string {
+    return x && \'foo\';
+}
+
+/**
+ * An expression on the left side of &&
+ */
+function logical3a(): string { // expected \`: boolean\`
+    var x: ?number = null;
+    return x != null && x > 10;
+}
+
+/**
+ * An expression on the left side of &&
+ */
+function logical3b(): number { // expected \`: boolean | number\`
+    var x: ?number = null;
+    return x != null && x;
+}
+
+/**
+ * An expression on the left side of &&
+ */
+function logical3c(): ?number { // expected \`: boolean | ?number\`
+    var x: ?number = null;
+    return x != undefined && x;
+}
+
+/**
+ * Maybe truthy returns both types
+ */
+function logical4(x: boolean): string { // expected \`: boolean | string\`
+    return x && \'123\';
+}
+
+/**
+ * A falsy variable on the left side of ||
+ */
+function logical5a(): number {
+    var x = false;
+    return x || 0;
+}
+
+/**
+ * A maybe variable on the left side of ||
+ */
+function logical5b(): number {
+    var x: ?number = null;
+    return x || 0;
+}
+
+/**
+ * A truthy variable on the left side of ||
+ */
+function logical5c(): string { // expected \`: boolean\`
+    var x = true;
+    return x || 0;
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6a(): string {
+    return false || \'123\';
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6b(): string {
+    return 0 || \'123\';
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6c(): number {
+    return \"\" || 123;
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6d(): number { // expected \`: boolean\`
+    return true || \'123\';
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6e(): string {
+    return \'foo\' || 123;
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6f(): number {
+    return 123 || \'foo\';
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7a(): number {
+    var x: ?number = null;
+    return x != null && x || 0;
+}
+
+/**
+ * A composite && and || where the truthiness is unknown
+ */
+function logical7b(x: boolean, y: number): number {
+    return x && y || 0;
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7c(x: string): number {
+    return x && 1 || 0;
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7d(x: number): string {
+    return x && \'foo\' || \'bar\';
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7e(x: number): string {
+    return false && x || \'bar\';
+}
+
+/**
+ * A composite || and &&
+ *
+ * \`x || 0\` always returns a number (never a boolean) and then short
+ * circuits the && because 0 is falsy, so this should just return number.
+ */
+function logical8a(): number {
+    var x = false;
+    return (x || 0) && \'foo\';
+}
+
+/**
+ * A composite || and &&
+ *
+ * \`x || 1\` always returns something truthy, so this returns a string
+ */
+function logical8b(): string {
+    var x = false;
+    return (x || 1) && \'foo\';
+}
+
+/**
+ * A composite || and &&
+ *
+ * \`x\` is always truthy, so this returns a string
+ */
+function logical8c(): string {
+    var x = true;
+    return (x || 1) && \'foo\';
+}
+
+/**
+ * A composite || and &&
+ */
+function logical8d(): number {
+    var x = false;
+    return x || (0 && \'foo\');
+}
+
+/**
+ * A composite || and &&
+ */
+function logical8e(): string {
+    var x = false;
+    return x || (1 && \'foo\');
+}
+
+/**
+ * A composite || and &&
+ */
+function logical8f(): string { // expected \`: boolean\`
+    var x = true;
+    return x || (1 && \'foo\');
+}
+
+/**
+ * A composite || and ||
+ */
+function logical9a(
+    x: number,
+    y: string
+): number | string { // expected \`: number | string | boolean\`
+    return x || y || false;
+}
+
+/**
+ * A composite || and ||
+ */
+function logical9b(x: number, y: string): number | string {
+    return false || x || y;
+}
+
+/**
+ * A composite || and ||
+ */
+function logical9c(x: number, y: boolean): string {
+    return \'a\' || x || y;
+}
+
+/**
+ * A composite && and &&
+ */
+function logical10a(
+    x: number,
+    y: string
+): number | string { // expected \`: number | string | boolean\`
+    return x && y && false;
+}
+
+/**
+ * A composite && and &&
+ */
+function logical10b(x: number, y: string): Array<any> { // expected \`: boolean\`
+    return false && x && y;
+}
+
+/**
+ * A composite && and &&
+ */
+function logical10c(x: number, y: string): Array<any> { // expected \`number | boolean\`
+    return x && false && y;
+}
+
+/**
+ * || in a loop
+ */
+function logical11a(): number {
+    var y = 1;
+    for (var x = 0; x < 5; x++) {
+        y = y || true;
+    }
+    return y;
+}
+
+/**
+ * || in a loop
+ */
+function logical11b(y: number): number {
+    for (var x = 0; x < 5; x++) {
+        y = y || true; // expected a number
+    }
+    return y;
+}
+
+/**
+ * && in a loop
+ */
+function logical12a(): number {
+    var y = 1;
+    var z = true;
+    for (var x = 0; x < 5; x++) {
+        y = z && y;
+        z = false;
+    }
+    return y;
+}
+
+/**
+ * && in a loop
+ */
+function logical12b(y: number): number {
+    for (var x = 0; x < 5; x++) {
+        y = y && true; // expected a number
+    }
+    return y;
+}
+
+/**
+ * Complex &&
+ */
+function logical13(x: number): Array<{x: string}> {
+    return [
+        {x: x && \"bar\"},
+        {x: true && \"bar\"},
+        {x: true && false},
+        {x: false && false},
+        {x: 1 && \"bar\"},
+        {x: \"foo\" && \"bar\"},
+        {x: \"foo\" && \"bar\"},
+        {x: \"foo\" && \"bar\"},
+    ];
+}
+
+/**
+ * Complex ||
+ */
+function logical14(x: number): Array<{x: string}> {
+    return [
+        {x: x || \"bar\"},
+        {x: false || \"bar\"},
+        {x: false || true},
+        {x: true || false},
+        {x: 0 || \"bar\"},
+        {x: \"foo\" || \"bar\"},
+        {x: \"foo\" || \"bar\"},
+        {x: \"foo\" || \"bar\"},
+    ];
+}
+
+/**
+ * || in an addition
+ */
+function logical15a(x: number): number {
+    return 5 + (x || 7);
+}
+
+/**
+ * || in an addition
+ */
+function logical15b(x: number): number {
+    return (x || 7) + 5;
+}
+
+/**
+ * && in an addition
+ */
+function logical15c(x: number): number {
+    return 5 + (x && 7);
+}
+
+/**
+ * && in an addition
+ */
+function logical15d(x: number): number {
+    return (x && 7) + 5;
+}
+
+/**
+ * || in a comparison
+ */
+function logical16a(x: number): boolean {
+    return 5 < (x || 7);
+}
+
+/**
+ * || in a comparison
+ */
+function logical16b(x: number): boolean {
+    return (x || 7) < 5;
+}
+
+/**
+ * && in a comparison
+ */
+function logical16c(x: number): boolean {
+    return 5 < (x && 7);
+}
+
+/**
+ * && in a comparison
+ */
+function logical16d(x: number): boolean {
+    return (x && 7) < 5;
+}
+
+/**
+ * || in an equality
+ */
+function logical17a(x: number): boolean {
+    return 5 == (x || 7);
+}
+
+/**
+ * || in an equality
+ */
+function logical17b(x: number): boolean {
+    return (x || 7) == 5;
+}
+
+/**
+ * && in an equality
+ */
+function logical17c(x: number): boolean {
+    return 5 == (x && 7);
+}
+
+/**
+ * && in an equality
+ */
+function logical17d(x: number): boolean {
+    return (x && 7) == 5;
+}
+
+/**
+ * Expressions on each side that return truthy things
+ */
+function logical18a(x: number, y: number): number {
+    return x - 1 || y - 1;
+}
+
+/**
+ * Sentinel properties should not interfere
+ */
+function logical18b(x: {a: number}, y: {b: number}): number {
+    return x.a - 1 || y.b - 1;
+}
+
+/**
+ * Layer of indirection in the LHS (get prop)
+ */
+function logical19a(x: { y: string, z: boolean }): boolean {
+  return (x.y && x.z); // error: x.y is a string
+}
+function logical19b(x: { y: string, z: boolean }): boolean {
+  return (x.y || x.z); // error: x.y is a string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/logical/jsfmt.spec.js b/tests/logical/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/logical/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/logical/logical.js b/tests/logical/logical.js
new file mode 100644
index 000000000000..b4aa1dcf90aa
--- /dev/null
+++ b/tests/logical/logical.js
@@ -0,0 +1,514 @@
+/* @flow */
+
+/**
+ * A falsy variable on the left side of &&
+ */
+function logical1a(): number { // expected `: boolean`
+    var x = false;
+    return x && '123';
+}
+
+/**
+ * A truthy variable on the left side of &&
+ */
+function logical1b(): string {
+    var x = true;
+    return x && '123';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2a(): number { // expected `: boolean`
+    return false && '123';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2b(): number {
+    return 0 && '123';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2c(): string {
+    return "" && 123;
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2d(): string {
+    return true && '123';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2e(): number {
+    return 'foo' && 123;
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2f(): string {
+    return 123 && 'foo';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2g(): string {
+    return [1,2,3] && 'foo';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2h(x: {a: number}): string {
+    return x && 'foo';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2i(x: Object): string {
+    return x && 'foo';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2j(x: (a: number) => number): string {
+    return x && 'foo';
+}
+
+/**
+ * A literal on the left side of &&
+ */
+function logical2k(x: Function): string {
+    return x && 'foo';
+}
+
+/**
+ * An expression on the left side of &&
+ */
+function logical3a(): string { // expected `: boolean`
+    var x: ?number = null;
+    return x != null && x > 10;
+}
+
+/**
+ * An expression on the left side of &&
+ */
+function logical3b(): number { // expected `: boolean | number`
+    var x: ?number = null;
+    return x != null && x;
+}
+
+/**
+ * An expression on the left side of &&
+ */
+function logical3c(): ?number { // expected `: boolean | ?number`
+    var x: ?number = null;
+    return x != undefined && x;
+}
+
+/**
+ * Maybe truthy returns both types
+ */
+function logical4(x: boolean): string { // expected `: boolean | string`
+    return x && '123';
+}
+
+/**
+ * A falsy variable on the left side of ||
+ */
+function logical5a(): number {
+    var x = false;
+    return x || 0;
+}
+
+/**
+ * A maybe variable on the left side of ||
+ */
+function logical5b(): number {
+    var x: ?number = null;
+    return x || 0;
+}
+
+/**
+ * A truthy variable on the left side of ||
+ */
+function logical5c(): string { // expected `: boolean`
+    var x = true;
+    return x || 0;
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6a(): string {
+    return false || '123';
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6b(): string {
+    return 0 || '123';
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6c(): number {
+    return "" || 123;
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6d(): number { // expected `: boolean`
+    return true || '123';
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6e(): string {
+    return 'foo' || 123;
+}
+
+/**
+ * A literal on the left side of ||
+ */
+function logical6f(): number {
+    return 123 || 'foo';
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7a(): number {
+    var x: ?number = null;
+    return x != null && x || 0;
+}
+
+/**
+ * A composite && and || where the truthiness is unknown
+ */
+function logical7b(x: boolean, y: number): number {
+    return x && y || 0;
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7c(x: string): number {
+    return x && 1 || 0;
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7d(x: number): string {
+    return x && 'foo' || 'bar';
+}
+
+/**
+ * A composite && and ||
+ */
+function logical7e(x: number): string {
+    return false && x || 'bar';
+}
+
+/**
+ * A composite || and &&
+ *
+ * `x || 0` always returns a number (never a boolean) and then short
+ * circuits the && because 0 is falsy, so this should just return number.
+ */
+function logical8a(): number {
+    var x = false;
+    return (x || 0) && 'foo';
+}
+
+/**
+ * A composite || and &&
+ *
+ * `x || 1` always returns something truthy, so this returns a string
+ */
+function logical8b(): string {
+    var x = false;
+    return (x || 1) && 'foo';
+}
+
+/**
+ * A composite || and &&
+ *
+ * `x` is always truthy, so this returns a string
+ */
+function logical8c(): string {
+    var x = true;
+    return (x || 1) && 'foo';
+}
+
+/**
+ * A composite || and &&
+ */
+function logical8d(): number {
+    var x = false;
+    return x || (0 && 'foo');
+}
+
+/**
+ * A composite || and &&
+ */
+function logical8e(): string {
+    var x = false;
+    return x || (1 && 'foo');
+}
+
+/**
+ * A composite || and &&
+ */
+function logical8f(): string { // expected `: boolean`
+    var x = true;
+    return x || (1 && 'foo');
+}
+
+/**
+ * A composite || and ||
+ */
+function logical9a(
+    x: number,
+    y: string
+): number | string { // expected `: number | string | boolean`
+    return x || y || false;
+}
+
+/**
+ * A composite || and ||
+ */
+function logical9b(x: number, y: string): number | string {
+    return false || x || y;
+}
+
+/**
+ * A composite || and ||
+ */
+function logical9c(x: number, y: boolean): string {
+    return 'a' || x || y;
+}
+
+/**
+ * A composite && and &&
+ */
+function logical10a(
+    x: number,
+    y: string
+): number | string { // expected `: number | string | boolean`
+    return x && y && false;
+}
+
+/**
+ * A composite && and &&
+ */
+function logical10b(x: number, y: string): Array<any> { // expected `: boolean`
+    return false && x && y;
+}
+
+/**
+ * A composite && and &&
+ */
+function logical10c(x: number, y: string): Array<any> { // expected `number | boolean`
+    return x && false && y;
+}
+
+/**
+ * || in a loop
+ */
+function logical11a(): number {
+    var y = 1;
+    for (var x = 0; x < 5; x++) {
+        y = y || true;
+    }
+    return y;
+}
+
+/**
+ * || in a loop
+ */
+function logical11b(y: number): number {
+    for (var x = 0; x < 5; x++) {
+        y = y || true; // expected a number
+    }
+    return y;
+}
+
+/**
+ * && in a loop
+ */
+function logical12a(): number {
+    var y = 1;
+    var z = true;
+    for (var x = 0; x < 5; x++) {
+        y = z && y;
+        z = false;
+    }
+    return y;
+}
+
+/**
+ * && in a loop
+ */
+function logical12b(y: number): number {
+    for (var x = 0; x < 5; x++) {
+        y = y && true; // expected a number
+    }
+    return y;
+}
+
+/**
+ * Complex &&
+ */
+function logical13(x: number): Array<{x: string}> {
+    return [
+        {x: x && "bar"},
+        {x: true && "bar"},
+        {x: true && false},
+        {x: false && false},
+        {x: 1 && "bar"},
+        {x: "foo" && "bar"},
+        {x: "foo" && "bar"},
+        {x: "foo" && "bar"},
+    ];
+}
+
+/**
+ * Complex ||
+ */
+function logical14(x: number): Array<{x: string}> {
+    return [
+        {x: x || "bar"},
+        {x: false || "bar"},
+        {x: false || true},
+        {x: true || false},
+        {x: 0 || "bar"},
+        {x: "foo" || "bar"},
+        {x: "foo" || "bar"},
+        {x: "foo" || "bar"},
+    ];
+}
+
+/**
+ * || in an addition
+ */
+function logical15a(x: number): number {
+    return 5 + (x || 7);
+}
+
+/**
+ * || in an addition
+ */
+function logical15b(x: number): number {
+    return (x || 7) + 5;
+}
+
+/**
+ * && in an addition
+ */
+function logical15c(x: number): number {
+    return 5 + (x && 7);
+}
+
+/**
+ * && in an addition
+ */
+function logical15d(x: number): number {
+    return (x && 7) + 5;
+}
+
+/**
+ * || in a comparison
+ */
+function logical16a(x: number): boolean {
+    return 5 < (x || 7);
+}
+
+/**
+ * || in a comparison
+ */
+function logical16b(x: number): boolean {
+    return (x || 7) < 5;
+}
+
+/**
+ * && in a comparison
+ */
+function logical16c(x: number): boolean {
+    return 5 < (x && 7);
+}
+
+/**
+ * && in a comparison
+ */
+function logical16d(x: number): boolean {
+    return (x && 7) < 5;
+}
+
+/**
+ * || in an equality
+ */
+function logical17a(x: number): boolean {
+    return 5 == (x || 7);
+}
+
+/**
+ * || in an equality
+ */
+function logical17b(x: number): boolean {
+    return (x || 7) == 5;
+}
+
+/**
+ * && in an equality
+ */
+function logical17c(x: number): boolean {
+    return 5 == (x && 7);
+}
+
+/**
+ * && in an equality
+ */
+function logical17d(x: number): boolean {
+    return (x && 7) == 5;
+}
+
+/**
+ * Expressions on each side that return truthy things
+ */
+function logical18a(x: number, y: number): number {
+    return x - 1 || y - 1;
+}
+
+/**
+ * Sentinel properties should not interfere
+ */
+function logical18b(x: {a: number}, y: {b: number}): number {
+    return x.a - 1 || y.b - 1;
+}
+
+/**
+ * Layer of indirection in the LHS (get prop)
+ */
+function logical19a(x: { y: string, z: boolean }): boolean {
+  return (x.y && x.z); // error: x.y is a string
+}
+function logical19b(x: { y: string, z: boolean }): boolean {
+  return (x.y || x.z); // error: x.y is a string
+}
diff --git a/tests/loners/__snapshots__/jsfmt.spec.js.snap b/tests/loners/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..515a6f93b424
--- /dev/null
+++ b/tests/loners/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,28 @@
+exports[`test loners.js 1`] = `
+"var o = { x: 5, y: \"jello\" };
+var z = o.z;
+var export_o: { x: number; } = o;
+
+function f(u,v?):number { return u; }
+var export_f: (u: number) => number = f;
+
+//exports = export_o;
+module.exports = export_f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/loners/jsfmt.spec.js b/tests/loners/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/loners/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/loners/loners.js b/tests/loners/loners.js
new file mode 100644
index 000000000000..291e2a8398a6
--- /dev/null
+++ b/tests/loners/loners.js
@@ -0,0 +1,9 @@
+var o = { x: 5, y: "jello" };
+var z = o.z;
+var export_o: { x: number; } = o;
+
+function f(u,v?):number { return u; }
+var export_f: (u: number) => number = f;
+
+//exports = export_o;
+module.exports = export_f;
diff --git a/tests/method_properties/__snapshots__/jsfmt.spec.js.snap b/tests/method_properties/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a4401005ba39
--- /dev/null
+++ b/tests/method_properties/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,74 @@
+exports[`test exports_optional_prop.js 1`] = `
+"// @flow
+
+declare class Foo {
+  bar?: () => string
+}
+
+export {Foo};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"class C {
+  C() { }
+  foo() { }
+  static bar() { }
+  qux() { this.constructor.x; }
+}
+C.x;
+(new C).foo.x;
+C.bar.x;
+
+import {Foo} from \'./exports_optional_prop\';
+const foo = new Foo();
+(foo.bar(): string); // error, could be undefined
+
+function f(x) {
+  (x.bar(): string); // error. caused by \`f(foo)\`; annotate x to track it down.
+}
+f(foo);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  C() {
+    
+  }
+  foo() {
+    
+  }
+  bar() {
+    
+  }
+  qux() {
+    this.constructor.x;
+  }
+}
+C.x;
+new C().foo.x;
+C.bar.x;
+import { Foo } from \"./exports_optional_prop\";
+const foo = new Foo();
+(foo.bar(): string);// error, could be undefined
+function f(x) {
+  (x.bar(): string);// error. caused by \`f(foo)\`; annotate x to track it down.
+}
+f(foo);
+
+"
+`;
diff --git a/tests/method_properties/exports_optional_prop.js b/tests/method_properties/exports_optional_prop.js
new file mode 100644
index 000000000000..b1eedca746eb
--- /dev/null
+++ b/tests/method_properties/exports_optional_prop.js
@@ -0,0 +1,7 @@
+// @flow
+
+declare class Foo {
+  bar?: () => string
+}
+
+export {Foo};
diff --git a/tests/method_properties/jsfmt.spec.js b/tests/method_properties/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/method_properties/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/method_properties/test.js b/tests/method_properties/test.js
new file mode 100644
index 000000000000..85fa157985ee
--- /dev/null
+++ b/tests/method_properties/test.js
@@ -0,0 +1,18 @@
+class C {
+  C() { }
+  foo() { }
+  static bar() { }
+  qux() { this.constructor.x; }
+}
+C.x;
+(new C).foo.x;
+C.bar.x;
+
+import {Foo} from './exports_optional_prop';
+const foo = new Foo();
+(foo.bar(): string); // error, could be undefined
+
+function f(x) {
+  (x.bar(): string); // error. caused by `f(foo)`; annotate x to track it down.
+}
+f(foo);
diff --git a/tests/misc/A.js b/tests/misc/A.js
new file mode 100644
index 000000000000..4e79aacb8bcf
--- /dev/null
+++ b/tests/misc/A.js
@@ -0,0 +1,14 @@
+
+/* @providesModule A */
+
+module.exports = {};
+
+var A = {x:true, ...{}};
+module.exports.cls = A;
+
+function f(x:boolean) { }
+module.exports.fn = f;
+
+A.y = "?";
+A.x = A.y;
+f(A.x); // A.x is now a string, by def assign
diff --git a/tests/misc/B.js b/tests/misc/B.js
new file mode 100644
index 000000000000..aa0fdbe1e8fe
--- /dev/null
+++ b/tests/misc/B.js
@@ -0,0 +1,15 @@
+
+/* @providesModule B */
+
+var A = require('A').cls;
+
+function B() {
+  this.b = "...";
+}
+
+function f():number { return this.b; }
+
+B.prototype.s = 0;
+B.prototype.fn = f;
+
+module.exports = B;
diff --git a/tests/misc/C.js b/tests/misc/C.js
new file mode 100644
index 000000000000..b882007e2382
--- /dev/null
+++ b/tests/misc/C.js
@@ -0,0 +1,14 @@
+
+/* @providesModule C */
+
+var B = require('B');
+var f = require('A').fn;
+
+function C() {
+  var o = new B();
+  f(o.b);
+  f(o.s);
+  o.fn();
+}
+
+module.exports = C;
diff --git a/tests/misc/D.js b/tests/misc/D.js
new file mode 100644
index 000000000000..1caac58291a1
--- /dev/null
+++ b/tests/misc/D.js
@@ -0,0 +1,14 @@
+
+/* @providesModule D */
+
+var f = require('A').fn;
+
+function g():string { return this.i; }
+
+var o = {fn: g, ...{}};
+o.i = true;
+
+var i = o.fn();
+f(i);
+
+module.exports = "D for dummy";
diff --git a/tests/misc/E.js b/tests/misc/E.js
new file mode 100644
index 000000000000..eddef9ab0577
--- /dev/null
+++ b/tests/misc/E.js
@@ -0,0 +1,10 @@
+
+/* @providesModule E */
+
+function h(x:number) { }
+var proto = { fn: h }
+
+var o = Object.create(proto);
+o.fn(false);
+
+module.exports = {obj: o};
diff --git a/tests/misc/F.js b/tests/misc/F.js
new file mode 100644
index 000000000000..0e389f461181
--- /dev/null
+++ b/tests/misc/F.js
@@ -0,0 +1,6 @@
+function fn2(x) { return x.length * 4; }
+fn2({length: 'hi'});
+
+function foo(x: Array<number>): string {
+  return x.length;
+}
diff --git a/tests/misc/G.js b/tests/misc/G.js
new file mode 100644
index 000000000000..d27c2932240f
--- /dev/null
+++ b/tests/misc/G.js
@@ -0,0 +1,7 @@
+var a = { length: "duck" };
+a.length = 123;
+a.length();
+
+var b = [ 123 ];
+b.length = "duck";
+b.length();
diff --git a/tests/misc/__snapshots__/jsfmt.spec.js.snap b/tests/misc/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6e97a6f0692a
--- /dev/null
+++ b/tests/misc/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,191 @@
+exports[`test A.js 1`] = `
+"
+/* @providesModule A */
+
+module.exports = {};
+
+var A = {x:true, ...{}};
+module.exports.cls = A;
+
+function f(x:boolean) { }
+module.exports.fn = f;
+
+A.y = \"?\";
+A.x = A.y;
+f(A.x); // A.x is now a string, by def assign
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule A */
+module.exports = {};
+var A = { x: true, ...{} };
+module.exports.cls = A;
+function f(x: boolean) {
+  
+}
+module.exports.fn = f;
+A.y = \"?\";
+A.x = A.y;
+f(A.x);// A.x is now a string, by def assign
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"
+/* @providesModule B */
+
+var A = require(\'A\').cls;
+
+function B() {
+  this.b = \"...\";
+}
+
+function f():number { return this.b; }
+
+B.prototype.s = 0;
+B.prototype.fn = f;
+
+module.exports = B;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule B */
+var A = require(\"A\").cls;
+function B() {
+  this.b = \"...\";
+}
+function f(): number {
+  return this.b;
+}
+B.prototype.s = 0;
+B.prototype.fn = f;
+module.exports = B;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"
+/* @providesModule C */
+
+var B = require(\'B\');
+var f = require(\'A\').fn;
+
+function C() {
+  var o = new B();
+  f(o.b);
+  f(o.s);
+  o.fn();
+}
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule C */
+var B = require(\"B\");
+var f = require(\"A\").fn;
+function C() {
+  var o = new B();
+  f(o.b);
+  f(o.s);
+  o.fn();
+}
+module.exports = C;
+
+"
+`;
+
+exports[`test D.js 1`] = `
+"
+/* @providesModule D */
+
+var f = require(\'A\').fn;
+
+function g():string { return this.i; }
+
+var o = {fn: g, ...{}};
+o.i = true;
+
+var i = o.fn();
+f(i);
+
+module.exports = \"D for dummy\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule D */
+var f = require(\"A\").fn;
+function g(): string {
+  return this.i;
+}
+var o = { fn: g, ...{} };
+o.i = true;
+var i = o.fn();
+f(i);
+module.exports = \"D for dummy\";
+
+"
+`;
+
+exports[`test E.js 1`] = `
+"
+/* @providesModule E */
+
+function h(x:number) { }
+var proto = { fn: h }
+
+var o = Object.create(proto);
+o.fn(false);
+
+module.exports = {obj: o};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule E */
+function h(x: number) {
+  
+}
+var proto = { fn: h };
+var o = Object.create(proto);
+o.fn(false);
+module.exports = { obj: o };
+
+"
+`;
+
+exports[`test F.js 1`] = `
+"function fn2(x) { return x.length * 4; }
+fn2({length: \'hi\'});
+
+function foo(x: Array<number>): string {
+  return x.length;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test G.js 1`] = `
+"var a = { length: \"duck\" };
+a.length = 123;
+a.length();
+
+var b = [ 123 ];
+b.length = \"duck\";
+b.length();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var a = { length: \"duck\" };
+a.length = 123;
+a.length();
+var b = [ 123 ];
+b.length = \"duck\";
+b.length();
+
+"
+`;
diff --git a/tests/misc/jsfmt.spec.js b/tests/misc/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/misc/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/missing_annotation/__snapshots__/jsfmt.spec.js.snap b/tests/missing_annotation/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9bb7d0b1529a
--- /dev/null
+++ b/tests/missing_annotation/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,107 @@
+exports[`test array.js 1`] = `
+"// @flow
+
+type Foo = {};
+var f: Foo = {};
+export var arr = [f];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type Foo = {};
+var f: Foo = {};
+export var arr = [ f ];
+
+"
+`;
+
+exports[`test async_return.js 1`] = `
+"// @flow
+
+export async function foo() {
+  return 123;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export async function foo() {
+  return 123;
+}
+
+"
+`;
+
+exports[`test infer.js 1`] = `
+"/* @flow */
+
+var Foo = {
+  a: function(arg) {  // missing arg annotation
+    return arg;
+  },
+
+  b: function(arg) {  // missing arg annotation
+    return {
+      bar: arg
+    };
+  },
+
+  c: function(arg: string) {  // no return annotation required
+    return {
+      bar: arg
+    };
+  },
+
+  d: function(arg: string): {
+    bar: string
+  } {
+    return {
+      bar: arg
+    };
+  },
+
+  // return type annotation may be omitted, but if so, input positions on
+  // observed return type (e.g. param types in a function type) must come
+  // from annotations
+  e: function(arg: string) {
+    return function(x) {  // missing param annotation
+      return x;
+    }
+  },
+
+  // ...if the return type is annotated explicitly, this is unnecessary
+  f: function(arg: string): (x:number) => number {
+    return function(x) {  // no error
+      return x;
+    }
+  }
+
+};
+
+var Bar = {
+  a: Foo.a(\'Foo\'),    // no annotation required
+
+  // object property types are inferred, so make sure that this doesn\'t cause
+  // us to also infer the parameter\'s type.
+  b: Foo.b(\'bar\'),    // no annotation required
+
+  c: Foo.c(\'bar\'),            // no annotation required
+
+  d: Foo.d(\'bar\'),            // no annotation required
+};
+
+module.exports = Foo, Bar;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/missing_annotation/array.js b/tests/missing_annotation/array.js
new file mode 100644
index 000000000000..4c90d239d23d
--- /dev/null
+++ b/tests/missing_annotation/array.js
@@ -0,0 +1,5 @@
+// @flow
+
+type Foo = {};
+var f: Foo = {};
+export var arr = [f];
diff --git a/tests/missing_annotation/async_return.js b/tests/missing_annotation/async_return.js
new file mode 100644
index 000000000000..1d533f773651
--- /dev/null
+++ b/tests/missing_annotation/async_return.js
@@ -0,0 +1,5 @@
+// @flow
+
+export async function foo() {
+  return 123;
+}
diff --git a/tests/missing_annotation/infer.js b/tests/missing_annotation/infer.js
new file mode 100644
index 000000000000..d3827d4e03ff
--- /dev/null
+++ b/tests/missing_annotation/infer.js
@@ -0,0 +1,58 @@
+/* @flow */
+
+var Foo = {
+  a: function(arg) {  // missing arg annotation
+    return arg;
+  },
+
+  b: function(arg) {  // missing arg annotation
+    return {
+      bar: arg
+    };
+  },
+
+  c: function(arg: string) {  // no return annotation required
+    return {
+      bar: arg
+    };
+  },
+
+  d: function(arg: string): {
+    bar: string
+  } {
+    return {
+      bar: arg
+    };
+  },
+
+  // return type annotation may be omitted, but if so, input positions on
+  // observed return type (e.g. param types in a function type) must come
+  // from annotations
+  e: function(arg: string) {
+    return function(x) {  // missing param annotation
+      return x;
+    }
+  },
+
+  // ...if the return type is annotated explicitly, this is unnecessary
+  f: function(arg: string): (x:number) => number {
+    return function(x) {  // no error
+      return x;
+    }
+  }
+
+};
+
+var Bar = {
+  a: Foo.a('Foo'),    // no annotation required
+
+  // object property types are inferred, so make sure that this doesn't cause
+  // us to also infer the parameter's type.
+  b: Foo.b('bar'),    // no annotation required
+
+  c: Foo.c('bar'),            // no annotation required
+
+  d: Foo.d('bar'),            // no annotation required
+};
+
+module.exports = Foo, Bar;
diff --git a/tests/missing_annotation/jsfmt.spec.js b/tests/missing_annotation/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/missing_annotation/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/modified_lib/__snapshots__/jsfmt.spec.js.snap b/tests/modified_lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..eabf387fb4aa
--- /dev/null
+++ b/tests/modified_lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,13 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+import {bar} from 'foo';
+
+bar(5);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { bar } from "foo";
+bar(5);
+
+"
+`;
diff --git a/tests/modified_lib/jsfmt.spec.js b/tests/modified_lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/modified_lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/modified_lib/lib/__snapshots__/jsfmt.spec.js.snap b/tests/modified_lib/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..83927dd4b0ac
--- /dev/null
+++ b/tests/modified_lib/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test lib.js 1`] = `
+"declare module \'foo\' {
+  declare function bar(str: string): number;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/modified_lib/lib/jsfmt.spec.js b/tests/modified_lib/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/modified_lib/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/modified_lib/lib/lib.js b/tests/modified_lib/lib/lib.js
new file mode 100644
index 000000000000..fcb3b4a27b45
--- /dev/null
+++ b/tests/modified_lib/lib/lib.js
@@ -0,0 +1,3 @@
+declare module 'foo' {
+  declare function bar(str: string): number;
+}
diff --git a/tests/modified_lib/test.js b/tests/modified_lib/test.js
new file mode 100644
index 000000000000..d889dc83ca19
--- /dev/null
+++ b/tests/modified_lib/test.js
@@ -0,0 +1,5 @@
+// @flow
+
+import {bar} from 'foo';
+
+bar(5);
diff --git a/tests/module_not_found_errors/src/__snapshots__/jsfmt.spec.js.snap b/tests/module_not_found_errors/src/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7ec34361073b
--- /dev/null
+++ b/tests/module_not_found_errors/src/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test index.js 1`] = `
+"// @flow
+
+require('module_completely_absent');
+
+// node_modules/module_outside_of_root/ sits outside of the Flow project root.
+// Flow should give a descriptive error about this
+require('module_outside_of_root');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+require("module_completely_absent");
+// node_modules/module_outside_of_root/ sits outside of the Flow project root.
+// Flow should give a descriptive error about this
+require("module_outside_of_root");
+
+"
+`;
diff --git a/tests/module_not_found_errors/src/index.js b/tests/module_not_found_errors/src/index.js
new file mode 100644
index 000000000000..f4e259cbbd87
--- /dev/null
+++ b/tests/module_not_found_errors/src/index.js
@@ -0,0 +1,7 @@
+// @flow
+
+require('module_completely_absent');
+
+// node_modules/module_outside_of_root/ sits outside of the Flow project root.
+// Flow should give a descriptive error about this
+require('module_outside_of_root');
diff --git a/tests/module_not_found_errors/src/jsfmt.spec.js b/tests/module_not_found_errors/src/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/module_not_found_errors/src/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/module_redirect/A.js b/tests/module_redirect/A.js
new file mode 100644
index 000000000000..d2f6a26c0d93
--- /dev/null
+++ b/tests/module_redirect/A.js
@@ -0,0 +1,3 @@
+declare module A {
+  declare function foo(): string;
+}
diff --git a/tests/module_redirect/B.js b/tests/module_redirect/B.js
new file mode 100644
index 000000000000..02b47f2182c0
--- /dev/null
+++ b/tests/module_redirect/B.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule B
+ * @flow
+ */
+
+module.exports = require('A');
diff --git a/tests/module_redirect/C.js b/tests/module_redirect/C.js
new file mode 100644
index 000000000000..04871ce2a640
--- /dev/null
+++ b/tests/module_redirect/C.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule C
+ * @flow
+ */
+
+module.exports = require('B');
diff --git a/tests/module_redirect/D.js b/tests/module_redirect/D.js
new file mode 100644
index 000000000000..dc166b39d33c
--- /dev/null
+++ b/tests/module_redirect/D.js
@@ -0,0 +1,8 @@
+/**
+ * @providesModule D
+ * @flow
+ */
+
+var bar1: string = require('A');
+var bar2: string = require('B');
+var bar3: string = require('C');
diff --git a/tests/module_redirect/__snapshots__/jsfmt.spec.js.snap b/tests/module_redirect/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5d49329b0caa
--- /dev/null
+++ b/tests/module_redirect/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,77 @@
+exports[`test A.js 1`] = `
+"declare module A {
+  declare function foo(): string;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test B.js 1`] = `
+"/**
+ * @providesModule B
+ * @flow
+ */
+
+module.exports = require(\'A\');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule B
+ * @flow
+ */
+module.exports = require(\"A\");
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"/**
+ * @providesModule C
+ * @flow
+ */
+
+module.exports = require(\'B\');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule C
+ * @flow
+ */
+module.exports = require(\"B\");
+
+"
+`;
+
+exports[`test D.js 1`] = `
+"/**
+ * @providesModule D
+ * @flow
+ */
+
+var bar1: string = require(\'A\');
+var bar2: string = require(\'B\');
+var bar3: string = require(\'C\');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule D
+ * @flow
+ */
+var bar1: string = require(\"A\");
+var bar2: string = require(\"B\");
+var bar3: string = require(\"C\");
+
+"
+`;
diff --git a/tests/module_redirect/jsfmt.spec.js b/tests/module_redirect/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/module_redirect/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/module_use_strict/__snapshots__/jsfmt.spec.js.snap b/tests/module_use_strict/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..dbd713f36296
--- /dev/null
+++ b/tests/module_use_strict/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+(01: number);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Invalid number (3:1)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.readNumber (/node_modules/babylon/lib/index.js:1180:12)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1020:21)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+"
+`;
diff --git a/tests/module_use_strict/jsfmt.spec.js b/tests/module_use_strict/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/module_use_strict/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/module_use_strict/test.js b/tests/module_use_strict/test.js
new file mode 100644
index 000000000000..9fcda932e9f9
--- /dev/null
+++ b/tests/module_use_strict/test.js
@@ -0,0 +1,3 @@
+// @flow
+
+(01: number);
diff --git a/tests/modules/__snapshots__/jsfmt.spec.js.snap b/tests/modules/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..748288f7203b
--- /dev/null
+++ b/tests/modules/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,53 @@
+exports[`test cli.js 1`] = `
+"/* @flow */
+
+var f = require('./lib');
+
+var y:number = f(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var f = require("./lib");
+var y: number = f(0);
+
+"
+`;
+
+exports[`test cli2.js 1`] = `
+"/* @flow */
+
+var f = require('./lib');
+
+f("...");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var f = require("./lib");
+f("...");
+
+"
+`;
+
+exports[`test lib.js 1`] = `
+"/* @flow */
+
+function g(x:string) { }
+
+//function f(x) { g(x); return x; }
+//function f(x:number) { g(x); return x; }
+function f(x:number):number { g(x); return x; }
+
+module.exports = f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function g(x: string) {
+  
+}
+//function f(x) { g(x); return x; }
+//function f(x:number) { g(x); return x; }
+function f(x: number): number {
+  g(x);
+  return x;
+}
+module.exports = f;
+
+"
+`;
diff --git a/tests/modules/cli.js b/tests/modules/cli.js
new file mode 100644
index 000000000000..5c3529d4b6d1
--- /dev/null
+++ b/tests/modules/cli.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+var f = require('./lib');
+
+var y:number = f(0);
diff --git a/tests/modules/cli2.js b/tests/modules/cli2.js
new file mode 100644
index 000000000000..f69b2cbe901e
--- /dev/null
+++ b/tests/modules/cli2.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+var f = require('./lib');
+
+f("...");
diff --git a/tests/modules/jsfmt.spec.js b/tests/modules/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/modules/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/modules/lib.js b/tests/modules/lib.js
new file mode 100644
index 000000000000..f37c923f472a
--- /dev/null
+++ b/tests/modules/lib.js
@@ -0,0 +1,9 @@
+/* @flow */
+
+function g(x:string) { }
+
+//function f(x) { g(x); return x; }
+//function f(x:number) { g(x); return x; }
+function f(x:number):number { g(x); return x; }
+
+module.exports = f;
diff --git a/tests/more_annot/__snapshots__/jsfmt.spec.js.snap b/tests/more_annot/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..eeb440765656
--- /dev/null
+++ b/tests/more_annot/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,81 @@
+exports[`test client_object.js 1`] = `
+"var o = require(\'./object\');
+
+var a:number = o.w.z.y;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = require(\"./object\");
+var a: number = o.w.z.y;
+
+"
+`;
+
+exports[`test object.js 1`] = `
+"var o1 = { x: 0, y: \"\" };
+var o2 = { z: o1 }
+
+var o3 = {};
+o3.w = o2;
+
+//declare var exports: { w: any };
+
+module.exports = o3;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o1 = { x: 0, y: \"\" };
+var o2 = { z: o1 };
+var o3 = {};
+o3.w = o2;
+//declare var exports: { w: any };
+module.exports = o3;
+
+"
+`;
+
+exports[`test proto.js 1`] = `
+"function Foo() { this.x = 0; }
+Foo.prototype.m = function() { }
+
+var o1: { x: number; m(): void } = new Foo();
+
+var o2: Foo = new Foo();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test super.js 1`] = `
+"class C { m() { } }
+class D extends C { }
+
+var d: { +m: () => void } = new D();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/more_annot/client_object.js b/tests/more_annot/client_object.js
new file mode 100644
index 000000000000..2a657fc3150a
--- /dev/null
+++ b/tests/more_annot/client_object.js
@@ -0,0 +1,3 @@
+var o = require('./object');
+
+var a:number = o.w.z.y;
diff --git a/tests/more_annot/jsfmt.spec.js b/tests/more_annot/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/more_annot/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/more_annot/object.js b/tests/more_annot/object.js
new file mode 100644
index 000000000000..db079d67aa3b
--- /dev/null
+++ b/tests/more_annot/object.js
@@ -0,0 +1,9 @@
+var o1 = { x: 0, y: "" };
+var o2 = { z: o1 }
+
+var o3 = {};
+o3.w = o2;
+
+//declare var exports: { w: any };
+
+module.exports = o3;
diff --git a/tests/more_annot/proto.js b/tests/more_annot/proto.js
new file mode 100644
index 000000000000..6baaa16ea640
--- /dev/null
+++ b/tests/more_annot/proto.js
@@ -0,0 +1,6 @@
+function Foo() { this.x = 0; }
+Foo.prototype.m = function() { }
+
+var o1: { x: number; m(): void } = new Foo();
+
+var o2: Foo = new Foo();
diff --git a/tests/more_annot/super.js b/tests/more_annot/super.js
new file mode 100644
index 000000000000..de7d6a2b30e4
--- /dev/null
+++ b/tests/more_annot/super.js
@@ -0,0 +1,4 @@
+class C { m() { } }
+class D extends C { }
+
+var d: { +m: () => void } = new D();
diff --git a/tests/more_classes/Bar.js b/tests/more_classes/Bar.js
new file mode 100644
index 000000000000..dc757801ca4a
--- /dev/null
+++ b/tests/more_classes/Bar.js
@@ -0,0 +1,20 @@
+
+/* @providesModule Bar */
+
+var Qux = require('Qux');
+
+class Bar {
+  y:number;
+  self:Bar;
+  constructor(y:number) {
+    this.y = y;
+    this.self = this;
+  }
+
+  bar(z:string,u:string):string {
+    new Qux().w = "?";
+    return z;
+  }
+}
+
+module.exports = Bar;
diff --git a/tests/more_classes/Foo.js b/tests/more_classes/Foo.js
new file mode 100644
index 000000000000..7def23ebcea1
--- /dev/null
+++ b/tests/more_classes/Foo.js
@@ -0,0 +1,26 @@
+
+/* @providesModule Foo */
+
+var Bar = require('Bar');
+var Qux = require('Qux');
+
+class Foo extends Qux {
+  x:string;
+  constructor(x:string) {
+    this.x = x;
+  }
+
+  foo(y:string,z):number {
+    this.x = y;
+    var u = new Foo("...").qux();
+    var v = new Bar(y);
+    v.self = v;
+    return v.bar(z,u);
+  }
+
+  fooqux(x:string) {
+    this.x;
+  }
+}
+
+module.exports = Foo;
diff --git a/tests/more_classes/Qux.js b/tests/more_classes/Qux.js
new file mode 100644
index 000000000000..dae3dfeb102d
--- /dev/null
+++ b/tests/more_classes/Qux.js
@@ -0,0 +1,12 @@
+
+/* @providesModule Qux */
+
+class Qux {
+  w:number;
+
+  qux() { return this.w; }
+
+  fooqux(x:number) { }
+}
+
+module.exports = Qux;
diff --git a/tests/more_classes/__snapshots__/jsfmt.spec.js.snap b/tests/more_classes/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c5442e72127e
--- /dev/null
+++ b/tests/more_classes/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,121 @@
+exports[`test Bar.js 1`] = `
+"
+/* @providesModule Bar */
+
+var Qux = require('Qux');
+
+class Bar {
+  y:number;
+  self:Bar;
+  constructor(y:number) {
+    this.y = y;
+    this.self = this;
+  }
+
+  bar(z:string,u:string):string {
+    new Qux().w = "?";
+    return z;
+  }
+}
+
+module.exports = Bar;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Bar */
+var Qux = require("Qux");
+class Bar {
+  y: number;
+  self: Bar;
+  constructor(y: number) {
+    this.y = y;
+    this.self = this;
+  }
+  bar(z: string, u: string): string {
+    new Qux().w = "?";
+    return z;
+  }
+}
+module.exports = Bar;
+
+"
+`;
+
+exports[`test Foo.js 1`] = `
+"
+/* @providesModule Foo */
+
+var Bar = require('Bar');
+var Qux = require('Qux');
+
+class Foo extends Qux {
+  x:string;
+  constructor(x:string) {
+    this.x = x;
+  }
+
+  foo(y:string,z):number {
+    this.x = y;
+    var u = new Foo("...").qux();
+    var v = new Bar(y);
+    v.self = v;
+    return v.bar(z,u);
+  }
+
+  fooqux(x:string) {
+    this.x;
+  }
+}
+
+module.exports = Foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Foo */
+var Bar = require("Bar");
+var Qux = require("Qux");
+class Foo extends Qux {
+  x: string;
+  constructor(x: string) {
+    this.x = x;
+  }
+  foo(y: string, z): number {
+    this.x = y;
+    var u = new Foo("...").qux();
+    var v = new Bar(y);
+    v.self = v;
+    return v.bar(z, u);
+  }
+  fooqux(x: string) {
+    this.x;
+  }
+}
+module.exports = Foo;
+
+"
+`;
+
+exports[`test Qux.js 1`] = `
+"
+/* @providesModule Qux */
+
+class Qux {
+  w:number;
+
+  qux() { return this.w; }
+
+  fooqux(x:number) { }
+}
+
+module.exports = Qux;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Qux */
+class Qux {
+  w: number;
+  qux() {
+    return this.w;
+  }
+  fooqux(x: number) {
+    
+  }
+}
+module.exports = Qux;
+
+"
+`;
diff --git a/tests/more_classes/jsfmt.spec.js b/tests/more_classes/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/more_classes/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/more_generics/__snapshots__/jsfmt.spec.js.snap b/tests/more_generics/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6d6ddfc3331d
--- /dev/null
+++ b/tests/more_generics/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,48 @@
+exports[`test poly.js 1`] = `
+"var foo1 = function<T>(x:T):T { return x; }
+
+function foo2<T,S>(x:T):S { return x; }
+
+var foo3 = function <T>(x:T):T { return foo3(x); }
+
+function foo4<T,S>(x:T):S { return foo4(x); }
+
+var x = [];
+function foo5<T>():Array<T> { return x; }
+/*
+ var a = foo5();
+ a[0] = 0;
+ var b = foo5();
+ var y: string = b[0];
+*/
+
+var foo6 = function<R>(x:R):R { return foo1(x); }
+
+function foo7<R>(x:R):R { return foo5(); }
+
+function foo8<U>(x:U,y):U {
+  var z = foo8(x,x);
+  y();
+  return x;
+}
+/*
+ foo8(0,void 0);
+*/
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/more_generics/jsfmt.spec.js b/tests/more_generics/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/more_generics/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/more_generics/poly.js b/tests/more_generics/poly.js
new file mode 100644
index 000000000000..dc0e5465bc93
--- /dev/null
+++ b/tests/more_generics/poly.js
@@ -0,0 +1,29 @@
+var foo1 = function<T>(x:T):T { return x; }
+
+function foo2<T,S>(x:T):S { return x; }
+
+var foo3 = function <T>(x:T):T { return foo3(x); }
+
+function foo4<T,S>(x:T):S { return foo4(x); }
+
+var x = [];
+function foo5<T>():Array<T> { return x; }
+/*
+ var a = foo5();
+ a[0] = 0;
+ var b = foo5();
+ var y: string = b[0];
+*/
+
+var foo6 = function<R>(x:R):R { return foo1(x); }
+
+function foo7<R>(x:R):R { return foo5(); }
+
+function foo8<U>(x:U,y):U {
+  var z = foo8(x,x);
+  y();
+  return x;
+}
+/*
+ foo8(0,void 0);
+*/
diff --git a/tests/more_path/Condition.js b/tests/more_path/Condition.js
new file mode 100644
index 000000000000..3fbf99d6f1ff
--- /dev/null
+++ b/tests/more_path/Condition.js
@@ -0,0 +1,57 @@
+/* @providesModule Condition */
+
+function f(x:number) { }
+function g() { return (42 || "hello"); }
+
+var x = g();
+if (typeof x === "string") {
+  x = 0;
+}
+f(x);
+
+class A {}
+function h() { return (42 || new A()); }
+
+var y = h();
+if (y instanceof A) {
+  y = 0;
+}
+//f(y);
+
+function bar() { return true; }
+
+class C { qux() { } }
+
+function foo() {
+
+  var c = "...";
+  c = new C();
+  if (bar()) {
+    c.qux();
+  }
+
+}
+
+function goofy() {
+  var x = g();
+  if (typeof x == 'function') {
+    x();
+  } else { // if (typeof x == 'number') {
+    //f(x);
+  }
+}
+
+function goofy2() {
+  var o = {x : 0}
+  if (typeof o.x == 'function') {
+    o.x();
+  }
+  var y = o.x;
+  if (typeof y == 'function') {
+    y();
+  } else {
+    //f(y);
+  }
+}
+
+module.exports = true;
diff --git a/tests/more_path/FlowSA.js b/tests/more_path/FlowSA.js
new file mode 100644
index 000000000000..51aa51ff367a
--- /dev/null
+++ b/tests/more_path/FlowSA.js
@@ -0,0 +1,12 @@
+
+/* @providesModule FlowSA */
+
+function check(x:string) { }
+
+function FlowSA() {
+  var x = 0;
+  x = "...";
+  check(x);
+}
+
+module.exports = FlowSA;
diff --git a/tests/more_path/Sigma.js b/tests/more_path/Sigma.js
new file mode 100644
index 000000000000..c5c871de1e29
--- /dev/null
+++ b/tests/more_path/Sigma.js
@@ -0,0 +1,40 @@
+
+/* @providesModule Sigma */
+
+class A { a() {} }
+
+class B extends A { b() {} }
+
+class C extends B { c() {} }
+
+function bar(x:B) {
+  if (x instanceof A) {
+    x.a();
+    x.c(); // error
+  } else {
+    x++; // TODO no error? since unreachable (x: B implies x: A)
+  }
+}
+
+function foo(x:A) {
+  if (x instanceof C) {
+    x.a();
+    x.b();
+    x.c();
+    x.d(); // error
+  } else {
+    x.a();
+    x.c(); // error
+  }
+}
+
+
+class D { d() {} }
+
+function baz(x:D) {
+  if (x instanceof A) {
+    // unreachable, TODO: this shouldn't throw
+  }
+}
+
+module.exports = "sigma";
diff --git a/tests/more_path/__snapshots__/jsfmt.spec.js.snap b/tests/more_path/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..882f81ebf68b
--- /dev/null
+++ b/tests/more_path/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,271 @@
+exports[`test Condition.js 1`] = `
+"/* @providesModule Condition */
+
+function f(x:number) { }
+function g() { return (42 || "hello"); }
+
+var x = g();
+if (typeof x === "string") {
+  x = 0;
+}
+f(x);
+
+class A {}
+function h() { return (42 || new A()); }
+
+var y = h();
+if (y instanceof A) {
+  y = 0;
+}
+//f(y);
+
+function bar() { return true; }
+
+class C { qux() { } }
+
+function foo() {
+
+  var c = "...";
+  c = new C();
+  if (bar()) {
+    c.qux();
+  }
+
+}
+
+function goofy() {
+  var x = g();
+  if (typeof x == 'function') {
+    x();
+  } else { // if (typeof x == 'number') {
+    //f(x);
+  }
+}
+
+function goofy2() {
+  var o = {x : 0}
+  if (typeof o.x == 'function') {
+    o.x();
+  }
+  var y = o.x;
+  if (typeof y == 'function') {
+    y();
+  } else {
+    //f(y);
+  }
+}
+
+module.exports = true;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Condition */
+function f(x: number) {
+  
+}
+function g() {
+  return 42 || "hello";
+}
+var x = g();
+if (typeof x === "string") {
+  x = 0;
+}
+f(x);
+class A {}
+function h() {
+  return 42 || new A();
+}
+var y = h();
+if (y instanceof A) {
+  y = 0;
+}
+//f(y);
+function bar() {
+  return true;
+}
+class C {
+  qux() {
+    
+  }
+}
+function foo() {
+  var c = "...";
+  c = new C();
+  if (bar()) {
+    c.qux();
+  }
+}
+function goofy() {
+  var x = g();
+  if (typeof x == "function") {
+    x();
+  } else {
+    
+  }
+}
+function goofy2() {
+  var o = { x: 0 };
+  if (typeof o.x == "function") {
+    o.x();
+  }
+  var y = o.x;
+  if (typeof y == "function") {
+    y();
+  } else {
+    
+  }
+}
+module.exports = true;
+
+"
+`;
+
+exports[`test FlowSA.js 1`] = `
+"
+/* @providesModule FlowSA */
+
+function check(x:string) { }
+
+function FlowSA() {
+  var x = 0;
+  x = "...";
+  check(x);
+}
+
+module.exports = FlowSA;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule FlowSA */
+function check(x: string) {
+  
+}
+function FlowSA() {
+  var x = 0;
+  x = "...";
+  check(x);
+}
+module.exports = FlowSA;
+
+"
+`;
+
+exports[`test Sigma.js 1`] = `
+"
+/* @providesModule Sigma */
+
+class A { a() {} }
+
+class B extends A { b() {} }
+
+class C extends B { c() {} }
+
+function bar(x:B) {
+  if (x instanceof A) {
+    x.a();
+    x.c(); // error
+  } else {
+    x++; // TODO no error? since unreachable (x: B implies x: A)
+  }
+}
+
+function foo(x:A) {
+  if (x instanceof C) {
+    x.a();
+    x.b();
+    x.c();
+    x.d(); // error
+  } else {
+    x.a();
+    x.c(); // error
+  }
+}
+
+
+class D { d() {} }
+
+function baz(x:D) {
+  if (x instanceof A) {
+    // unreachable, TODO: this shouldn't throw
+  }
+}
+
+module.exports = "sigma";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Sigma */
+class A {
+  a() {
+    
+  }
+}
+class B extends A {
+  b() {
+    
+  }
+}
+class C extends B {
+  c() {
+    
+  }
+}
+function bar(x: B) {
+  if (x instanceof A) {
+    x.a();
+    x.c();// error
+  } else {
+    x++;// TODO no error? since unreachable (x: B implies x: A)
+  }
+}
+function foo(x: A) {
+  if (x instanceof C) {
+    x.a();
+    x.b();
+    x.c();
+    x.d();// error
+  } else {
+    x.a();
+    x.c();// error
+  }
+}
+class D {
+  d() {
+    
+  }
+}
+function baz(x: D) {
+  if (x instanceof A) {
+    
+  }
+}
+module.exports = "sigma";
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"class BaseClass {
+  baseProp: string;
+}
+
+class ChildClass extends BaseClass {
+  childProp: string;
+}
+
+function test(obj: BaseClass): string {
+  if (obj instanceof ChildClass) {
+    return obj.childProp_TYPO; // error (obj: ChildClass)
+  }
+  return obj.baseProp;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class BaseClass {
+  baseProp: string;
+}
+class ChildClass extends BaseClass {
+  childProp: string;
+}
+function test(obj: BaseClass): string {
+  if (obj instanceof ChildClass) {
+    return obj.childProp_TYPO;// error (obj: ChildClass)
+  }
+  return obj.baseProp;
+}
+
+"
+`;
diff --git a/tests/more_path/jsfmt.spec.js b/tests/more_path/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/more_path/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/more_path/test.js b/tests/more_path/test.js
new file mode 100644
index 000000000000..e54e1def4d8d
--- /dev/null
+++ b/tests/more_path/test.js
@@ -0,0 +1,14 @@
+class BaseClass {
+  baseProp: string;
+}
+
+class ChildClass extends BaseClass {
+  childProp: string;
+}
+
+function test(obj: BaseClass): string {
+  if (obj instanceof ChildClass) {
+    return obj.childProp_TYPO; // error (obj: ChildClass)
+  }
+  return obj.baseProp;
+}
diff --git a/tests/more_react/API.react.js b/tests/more_react/API.react.js
new file mode 100644
index 000000000000..1cb0cafd8bcd
--- /dev/null
+++ b/tests/more_react/API.react.js
@@ -0,0 +1,8 @@
+
+var app = require('JSX');
+
+app.setProps({y:42}); // error, y:number but foo expects string in App.react
+app.setState({z:42}); // error, z:number but foo expects string in App.react
+
+function bar(x:number) { }
+bar(app.props.children); // No error, App doesn't specify propTypes so anything goes
diff --git a/tests/more_react/App.react.js b/tests/more_react/App.react.js
new file mode 100644
index 000000000000..9121b661cd2b
--- /dev/null
+++ b/tests/more_react/App.react.js
@@ -0,0 +1,43 @@
+
+/**
+ * @providesModule App.react
+ * @jsx React.DOM
+ */
+
+var React = require('react');
+
+// expect args to be strings
+function foo(p:string,q:string):string { return p+q; }
+
+var App = React.createClass({
+
+  getDefaultProps: function(): { y: string } {
+    return {y:""}; // infer props.y: string
+  },
+
+  getInitialState: function() {
+    return {z:0}; // infer state.z: number
+  },
+
+  handler: function() {
+    this.setState({z:42}); // ok
+  },
+
+  render: function() {
+    var x = this.props.x;
+    var y = this.props.y;
+    var z = this.state.z;
+
+    //this.state;
+
+    return (
+      <div>
+        {foo(x,y)}
+        {foo(z,x)} // error, since z: number
+      </div>
+    );
+  }
+
+});
+
+module.exports = App;
diff --git a/tests/more_react/JSX.js b/tests/more_react/JSX.js
new file mode 100644
index 000000000000..68a256f9c3e7
--- /dev/null
+++ b/tests/more_react/JSX.js
@@ -0,0 +1,12 @@
+
+/* @providesModule JSX */
+
+var React = require('react');
+var App = require('App.react');
+
+var app =
+  <App y={42}> // error, y: number but foo expects string in App.react
+    Some text.
+  </App>;
+
+module.exports = app;
diff --git a/tests/more_react/__snapshots__/jsfmt.spec.js.snap b/tests/more_react/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d749aeba2738
--- /dev/null
+++ b/tests/more_react/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,160 @@
+exports[`test API.react.js 1`] = `
+"
+var app = require('JSX');
+
+app.setProps({y:42}); // error, y:number but foo expects string in App.react
+app.setState({z:42}); // error, z:number but foo expects string in App.react
+
+function bar(x:number) { }
+bar(app.props.children); // No error, App doesn't specify propTypes so anything goes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var app = require("JSX");
+app.setProps({ y: 42 });// error, y:number but foo expects string in App.react
+app.setState({ z: 42 });// error, z:number but foo expects string in App.react
+function bar(x: number) {
+  
+}
+bar(
+  app.props.children
+);// No error, App doesn't specify propTypes so anything goes
+
+"
+`;
+
+exports[`test App.react.js 1`] = `
+"
+/**
+ * @providesModule App.react
+ * @jsx React.DOM
+ */
+
+var React = require('react');
+
+// expect args to be strings
+function foo(p:string,q:string):string { return p+q; }
+
+var App = React.createClass({
+
+  getDefaultProps: function(): { y: string } {
+    return {y:""}; // infer props.y: string
+  },
+
+  getInitialState: function() {
+    return {z:0}; // infer state.z: number
+  },
+
+  handler: function() {
+    this.setState({z:42}); // ok
+  },
+
+  render: function() {
+    var x = this.props.x;
+    var y = this.props.y;
+    var z = this.state.z;
+
+    //this.state;
+
+    return (
+      <div>
+        {foo(x,y)}
+        {foo(z,x)} // error, since z: number
+      </div>
+    );
+  }
+
+});
+
+module.exports = App;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule App.react
+ * @jsx React.DOM
+ */
+var React = require("react");
+// expect args to be strings
+function foo(p: string, q: string): string {
+  return p + q;
+}
+var App = React.createClass({
+  getDefaultProps: function(): { y: string } {
+    return { y: "" };// infer props.y: string
+  },
+  getInitialState: function() {
+    return { z: 0 };// infer state.z: number
+  },
+  handler: function() {
+    this.setState({ z: 42 });// ok
+  },
+  render: function() {
+    var x = this.props.x;
+    var y = this.props.y;
+    var z = this.state.z;
+    //this.state;
+    return (
+      <div>
+        {foo(x, y)}
+        {foo(z, x)}// error, since z: number</div>
+    );
+  }
+});
+module.exports = App;
+
+"
+`;
+
+exports[`test JSX.js 1`] = `
+"
+/* @providesModule JSX */
+
+var React = require('react');
+var App = require('App.react');
+
+var app =
+  <App y={42}> // error, y: number but foo expects string in App.react
+    Some text.
+  </App>;
+
+module.exports = app;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule JSX */
+var React = require("react");
+var App = require("App.react");
+var app = <App y={42}>// error, y: number but foo expects string in App.react[object Object]    Some text.</App>;
+module.exports = app;
+
+"
+`;
+
+exports[`test propTypes.js 1`] = `
+"var React = require('React');
+
+var C = React.createClass({
+  propTypes: {
+    title: React.PropTypes.string.isRequired,
+  }
+});
+var D = React.createClass({
+  propTypes: {
+    name: React.PropTypes.string.isRequired,
+    ...C.propTypes,
+  }
+});
+
+<D
+  namee='foo' // error (as usual)
+  titlee='bar' // OK (error ignored when spread is used)
+/>;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require("React");
+var C = React.createClass({
+  propTypes: { title: React.PropTypes.string.isRequired }
+});
+var D = React.createClass({
+  propTypes: { name: React.PropTypes.string.isRequired, ...C.propTypes }
+});
+<D // error (as usual)
+namee="foo" // OK (error ignored when spread is used)
+titlee="bar"/>;
+
+"
+`;
diff --git a/tests/more_react/jsfmt.spec.js b/tests/more_react/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/more_react/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/more_react/propTypes.js b/tests/more_react/propTypes.js
new file mode 100644
index 000000000000..3bb8a2a05f60
--- /dev/null
+++ b/tests/more_react/propTypes.js
@@ -0,0 +1,18 @@
+var React = require('React');
+
+var C = React.createClass({
+  propTypes: {
+    title: React.PropTypes.string.isRequired,
+  }
+});
+var D = React.createClass({
+  propTypes: {
+    name: React.PropTypes.string.isRequired,
+    ...C.propTypes,
+  }
+});
+
+<D
+  namee='foo' // error (as usual)
+  titlee='bar' // OK (error ignored when spread is used)
+/>;
diff --git a/tests/more_statics/__snapshots__/jsfmt.spec.js.snap b/tests/more_statics/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2496ab6a3ed1
--- /dev/null
+++ b/tests/more_statics/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test class_static.js 1`] = `
+"class B {
+    static foo(): string { return ""; }
+}
+
+class C extends B {
+    static bar(): string { return ""; }
+}
+
+var x: number = C.bar();
+var y: number = C.foo();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class B {
+  foo(): string {
+    return "";
+  }
+}
+class C extends B {
+  bar(): string {
+    return "";
+  }
+}
+var x: number = C.bar();
+var y: number = C.foo();
+
+"
+`;
diff --git a/tests/more_statics/class_static.js b/tests/more_statics/class_static.js
new file mode 100644
index 000000000000..b66fb6dd07d5
--- /dev/null
+++ b/tests/more_statics/class_static.js
@@ -0,0 +1,10 @@
+class B {
+    static foo(): string { return ""; }
+}
+
+class C extends B {
+    static bar(): string { return ""; }
+}
+
+var x: number = C.bar();
+var y: number = C.foo();
diff --git a/tests/more_statics/jsfmt.spec.js b/tests/more_statics/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/more_statics/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/name_prop/__snapshots__/jsfmt.spec.js.snap b/tests/name_prop/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..87c5c721291c
--- /dev/null
+++ b/tests/name_prop/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,34 @@
+exports[`test class.js 1`] = `
+"class A {}
+
+var test1 = A.bar; // Error bar doesn't exist
+var test2: string = A.name;
+var test3: number = A.name; // Error string ~> number
+
+var a = new A();
+var test4 = a.constructor.bar; // Error bar doesn't exist
+var test5: string = a.constructor.name;
+var test6: number = a.constructor.name; // Error string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {}
+var test1 = A.bar;// Error bar doesn't exist
+var test2: string = A.name;
+var test3: number = A.name;// Error string ~> number
+var a = new A();
+var test4 = a.constructor.bar;// Error bar doesn't exist
+var test5: string = a.constructor.name;
+var test6: number = a.constructor.name;// Error string ~> number
+
+"
+`;
+
+exports[`test function.js 1`] = `
+"/* TODO - we currently say that a function's statics are an AnyObjT and
+ * anything goes. When we start enforcing the statics properly, we'll need to
+ * know that .name exists
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/name_prop/class.js b/tests/name_prop/class.js
new file mode 100644
index 000000000000..0076d3e7af4c
--- /dev/null
+++ b/tests/name_prop/class.js
@@ -0,0 +1,10 @@
+class A {}
+
+var test1 = A.bar; // Error bar doesn't exist
+var test2: string = A.name;
+var test3: number = A.name; // Error string ~> number
+
+var a = new A();
+var test4 = a.constructor.bar; // Error bar doesn't exist
+var test5: string = a.constructor.name;
+var test6: number = a.constructor.name; // Error string ~> number
diff --git a/tests/name_prop/function.js b/tests/name_prop/function.js
new file mode 100644
index 000000000000..304356168f1b
--- /dev/null
+++ b/tests/name_prop/function.js
@@ -0,0 +1,4 @@
+/* TODO - we currently say that a function's statics are an AnyObjT and
+ * anything goes. When we start enforcing the statics properly, we'll need to
+ * know that .name exists
+ */
diff --git a/tests/name_prop/jsfmt.spec.js b/tests/name_prop/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/name_prop/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/namespace/__snapshots__/jsfmt.spec.js.snap b/tests/namespace/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6dc7580c8a6a
--- /dev/null
+++ b/tests/namespace/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,47 @@
+exports[`test client.js 1`] = `
+"var ns = require(\'./namespace\')
+
+var bar: string = ns.foo
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var ns = require(\"./namespace\");
+var bar: string = ns.foo;
+
+"
+`;
+
+exports[`test namespace.js 1`] = `
+"/*@flow*/// import type { T } from \'...\'
+type T = (x:number) => void;
+var f: T = function(x:string): void { }
+
+type Map<X,Y> = (x:X) => Y;
+
+function bar<U,V>(x:U, f:Map<U,V>): V {
+    return f(x);
+}
+
+var y:number = bar(0, x => \"\");
+
+type Seq = number | Array<Seq>;
+var s1:Seq = [0,[0]];
+var s2:Seq = [[\"\"]];
+
+module.exports = { foo: (\"\": number) };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/namespace/client.js b/tests/namespace/client.js
new file mode 100644
index 000000000000..9ce64259134b
--- /dev/null
+++ b/tests/namespace/client.js
@@ -0,0 +1,3 @@
+var ns = require('./namespace')
+
+var bar: string = ns.foo
diff --git a/tests/namespace/jsfmt.spec.js b/tests/namespace/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/namespace/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/namespace/namespace.js b/tests/namespace/namespace.js
new file mode 100644
index 000000000000..ab51ee36eae3
--- /dev/null
+++ b/tests/namespace/namespace.js
@@ -0,0 +1,17 @@
+/*@flow*/// import type { T } from '...'
+type T = (x:number) => void;
+var f: T = function(x:string): void { }
+
+type Map<X,Y> = (x:X) => Y;
+
+function bar<U,V>(x:U, f:Map<U,V>): V {
+    return f(x);
+}
+
+var y:number = bar(0, x => "");
+
+type Seq = number | Array<Seq>;
+var s1:Seq = [0,[0]];
+var s2:Seq = [[""]];
+
+module.exports = { foo: ("": number) };
diff --git a/tests/new_react/FeedUFI.react.js b/tests/new_react/FeedUFI.react.js
new file mode 100644
index 000000000000..3566747e36ce
--- /dev/null
+++ b/tests/new_react/FeedUFI.react.js
@@ -0,0 +1,42 @@
+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ *
+ * @providesModule FeedUFI.react
+ * @flow
+ */
+
+'use strict';
+
+var UFILikeCount = require('UFILikeCount.react');
+var React = require('react');
+
+var FeedUFI = React.createClass({
+  _renderLikeCount: function(
+      feedback: any
+  ) {
+    var props = {
+      className: "",
+      key: "",
+      feedback: {feedback},
+      permalink: "",
+    };
+    var ignored = <UFILikeCount {...props} />;
+    return (
+      <UFILikeCount
+        className=""
+        key=""
+        feedback={feedback}
+        permalink=""
+      />
+    );
+  },
+
+  render: function(): ?React.Element<any> {
+    return (
+      <div/>
+    );
+  }
+
+});
+
+module.exports = FeedUFI;
diff --git a/tests/new_react/Mixin.js b/tests/new_react/Mixin.js
new file mode 100644
index 000000000000..8a3aebf5bbba
--- /dev/null
+++ b/tests/new_react/Mixin.js
@@ -0,0 +1,4 @@
+/* @providesModule Mixin */
+module.exports = {
+    success: function() { }
+};
diff --git a/tests/new_react/UFILikeCount.react.js b/tests/new_react/UFILikeCount.react.js
new file mode 100644
index 000000000000..75cc89f20983
--- /dev/null
+++ b/tests/new_react/UFILikeCount.react.js
@@ -0,0 +1,23 @@
+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ *
+ * @providesModule UFILikeCount.react
+ * @flow
+ */
+
+'use strict';
+
+var React = require('react');
+
+var UFILikeCount = React.createClass({
+  propTypes: {
+    permalink: React.PropTypes.string,
+    feedback: React.PropTypes.object.isRequired
+  },
+
+  render: function(): ?React.Element<any> {
+    return <div/>;
+  }
+});
+
+module.exports = UFILikeCount;
diff --git a/tests/new_react/__snapshots__/jsfmt.spec.js.snap b/tests/new_react/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4db6b5d1e26e
--- /dev/null
+++ b/tests/new_react/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,845 @@
+exports[`test FeedUFI.react.js 1`] = `
+"/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ *
+ * @providesModule FeedUFI.react
+ * @flow
+ */
+
+\'use strict\';
+
+var UFILikeCount = require(\'UFILikeCount.react\');
+var React = require(\'react\');
+
+var FeedUFI = React.createClass({
+  _renderLikeCount: function(
+      feedback: any
+  ) {
+    var props = {
+      className: \"\",
+      key: \"\",
+      feedback: {feedback},
+      permalink: \"\",
+    };
+    var ignored = <UFILikeCount {...props} />;
+    return (
+      <UFILikeCount
+        className=\"\"
+        key=\"\"
+        feedback={feedback}
+        permalink=\"\"
+      />
+    );
+  },
+
+  render: function(): ?React.Element<any> {
+    return (
+      <div/>
+    );
+  }
+
+});
+
+module.exports = FeedUFI;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test Mixin.js 1`] = `
+"/* @providesModule Mixin */
+module.exports = {
+    success: function() { }
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Mixin */
+module.exports = {
+  success: function() {
+    
+  }
+};
+
+"
+`;
+
+exports[`test UFILikeCount.react.js 1`] = `
+"/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ *
+ * @providesModule UFILikeCount.react
+ * @flow
+ */
+
+\'use strict\';
+
+var React = require(\'react\');
+
+var UFILikeCount = React.createClass({
+  propTypes: {
+    permalink: React.PropTypes.string,
+    feedback: React.PropTypes.object.isRequired
+  },
+
+  render: function(): ?React.Element<any> {
+    return <div/>;
+  }
+});
+
+module.exports = UFILikeCount;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test bad_default_props.js 1`] = `
+"var React = require(\'React\');
+
+type T1 = { }
+type T2 = { x: number }
+type T3 = { x: number, y: number }
+
+class C1 extends React.Component<T1, T2, any> { // error
+}
+
+class C2 extends React.Component<void, T2, any> { // OK
+}
+
+// no need to add type arguments to React.Component
+class C3 extends React.Component { // OK
+  static defaultProps: T1;
+  props: T2;
+}
+
+class C4 extends React.Component { // OK, recommended
+  // no need to declare defaultProps unless necessary
+  props: T2;
+}
+
+class C5 extends React.Component<T2, T3, any> { // error
+}
+
+class C6 extends React.Component { // OK, recommended
+  static defaultProps: T2;
+  props: T3;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1180:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test classes.js 1`] = `
+"var React = require(\'React\');
+
+type DefaultProps = { };
+type Props = { x: number };
+type State = { y: number };
+
+class Foo extends React.Component {
+  props: Props;
+  state: State;
+  static defaultProps: DefaultProps;
+
+  is_mounted: boolean;
+
+  static bar(): void {}
+
+  qux(): void {
+    var _: string = this.props.x;
+  }
+
+  constructor(props) {
+    super(props);
+    this.state = { y: \"\" };
+  }
+
+  setState(o: { y_: string }): void { }
+
+  componentDidMount(): void {
+    this.is_mounted = true;
+  }
+
+  componentWillReceiveProps(
+    nextProps: Object,
+    nextContext: any
+  ): void {
+    this.qux();
+  }
+
+}
+
+Foo.defaultProps = 0;
+var foo: $jsx<number> = <Foo/>;
+
+Foo.bar();
+
+var FooLegacy = React.createClass({
+  is_mounted: (undefined: ?boolean),
+
+  propTypes: {
+    x: React.PropTypes.number.isRequired
+  },
+
+  getDefaultProps(): DefaultProps { return {} },
+
+  statics: {
+    bar(): void {}
+  },
+
+  qux(): void {
+    var _: string = this.props.x;
+  },
+
+  getInitialState(): { y: string } {
+    return { y: \"\" };
+  },
+
+  setState(o: { y_: string }): void { },
+
+  componentDidMount(): void {
+    this.is_mounted = true;
+  },
+
+  componentWillReceiveProps(
+    nextProps: Object,
+    nextContext: any
+  ): void {
+    this.qux();
+  },
+});
+
+FooLegacy.defaultProps = 0; // TODO: should be error
+var foo_legacy: $jsx<number> = <FooLegacy/>;
+
+FooLegacy.bar();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test import-react.js 1`] = `
+"/* @flow */
+
+// Testing local binding of React in all kinds of ways. The only reason this
+// might even be an issue is that internally, the use of JSX triggers an
+// implicit require(\'react\'), so any bugs in (1) interop of CJS require and ES6
+// import (2) module re-export, as used to redirect the module name \'React\' to
+// \'react\' might show up here.
+
+import React from \"react\";
+//import React from \"React\";
+//var React = require(\"react\");
+//var React = require(\"React\");
+
+class HelloMessage extends React.Component {
+  props: { name: string };
+}
+
+<HelloMessage name={007} />; // number ~/~> string error
+<HelloMessage name=\"Bond\" />; // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:5687
+          throw jsxError || err;
+          ^
+
+SyntaxError: Invalid number (18:20)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.readNumber (/node_modules/babylon/lib/index.js:1180:12)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1020:21)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.pp$8.jsxParseExpressionContainer (/node_modules/babylon/lib/index.js:6285:8)
+    at Parser.pp$8.jsxParseAttributeValue (/node_modules/babylon/lib/index.js:6241:19)
+"
+`;
+
+exports[`test new_react.js 1`] = `
+"var React = require(\'react\');
+var Mixin = require(\'Mixin\');
+var C = React.createClass({
+    mixins: [Mixin],
+    propTypes: {
+        x: React.PropTypes.string.isRequired,
+        y: React.PropTypes.array,
+        z: React.PropTypes.number
+    },
+    replaceProps(props: { }) { },
+
+    getDefaultProps(): { z: number } {
+        return { z: 0 };
+    },
+    getInitialState() { return 4; },
+    render() {
+        var foo: string = this.state;
+        var bar: string = this.props;
+        var qux: string = this.props.z;
+        var w:number = this.props.x;
+        this.props.y[0];
+        var len:number = this.props.x.length;
+        this.success();
+        return <div/>;
+    }
+
+})
+
+var element = <C x = {0}/>;
+var element_ = <C/>;
+
+var x: number = C.displayName;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"react\");
+var Mixin = require(\"Mixin\");
+var C = React.createClass({
+  mixins: [ Mixin ],
+  propTypes: {
+    x: React.PropTypes.string.isRequired,
+    y: React.PropTypes.array,
+    z: React.PropTypes.number
+  },
+  replaceProps(props: {}) {
+    
+  },
+  getDefaultProps(): { z: number } {
+    return { z: 0 };
+  },
+  getInitialState() {
+    return 4;
+  },
+  render() {
+    var foo: string = this.state;
+    var bar: string = this.props;
+    var qux: string = this.props.z;
+    var w: number = this.props.x;
+    this.props.y[0];
+    var len: number = this.props.x.length;
+    this.success();
+    return <div/>;
+  }
+});
+var element = <C x={0}/>;
+var element_ = <C/>;
+var x: number = C.displayName;
+
+"
+`;
+
+exports[`test propTypes.js 1`] = `
+"var React = require(\'react\');
+var PropTypes = React.PropTypes;
+
+var C = React.createClass({
+  propTypes: {
+    statistics: PropTypes.arrayOf(PropTypes.shape({
+      label: PropTypes.string.isRequired,
+      value: PropTypes.number,
+    })).isRequired,
+  }
+});
+
+<C statistics={[
+  {},
+  {label:\"\",value:undefined},
+]}/>; // error (label is required, value not required)
+
+var props: Array<{label: string, value?: number}> = [
+  {},
+  {label:\"\",value:undefined},
+]; // error (same as ^)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test props.js 1`] = `
+"var React = require(\'react\');
+var TestProps = React.createClass({
+
+    propTypes: {
+        x: React.PropTypes.string,
+        z: React.PropTypes.number
+    },
+
+    getDefaultProps: function() {
+        return {x: \'\', y: 0}
+    },
+
+    test: function() {
+        var a: number = this.props.x; // error
+        var b: string = this.props.y; // error
+        var c: string = this.props.z; // error
+    }
+});
+
+var element = <TestProps x={false} y={false} z={false} />; // 3 errors
+
+(element: $jsx<*>);
+(element: $jsx<TestProps>);
+var FooProps = React.createClass({
+    propTypes: { w: React.PropTypes.string.isRequired }
+});
+(element: $jsx<FooProps>);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test props2.js 1`] = `
+"var React = require(\'react\');
+var C = React.createClass({
+    propTypes: {
+        foo: React.PropTypes.string.isRequired,
+        bar: React.PropTypes.string.isRequired,
+    }
+});
+var D = React.createClass({
+    getInitialState: function(): { bar: number } {
+        return { bar: 0 };
+    },
+    render: function() {
+        var obj = { bar: 0 };
+        var s: string = this.state.bar;
+        return <C {...this.state} foo = {0} />;
+    }
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"react\");
+var C = React.createClass({
+  propTypes: {
+    foo: React.PropTypes.string.isRequired,
+    bar: React.PropTypes.string.isRequired
+  }
+});
+var D = React.createClass({
+  getInitialState: function(): { bar: number } {
+    return { bar: 0 };
+  },
+  render: function() {
+    var obj = { bar: 0 };
+    var s: string = this.state.bar;
+    return <C {...this.state} foo={0}/>;
+  }
+});
+
+"
+`;
+
+exports[`test props3.js 1`] = `
+"var React = require(\'react\');
+var TestProps = React.createClass({
+    // Do something illegal inside of propTypes and make sure Flow notices
+    propTypes: {
+      arr: React.PropTypes.array,
+      arr_rec: React.PropTypes.array.isRequired,
+      bool: React.PropTypes.bool,
+      bool_rec: React.PropTypes.bool.isRequired,
+      func: React.PropTypes.func,
+      func_rec: React.PropTypes.func.isRequired,
+      number: React.PropTypes.number,
+      number_rec: React.PropTypes.number.isRequired,
+      object: React.PropTypes.object,
+      object_rec: React.PropTypes.object.isRequired,
+      string: React.PropTypes.string,
+      string_rec: React.PropTypes.string.isRequired,
+
+      any: React.PropTypes.any,
+      any_rec: React.PropTypes.any.isRequired,
+      element: React.PropTypes.element,
+      element_rec: React.PropTypes.element.isRequired,
+      node: React.PropTypes.node,
+      node_rec: React.PropTypes.node.isRequired,
+
+      arrayOf: React.PropTypes.arrayOf(React.PropTypes.string),
+      arrayOf_rec: React.PropTypes.arrayOf(React.PropTypes.string).isRequired,
+      instanceOf: React.PropTypes.instanceOf(Object),
+      instanceOf_rec: React.PropTypes.instanceOf(Object).isRequired,
+      objectOf: React.PropTypes.objectOf(React.PropTypes.string),
+      objectOf_rec: React.PropTypes.objectOf(React.PropTypes.string).isRequired,
+      oneOf: React.PropTypes.oneOf([\"yes\", \"no\"]),
+      oneOf_rec: React.PropTypes.oneOf([\"yes\", \"no\"]).isRequired,
+      oneOfType: React.PropTypes.oneOfType(
+        [React.PropTypes.string, React.PropTypes.number]
+      ),
+      oneOfType_rec: React.PropTypes.oneOfType(
+        [React.PropTypes.string, React.PropTypes.number]
+      ).isRequired,
+      shape: React.PropTypes.shape({
+        foo: React.PropTypes.string,
+        bar: React.PropTypes.number,
+      }),
+      shape_rec: React.PropTypes.shape({
+        foo: React.PropTypes.string,
+        bar: React.PropTypes.number,
+      }).isRequired,
+
+      // And do something bad here
+      bad_one: React.PropTypes.imaginaryType,
+      bad_two: React.PropTypes.string.inRequired,
+    },
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"react\");
+var TestProps = React.createClass({
+  // Do something illegal inside of propTypes and make sure Flow notices
+  propTypes: {
+    arr: React.PropTypes.array,
+    arr_rec: React.PropTypes.array.isRequired,
+    bool: React.PropTypes.bool,
+    bool_rec: React.PropTypes.bool.isRequired,
+    func: React.PropTypes.func,
+    func_rec: React.PropTypes.func.isRequired,
+    number: React.PropTypes.number,
+    number_rec: React.PropTypes.number.isRequired,
+    object: React.PropTypes.object,
+    object_rec: React.PropTypes.object.isRequired,
+    string: React.PropTypes.string,
+    string_rec: React.PropTypes.string.isRequired,
+    any: React.PropTypes.any,
+    any_rec: React.PropTypes.any.isRequired,
+    element: React.PropTypes.element,
+    element_rec: React.PropTypes.element.isRequired,
+    node: React.PropTypes.node,
+    node_rec: React.PropTypes.node.isRequired,
+    arrayOf: React.PropTypes.arrayOf(React.PropTypes.string),
+    arrayOf_rec: React.PropTypes.arrayOf(React.PropTypes.string).isRequired,
+    instanceOf: React.PropTypes.instanceOf(Object),
+    instanceOf_rec: React.PropTypes.instanceOf(Object).isRequired,
+    objectOf: React.PropTypes.objectOf(React.PropTypes.string),
+    objectOf_rec: React.PropTypes.objectOf(React.PropTypes.string).isRequired,
+    oneOf: React.PropTypes.oneOf([ \"yes\", \"no\" ]),
+    oneOf_rec: React.PropTypes.oneOf([ \"yes\", \"no\" ]).isRequired,
+    oneOfType: React.PropTypes.oneOfType(
+      [ React.PropTypes.string, React.PropTypes.number ]
+    ),
+    oneOfType_rec: React.PropTypes.oneOfType(
+      [ React.PropTypes.string, React.PropTypes.number ]
+    ).isRequired,
+    shape: React.PropTypes.shape({
+      foo: React.PropTypes.string,
+      bar: React.PropTypes.number
+    }),
+    shape_rec: React.PropTypes.shape({
+      foo: React.PropTypes.string,
+      bar: React.PropTypes.number
+    }).isRequired,
+    // And do something bad here bad_one: React.PropTypes.imaginaryType,
+    bad_two: React.PropTypes.string.inRequired
+  }
+});
+
+"
+`;
+
+exports[`test props4.js 1`] = `
+"// @flow
+
+import React from \"React\";
+
+class JDiv extends React.Component {
+  // static defaultProps: { };
+  props: {
+    id: string
+  };
+}
+
+// Should be a type error (\'id\' takes a string, not a number..)
+<JDiv id={42} />;
+
+class Example extends React.Component {
+  props: { bar: string };
+
+  render() {
+    return <div>{this.props.bar}</div>
+  }
+}
+
+React.render(
+  <Example foo=\"foo\" />,
+  document.body
+);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import React from \"React\";
+class JDiv extends React.Component {
+  // static defaultProps: { };
+  props: { id: string };
+}
+// Should be a type error (\'id\' takes a string, not a number..)
+<JDiv id={42}/>;
+class Example extends React.Component {
+  props: { bar: string };
+  render() {
+    return <div>{this.props.bar}</div>;
+  }
+}
+React.render(<Example foo=\"foo\"/>, document.body);
+
+"
+`;
+
+exports[`test props5.js 1`] = `
+"var React = require(\'React\');
+
+var C = React.createClass({
+  getDefaultProps: function() {
+    return { x: 0 };
+  }
+});
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"React\");
+var C = React.createClass({
+  getDefaultProps: function() {
+    return { x: 0 };
+  }
+});
+module.exports = C;
+
+"
+`;
+
+exports[`test state.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+
+type State = {
+    bar: ?{ qux: string; };
+};
+
+var ReactClass = React.createClass({
+    getInitialState: function():State {
+        return { bar: null };
+    },
+
+    render: function(): any {
+        // Any state access here seems to make state any
+        this.state;
+        return (
+        <div>
+                {this.state.bar.qux}
+        </div>
+        );
+    }
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+type State = { bar: ?{ qux: string } };
+var ReactClass = React.createClass({
+  getInitialState: function(): State {
+    return { bar: null };
+  },
+  render: function(): any {
+    // Any state access here seems to make state any
+    this.state;
+    return (
+      <div>
+        {this.state.bar.qux}
+      </div>
+    );
+  }
+});
+
+"
+`;
+
+exports[`test state2.js 1`] = `
+"// @flow
+
+var React = require(\'react\');
+
+type FooState = {
+    key: ?Object;
+};
+
+var Comp = React.createClass({
+    getInitialState: function(): FooState {
+        return {
+            key: null, // this used to cause a missing annotation error
+        };
+    }
+});
+
+module.exports = Comp;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var React = require(\"react\");
+type FooState = { key: ?Object };
+var Comp = React.createClass({
+  getInitialState: function(): FooState {
+    return { // this used to cause a missing annotation error key: null };
+  }
+});
+module.exports = Comp;
+
+"
+`;
+
+exports[`test state3.js 1`] = `
+"var React = require(\'react\');
+var TestState = React.createClass({
+
+    getInitialState: function(): { x: string; } {
+        return {
+            x: \'\'
+        }
+    },
+
+    test: function() {
+        var a: number = this.state.x; // error
+
+        this.setState({
+            x: false // error
+        })
+    }
+
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"react\");
+var TestState = React.createClass({
+  getInitialState: function(): { x: string } {
+    return { x: \"\" };
+  },
+  test: function() {
+    var a: number = this.state.x;// error
+    this.setState({ // error x: false });
+  }
+});
+
+"
+`;
+
+exports[`test state4.js 1`] = `
+"var React = require(\'React\');
+
+var C = React.createClass({
+  getInitialState: function() {
+    return { x: 0 };
+  },
+
+  render() {
+    this.setState({ y: 0 });
+    return <div>{this.state.z}</div>
+  }
+
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"React\");
+var C = React.createClass({
+  getInitialState: function() {
+    return { x: 0 };
+  },
+  render() {
+    this.setState({ y: 0 });
+    return <div>{this.state.z}</div>;
+  }
+});
+
+"
+`;
+
+exports[`test state5.js 1`] = `
+"var React = require(\'React\');
+
+class C extends React.Component {
+  foo(): number {
+    return this.state.x; // error: need to declare type of state
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require(\"React\");
+class C extends React.Component {
+  foo(): number {
+    return this.state.x;// error: need to declare type of state
+  }
+}
+
+"
+`;
diff --git a/tests/new_react/bad_default_props.js b/tests/new_react/bad_default_props.js
new file mode 100644
index 000000000000..9dd3159f431a
--- /dev/null
+++ b/tests/new_react/bad_default_props.js
@@ -0,0 +1,30 @@
+var React = require('React');
+
+type T1 = { }
+type T2 = { x: number }
+type T3 = { x: number, y: number }
+
+class C1 extends React.Component<T1, T2, any> { // error
+}
+
+class C2 extends React.Component<void, T2, any> { // OK
+}
+
+// no need to add type arguments to React.Component
+class C3 extends React.Component { // OK
+  static defaultProps: T1;
+  props: T2;
+}
+
+class C4 extends React.Component { // OK, recommended
+  // no need to declare defaultProps unless necessary
+  props: T2;
+}
+
+class C5 extends React.Component<T2, T3, any> { // error
+}
+
+class C6 extends React.Component { // OK, recommended
+  static defaultProps: T2;
+  props: T3;
+}
diff --git a/tests/new_react/classes.js b/tests/new_react/classes.js
new file mode 100644
index 000000000000..7574a00af3b7
--- /dev/null
+++ b/tests/new_react/classes.js
@@ -0,0 +1,83 @@
+var React = require('React');
+
+type DefaultProps = { };
+type Props = { x: number };
+type State = { y: number };
+
+class Foo extends React.Component {
+  props: Props;
+  state: State;
+  static defaultProps: DefaultProps;
+
+  is_mounted: boolean;
+
+  static bar(): void {}
+
+  qux(): void {
+    var _: string = this.props.x;
+  }
+
+  constructor(props) {
+    super(props);
+    this.state = { y: "" };
+  }
+
+  setState(o: { y_: string }): void { }
+
+  componentDidMount(): void {
+    this.is_mounted = true;
+  }
+
+  componentWillReceiveProps(
+    nextProps: Object,
+    nextContext: any
+  ): void {
+    this.qux();
+  }
+
+}
+
+Foo.defaultProps = 0;
+var foo: $jsx<number> = <Foo/>;
+
+Foo.bar();
+
+var FooLegacy = React.createClass({
+  is_mounted: (undefined: ?boolean),
+
+  propTypes: {
+    x: React.PropTypes.number.isRequired
+  },
+
+  getDefaultProps(): DefaultProps { return {} },
+
+  statics: {
+    bar(): void {}
+  },
+
+  qux(): void {
+    var _: string = this.props.x;
+  },
+
+  getInitialState(): { y: string } {
+    return { y: "" };
+  },
+
+  setState(o: { y_: string }): void { },
+
+  componentDidMount(): void {
+    this.is_mounted = true;
+  },
+
+  componentWillReceiveProps(
+    nextProps: Object,
+    nextContext: any
+  ): void {
+    this.qux();
+  },
+});
+
+FooLegacy.defaultProps = 0; // TODO: should be error
+var foo_legacy: $jsx<number> = <FooLegacy/>;
+
+FooLegacy.bar();
diff --git a/tests/new_react/fakelib/__snapshots__/jsfmt.spec.js.snap b/tests/new_react/fakelib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4a9d5f412fd7
--- /dev/null
+++ b/tests/new_react/fakelib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test type_aliases.js 1`] = `
+"declare var $React: $Exports<\'react\'>; // fake import
+// Strawman: revised definition of $jsx (alternatively, React.Element).
+// Using bounded poly to specify a constraint on a type parameter, and
+// existentials to elide type arguments.
+type _ReactElement<DefaultProps, Props, Config: $Diff<Props, DefaultProps>, C: $React.Component<DefaultProps, Props, any>> = $React.Element<Config>;
+type $jsx<C> = _ReactElement<*, *, *, C>;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/new_react/fakelib/jsfmt.spec.js b/tests/new_react/fakelib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/new_react/fakelib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/new_react/fakelib/type_aliases.js b/tests/new_react/fakelib/type_aliases.js
new file mode 100644
index 000000000000..864772039b5c
--- /dev/null
+++ b/tests/new_react/fakelib/type_aliases.js
@@ -0,0 +1,6 @@
+declare var $React: $Exports<'react'>; // fake import
+// Strawman: revised definition of $jsx (alternatively, React.Element).
+// Using bounded poly to specify a constraint on a type parameter, and
+// existentials to elide type arguments.
+type _ReactElement<DefaultProps, Props, Config: $Diff<Props, DefaultProps>, C: $React.Component<DefaultProps, Props, any>> = $React.Element<Config>;
+type $jsx<C> = _ReactElement<*, *, *, C>;
diff --git a/tests/new_react/import-react.js b/tests/new_react/import-react.js
new file mode 100644
index 000000000000..f4fda4d77d95
--- /dev/null
+++ b/tests/new_react/import-react.js
@@ -0,0 +1,19 @@
+/* @flow */
+
+// Testing local binding of React in all kinds of ways. The only reason this
+// might even be an issue is that internally, the use of JSX triggers an
+// implicit require('react'), so any bugs in (1) interop of CJS require and ES6
+// import (2) module re-export, as used to redirect the module name 'React' to
+// 'react' might show up here.
+
+import React from "react";
+//import React from "React";
+//var React = require("react");
+//var React = require("React");
+
+class HelloMessage extends React.Component {
+  props: { name: string };
+}
+
+<HelloMessage name={007} />; // number ~/~> string error
+<HelloMessage name="Bond" />; // ok
diff --git a/tests/new_react/jsfmt.spec.js b/tests/new_react/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/new_react/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/new_react/new_react.js b/tests/new_react/new_react.js
new file mode 100644
index 000000000000..70444d1cf288
--- /dev/null
+++ b/tests/new_react/new_react.js
@@ -0,0 +1,32 @@
+var React = require('react');
+var Mixin = require('Mixin');
+var C = React.createClass({
+    mixins: [Mixin],
+    propTypes: {
+        x: React.PropTypes.string.isRequired,
+        y: React.PropTypes.array,
+        z: React.PropTypes.number
+    },
+    replaceProps(props: { }) { },
+
+    getDefaultProps(): { z: number } {
+        return { z: 0 };
+    },
+    getInitialState() { return 4; },
+    render() {
+        var foo: string = this.state;
+        var bar: string = this.props;
+        var qux: string = this.props.z;
+        var w:number = this.props.x;
+        this.props.y[0];
+        var len:number = this.props.x.length;
+        this.success();
+        return <div/>;
+    }
+
+})
+
+var element = <C x = {0}/>;
+var element_ = <C/>;
+
+var x: number = C.displayName;
diff --git a/tests/new_react/propTypes.js b/tests/new_react/propTypes.js
new file mode 100644
index 000000000000..2acaef6fafcf
--- /dev/null
+++ b/tests/new_react/propTypes.js
@@ -0,0 +1,21 @@
+var React = require('react');
+var PropTypes = React.PropTypes;
+
+var C = React.createClass({
+  propTypes: {
+    statistics: PropTypes.arrayOf(PropTypes.shape({
+      label: PropTypes.string.isRequired,
+      value: PropTypes.number,
+    })).isRequired,
+  }
+});
+
+<C statistics={[
+  {},
+  {label:"",value:undefined},
+]}/>; // error (label is required, value not required)
+
+var props: Array<{label: string, value?: number}> = [
+  {},
+  {label:"",value:undefined},
+]; // error (same as ^)
diff --git a/tests/new_react/props.js b/tests/new_react/props.js
new file mode 100644
index 000000000000..055d608ef2f3
--- /dev/null
+++ b/tests/new_react/props.js
@@ -0,0 +1,27 @@
+var React = require('react');
+var TestProps = React.createClass({
+
+    propTypes: {
+        x: React.PropTypes.string,
+        z: React.PropTypes.number
+    },
+
+    getDefaultProps: function() {
+        return {x: '', y: 0}
+    },
+
+    test: function() {
+        var a: number = this.props.x; // error
+        var b: string = this.props.y; // error
+        var c: string = this.props.z; // error
+    }
+});
+
+var element = <TestProps x={false} y={false} z={false} />; // 3 errors
+
+(element: $jsx<*>);
+(element: $jsx<TestProps>);
+var FooProps = React.createClass({
+    propTypes: { w: React.PropTypes.string.isRequired }
+});
+(element: $jsx<FooProps>);
diff --git a/tests/new_react/props2.js b/tests/new_react/props2.js
new file mode 100644
index 000000000000..6f8fd76c440f
--- /dev/null
+++ b/tests/new_react/props2.js
@@ -0,0 +1,17 @@
+var React = require('react');
+var C = React.createClass({
+    propTypes: {
+        foo: React.PropTypes.string.isRequired,
+        bar: React.PropTypes.string.isRequired,
+    }
+});
+var D = React.createClass({
+    getInitialState: function(): { bar: number } {
+        return { bar: 0 };
+    },
+    render: function() {
+        var obj = { bar: 0 };
+        var s: string = this.state.bar;
+        return <C {...this.state} foo = {0} />;
+    }
+});
diff --git a/tests/new_react/props3.js b/tests/new_react/props3.js
new file mode 100644
index 000000000000..169b85c9afc4
--- /dev/null
+++ b/tests/new_react/props3.js
@@ -0,0 +1,52 @@
+var React = require('react');
+var TestProps = React.createClass({
+    // Do something illegal inside of propTypes and make sure Flow notices
+    propTypes: {
+      arr: React.PropTypes.array,
+      arr_rec: React.PropTypes.array.isRequired,
+      bool: React.PropTypes.bool,
+      bool_rec: React.PropTypes.bool.isRequired,
+      func: React.PropTypes.func,
+      func_rec: React.PropTypes.func.isRequired,
+      number: React.PropTypes.number,
+      number_rec: React.PropTypes.number.isRequired,
+      object: React.PropTypes.object,
+      object_rec: React.PropTypes.object.isRequired,
+      string: React.PropTypes.string,
+      string_rec: React.PropTypes.string.isRequired,
+
+      any: React.PropTypes.any,
+      any_rec: React.PropTypes.any.isRequired,
+      element: React.PropTypes.element,
+      element_rec: React.PropTypes.element.isRequired,
+      node: React.PropTypes.node,
+      node_rec: React.PropTypes.node.isRequired,
+
+      arrayOf: React.PropTypes.arrayOf(React.PropTypes.string),
+      arrayOf_rec: React.PropTypes.arrayOf(React.PropTypes.string).isRequired,
+      instanceOf: React.PropTypes.instanceOf(Object),
+      instanceOf_rec: React.PropTypes.instanceOf(Object).isRequired,
+      objectOf: React.PropTypes.objectOf(React.PropTypes.string),
+      objectOf_rec: React.PropTypes.objectOf(React.PropTypes.string).isRequired,
+      oneOf: React.PropTypes.oneOf(["yes", "no"]),
+      oneOf_rec: React.PropTypes.oneOf(["yes", "no"]).isRequired,
+      oneOfType: React.PropTypes.oneOfType(
+        [React.PropTypes.string, React.PropTypes.number]
+      ),
+      oneOfType_rec: React.PropTypes.oneOfType(
+        [React.PropTypes.string, React.PropTypes.number]
+      ).isRequired,
+      shape: React.PropTypes.shape({
+        foo: React.PropTypes.string,
+        bar: React.PropTypes.number,
+      }),
+      shape_rec: React.PropTypes.shape({
+        foo: React.PropTypes.string,
+        bar: React.PropTypes.number,
+      }).isRequired,
+
+      // And do something bad here
+      bad_one: React.PropTypes.imaginaryType,
+      bad_two: React.PropTypes.string.inRequired,
+    },
+});
diff --git a/tests/new_react/props4.js b/tests/new_react/props4.js
new file mode 100644
index 000000000000..ba428355b20a
--- /dev/null
+++ b/tests/new_react/props4.js
@@ -0,0 +1,26 @@
+// @flow
+
+import React from "React";
+
+class JDiv extends React.Component {
+  // static defaultProps: { };
+  props: {
+    id: string
+  };
+}
+
+// Should be a type error ('id' takes a string, not a number..)
+<JDiv id={42} />;
+
+class Example extends React.Component {
+  props: { bar: string };
+
+  render() {
+    return <div>{this.props.bar}</div>
+  }
+}
+
+React.render(
+  <Example foo="foo" />,
+  document.body
+);
diff --git a/tests/new_react/props5.js b/tests/new_react/props5.js
new file mode 100644
index 000000000000..0e236158260a
--- /dev/null
+++ b/tests/new_react/props5.js
@@ -0,0 +1,9 @@
+var React = require('React');
+
+var C = React.createClass({
+  getDefaultProps: function() {
+    return { x: 0 };
+  }
+});
+
+module.exports = C;
diff --git a/tests/new_react/state.js b/tests/new_react/state.js
new file mode 100644
index 000000000000..aa3bac629751
--- /dev/null
+++ b/tests/new_react/state.js
@@ -0,0 +1,23 @@
+/* @flow */
+
+var React = require('react');
+
+type State = {
+    bar: ?{ qux: string; };
+};
+
+var ReactClass = React.createClass({
+    getInitialState: function():State {
+        return { bar: null };
+    },
+
+    render: function(): any {
+        // Any state access here seems to make state any
+        this.state;
+        return (
+        <div>
+                {this.state.bar.qux}
+        </div>
+        );
+    }
+});
diff --git a/tests/new_react/state2.js b/tests/new_react/state2.js
new file mode 100644
index 000000000000..213d7679f51e
--- /dev/null
+++ b/tests/new_react/state2.js
@@ -0,0 +1,17 @@
+// @flow
+
+var React = require('react');
+
+type FooState = {
+    key: ?Object;
+};
+
+var Comp = React.createClass({
+    getInitialState: function(): FooState {
+        return {
+            key: null, // this used to cause a missing annotation error
+        };
+    }
+});
+
+module.exports = Comp;
diff --git a/tests/new_react/state3.js b/tests/new_react/state3.js
new file mode 100644
index 000000000000..4b7541d604d4
--- /dev/null
+++ b/tests/new_react/state3.js
@@ -0,0 +1,18 @@
+var React = require('react');
+var TestState = React.createClass({
+
+    getInitialState: function(): { x: string; } {
+        return {
+            x: ''
+        }
+    },
+
+    test: function() {
+        var a: number = this.state.x; // error
+
+        this.setState({
+            x: false // error
+        })
+    }
+
+});
diff --git a/tests/new_react/state4.js b/tests/new_react/state4.js
new file mode 100644
index 000000000000..9b1ea8251736
--- /dev/null
+++ b/tests/new_react/state4.js
@@ -0,0 +1,13 @@
+var React = require('React');
+
+var C = React.createClass({
+  getInitialState: function() {
+    return { x: 0 };
+  },
+
+  render() {
+    this.setState({ y: 0 });
+    return <div>{this.state.z}</div>
+  }
+
+});
diff --git a/tests/new_react/state5.js b/tests/new_react/state5.js
new file mode 100644
index 000000000000..f14b3db25a1e
--- /dev/null
+++ b/tests/new_react/state5.js
@@ -0,0 +1,7 @@
+var React = require('React');
+
+class C extends React.Component {
+  foo(): number {
+    return this.state.x; // error: need to declare type of state
+  }
+}
diff --git a/tests/node_haste/__snapshots__/jsfmt.spec.js.snap b/tests/node_haste/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2794c8648aa9
--- /dev/null
+++ b/tests/node_haste/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test client.js 1`] = `
+"var md5 = require('./md5');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var md5 = require("./md5");
+
+"
+`;
+
+exports[`test md5.js 1`] = `
+"/* @providesModule md5 */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/node_haste/client.js b/tests/node_haste/client.js
new file mode 100644
index 000000000000..7c4f789d466a
--- /dev/null
+++ b/tests/node_haste/client.js
@@ -0,0 +1 @@
+var md5 = require('./md5');
diff --git a/tests/node_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap b/tests/node_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..af2f32ce6008
--- /dev/null
+++ b/tests/node_haste/external/_d3/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,6 @@
+exports[`test min.js 1`] = `
+"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/node_haste/external/_d3/jsfmt.spec.js b/tests/node_haste/external/_d3/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_haste/external/_d3/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_haste/external/_d3/min.js b/tests/node_haste/external/_d3/min.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/node_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap b/tests/node_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..86fe21ff2a9b
--- /dev/null
+++ b/tests/node_haste/foo/bar/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test client.js 1`] = `
+"var docblock = require('qux/docblock');
+var min = require('d3/min.js');
+var corge = require('qux/corge');
+
+// make sure we don't pick up non-header @providesModule
+// annotations - see node_modules/qux/docblock.js
+var unreachable = require('annotation');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var docblock = require("qux/docblock");
+var min = require("d3/min.js");
+var corge = require("qux/corge");
+// make sure we don't pick up non-header @providesModule
+// annotations - see node_modules/qux/docblock.js
+var unreachable = require("annotation");
+
+"
+`;
diff --git a/tests/node_haste/foo/bar/client.js b/tests/node_haste/foo/bar/client.js
new file mode 100644
index 000000000000..f77729c44c56
--- /dev/null
+++ b/tests/node_haste/foo/bar/client.js
@@ -0,0 +1,7 @@
+var docblock = require('qux/docblock');
+var min = require('d3/min.js');
+var corge = require('qux/corge');
+
+// make sure we don't pick up non-header @providesModule
+// annotations - see node_modules/qux/docblock.js
+var unreachable = require('annotation');
diff --git a/tests/node_haste/foo/bar/jsfmt.spec.js b/tests/node_haste/foo/bar/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_haste/foo/bar/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_haste/jsfmt.spec.js b/tests/node_haste/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_haste/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_haste/md5.js b/tests/node_haste/md5.js
new file mode 100644
index 000000000000..c358d72168a6
--- /dev/null
+++ b/tests/node_haste/md5.js
@@ -0,0 +1 @@
+/* @providesModule md5 */
diff --git a/tests/node_haste/ws/__snapshots__/jsfmt.spec.js.snap b/tests/node_haste/ws/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..72caaf084cb1
--- /dev/null
+++ b/tests/node_haste/ws/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,6 @@
+exports[`test index.js 1`] = `
+"~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/node_haste/ws/index.js b/tests/node_haste/ws/index.js
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/tests/node_haste/ws/jsfmt.spec.js b/tests/node_haste/ws/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_haste/ws/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_haste/ws/test/__snapshots__/jsfmt.spec.js.snap b/tests/node_haste/ws/test/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f54d0216ceb7
--- /dev/null
+++ b/tests/node_haste/ws/test/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test client.js 1`] = `
+"var ws = require('../');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var ws = require("../");
+
+"
+`;
diff --git a/tests/node_haste/ws/test/client.js b/tests/node_haste/ws/test/client.js
new file mode 100644
index 000000000000..2fb0ed6d4dfd
--- /dev/null
+++ b/tests/node_haste/ws/test/client.js
@@ -0,0 +1 @@
+var ws = require('../');
diff --git a/tests/node_haste/ws/test/jsfmt.spec.js b/tests/node_haste/ws/test/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_haste/ws/test/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_modules_with_symlinks/root/__snapshots__/jsfmt.spec.js.snap b/tests/node_modules_with_symlinks/root/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b2745f3910e8
--- /dev/null
+++ b/tests/node_modules_with_symlinks/root/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,13 @@
+exports[`test foo.js 1`] = `
+"var x = require('symlink_lib');
+var y = require('symlink_lib_outside_root');
+console.log(x);
+console.log(y);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("symlink_lib");
+var y = require("symlink_lib_outside_root");
+console.log(x);
+console.log(y);
+
+"
+`;
diff --git a/tests/node_modules_with_symlinks/root/foo.js b/tests/node_modules_with_symlinks/root/foo.js
new file mode 100644
index 000000000000..a281d0aade1d
--- /dev/null
+++ b/tests/node_modules_with_symlinks/root/foo.js
@@ -0,0 +1,4 @@
+var x = require('symlink_lib');
+var y = require('symlink_lib_outside_root');
+console.log(x);
+console.log(y);
diff --git a/tests/node_modules_with_symlinks/root/jsfmt.spec.js b/tests/node_modules_with_symlinks/root/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_modules_with_symlinks/root/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_modules_with_symlinks/root/symlink_lib/__snapshots__/jsfmt.spec.js.snap b/tests/node_modules_with_symlinks/root/symlink_lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9ccacc6e6df6
--- /dev/null
+++ b/tests/node_modules_with_symlinks/root/symlink_lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test index.js 1`] = `
+"module.exports = { bar: "bar" };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = { bar: "bar" };
+
+"
+`;
diff --git a/tests/node_modules_with_symlinks/root/symlink_lib/index.js b/tests/node_modules_with_symlinks/root/symlink_lib/index.js
new file mode 100644
index 000000000000..206c5837e74d
--- /dev/null
+++ b/tests/node_modules_with_symlinks/root/symlink_lib/index.js
@@ -0,0 +1 @@
+module.exports = { bar: "bar" };
diff --git a/tests/node_modules_with_symlinks/root/symlink_lib/jsfmt.spec.js b/tests/node_modules_with_symlinks/root/symlink_lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_modules_with_symlinks/root/symlink_lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_modules_with_symlinks/symlink_lib_outside_root/__snapshots__/jsfmt.spec.js.snap b/tests/node_modules_with_symlinks/symlink_lib_outside_root/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9ccacc6e6df6
--- /dev/null
+++ b/tests/node_modules_with_symlinks/symlink_lib_outside_root/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test index.js 1`] = `
+"module.exports = { bar: "bar" };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = { bar: "bar" };
+
+"
+`;
diff --git a/tests/node_modules_with_symlinks/symlink_lib_outside_root/index.js b/tests/node_modules_with_symlinks/symlink_lib_outside_root/index.js
new file mode 100644
index 000000000000..206c5837e74d
--- /dev/null
+++ b/tests/node_modules_with_symlinks/symlink_lib_outside_root/index.js
@@ -0,0 +1 @@
+module.exports = { bar: "bar" };
diff --git a/tests/node_modules_with_symlinks/symlink_lib_outside_root/jsfmt.spec.js b/tests/node_modules_with_symlinks/symlink_lib_outside_root/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_modules_with_symlinks/symlink_lib_outside_root/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_modules_without_json/__snapshots__/jsfmt.spec.js.snap b/tests/node_modules_without_json/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9b9f9ace19db
--- /dev/null
+++ b/tests/node_modules_without_json/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+let foo = require('foo');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let foo = require("foo");
+
+"
+`;
diff --git a/tests/node_modules_without_json/jsfmt.spec.js b/tests/node_modules_without_json/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_modules_without_json/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_modules_without_json/test.js b/tests/node_modules_without_json/test.js
new file mode 100644
index 000000000000..0929d36bbcdb
--- /dev/null
+++ b/tests/node_modules_without_json/test.js
@@ -0,0 +1,3 @@
+// @flow
+
+let foo = require('foo');
diff --git a/tests/node_tests/assert/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/assert/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..917ce8adb7d3
--- /dev/null
+++ b/tests/node_tests/assert/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,14 @@
+exports[`test assert.js 1`] = `
+"/* @flow */
+
+var assert = require("assert")
+assert(true) // ok
+assert.ok(true) // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var assert = require("assert");
+assert(true);// ok
+assert.ok(true);// ok
+
+"
+`;
diff --git a/tests/node_tests/assert/assert.js b/tests/node_tests/assert/assert.js
new file mode 100644
index 000000000000..cc8f9feeffdd
--- /dev/null
+++ b/tests/node_tests/assert/assert.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+var assert = require("assert")
+assert(true) // ok
+assert.ok(true) // ok
diff --git a/tests/node_tests/assert/jsfmt.spec.js b/tests/node_tests/assert/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/assert/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/basic/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/basic/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..cd7e6db3e4d9
--- /dev/null
+++ b/tests/node_tests/basic/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test bar.js 1`] = `
+"module.exports = "bar";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = "bar";
+
+"
+`;
+
+exports[`test foo.js 1`] = `
+"var x = require('./bar.js');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("./bar.js");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/basic/bar.js b/tests/node_tests/basic/bar.js
new file mode 100644
index 000000000000..a7f281456cc7
--- /dev/null
+++ b/tests/node_tests/basic/bar.js
@@ -0,0 +1 @@
+module.exports = "bar";
diff --git a/tests/node_tests/basic/foo.js b/tests/node_tests/basic/foo.js
new file mode 100644
index 000000000000..cebd25bedbde
--- /dev/null
+++ b/tests/node_tests/basic/foo.js
@@ -0,0 +1,2 @@
+var x = require('./bar.js');
+console.log(x);
diff --git a/tests/node_tests/basic/jsfmt.spec.js b/tests/node_tests/basic/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/basic/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/basic_file/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/basic_file/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b4a5902fad5e
--- /dev/null
+++ b/tests/node_tests/basic_file/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test bar.js 1`] = `
+"module.exports = "bar";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = "bar";
+
+"
+`;
+
+exports[`test foo.js 1`] = `
+"var x = require('./bar'); // bar.js does not work
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("./bar");// bar.js does not work
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/basic_file/bar.js b/tests/node_tests/basic_file/bar.js
new file mode 100644
index 000000000000..a7f281456cc7
--- /dev/null
+++ b/tests/node_tests/basic_file/bar.js
@@ -0,0 +1 @@
+module.exports = "bar";
diff --git a/tests/node_tests/basic_file/foo.js b/tests/node_tests/basic_file/foo.js
new file mode 100644
index 000000000000..93cbf0128dbf
--- /dev/null
+++ b/tests/node_tests/basic_file/foo.js
@@ -0,0 +1,2 @@
+var x = require('./bar'); // bar.js does not work
+console.log(x);
diff --git a/tests/node_tests/basic_file/jsfmt.spec.js b/tests/node_tests/basic_file/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/basic_file/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/basic_node_modules/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/basic_node_modules/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..677c14aba703
--- /dev/null
+++ b/tests/node_tests/basic_node_modules/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('bar.js');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("bar.js");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/basic_node_modules/foo.js b/tests/node_tests/basic_node_modules/foo.js
new file mode 100644
index 000000000000..8f06577c8d27
--- /dev/null
+++ b/tests/node_tests/basic_node_modules/foo.js
@@ -0,0 +1,2 @@
+var x = require('bar.js');
+console.log(x);
diff --git a/tests/node_tests/basic_node_modules/jsfmt.spec.js b/tests/node_tests/basic_node_modules/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/basic_node_modules/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/basic_node_modules_with_path/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/basic_node_modules_with_path/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a17a80ce4244
--- /dev/null
+++ b/tests/node_tests/basic_node_modules_with_path/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('bar_lib/bar');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("bar_lib/bar");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/basic_node_modules_with_path/foo.js b/tests/node_tests/basic_node_modules_with_path/foo.js
new file mode 100644
index 000000000000..ba511e6ca239
--- /dev/null
+++ b/tests/node_tests/basic_node_modules_with_path/foo.js
@@ -0,0 +1,2 @@
+var x = require('bar_lib/bar');
+console.log(x);
diff --git a/tests/node_tests/basic_node_modules_with_path/jsfmt.spec.js b/tests/node_tests/basic_node_modules_with_path/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/basic_node_modules_with_path/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/basic_package/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/basic_package/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..02758dca30b4
--- /dev/null
+++ b/tests/node_tests/basic_package/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('./bar_lib'); // 'bar_lib' does not work!
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("./bar_lib");// 'bar_lib' does not work!
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/basic_package/bar_lib/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/basic_package/bar_lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..23901fc4ada1
--- /dev/null
+++ b/tests/node_tests/basic_package/bar_lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test bar.js 1`] = `
+"module.exports = "bar";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = "bar";
+
+"
+`;
diff --git a/tests/node_tests/basic_package/bar_lib/bar.js b/tests/node_tests/basic_package/bar_lib/bar.js
new file mode 100644
index 000000000000..a7f281456cc7
--- /dev/null
+++ b/tests/node_tests/basic_package/bar_lib/bar.js
@@ -0,0 +1 @@
+module.exports = "bar";
diff --git a/tests/node_tests/basic_package/bar_lib/jsfmt.spec.js b/tests/node_tests/basic_package/bar_lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/basic_package/bar_lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/basic_package/foo.js b/tests/node_tests/basic_package/foo.js
new file mode 100644
index 000000000000..11c0d1d81528
--- /dev/null
+++ b/tests/node_tests/basic_package/foo.js
@@ -0,0 +1,2 @@
+var x = require('./bar_lib'); // 'bar_lib' does not work!
+console.log(x);
diff --git a/tests/node_tests/basic_package/jsfmt.spec.js b/tests/node_tests/basic_package/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/basic_package/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/buffer/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/buffer/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a5d8d12edbc7
--- /dev/null
+++ b/tests/node_tests/buffer/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,76 @@
+exports[`test buffer.js 1`] = `
+"/* @flow */
+
+let bool: boolean = false;
+let buffer: Buffer = new Buffer(0);
+let num: number = 0;
+let maybeNum: ?number;
+
+// Uint8Array properties. All of these should type check ok.
+buffer.length;
+buffer.buffer;
+buffer.byteOffset;
+buffer.byteLength;
+buffer[1];
+
+// A few Uint8Array instance methods. All of these should type check ok.
+buffer.copyWithin(0, 0);
+buffer.copyWithin(0, 0, 0);
+
+const it1: Iterator<[number, number]> = buffer.entries();
+
+bool = buffer.every((element: number) => false);
+bool = buffer.every((element: number) => false, buffer);
+
+buffer = buffer.fill(1);
+buffer = buffer.fill(1, 0, 0);
+buffer = buffer.fill(\"a\");
+buffer = buffer.fill(\"a\", 0, 0);
+buffer = buffer.fill(\"a\", 0, 0, \"utf8\");
+buffer = buffer.fill(\"a\", \"utf8\");
+
+maybeNum = buffer.find((element: number, index: number, array:Uint8Array) => false);
+maybeNum = buffer.find((element: number, index: number, array:Uint8Array) => false, buffer);
+
+num = buffer.findIndex((element: number, index: number, array:Uint8Array) => false);
+num = buffer.findIndex((element: number, index: number, array:Uint8Array) => false, buffer);
+
+buffer.forEach((value: number) => console.log(value), buffer);
+buffer.forEach((value: number, index:number, array:Uint8Array) => console.log(value), buffer);
+
+bool = buffer.includes(3);
+bool = buffer.includes(3, 4);
+
+num = buffer.indexOf(3);
+num = buffer.indexOf(3, 4);
+
+// static methods
+buffer = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
+const typedArray = new Uint8Array([0x34]);
+buffer = Buffer.from(typedArray.buffer, typedArray.byteOffset, typedArray.byteLength);
+buffer = Buffer.from(new Buffer(0));
+buffer = Buffer.from(\"foo\", \"utf8\");
+
+// This call to from() does type check ok, but should not. Unfortunately, Buffer
+// extends Uint8Array but gets rid of this signature to .from(). Understandably,
+// flow doesn\'t support a subclass hiding a superclass member, so this checks out as
+// ok, even though it is not correct.
+buffer = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72], (a:number) => a + 1, {}); // should error but doesn\'t
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/node_tests/buffer/buffer.js b/tests/node_tests/buffer/buffer.js
new file mode 100644
index 000000000000..9c53197948c6
--- /dev/null
+++ b/tests/node_tests/buffer/buffer.js
@@ -0,0 +1,57 @@
+/* @flow */
+
+let bool: boolean = false;
+let buffer: Buffer = new Buffer(0);
+let num: number = 0;
+let maybeNum: ?number;
+
+// Uint8Array properties. All of these should type check ok.
+buffer.length;
+buffer.buffer;
+buffer.byteOffset;
+buffer.byteLength;
+buffer[1];
+
+// A few Uint8Array instance methods. All of these should type check ok.
+buffer.copyWithin(0, 0);
+buffer.copyWithin(0, 0, 0);
+
+const it1: Iterator<[number, number]> = buffer.entries();
+
+bool = buffer.every((element: number) => false);
+bool = buffer.every((element: number) => false, buffer);
+
+buffer = buffer.fill(1);
+buffer = buffer.fill(1, 0, 0);
+buffer = buffer.fill("a");
+buffer = buffer.fill("a", 0, 0);
+buffer = buffer.fill("a", 0, 0, "utf8");
+buffer = buffer.fill("a", "utf8");
+
+maybeNum = buffer.find((element: number, index: number, array:Uint8Array) => false);
+maybeNum = buffer.find((element: number, index: number, array:Uint8Array) => false, buffer);
+
+num = buffer.findIndex((element: number, index: number, array:Uint8Array) => false);
+num = buffer.findIndex((element: number, index: number, array:Uint8Array) => false, buffer);
+
+buffer.forEach((value: number) => console.log(value), buffer);
+buffer.forEach((value: number, index:number, array:Uint8Array) => console.log(value), buffer);
+
+bool = buffer.includes(3);
+bool = buffer.includes(3, 4);
+
+num = buffer.indexOf(3);
+num = buffer.indexOf(3, 4);
+
+// static methods
+buffer = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
+const typedArray = new Uint8Array([0x34]);
+buffer = Buffer.from(typedArray.buffer, typedArray.byteOffset, typedArray.byteLength);
+buffer = Buffer.from(new Buffer(0));
+buffer = Buffer.from("foo", "utf8");
+
+// This call to from() does type check ok, but should not. Unfortunately, Buffer
+// extends Uint8Array but gets rid of this signature to .from(). Understandably,
+// flow doesn't support a subclass hiding a superclass member, so this checks out as
+// ok, even though it is not correct.
+buffer = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72], (a:number) => a + 1, {}); // should error but doesn't
diff --git a/tests/node_tests/buffer/jsfmt.spec.js b/tests/node_tests/buffer/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/buffer/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/child_process/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/child_process/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ad8791456df2
--- /dev/null
+++ b/tests/node_tests/child_process/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,200 @@
+exports[`test exec.js 1`] = `
+"/* @flow */
+
+var exec = require(\'child_process\').exec;
+
+// callback only.
+exec(\'ls\', function(error, stdout, stderr) {
+  console.info(stdout);
+});
+
+// options only.
+exec(\'ls\', {timeout: 250});
+
+// options + callback.
+exec(\'ls\', {maxBuffer: 100}, function(error, stdout, stderr) {
+  console.info(stdout);
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var exec = require(\"child_process\").exec;
+// callback only.
+exec(
+  \"ls\",
+  function(error, stdout, stderr) {
+    console.info(stdout);
+  }
+);
+// options only.
+exec(\"ls\", { timeout: 250 });
+// options + callback.
+exec(
+  \"ls\",
+  { maxBuffer: 100 },
+  function(error, stdout, stderr) {
+    console.info(stdout);
+  }
+);
+
+"
+`;
+
+exports[`test execFile.js 1`] = `
+"/* @flow */
+
+var execFile = require(\'child_process\').execFile;
+
+// args only.
+execFile(\'ls\', [\'-lh\']);
+
+// callback only.
+execFile(\'ls\', function(error, stdout, stderr) {
+  console.info(stdout);
+});
+
+// options only.
+execFile(\'wc\', {timeout: 250});
+
+// args + callback.
+execFile(\'ls\', [\'-l\'], function(error, stdout, stderr) {
+  console.info(stdout);
+});
+
+// args + options.
+execFile(\'ls\', [\'-l\'], {timeout: 250});
+
+// Put it all together.
+execFile(\'ls\', [\'-l\'], {timeout: 250}, function(error, stdout, stderr) {
+  console.info(stdout);
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var execFile = require(\"child_process\").execFile;
+// args only.
+execFile(\"ls\", [ \"-lh\" ]);
+// callback only.
+execFile(
+  \"ls\",
+  function(error, stdout, stderr) {
+    console.info(stdout);
+  }
+);
+// options only.
+execFile(\"wc\", { timeout: 250 });
+// args + callback.
+execFile(
+  \"ls\",
+  [ \"-l\" ],
+  function(error, stdout, stderr) {
+    console.info(stdout);
+  }
+);
+// args + options.
+execFile(\"ls\", [ \"-l\" ], { timeout: 250 });
+// Put it all together.
+execFile(
+  \"ls\",
+  [ \"-l\" ],
+  { timeout: 250 },
+  function(error, stdout, stderr) {
+    console.info(stdout);
+  }
+);
+
+"
+`;
+
+exports[`test execSync.js 1`] = `
+"/* @flow */
+
+var execSync = require(\'child_process\').execSync;
+
+(execSync(\'ls\'): Buffer); // returns Buffer
+(execSync(\'ls\', {encoding: \'buffer\'}): Buffer); // returns Buffer
+(execSync(\'ls\', {encoding: \'utf8\'}): string); // returns string
+(execSync(\'ls\', {timeout: \'250\'})); // error, no signatures match
+(execSync(\'ls\', {stdio: \'inherit\'})); // error, no signatures match
+(execSync(\'ls\', {stdio: [\'inherit\']})); // error, no signatures match
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var execSync = require(\"child_process\").execSync;
+(execSync(\"ls\"): Buffer);// returns Buffer
+(execSync(\"ls\", { encoding: \"buffer\" }): Buffer);// returns Buffer
+(execSync(\"ls\", { encoding: \"utf8\" }): string);// returns string
+execSync(\"ls\", { timeout: \"250\" });// error, no signatures match
+execSync(\"ls\", { stdio: \"inherit\" });// error, no signatures match
+execSync(\"ls\", { stdio: [ \"inherit\" ] });// error, no signatures match
+
+"
+`;
+
+exports[`test spawn.js 1`] = `
+"/* @flow */
+
+var child_process = require(\'child_process\');
+
+var ls = child_process.spawn(\'ls\');
+var wc = child_process.spawn(\'wc\', [\'-l\']);
+
+// args + options.
+child_process.spawn(\'echo\', [\'-n\', \'\"Testing...\"\'], {env: {TEST: \'foo\'}});
+
+// options only.
+child_process.spawn(\'echo\', {env: {FOO: 2}});
+
+ls.stdout.on(\'data\', function(data) {
+  wc.stdin.write(data);
+});
+
+ls.stderr.on(\'data\', function(data) {
+  console.warn(data);
+});
+
+ls.on(\'close\', function(code) {
+  if (code !== 0) {
+    console.warn(\'\`ls\` exited with code %s\', code);
+  }
+  wc.stdin.end();
+});
+
+wc.stdout.pipe(process.stdout);
+wc.stderr.pipe(process.stderr);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var child_process = require(\"child_process\");
+var ls = child_process.spawn(\"ls\");
+var wc = child_process.spawn(\"wc\", [ \"-l\" ]);
+// args + options.
+child_process.spawn(
+  \"echo\",
+  [ \"-n\", \"\\\"Testing...\\\"\" ],
+  { env: { TEST: \"foo\" } }
+);
+// options only.
+child_process.spawn(\"echo\", { env: { FOO: 2 } });
+ls.stdout.on(
+  \"data\",
+  function(data) {
+    wc.stdin.write(data);
+  }
+);
+ls.stderr.on(
+  \"data\",
+  function(data) {
+    console.warn(data);
+  }
+);
+ls.on(
+  \"close\",
+  function(code) {
+    if (code !== 0) {
+      console.warn(\"\`ls\` exited with code %s\", code);
+    }
+    wc.stdin.end();
+  }
+);
+wc.stdout.pipe(process.stdout);
+wc.stderr.pipe(process.stderr);
+
+"
+`;
diff --git a/tests/node_tests/child_process/exec.js b/tests/node_tests/child_process/exec.js
new file mode 100644
index 000000000000..395a75b59946
--- /dev/null
+++ b/tests/node_tests/child_process/exec.js
@@ -0,0 +1,16 @@
+/* @flow */
+
+var exec = require('child_process').exec;
+
+// callback only.
+exec('ls', function(error, stdout, stderr) {
+  console.info(stdout);
+});
+
+// options only.
+exec('ls', {timeout: 250});
+
+// options + callback.
+exec('ls', {maxBuffer: 100}, function(error, stdout, stderr) {
+  console.info(stdout);
+});
diff --git a/tests/node_tests/child_process/execFile.js b/tests/node_tests/child_process/execFile.js
new file mode 100644
index 000000000000..65963c46413e
--- /dev/null
+++ b/tests/node_tests/child_process/execFile.js
@@ -0,0 +1,27 @@
+/* @flow */
+
+var execFile = require('child_process').execFile;
+
+// args only.
+execFile('ls', ['-lh']);
+
+// callback only.
+execFile('ls', function(error, stdout, stderr) {
+  console.info(stdout);
+});
+
+// options only.
+execFile('wc', {timeout: 250});
+
+// args + callback.
+execFile('ls', ['-l'], function(error, stdout, stderr) {
+  console.info(stdout);
+});
+
+// args + options.
+execFile('ls', ['-l'], {timeout: 250});
+
+// Put it all together.
+execFile('ls', ['-l'], {timeout: 250}, function(error, stdout, stderr) {
+  console.info(stdout);
+});
diff --git a/tests/node_tests/child_process/execSync.js b/tests/node_tests/child_process/execSync.js
new file mode 100644
index 000000000000..171fd1748834
--- /dev/null
+++ b/tests/node_tests/child_process/execSync.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+var execSync = require('child_process').execSync;
+
+(execSync('ls'): Buffer); // returns Buffer
+(execSync('ls', {encoding: 'buffer'}): Buffer); // returns Buffer
+(execSync('ls', {encoding: 'utf8'}): string); // returns string
+(execSync('ls', {timeout: '250'})); // error, no signatures match
+(execSync('ls', {stdio: 'inherit'})); // error, no signatures match
+(execSync('ls', {stdio: ['inherit']})); // error, no signatures match
diff --git a/tests/node_tests/child_process/jsfmt.spec.js b/tests/node_tests/child_process/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/child_process/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/child_process/spawn.js b/tests/node_tests/child_process/spawn.js
new file mode 100644
index 000000000000..760c3cf25c9d
--- /dev/null
+++ b/tests/node_tests/child_process/spawn.js
@@ -0,0 +1,30 @@
+/* @flow */
+
+var child_process = require('child_process');
+
+var ls = child_process.spawn('ls');
+var wc = child_process.spawn('wc', ['-l']);
+
+// args + options.
+child_process.spawn('echo', ['-n', '"Testing..."'], {env: {TEST: 'foo'}});
+
+// options only.
+child_process.spawn('echo', {env: {FOO: 2}});
+
+ls.stdout.on('data', function(data) {
+  wc.stdin.write(data);
+});
+
+ls.stderr.on('data', function(data) {
+  console.warn(data);
+});
+
+ls.on('close', function(code) {
+  if (code !== 0) {
+    console.warn('`ls` exited with code %s', code);
+  }
+  wc.stdin.end();
+});
+
+wc.stdout.pipe(process.stdout);
+wc.stderr.pipe(process.stderr);
diff --git a/tests/node_tests/crypto/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/crypto/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..34bdcbc30cc0
--- /dev/null
+++ b/tests/node_tests/crypto/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,57 @@
+exports[`test crypto.js 1`] = `
+"/* @flow */
+
+const crypto = require(\'crypto\');
+
+let tests = [
+  // Hmac is a duplex stream
+  function() {
+    const hmac = crypto.createHmac(\'sha256\', \'a secret\');
+
+    hmac.on(\'readable\', () => {
+      (hmac.read(): ?(string | Buffer));
+      (hmac.read(): number); // 4 errors: null, void, string, Buffer
+    });
+
+    hmac.write(\'some data to hash\');
+    hmac.write(123); // 2 errors: not a string or a Buffer
+    hmac.end();
+  },
+
+  // Hmac supports update and digest functions too
+  function(buf: Buffer) {
+    const hmac = crypto.createHmac(\'sha256\', \'a secret\');
+
+    hmac.update(\'some data to hash\');
+    hmac.update(\'foo\', \'utf8\');
+    hmac.update(\'foo\', \'bogus\'); // 1 error
+    hmac.update(buf);
+    hmac.update(buf, \'utf8\'); // 1 error: no encoding when passing a buffer
+
+    // it\'s also chainable
+    (hmac.update(\'some data to hash\').update(buf).digest(): Buffer);
+
+    (hmac.digest(\'hex\'): string);
+    (hmac.digest(): Buffer);
+    (hmac.digest(\'hex\'): void); // 1 error
+    (hmac.digest(): void); // 1 error
+  }
+]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1412:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/node_tests/crypto/crypto.js b/tests/node_tests/crypto/crypto.js
new file mode 100644
index 000000000000..a8544654e399
--- /dev/null
+++ b/tests/node_tests/crypto/crypto.js
@@ -0,0 +1,38 @@
+/* @flow */
+
+const crypto = require('crypto');
+
+let tests = [
+  // Hmac is a duplex stream
+  function() {
+    const hmac = crypto.createHmac('sha256', 'a secret');
+
+    hmac.on('readable', () => {
+      (hmac.read(): ?(string | Buffer));
+      (hmac.read(): number); // 4 errors: null, void, string, Buffer
+    });
+
+    hmac.write('some data to hash');
+    hmac.write(123); // 2 errors: not a string or a Buffer
+    hmac.end();
+  },
+
+  // Hmac supports update and digest functions too
+  function(buf: Buffer) {
+    const hmac = crypto.createHmac('sha256', 'a secret');
+
+    hmac.update('some data to hash');
+    hmac.update('foo', 'utf8');
+    hmac.update('foo', 'bogus'); // 1 error
+    hmac.update(buf);
+    hmac.update(buf, 'utf8'); // 1 error: no encoding when passing a buffer
+
+    // it's also chainable
+    (hmac.update('some data to hash').update(buf).digest(): Buffer);
+
+    (hmac.digest('hex'): string);
+    (hmac.digest(): Buffer);
+    (hmac.digest('hex'): void); // 1 error
+    (hmac.digest(): void); // 1 error
+  }
+]
diff --git a/tests/node_tests/crypto/jsfmt.spec.js b/tests/node_tests/crypto/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/crypto/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/fs/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/fs/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..76ebd2adc28a
--- /dev/null
+++ b/tests/node_tests/fs/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,76 @@
+exports[`test fs.js 1`] = `
+"var fs = require("fs");
+
+/* readFile */
+
+fs.readFile("file.exp", (_, data) => {
+  (data : Buffer);
+});
+
+fs.readFile("file.exp", "blah", (_, data) => {
+  (data : string);
+});
+
+fs.readFile("file.exp", { encoding: "blah" }, (_, data) => {
+  (data : string);
+});
+
+fs.readFile("file.exp", {}, (_, data) => {
+  (data : Buffer);
+});
+
+/* readFileSync */
+
+(fs.readFileSync("file.exp") : Buffer);
+(fs.readFileSync("file.exp") : string); // error
+
+(fs.readFileSync("file.exp", "blah") : string);
+(fs.readFileSync("file.exp", "blah") : Buffer); // error
+
+(fs.readFileSync("file.exp", { encoding: "blah" }) : string);
+(fs.readFileSync("file.exp", { encoding: "blah" }) : Buffer); // error
+
+(fs.readFileSync("file.exp", {}) : Buffer);
+(fs.readFileSync("file.exp", {}) : string); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var fs = require("fs");
+/* readFile */
+fs.readFile(
+  "file.exp",
+  (_, data) => {
+    (data: Buffer);
+  }
+);
+fs.readFile(
+  "file.exp",
+  "blah",
+  (_, data) => {
+    (data: string);
+  }
+);
+fs.readFile(
+  "file.exp",
+  { encoding: "blah" },
+  (_, data) => {
+    (data: string);
+  }
+);
+fs.readFile(
+  "file.exp",
+  {},
+  (_, data) => {
+    (data: Buffer);
+  }
+);
+/* readFileSync */
+(fs.readFileSync("file.exp"): Buffer);
+(fs.readFileSync("file.exp"): string);// error
+(fs.readFileSync("file.exp", "blah"): string);
+(fs.readFileSync("file.exp", "blah"): Buffer);// error
+(fs.readFileSync("file.exp", { encoding: "blah" }): string);
+(fs.readFileSync("file.exp", { encoding: "blah" }): Buffer);// error
+(fs.readFileSync("file.exp", {}): Buffer);
+(fs.readFileSync("file.exp", {}): string);// error
+
+"
+`;
diff --git a/tests/node_tests/fs/fs.js b/tests/node_tests/fs/fs.js
new file mode 100644
index 000000000000..8a05bd98a384
--- /dev/null
+++ b/tests/node_tests/fs/fs.js
@@ -0,0 +1,33 @@
+var fs = require("fs");
+
+/* readFile */
+
+fs.readFile("file.exp", (_, data) => {
+  (data : Buffer);
+});
+
+fs.readFile("file.exp", "blah", (_, data) => {
+  (data : string);
+});
+
+fs.readFile("file.exp", { encoding: "blah" }, (_, data) => {
+  (data : string);
+});
+
+fs.readFile("file.exp", {}, (_, data) => {
+  (data : Buffer);
+});
+
+/* readFileSync */
+
+(fs.readFileSync("file.exp") : Buffer);
+(fs.readFileSync("file.exp") : string); // error
+
+(fs.readFileSync("file.exp", "blah") : string);
+(fs.readFileSync("file.exp", "blah") : Buffer); // error
+
+(fs.readFileSync("file.exp", { encoding: "blah" }) : string);
+(fs.readFileSync("file.exp", { encoding: "blah" }) : Buffer); // error
+
+(fs.readFileSync("file.exp", {}) : Buffer);
+(fs.readFileSync("file.exp", {}) : string); // error
diff --git a/tests/node_tests/fs/jsfmt.spec.js b/tests/node_tests/fs/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/fs/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/json_file/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/json_file/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5d8a9dd3ad97
--- /dev/null
+++ b/tests/node_tests/json_file/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,42 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+let data = require(\'./package/index.json\');
+(data.foo: void); // error, should be object literal
+(data.foo.bar: void); // error, should be boolean
+(data.abc: boolean); // error, should be ?string
+
+let data2 = require(\'./package\');
+(data2.baz: void); // error, should be string
+
+let data3 = require(\'./package2\');
+(data3.foo: void); // error, should be number (not string! index.js wins)
+
+let data4 = require(\'./json_array\');
+(data4: Array<number>);
+(data4: void); // error, should be Array<number>
+
+(require(\'./json_string\'): void); // error, should be string
+(require(\'./json_number\'): void); // error, should be number
+(require(\'./json_true\'): void); // error, should be true
+(require(\'./json_false\'): void); // error, should be false
+(require(\'./json_null\'): void); // error, should be null
+(require(\'./json_negative_number\'): -1); // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/node_tests/json_file/jsfmt.spec.js b/tests/node_tests/json_file/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/json_file/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/json_file/package2/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/json_file/package2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fd6af48c9dd6
--- /dev/null
+++ b/tests/node_tests/json_file/package2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,12 @@
+exports[`test index.js 1`] = `
+"// @flow
+
+module.exports = {
+  foo: 123
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+module.exports = { foo: 123 };
+
+"
+`;
diff --git a/tests/node_tests/json_file/package2/index.js b/tests/node_tests/json_file/package2/index.js
new file mode 100644
index 000000000000..30453d22029a
--- /dev/null
+++ b/tests/node_tests/json_file/package2/index.js
@@ -0,0 +1,5 @@
+// @flow
+
+module.exports = {
+  foo: 123
+};
diff --git a/tests/node_tests/json_file/package2/jsfmt.spec.js b/tests/node_tests/json_file/package2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/json_file/package2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/json_file/test.js b/tests/node_tests/json_file/test.js
new file mode 100644
index 000000000000..c18576cfc6cf
--- /dev/null
+++ b/tests/node_tests/json_file/test.js
@@ -0,0 +1,23 @@
+// @flow
+
+let data = require('./package/index.json');
+(data.foo: void); // error, should be object literal
+(data.foo.bar: void); // error, should be boolean
+(data.abc: boolean); // error, should be ?string
+
+let data2 = require('./package');
+(data2.baz: void); // error, should be string
+
+let data3 = require('./package2');
+(data3.foo: void); // error, should be number (not string! index.js wins)
+
+let data4 = require('./json_array');
+(data4: Array<number>);
+(data4: void); // error, should be Array<number>
+
+(require('./json_string'): void); // error, should be string
+(require('./json_number'): void); // error, should be number
+(require('./json_true'): void); // error, should be true
+(require('./json_false'): void); // error, should be false
+(require('./json_null'): void); // error, should be null
+(require('./json_negative_number'): -1); // ok
diff --git a/tests/node_tests/os/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/os/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fb845385abea
--- /dev/null
+++ b/tests/node_tests/os/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,31 @@
+exports[`test userInfo.js 1`] = `
+"/* @flow */
+
+var os = require('os');
+
+var u1 = os.userInfo();
+(u1.username: string);
+(u1.username: Buffer); // error
+
+var u2 = os.userInfo({encoding: 'utf8'});
+(u2.username: string);
+(u2.username: Buffer); // error
+
+var u3 = os.userInfo({encoding: 'buffer'});
+(u3.username: string); // error
+(u3.username: Buffer);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var os = require("os");
+var u1 = os.userInfo();
+(u1.username: string);
+(u1.username: Buffer);// error
+var u2 = os.userInfo({ encoding: "utf8" });
+(u2.username: string);
+(u2.username: Buffer);// error
+var u3 = os.userInfo({ encoding: "buffer" });
+(u3.username: string);// error
+(u3.username: Buffer);
+
+"
+`;
diff --git a/tests/node_tests/os/jsfmt.spec.js b/tests/node_tests/os/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/os/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/os/userInfo.js b/tests/node_tests/os/userInfo.js
new file mode 100644
index 000000000000..d2644f249bc6
--- /dev/null
+++ b/tests/node_tests/os/userInfo.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+var os = require('os');
+
+var u1 = os.userInfo();
+(u1.username: string);
+(u1.username: Buffer); // error
+
+var u2 = os.userInfo({encoding: 'utf8'});
+(u2.username: string);
+(u2.username: Buffer); // error
+
+var u3 = os.userInfo({encoding: 'buffer'});
+(u3.username: string); // error
+(u3.username: Buffer);
diff --git a/tests/node_tests/package_file/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/package_file/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..addfa1957571
--- /dev/null
+++ b/tests/node_tests/package_file/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test bar_lib.js 1`] = `
+"module.exports = "bar_lib";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = "bar_lib";
+
+"
+`;
+
+exports[`test foo.js 1`] = `
+"var x: string = require('./bar_lib'); // 'bar_lib' does not work!
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: string = require("./bar_lib");// 'bar_lib' does not work!
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/package_file/bar_lib.js b/tests/node_tests/package_file/bar_lib.js
new file mode 100644
index 000000000000..411baf0101f2
--- /dev/null
+++ b/tests/node_tests/package_file/bar_lib.js
@@ -0,0 +1 @@
+module.exports = "bar_lib";
diff --git a/tests/node_tests/package_file/bar_lib/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/package_file/bar_lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e0181c12d007
--- /dev/null
+++ b/tests/node_tests/package_file/bar_lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test bar.js 1`] = `
+"module.exports = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = 0;
+
+"
+`;
diff --git a/tests/node_tests/package_file/bar_lib/bar.js b/tests/node_tests/package_file/bar_lib/bar.js
new file mode 100644
index 000000000000..d5b2e8bb3efb
--- /dev/null
+++ b/tests/node_tests/package_file/bar_lib/bar.js
@@ -0,0 +1 @@
+module.exports = 0;
diff --git a/tests/node_tests/package_file/bar_lib/jsfmt.spec.js b/tests/node_tests/package_file/bar_lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/package_file/bar_lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/package_file/foo.js b/tests/node_tests/package_file/foo.js
new file mode 100644
index 000000000000..24c3a1e4a93e
--- /dev/null
+++ b/tests/node_tests/package_file/foo.js
@@ -0,0 +1,2 @@
+var x: string = require('./bar_lib'); // 'bar_lib' does not work!
+console.log(x);
diff --git a/tests/node_tests/package_file/jsfmt.spec.js b/tests/node_tests/package_file/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/package_file/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/package_file_node_modules/foo/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/package_file_node_modules/foo/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d1860d5e0c67
--- /dev/null
+++ b/tests/node_tests/package_file_node_modules/foo/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x: string = require('bar_lib'); // 'bar_lib' does not work!
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: string = require("bar_lib");// 'bar_lib' does not work!
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/package_file_node_modules/foo/foo.js b/tests/node_tests/package_file_node_modules/foo/foo.js
new file mode 100644
index 000000000000..680a16b26253
--- /dev/null
+++ b/tests/node_tests/package_file_node_modules/foo/foo.js
@@ -0,0 +1,2 @@
+var x: string = require('bar_lib'); // 'bar_lib' does not work!
+console.log(x);
diff --git a/tests/node_tests/package_file_node_modules/foo/jsfmt.spec.js b/tests/node_tests/package_file_node_modules/foo/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/package_file_node_modules/foo/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/path_node_modules/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/path_node_modules/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c35d8d2fd0f5
--- /dev/null
+++ b/tests/node_tests/path_node_modules/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('bar_lib/src/lib/bar');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("bar_lib/src/lib/bar");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/path_node_modules/foo.js b/tests/node_tests/path_node_modules/foo.js
new file mode 100644
index 000000000000..ff7947a598eb
--- /dev/null
+++ b/tests/node_tests/path_node_modules/foo.js
@@ -0,0 +1,2 @@
+var x = require('bar_lib/src/lib/bar');
+console.log(x);
diff --git a/tests/node_tests/path_node_modules/jsfmt.spec.js b/tests/node_tests/path_node_modules/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/path_node_modules/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/path_node_modules_with_short_main/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/path_node_modules_with_short_main/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f63b520200fb
--- /dev/null
+++ b/tests/node_tests/path_node_modules_with_short_main/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('bar_lib');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("bar_lib");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/path_node_modules_with_short_main/foo.js b/tests/node_tests/path_node_modules_with_short_main/foo.js
new file mode 100644
index 000000000000..bb32aaa21c20
--- /dev/null
+++ b/tests/node_tests/path_node_modules_with_short_main/foo.js
@@ -0,0 +1,2 @@
+var x = require('bar_lib');
+console.log(x);
diff --git a/tests/node_tests/path_node_modules_with_short_main/jsfmt.spec.js b/tests/node_tests/path_node_modules_with_short_main/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/path_node_modules_with_short_main/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/path_node_modules_without_main/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/path_node_modules_without_main/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f63b520200fb
--- /dev/null
+++ b/tests/node_tests/path_node_modules_without_main/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('bar_lib');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("bar_lib");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/path_node_modules_without_main/foo.js b/tests/node_tests/path_node_modules_without_main/foo.js
new file mode 100644
index 000000000000..bb32aaa21c20
--- /dev/null
+++ b/tests/node_tests/path_node_modules_without_main/foo.js
@@ -0,0 +1,2 @@
+var x = require('bar_lib');
+console.log(x);
diff --git a/tests/node_tests/path_node_modules_without_main/jsfmt.spec.js b/tests/node_tests/path_node_modules_without_main/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/path_node_modules_without_main/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/path_package/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/path_package/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bfaab3d36a4f
--- /dev/null
+++ b/tests/node_tests/path_package/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test foo.js 1`] = `
+"var x = require('bar_lib/src/lib');
+console.log(x);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = require("bar_lib/src/lib");
+console.log(x);
+
+"
+`;
diff --git a/tests/node_tests/path_package/foo.js b/tests/node_tests/path_package/foo.js
new file mode 100644
index 000000000000..a063eb60223b
--- /dev/null
+++ b/tests/node_tests/path_package/foo.js
@@ -0,0 +1,2 @@
+var x = require('bar_lib/src/lib');
+console.log(x);
diff --git a/tests/node_tests/path_package/jsfmt.spec.js b/tests/node_tests/path_package/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/path_package/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/stream/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/stream/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3c48fa7d08e2
--- /dev/null
+++ b/tests/node_tests/stream/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,84 @@
+exports[`test stream.js 1`] = `
+"/* @flow */
+
+var child_process = require('child_process');
+var fs = require('fs');
+var stream = require('stream');
+var ls = child_process.spawn('ls');
+
+var data = "foo";
+
+ls.stdin.write(data);
+ls.stdin.write(data, "utf-8");
+ls.stdin.write(data, () => {});
+ls.stdin.write(data, "utf-8", () => {});
+
+ls.stdin.end();
+ls.stdin.end(data);
+ls.stdin.end(data, "utf-8");
+ls.stdin.end(data, () => {});
+ls.stdin.end(data, "utf-8", () => {});
+
+var ws = fs.createWriteStream('/dev/null');
+ls.stdout.pipe(ws).end();
+
+class MyReadStream extends stream.Readable {}
+class MyWriteStream extends stream.Writable {}
+class MyDuplex extends stream.Duplex {}
+class MyTransform extends stream.Duplex {}
+
+new MyReadStream()
+  .pipe(new MyDuplex())
+  .pipe(new MyTransform())
+  .pipe(new MyWriteStream());
+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var child_process = require("child_process");
+var fs = require("fs");
+var stream = require("stream");
+var ls = child_process.spawn("ls");
+var data = "foo";
+ls.stdin.write(data);
+ls.stdin.write(data, "utf-8");
+ls.stdin.write(
+  data,
+  () => {
+    
+  }
+);
+ls.stdin.write(
+  data,
+  "utf-8",
+  () => {
+    
+  }
+);
+ls.stdin.end();
+ls.stdin.end(data);
+ls.stdin.end(data, "utf-8");
+ls.stdin.end(
+  data,
+  () => {
+    
+  }
+);
+ls.stdin.end(
+  data,
+  "utf-8",
+  () => {
+    
+  }
+);
+var ws = fs.createWriteStream("/dev/null");
+ls.stdout.pipe(ws).end();
+class MyReadStream extends stream.Readable {}
+class MyWriteStream extends stream.Writable {}
+class MyDuplex extends stream.Duplex {}
+class MyTransform extends stream.Duplex {}
+new MyReadStream().pipe(new MyDuplex()).pipe(new MyTransform()).pipe(
+  new MyWriteStream()
+);
+
+"
+`;
diff --git a/tests/node_tests/stream/jsfmt.spec.js b/tests/node_tests/stream/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/stream/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/stream/stream.js b/tests/node_tests/stream/stream.js
new file mode 100644
index 000000000000..61cd149e3f64
--- /dev/null
+++ b/tests/node_tests/stream/stream.js
@@ -0,0 +1,33 @@
+/* @flow */
+
+var child_process = require('child_process');
+var fs = require('fs');
+var stream = require('stream');
+var ls = child_process.spawn('ls');
+
+var data = "foo";
+
+ls.stdin.write(data);
+ls.stdin.write(data, "utf-8");
+ls.stdin.write(data, () => {});
+ls.stdin.write(data, "utf-8", () => {});
+
+ls.stdin.end();
+ls.stdin.end(data);
+ls.stdin.end(data, "utf-8");
+ls.stdin.end(data, () => {});
+ls.stdin.end(data, "utf-8", () => {});
+
+var ws = fs.createWriteStream('/dev/null');
+ls.stdout.pipe(ws).end();
+
+class MyReadStream extends stream.Readable {}
+class MyWriteStream extends stream.Writable {}
+class MyDuplex extends stream.Duplex {}
+class MyTransform extends stream.Duplex {}
+
+new MyReadStream()
+  .pipe(new MyDuplex())
+  .pipe(new MyTransform())
+  .pipe(new MyWriteStream());
+
diff --git a/tests/node_tests/timers/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/timers/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..309a91c9044f
--- /dev/null
+++ b/tests/node_tests/timers/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test timers.js 1`] = `
+"// @flow
+
+function setImmediateCallback(): number {
+  return 0;
+}
+
+setImmediate(setImmediateCallback);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function setImmediateCallback(): number {
+  return 0;
+}
+setImmediate(setImmediateCallback);
+
+"
+`;
diff --git a/tests/node_tests/timers/jsfmt.spec.js b/tests/node_tests/timers/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/timers/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/timers/timers.js b/tests/node_tests/timers/timers.js
new file mode 100644
index 000000000000..28f9462aea1b
--- /dev/null
+++ b/tests/node_tests/timers/timers.js
@@ -0,0 +1,7 @@
+// @flow
+
+function setImmediateCallback(): number {
+  return 0;
+}
+
+setImmediate(setImmediateCallback);
diff --git a/tests/node_tests/url/__snapshots__/jsfmt.spec.js.snap b/tests/node_tests/url/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..786180dca476
--- /dev/null
+++ b/tests/node_tests/url/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test url.js 1`] = `
+"const url = require('url');
+url.format(url.parse('https://example.com/foo'));
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+const url = require("url");
+url.format(url.parse("https://example.com/foo"));
+
+"
+`;
diff --git a/tests/node_tests/url/jsfmt.spec.js b/tests/node_tests/url/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/node_tests/url/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/node_tests/url/url.js b/tests/node_tests/url/url.js
new file mode 100644
index 000000000000..45b9072eda4b
--- /dev/null
+++ b/tests/node_tests/url/url.js
@@ -0,0 +1,2 @@
+const url = require('url');
+url.format(url.parse('https://example.com/foo'));
diff --git a/tests/nullable/__snapshots__/jsfmt.spec.js.snap b/tests/nullable/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3beb79eaa81c
--- /dev/null
+++ b/tests/nullable/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,77 @@
+exports[`test maybe.js 1`] = `
+"// @flow
+
+// unwrapping nested maybes should work
+((\'foo\': ?(?string)): ?string); // ok
+((123: ?(?number)): ?string); // error (only num ~> string)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// unwrapping nested maybes should work
+((\"foo\": ??string): ?string);// ok
+((123: ??number): ?string);// error (only num ~> string)
+
+"
+`;
+
+exports[`test nullable.js 1`] = `
+"function foo():string { return null; }
+
+function bar():?string { return null; }
+
+function qux(x:string) { }
+
+function corge(x:number) { }
+
+var x = bar(); // x: ?string
+if (x != null) qux(x); // x: ?string | null
+if (x != null) corge(x); // x: ?string | null
+
+function grault() { x = null; }
+if (x != null) {
+  grault(); qux(x);
+}
+
+var array_of_nullable: Array<?number> = [null, 3];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test simple_nullable.js 1`] = `
+"function foo(x:?string) {}
+function bar(x:?number) {}
+foo(\'hmm\');
+bar(\'hmm\');
+
+function fn(data: ?{}) {}
+fn({some: \'literal\'});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(x: ?string) {
+  
+}
+function bar(x: ?number) {
+  
+}
+foo(\"hmm\");
+bar(\"hmm\");
+function fn(data: ?{}) {
+  
+}
+fn({ some: \"literal\" });
+
+"
+`;
diff --git a/tests/nullable/jsfmt.spec.js b/tests/nullable/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/nullable/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/nullable/maybe.js b/tests/nullable/maybe.js
new file mode 100644
index 000000000000..f6bb901ab3ef
--- /dev/null
+++ b/tests/nullable/maybe.js
@@ -0,0 +1,5 @@
+// @flow
+
+// unwrapping nested maybes should work
+(('foo': ?(?string)): ?string); // ok
+((123: ?(?number)): ?string); // error (only num ~> string)
diff --git a/tests/nullable/nullable.js b/tests/nullable/nullable.js
new file mode 100644
index 000000000000..642e8a55b0f1
--- /dev/null
+++ b/tests/nullable/nullable.js
@@ -0,0 +1,18 @@
+function foo():string { return null; }
+
+function bar():?string { return null; }
+
+function qux(x:string) { }
+
+function corge(x:number) { }
+
+var x = bar(); // x: ?string
+if (x != null) qux(x); // x: ?string | null
+if (x != null) corge(x); // x: ?string | null
+
+function grault() { x = null; }
+if (x != null) {
+  grault(); qux(x);
+}
+
+var array_of_nullable: Array<?number> = [null, 3];
diff --git a/tests/nullable/simple_nullable.js b/tests/nullable/simple_nullable.js
new file mode 100644
index 000000000000..d537956c14e5
--- /dev/null
+++ b/tests/nullable/simple_nullable.js
@@ -0,0 +1,7 @@
+function foo(x:?string) {}
+function bar(x:?number) {}
+foo('hmm');
+bar('hmm');
+
+function fn(data: ?{}) {}
+fn({some: 'literal'});
diff --git a/tests/number_constants/__snapshots__/jsfmt.spec.js.snap b/tests/number_constants/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1c8a6bf8971a
--- /dev/null
+++ b/tests/number_constants/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,29 @@
+exports[`test number_constants.js 1`] = `
+"var a: number = Number.MAX_SAFE_INTEGER;
+var b: string = Number.MAX_SAFE_INTEGER;
+var c: number = Number.MIN_SAFE_INTEGER;
+var d: string = Number.MIN_SAFE_INTEGER;
+var e: number = Number.MAX_VALUE;
+var f: string = Number.MAX_VALUE;
+var g: number = Number.MIN_VALUE;
+var h: string = Number.MIN_VALUE;
+var i: number = Number.NaN;
+var j: string = Number.NaN;
+var k: number = Number.EPSILON;
+var l: string = Number.EPSILON;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var a: number = Number.MAX_SAFE_INTEGER;
+var b: string = Number.MAX_SAFE_INTEGER;
+var c: number = Number.MIN_SAFE_INTEGER;
+var d: string = Number.MIN_SAFE_INTEGER;
+var e: number = Number.MAX_VALUE;
+var f: string = Number.MAX_VALUE;
+var g: number = Number.MIN_VALUE;
+var h: string = Number.MIN_VALUE;
+var i: number = Number.NaN;
+var j: string = Number.NaN;
+var k: number = Number.EPSILON;
+var l: string = Number.EPSILON;
+
+"
+`;
diff --git a/tests/number_constants/jsfmt.spec.js b/tests/number_constants/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/number_constants/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/number_constants/number_constants.js b/tests/number_constants/number_constants.js
new file mode 100644
index 000000000000..51f89d21e00f
--- /dev/null
+++ b/tests/number_constants/number_constants.js
@@ -0,0 +1,12 @@
+var a: number = Number.MAX_SAFE_INTEGER;
+var b: string = Number.MAX_SAFE_INTEGER;
+var c: number = Number.MIN_SAFE_INTEGER;
+var d: string = Number.MIN_SAFE_INTEGER;
+var e: number = Number.MAX_VALUE;
+var f: string = Number.MAX_VALUE;
+var g: number = Number.MIN_VALUE;
+var h: string = Number.MIN_VALUE;
+var i: number = Number.NaN;
+var j: string = Number.NaN;
+var k: number = Number.EPSILON;
+var l: string = Number.EPSILON;
diff --git a/tests/object-method/__snapshots__/jsfmt.spec.js.snap b/tests/object-method/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..96b4ef5f3b1e
--- /dev/null
+++ b/tests/object-method/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,150 @@
+exports[`test id.js 1`] = `
+"declare function id<X>(_: X): X;
+
+module.exports = id;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test subtype.js 1`] = `
+"interface Interface {
+  m(): void;
+}
+import type { ObjectType } from \'./test\';
+
+function subtypeCheck(x: Interface): ObjectType { return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test test.js 1`] = `
+"const id = require(\'./id\');
+
+export type ObjectType = {
+  +m: () => void,
+};
+
+function methodCaller(x: ObjectType) {
+  x.m();
+};
+
+module.exports = id(
+  methodCaller
+);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"/* @flow */
+
+function f() {
+  return this.p;
+}
+
+var a = {
+  p: 0,
+  f
+}
+
+var b = {
+  f
+}
+
+a.f(); // okey-dokie
+b.f(); // error, property \`p\` not found
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function f() {
+  return this.p;
+}
+var a = { p: 0, f };
+var b = { f };
+a.f();// okey-dokie
+b.f();// error, property \`p\` not found
+
+"
+`;
+
+exports[`test test3.js 1`] = `
+"/* @flow */
+
+function foo() {
+  this.m();
+}
+
+function bar(f: () => void) {
+  f(); // passing global object as \`this\`
+  ({ f }).f(); // passing container object as \`this\`
+}
+
+bar(foo); // error, since \`this\` is used non-trivially in \`foo\`
+
+function qux(o: { f: () => void }) {
+  o.f(); // passing o as \`this\`
+}
+
+qux({ f: foo });  // error, since \`this\` is used non-trivially in \`foo\`
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/object-method/id.js b/tests/object-method/id.js
new file mode 100644
index 000000000000..73650e97515d
--- /dev/null
+++ b/tests/object-method/id.js
@@ -0,0 +1,3 @@
+declare function id<X>(_: X): X;
+
+module.exports = id;
diff --git a/tests/object-method/jsfmt.spec.js b/tests/object-method/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/object-method/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/object-method/subtype.js b/tests/object-method/subtype.js
new file mode 100644
index 000000000000..810b2c8d0ffe
--- /dev/null
+++ b/tests/object-method/subtype.js
@@ -0,0 +1,6 @@
+interface Interface {
+  m(): void;
+}
+import type { ObjectType } from './test';
+
+function subtypeCheck(x: Interface): ObjectType { return x; }
diff --git a/tests/object-method/test.js b/tests/object-method/test.js
new file mode 100644
index 000000000000..033b1abf3229
--- /dev/null
+++ b/tests/object-method/test.js
@@ -0,0 +1,13 @@
+const id = require('./id');
+
+export type ObjectType = {
+  +m: () => void,
+};
+
+function methodCaller(x: ObjectType) {
+  x.m();
+};
+
+module.exports = id(
+  methodCaller
+);
diff --git a/tests/object-method/test2.js b/tests/object-method/test2.js
new file mode 100644
index 000000000000..652c93c8735f
--- /dev/null
+++ b/tests/object-method/test2.js
@@ -0,0 +1,17 @@
+/* @flow */
+
+function f() {
+  return this.p;
+}
+
+var a = {
+  p: 0,
+  f
+}
+
+var b = {
+  f
+}
+
+a.f(); // okey-dokie
+b.f(); // error, property `p` not found
diff --git a/tests/object-method/test3.js b/tests/object-method/test3.js
new file mode 100644
index 000000000000..365e8e460805
--- /dev/null
+++ b/tests/object-method/test3.js
@@ -0,0 +1,18 @@
+/* @flow */
+
+function foo() {
+  this.m();
+}
+
+function bar(f: () => void) {
+  f(); // passing global object as `this`
+  ({ f }).f(); // passing container object as `this`
+}
+
+bar(foo); // error, since `this` is used non-trivially in `foo`
+
+function qux(o: { f: () => void }) {
+  o.f(); // passing o as `this`
+}
+
+qux({ f: foo });  // error, since `this` is used non-trivially in `foo`
diff --git a/tests/object_annot/__snapshots__/jsfmt.spec.js.snap b/tests/object_annot/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..83a6c2b5f013
--- /dev/null
+++ b/tests/object_annot/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test test.js 1`] = `
+"function foo(x: Array<Object>): Array<Object> {
+    return x.sort((a, b) => a.foo - b.foo);
+}
+
+// Make sure Object works with Object.keys()
+function bar(x: Object): Array<string> {
+  return Object.keys(x);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/object_annot/jsfmt.spec.js b/tests/object_annot/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/object_annot/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/object_annot/test.js b/tests/object_annot/test.js
new file mode 100644
index 000000000000..88565b11935c
--- /dev/null
+++ b/tests/object_annot/test.js
@@ -0,0 +1,8 @@
+function foo(x: Array<Object>): Array<Object> {
+    return x.sort((a, b) => a.foo - b.foo);
+}
+
+// Make sure Object works with Object.keys()
+function bar(x: Object): Array<string> {
+  return Object.keys(x);
+}
diff --git a/tests/object_api/__snapshots__/jsfmt.spec.js.snap b/tests/object_api/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..53a9dd7b2de1
--- /dev/null
+++ b/tests/object_api/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,401 @@
+exports[`test a.js 1`] = `
+"/* @flow */
+
+module.exports = { a() {} };~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports = {
+  a() {
+    
+  }
+};
+
+"
+`;
+
+exports[`test b.js 1`] = `
+"/* @flow */
+
+var a = require(\'./a\');
+var b = Object.assign({ bar() {}, ...{} }, a);
+b.a(); // works here
+module.exports = b;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var a = require(\"./a\");
+var b = Object.assign(
+  {
+    bar() {
+      
+    },
+    ...{}
+  },
+  a
+);
+b.a();// works here
+module.exports = b;
+
+"
+`;
+
+exports[`test c.js 1`] = `
+"/* @flow */
+
+var c = require(\'./b\');
+c.a();
+c.foo();~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var c = require(\"./b\");
+c.a();
+c.foo();
+
+"
+`;
+
+exports[`test object_assign.js 1`] = `
+"/* @flow */
+
+var export_ = Object.assign({}, {
+    foo: function(param) { return param; }
+});
+
+var decl_export_: { foo: any; bar: any } = Object.assign({}, export_);
+
+let anyObj: Object = {};
+Object.assign(anyObj, anyObj); // makes sure this terminates
+
+module.exports = export_;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var export_ = Object.assign(
+  {},
+  {
+    foo: function(param) {
+      return param;
+    }
+  }
+);
+var decl_export_: { foo: any, bar: any } = Object.assign({}, export_);
+let anyObj: Object = {};
+Object.assign(anyObj, anyObj);// makes sure this terminates
+module.exports = export_;
+
+"
+`;
+
+exports[`test object_create.js 1`] = `
+"/* @flow */
+
+class C { foo: string; }
+
+// OK, \`instanceof C\` would be true
+(Object.create(C.prototype): C);
+
+// OK, \`instanceof C\` would be true
+(Object.create(new C): C);
+
+// error, object literals don\'t structurally match instances
+({ foo: \"foo\" }: C);
+
+// error, object types don\'t structurally match instances
+type O = { foo: string; }
+declare var o: O;
+(o: C);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class C {
+  foo: string;
+}
+// OK, \`instanceof C\` would be true
+(Object.create(C.prototype): C);
+// OK, \`instanceof C\` would be true
+(Object.create(new C()): C);
+// error, object literals don\'t structurally match instances
+({ foo: \"foo\" }: C);
+// error, object types don\'t structurally match instances
+type O = { foo: string };
+declare var o: O;
+(o: C);
+
+"
+`;
+
+exports[`test object_getprototypeof.js 1`] = `
+"// @flow
+
+class Foo {}
+class Bar extends Foo {}
+
+let tests = [
+  function() {
+    const x = new Bar();
+    (Object.getPrototypeOf(x): Foo);
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class Foo {}
+class Bar extends Foo {}
+let tests = [
+  function() {
+    const x = new Bar();
+    (Object.getPrototypeOf(x): Foo);
+  }
+];
+
+"
+`;
+
+exports[`test object_keys.js 1`] = `
+"/* @flow */
+
+var sealed = {one: \'one\', two: \'two\'};
+(Object.keys(sealed): Array<\'one\'|\'two\'>);
+(Object.keys(sealed): void); // error, Array<string>
+
+var unsealed = {};
+Object.keys(unsealed).forEach(k => {
+  (k : number) // error: number ~> string
+});
+
+var dict: { [k: number]: string } = {};
+Object.keys(dict).forEach(k => {
+  (k : number) // error: number ~> string
+});
+
+var any: Object = {};
+(Object.keys(any): Array<number>); // error, Array<string>
+
+class Foo {
+  prop: string;
+  foo() {}
+}
+// constructor and foo not enumerable
+(Object.keys(new Foo()): Array<\'error\'>); // error: prop ~> error
+
+class Bar extends Foo {
+  bar_prop: string;
+  bar() {}
+}
+// only own enumerable props
+(Object.keys(new Bar()): Array<\'error\'>); // error: bar_prop ~> error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test object_missing.js 1`] = `
+"// @flow
+
+let tests = [
+  function() {
+    Object.doesNotExist();
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  function() {
+    Object.doesNotExist();
+  }
+];
+
+"
+`;
+
+exports[`test object_prototype.js 1`] = `
+"/* @flow */
+
+function takesABool(x: boolean) {}
+function takesAString(x: string) {}
+function takesANumber(x: number) {}
+function takesAnObject(x: Object) {}
+
+class Foo {}
+
+var a = { foo: \'bar\' };
+var b = { foo: \'bar\', ...{}};
+var c = { foo: \'bar\', toString: function(): number { return 123; }};
+var d : { [key: string]: string } = { foo: \'bar\' };
+var x = new Date();
+var y = new Foo();
+
+//
+// toString
+//
+
+// call
+takesAString(a.toString());
+d.toString(); // ok, even though dict specifies strings, this is a function
+
+// get
+var aToString : () => string = a.toString;
+var aToString2 = a.toString;
+takesAString(aToString2());
+
+// set
+b.toString = function(): string { return \'foo\'; };
+c.toString = function(): number { return 123; };
+
+// override
+var cToString : () => number = c.toString;
+
+// ... on a built-in instance
+var xToString : number = x.toString; // error
+var xToString2 : () => number = x.toString; // error
+takesAString(x.toString());
+
+// ... on an instance
+var yToString : number = y.toString; // error
+takesAString(y.toString());
+
+// ... on a primitive
+(123).toString();
+(123).toString;
+(123).toString = function() {}; // error
+(123).toString(2);
+(123).toString(\'foo\'); // error
+(123).toString(null); // error
+
+
+//
+// hasOwnProperty
+//
+
+// call
+takesABool(a.hasOwnProperty(\'foo\'));
+
+// get
+var aHasOwnProperty : (prop: string) => boolean = a.hasOwnProperty;
+var aHasOwnProperty2 = a.hasOwnProperty;
+takesABool(aHasOwnProperty2(\'bar\'));
+
+// set
+b.hasOwnProperty = function() { return false; };
+
+// ... on a built-in instance
+var xHasOwnProperty : number = x.hasOwnProperty; // error
+var xHasOwnProperty2 : (prop: string) => number = x.hasOwnProperty; // error
+takesABool(x.hasOwnProperty(\'foo\'));
+
+// ... on an instance
+var yHasOwnProperty : number = y.hasOwnProperty; // error
+takesABool(y.hasOwnProperty(\'foo\'));
+
+
+//
+// propertyIsEnumerable
+//
+
+// call
+takesABool(a.propertyIsEnumerable(\'foo\'));
+
+// get
+var aPropertyIsEnumerable : (prop: string) => boolean = a.propertyIsEnumerable;
+var aPropertyIsEnumerable2 = a.propertyIsEnumerable;
+takesABool(aPropertyIsEnumerable2(\'bar\'));
+
+// set
+b.propertyIsEnumerable = function() { return false; };
+
+// ... on a built-in instance
+var xPropertyIsEnumerable : number = x.propertyIsEnumerable; // error
+var xPropertyIsEnumerable2 : (prop: string) => number =
+  x.propertyIsEnumerable; // error
+takesABool(x.propertyIsEnumerable(\'foo\'));
+
+// ... on an instance
+var yPropertyIsEnumerable : number = y.propertyIsEnumerable; // error
+takesABool(y.propertyIsEnumerable(\'foo\'));
+
+
+//
+// valueOf
+//
+
+// call
+takesAnObject(a.valueOf());
+
+// get
+var aValueOf : () => Object = a.valueOf;
+var aValueOf2 = a.valueOf;
+takesAnObject(aValueOf2());
+
+// set
+b.valueOf = function() { return {}; };
+
+// ... on a built-in instance
+var xValueOf : number = x.valueOf; // error
+takesANumber(x.valueOf());
+
+// ... on an instance
+var yValueOf : number = y.valueOf; // error
+takesAnObject(y.valueOf());
+
+// ... on a literal
+var strValueOf : string = (\"foo\").valueOf();
+var numValueOf : number = (123).valueOf();
+var boolValueOf : boolean = (true).valueOf();
+
+//
+// toLocaleString
+//
+
+// call
+takesAString(a.toLocaleString());
+
+// get
+var aToLocaleString : () => string = a.toLocaleString;
+var aToLocaleString2 = a.toLocaleString;
+takesAString(aToLocaleString2());
+
+// set
+b.toLocaleString = function() { return \'derp\'; };
+
+// ... on a built-in instance
+var xToLocaleString : number = x.toLocaleString; // error
+var xToLocaleString2 : () => number = x.toLocaleString; // error
+takesAString(x.toLocaleString());
+
+// ... on an instance
+var yToLocaleString : number = y.toLocaleString; // error
+takesAString(y.toLocaleString());
+
+
+//
+// constructor
+//
+
+var k : Object = a.constructor;
+(123).constructor;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/object_api/a.js b/tests/object_api/a.js
new file mode 100644
index 000000000000..934ca8eb8e02
--- /dev/null
+++ b/tests/object_api/a.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+module.exports = { a() {} };
\ No newline at end of file
diff --git a/tests/object_api/b.js b/tests/object_api/b.js
new file mode 100644
index 000000000000..8b324fb26c73
--- /dev/null
+++ b/tests/object_api/b.js
@@ -0,0 +1,6 @@
+/* @flow */
+
+var a = require('./a');
+var b = Object.assign({ bar() {}, ...{} }, a);
+b.a(); // works here
+module.exports = b;
diff --git a/tests/object_api/c.js b/tests/object_api/c.js
new file mode 100644
index 000000000000..69a6c4b46ea1
--- /dev/null
+++ b/tests/object_api/c.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+var c = require('./b');
+c.a();
+c.foo();
\ No newline at end of file
diff --git a/tests/object_api/jsfmt.spec.js b/tests/object_api/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/object_api/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/object_api/object_assign.js b/tests/object_api/object_assign.js
new file mode 100644
index 000000000000..16e86b66e88c
--- /dev/null
+++ b/tests/object_api/object_assign.js
@@ -0,0 +1,12 @@
+/* @flow */
+
+var export_ = Object.assign({}, {
+    foo: function(param) { return param; }
+});
+
+var decl_export_: { foo: any; bar: any } = Object.assign({}, export_);
+
+let anyObj: Object = {};
+Object.assign(anyObj, anyObj); // makes sure this terminates
+
+module.exports = export_;
diff --git a/tests/object_api/object_create.js b/tests/object_api/object_create.js
new file mode 100644
index 000000000000..b73c200590db
--- /dev/null
+++ b/tests/object_api/object_create.js
@@ -0,0 +1,17 @@
+/* @flow */
+
+class C { foo: string; }
+
+// OK, `instanceof C` would be true
+(Object.create(C.prototype): C);
+
+// OK, `instanceof C` would be true
+(Object.create(new C): C);
+
+// error, object literals don't structurally match instances
+({ foo: "foo" }: C);
+
+// error, object types don't structurally match instances
+type O = { foo: string; }
+declare var o: O;
+(o: C);
diff --git a/tests/object_api/object_getprototypeof.js b/tests/object_api/object_getprototypeof.js
new file mode 100644
index 000000000000..74d5355376f2
--- /dev/null
+++ b/tests/object_api/object_getprototypeof.js
@@ -0,0 +1,11 @@
+// @flow
+
+class Foo {}
+class Bar extends Foo {}
+
+let tests = [
+  function() {
+    const x = new Bar();
+    (Object.getPrototypeOf(x): Foo);
+  },
+];
diff --git a/tests/object_api/object_keys.js b/tests/object_api/object_keys.js
new file mode 100644
index 000000000000..2af5c7fc21d6
--- /dev/null
+++ b/tests/object_api/object_keys.js
@@ -0,0 +1,32 @@
+/* @flow */
+
+var sealed = {one: 'one', two: 'two'};
+(Object.keys(sealed): Array<'one'|'two'>);
+(Object.keys(sealed): void); // error, Array<string>
+
+var unsealed = {};
+Object.keys(unsealed).forEach(k => {
+  (k : number) // error: number ~> string
+});
+
+var dict: { [k: number]: string } = {};
+Object.keys(dict).forEach(k => {
+  (k : number) // error: number ~> string
+});
+
+var any: Object = {};
+(Object.keys(any): Array<number>); // error, Array<string>
+
+class Foo {
+  prop: string;
+  foo() {}
+}
+// constructor and foo not enumerable
+(Object.keys(new Foo()): Array<'error'>); // error: prop ~> error
+
+class Bar extends Foo {
+  bar_prop: string;
+  bar() {}
+}
+// only own enumerable props
+(Object.keys(new Bar()): Array<'error'>); // error: bar_prop ~> error
diff --git a/tests/object_api/object_missing.js b/tests/object_api/object_missing.js
new file mode 100644
index 000000000000..8c33c2d94029
--- /dev/null
+++ b/tests/object_api/object_missing.js
@@ -0,0 +1,7 @@
+// @flow
+
+let tests = [
+  function() {
+    Object.doesNotExist();
+  },
+];
diff --git a/tests/object_api/object_prototype.js b/tests/object_api/object_prototype.js
new file mode 100644
index 000000000000..233028a7e6c0
--- /dev/null
+++ b/tests/object_api/object_prototype.js
@@ -0,0 +1,164 @@
+/* @flow */
+
+function takesABool(x: boolean) {}
+function takesAString(x: string) {}
+function takesANumber(x: number) {}
+function takesAnObject(x: Object) {}
+
+class Foo {}
+
+var a = { foo: 'bar' };
+var b = { foo: 'bar', ...{}};
+var c = { foo: 'bar', toString: function(): number { return 123; }};
+var d : { [key: string]: string } = { foo: 'bar' };
+var x = new Date();
+var y = new Foo();
+
+//
+// toString
+//
+
+// call
+takesAString(a.toString());
+d.toString(); // ok, even though dict specifies strings, this is a function
+
+// get
+var aToString : () => string = a.toString;
+var aToString2 = a.toString;
+takesAString(aToString2());
+
+// set
+b.toString = function(): string { return 'foo'; };
+c.toString = function(): number { return 123; };
+
+// override
+var cToString : () => number = c.toString;
+
+// ... on a built-in instance
+var xToString : number = x.toString; // error
+var xToString2 : () => number = x.toString; // error
+takesAString(x.toString());
+
+// ... on an instance
+var yToString : number = y.toString; // error
+takesAString(y.toString());
+
+// ... on a primitive
+(123).toString();
+(123).toString;
+(123).toString = function() {}; // error
+(123).toString(2);
+(123).toString('foo'); // error
+(123).toString(null); // error
+
+
+//
+// hasOwnProperty
+//
+
+// call
+takesABool(a.hasOwnProperty('foo'));
+
+// get
+var aHasOwnProperty : (prop: string) => boolean = a.hasOwnProperty;
+var aHasOwnProperty2 = a.hasOwnProperty;
+takesABool(aHasOwnProperty2('bar'));
+
+// set
+b.hasOwnProperty = function() { return false; };
+
+// ... on a built-in instance
+var xHasOwnProperty : number = x.hasOwnProperty; // error
+var xHasOwnProperty2 : (prop: string) => number = x.hasOwnProperty; // error
+takesABool(x.hasOwnProperty('foo'));
+
+// ... on an instance
+var yHasOwnProperty : number = y.hasOwnProperty; // error
+takesABool(y.hasOwnProperty('foo'));
+
+
+//
+// propertyIsEnumerable
+//
+
+// call
+takesABool(a.propertyIsEnumerable('foo'));
+
+// get
+var aPropertyIsEnumerable : (prop: string) => boolean = a.propertyIsEnumerable;
+var aPropertyIsEnumerable2 = a.propertyIsEnumerable;
+takesABool(aPropertyIsEnumerable2('bar'));
+
+// set
+b.propertyIsEnumerable = function() { return false; };
+
+// ... on a built-in instance
+var xPropertyIsEnumerable : number = x.propertyIsEnumerable; // error
+var xPropertyIsEnumerable2 : (prop: string) => number =
+  x.propertyIsEnumerable; // error
+takesABool(x.propertyIsEnumerable('foo'));
+
+// ... on an instance
+var yPropertyIsEnumerable : number = y.propertyIsEnumerable; // error
+takesABool(y.propertyIsEnumerable('foo'));
+
+
+//
+// valueOf
+//
+
+// call
+takesAnObject(a.valueOf());
+
+// get
+var aValueOf : () => Object = a.valueOf;
+var aValueOf2 = a.valueOf;
+takesAnObject(aValueOf2());
+
+// set
+b.valueOf = function() { return {}; };
+
+// ... on a built-in instance
+var xValueOf : number = x.valueOf; // error
+takesANumber(x.valueOf());
+
+// ... on an instance
+var yValueOf : number = y.valueOf; // error
+takesAnObject(y.valueOf());
+
+// ... on a literal
+var strValueOf : string = ("foo").valueOf();
+var numValueOf : number = (123).valueOf();
+var boolValueOf : boolean = (true).valueOf();
+
+//
+// toLocaleString
+//
+
+// call
+takesAString(a.toLocaleString());
+
+// get
+var aToLocaleString : () => string = a.toLocaleString;
+var aToLocaleString2 = a.toLocaleString;
+takesAString(aToLocaleString2());
+
+// set
+b.toLocaleString = function() { return 'derp'; };
+
+// ... on a built-in instance
+var xToLocaleString : number = x.toLocaleString; // error
+var xToLocaleString2 : () => number = x.toLocaleString; // error
+takesAString(x.toLocaleString());
+
+// ... on an instance
+var yToLocaleString : number = y.toLocaleString; // error
+takesAString(y.toLocaleString());
+
+
+//
+// constructor
+//
+
+var k : Object = a.constructor;
+(123).constructor;
diff --git a/tests/object_assign/A.js b/tests/object_assign/A.js
new file mode 100644
index 000000000000..8a7fa79901e7
--- /dev/null
+++ b/tests/object_assign/A.js
@@ -0,0 +1,26 @@
+/**
+ * @flow
+ */
+
+var EventEmitter = require('events').EventEmitter;
+
+// This pattern seems to cause the trouble.
+var Bad = Object.assign({}, EventEmitter.prototype, {
+  foo: function(): string { return 'hi'; }
+});
+
+// Calling Bad.foo() in the same file doesn't error
+var bad: number = Bad.foo();
+
+// Doesn't repro if I extend the class myself
+class MyEventEmitter extends events$EventEmitter {}
+var Good = Object.assign({}, MyEventEmitter.prototype, {
+  foo: function(): string { return 'hi'; }
+});
+// Calling Good.foo() in the same file doesn't error
+var good: number = Good.foo();
+
+module.exports = {
+  Bad: Bad,
+  Good: Good,
+};
diff --git a/tests/object_assign/B.js b/tests/object_assign/B.js
new file mode 100644
index 000000000000..40278d660844
--- /dev/null
+++ b/tests/object_assign/B.js
@@ -0,0 +1,17 @@
+/**
+ * @flow
+ */
+
+var A = require('./A.js');
+
+var good: number = A.Good.foo();
+
+var f = A.Bad.foo; // Property access is fine
+var bad_: number = f(); // Calling the function is fine
+
+var bad: number = A.Bad.foo(); // Method call is not fine
+/*
+B.js|12 col 1 error|  call of method foo
+|| Property not found in
+A.js|8 col 23 error|  object literal
+*/
diff --git a/tests/object_assign/__snapshots__/jsfmt.spec.js.snap b/tests/object_assign/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..47c18dc07b7e
--- /dev/null
+++ b/tests/object_assign/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,166 @@
+exports[`test A.js 1`] = `
+"/**
+ * @flow
+ */
+
+var EventEmitter = require('events').EventEmitter;
+
+// This pattern seems to cause the trouble.
+var Bad = Object.assign({}, EventEmitter.prototype, {
+  foo: function(): string { return 'hi'; }
+});
+
+// Calling Bad.foo() in the same file doesn't error
+var bad: number = Bad.foo();
+
+// Doesn't repro if I extend the class myself
+class MyEventEmitter extends events$EventEmitter {}
+var Good = Object.assign({}, MyEventEmitter.prototype, {
+  foo: function(): string { return 'hi'; }
+});
+// Calling Good.foo() in the same file doesn't error
+var good: number = Good.foo();
+
+module.exports = {
+  Bad: Bad,
+  Good: Good,
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+var EventEmitter = require("events").EventEmitter;
+// This pattern seems to cause the trouble.
+var Bad = Object.assign(
+  {},
+  EventEmitter.prototype,
+  {
+    foo: function(): string {
+      return "hi";
+    }
+  }
+);
+// Calling Bad.foo() in the same file doesn't error
+var bad: number = Bad.foo();
+// Doesn't repro if I extend the class myself
+class MyEventEmitter extends events$EventEmitter {}
+var Good = Object.assign(
+  {},
+  MyEventEmitter.prototype,
+  {
+    foo: function(): string {
+      return "hi";
+    }
+  }
+);
+// Calling Good.foo() in the same file doesn't error
+var good: number = Good.foo();
+module.exports = { Bad: Bad, Good: Good };
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"/**
+ * @flow
+ */
+
+var A = require('./A.js');
+
+var good: number = A.Good.foo();
+
+var f = A.Bad.foo; // Property access is fine
+var bad_: number = f(); // Calling the function is fine
+
+var bad: number = A.Bad.foo(); // Method call is not fine
+/*
+B.js|12 col 1 error|  call of method foo
+|| Property not found in
+A.js|8 col 23 error|  object literal
+*/
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+var A = require("./A.js");
+var good: number = A.Good.foo();
+var f = A.Bad.foo;// Property access is fine
+var bad_: number = f();// Calling the function is fine
+var bad: number = A.Bad.foo();// Method call is not fine/*
+B.js|12 col 1 error|  call of method foo
+|| Property not found in
+A.js|8 col 23 error|  object literal
+*/
+
+"
+`;
+
+exports[`test apply.js 1`] = `
+"// @flow
+
+(Object.assign.apply(null, [{}, {a: 1}, {b: 'foo'}]): {a: number, b: string});
+(Object.assign({}, ...[{a: 1}, {b: 'foo'}]): {a: number, b: string});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+(Object.assign.apply(null, [ {}, { a: 1 }, { b: "foo" } ]): {
+  a: number,
+  b: string
+});
+(Object.assign({}, ...[ { a: 1 }, { b: "foo" } ]): { a: number, b: string });
+
+"
+`;
+
+exports[`test non_objects.js 1`] = `
+"/* @flow */
+
+Object.assign("123", {a: "foo"});
+Object.assign(123, {a: "foo"});
+Object.assign({a: "foo"}, 123);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+Object.assign("123", { a: "foo" });
+Object.assign(123, { a: "foo" });
+Object.assign({ a: "foo" }, 123);
+
+"
+`;
+
+exports[`test undefined.js 1`] = `
+"/* @flow */
+
+var React = require('react');
+
+type DefaultProps = {
+  foo: number,
+}
+
+type Props = {
+  foo: number,
+}
+
+class MyReactThing extends React.Component {
+  props: Props;
+  static defaultProps: DefaultProps;
+  getFoo(): number { return this.props.foo; }
+}
+
+<MyReactThing />; // works
+<MyReactThing foo={undefined} />; // also works
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require("react");
+type DefaultProps = { foo: number };
+type Props = { foo: number };
+class MyReactThing extends React.Component {
+  props: Props;
+  static defaultProps: DefaultProps;
+  getFoo(): number {
+    return this.props.foo;
+  }
+}
+<MyReactThing/>;// works
+<MyReactThing foo={undefined}/>;// also works
+
+"
+`;
diff --git a/tests/object_assign/apply.js b/tests/object_assign/apply.js
new file mode 100644
index 000000000000..6bb4c551eab8
--- /dev/null
+++ b/tests/object_assign/apply.js
@@ -0,0 +1,4 @@
+// @flow
+
+(Object.assign.apply(null, [{}, {a: 1}, {b: 'foo'}]): {a: number, b: string});
+(Object.assign({}, ...[{a: 1}, {b: 'foo'}]): {a: number, b: string});
diff --git a/tests/object_assign/jsfmt.spec.js b/tests/object_assign/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/object_assign/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/object_assign/non_objects.js b/tests/object_assign/non_objects.js
new file mode 100644
index 000000000000..8cb9b564d6ee
--- /dev/null
+++ b/tests/object_assign/non_objects.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+Object.assign("123", {a: "foo"});
+Object.assign(123, {a: "foo"});
+Object.assign({a: "foo"}, 123);
diff --git a/tests/object_assign/undefined.js b/tests/object_assign/undefined.js
new file mode 100644
index 000000000000..27b1d0b9f44d
--- /dev/null
+++ b/tests/object_assign/undefined.js
@@ -0,0 +1,20 @@
+/* @flow */
+
+var React = require('react');
+
+type DefaultProps = {
+  foo: number,
+}
+
+type Props = {
+  foo: number,
+}
+
+class MyReactThing extends React.Component {
+  props: Props;
+  static defaultProps: DefaultProps;
+  getFoo(): number { return this.props.foo; }
+}
+
+<MyReactThing />; // works
+<MyReactThing foo={undefined} />; // also works
diff --git a/tests/object_freeze/__snapshots__/jsfmt.spec.js.snap b/tests/object_freeze/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2eed145c9e9b
--- /dev/null
+++ b/tests/object_freeze/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,41 @@
+exports[`test object_freeze.js 1`] = `
+"/* @flow */
+
+var foo = Object.freeze({bar: '12345'});
+foo.bar = '23456'; // error
+
+Object.assign(foo, {bar: '12345'}); // error
+
+var baz = {baz: 12345};
+var bliffl = Object.freeze({bar: '12345', ...baz});
+bliffl.bar = '23456'; // error
+bliffl.baz = 3456; // error
+bliffl.corge; // error
+bliffl.constructor = baz; // error
+bliffl.toString = function() {}; // error
+
+baz.baz = 0;
+
+var x : number = Object.freeze(123);
+
+var xx : { x: number } = Object.freeze({ x: "error" })
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var foo = Object.freeze({ bar: "12345" });
+foo.bar = "23456";// error
+Object.assign(foo, { bar: "12345" });// error
+var baz = { baz: 12345 };
+var bliffl = Object.freeze({ bar: "12345", ...baz });
+bliffl.bar = "23456";// error
+bliffl.baz = 3456;// error
+bliffl.corge;// error
+bliffl.constructor = baz;// error
+bliffl.toString = function() {
+  
+};// error
+baz.baz = 0;
+var x: number = Object.freeze(123);
+var xx: { x: number } = Object.freeze({ x: "error" });
+
+"
+`;
diff --git a/tests/object_freeze/jsfmt.spec.js b/tests/object_freeze/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/object_freeze/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/object_freeze/object_freeze.js b/tests/object_freeze/object_freeze.js
new file mode 100644
index 000000000000..cc192b2115aa
--- /dev/null
+++ b/tests/object_freeze/object_freeze.js
@@ -0,0 +1,20 @@
+/* @flow */
+
+var foo = Object.freeze({bar: '12345'});
+foo.bar = '23456'; // error
+
+Object.assign(foo, {bar: '12345'}); // error
+
+var baz = {baz: 12345};
+var bliffl = Object.freeze({bar: '12345', ...baz});
+bliffl.bar = '23456'; // error
+bliffl.baz = 3456; // error
+bliffl.corge; // error
+bliffl.constructor = baz; // error
+bliffl.toString = function() {}; // error
+
+baz.baz = 0;
+
+var x : number = Object.freeze(123);
+
+var xx : { x: number } = Object.freeze({ x: "error" })
diff --git a/tests/object_is/__snapshots__/jsfmt.spec.js.snap b/tests/object_is/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..712ce14a0089
--- /dev/null
+++ b/tests/object_is/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,46 @@
+exports[`test object_is.js 1`] = `
+"Object.is(1, 1);
+Object.is(1, 2);
+Object.is(1, {});
+Object.is(1, NaN);
+Object.is(0, 0);
+Object.is(0, -0);
+Object.is(NaN, NaN);
+Object.is({}, {});
+
+var emptyObject = {};
+var emptyArray = [];
+Object.is(emptyObject, emptyObject);
+Object.is(emptyArray, emptyArray);
+Object.is(emptyObject, emptyArray);
+
+var squared = x => x * x;
+Object.is(squared, squared);
+
+var a: boolean = Object.is('a', 'a');
+var b: string = Object.is('a', 'a');
+var c: boolean = Object.is('a');
+var d: boolean = Object.is('a', 'b', 'c');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Object.is(1, 1);
+Object.is(1, 2);
+Object.is(1, {});
+Object.is(1, NaN);
+Object.is(0, 0);
+Object.is(0, -0);
+Object.is(NaN, NaN);
+Object.is({}, {});
+var emptyObject = {};
+var emptyArray = [  ];
+Object.is(emptyObject, emptyObject);
+Object.is(emptyArray, emptyArray);
+Object.is(emptyObject, emptyArray);
+var squared = x => x * x;
+Object.is(squared, squared);
+var a: boolean = Object.is("a", "a");
+var b: string = Object.is("a", "a");
+var c: boolean = Object.is("a");
+var d: boolean = Object.is("a", "b", "c");
+
+"
+`;
diff --git a/tests/object_is/jsfmt.spec.js b/tests/object_is/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/object_is/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/object_is/object_is.js b/tests/object_is/object_is.js
new file mode 100644
index 000000000000..a13f2e3baed7
--- /dev/null
+++ b/tests/object_is/object_is.js
@@ -0,0 +1,22 @@
+Object.is(1, 1);
+Object.is(1, 2);
+Object.is(1, {});
+Object.is(1, NaN);
+Object.is(0, 0);
+Object.is(0, -0);
+Object.is(NaN, NaN);
+Object.is({}, {});
+
+var emptyObject = {};
+var emptyArray = [];
+Object.is(emptyObject, emptyObject);
+Object.is(emptyArray, emptyArray);
+Object.is(emptyObject, emptyArray);
+
+var squared = x => x * x;
+Object.is(squared, squared);
+
+var a: boolean = Object.is('a', 'a');
+var b: string = Object.is('a', 'a');
+var c: boolean = Object.is('a');
+var d: boolean = Object.is('a', 'b', 'c');
diff --git a/tests/objects/__snapshots__/jsfmt.spec.js.snap b/tests/objects/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..daae00078b05
--- /dev/null
+++ b/tests/objects/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,125 @@
+exports[`test conversion.js 1`] = `
+"/* @flow */
+
+(Object({foo: \'bar\'}): {foo: string});
+(Object(\"123\"): String);
+(Object(123): Number);
+(Object(true): Boolean);
+(Object(null): {});
+(Object(undefined): {});
+(Object(void(0)): {});
+(Object(undefined): Number); // error
+
+var x = Object(null);
+x.foo = \"bar\";
+
+var y = Object(\"123\");
+(y.charAt(0): string);
+
+var z = Object(123); // error (next line makes this not match any signatures)
+(z.charAt(0): string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+(Object({ foo: \"bar\" }): { foo: string });
+(Object(\"123\"): String);
+(Object(123): Number);
+(Object(true): Boolean);
+(Object(null): {});
+(Object(undefined): {});
+(Object(void 0): {});
+(Object(undefined): Number);// error
+var x = Object(null);
+x.foo = \"bar\";
+var y = Object(\"123\");
+(y.charAt(0): string);
+var z = Object(123);// error (next line makes this not match any signatures)
+(z.charAt(0): string);
+
+"
+`;
+
+exports[`test objects.js 1`] = `
+"/* @flow */
+
+var x : {\'123\': string, bar: string} = {\'123\': \'val\', bar: \'bar\'};
+(x.foo : string);     // error, key doesn\'t exist
+(x[\'foo\'] : string);  // error, key doesn\'t exist
+(x[123] : boolean);   // TODO: use the number\'s value to error here
+(x.bar: boolean);     // error, string !~> boolean
+(x[\'123\'] : boolean); // error, string !~> boolean
+x[\'123\'] = false;     // error, boolean !~> string
+x[123] = false;       // TODO: use the number\'s value to error here
+x[\'foo\'+\'bar\'] = \'derp\'; // ok since we can\'t tell
+(x[\`foo\`]: string);   // error, key doesn\'t exist
+
+var y : {foo: string} = {foo: \'bar\'};
+y[\'foo\'] = 123; // error, number !~> string
+y[\'bar\'] = \'abc\'; // error, property not found
+
+(y[\'hasOwnProperty\']: string); // error, prototype method is not a string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var x: { \"123\": string, bar: string } = { \"123\": \"val\", bar: \"bar\" };
+(x.foo: string);// error, key doesn\'t exist
+(x[\"foo\"]: string);// error, key doesn\'t exist
+(x[123]: boolean);// TODO: use the number\'s value to error here
+(x.bar: boolean);// error, string !~> boolean
+(x[\"123\"]: boolean);// error, string !~> boolean
+x[\"123\"] = false;// error, boolean !~> string
+x[123] = false;// TODO: use the number\'s value to error here
+x[\"foo\" + \"bar\"] = \"derp\";// ok since we can\'t tell
+(x[\`foo\`]: string);// error, key doesn\'t exist
+var y: { foo: string } = { foo: \"bar\" };
+y[\"foo\"] = 123;// error, number !~> string
+y[\"bar\"] = \"abc\";// error, property not found
+(y[\"hasOwnProperty\"]: string);// error, prototype method is not a string
+
+"
+`;
+
+exports[`test unaliased_assign.js 1`] = `
+"/**
+ * test handling of unaliased value assignment.
+ *
+ * An unaliased object rvalue may be assigned to a supertype lvalue,
+ * because later widening mutations on the rvalue can\'t break assumptions
+ * made by other lvalues.
+ *
+ * However, upon assignment the rvalue must take on the type of the
+ * lvalue, to avoid both false positives and false negatives
+ * (unsoundness), as shown below.
+ *
+ * @flow
+ */
+
+var glob: { x: string } = { x: \"hey\" };
+
+function assign_then_alias() {
+  var obj: { x: string | number };
+  obj = { x: \"hey\" };
+  glob = obj;    // error: subsequent assignment might make glob.x a number
+}
+
+function assign_then_widen() {
+  var obj: { x: string | number };
+  obj = { x: \"hey\" };
+  obj.x = 10;  // ok, by lvalue\'s given type
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/objects/conversion.js b/tests/objects/conversion.js
new file mode 100644
index 000000000000..48cc52980743
--- /dev/null
+++ b/tests/objects/conversion.js
@@ -0,0 +1,19 @@
+/* @flow */
+
+(Object({foo: 'bar'}): {foo: string});
+(Object("123"): String);
+(Object(123): Number);
+(Object(true): Boolean);
+(Object(null): {});
+(Object(undefined): {});
+(Object(void(0)): {});
+(Object(undefined): Number); // error
+
+var x = Object(null);
+x.foo = "bar";
+
+var y = Object("123");
+(y.charAt(0): string);
+
+var z = Object(123); // error (next line makes this not match any signatures)
+(z.charAt(0): string);
diff --git a/tests/objects/jsfmt.spec.js b/tests/objects/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/objects/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/objects/objects.js b/tests/objects/objects.js
new file mode 100644
index 000000000000..5eea185f7041
--- /dev/null
+++ b/tests/objects/objects.js
@@ -0,0 +1,18 @@
+/* @flow */
+
+var x : {'123': string, bar: string} = {'123': 'val', bar: 'bar'};
+(x.foo : string);     // error, key doesn't exist
+(x['foo'] : string);  // error, key doesn't exist
+(x[123] : boolean);   // TODO: use the number's value to error here
+(x.bar: boolean);     // error, string !~> boolean
+(x['123'] : boolean); // error, string !~> boolean
+x['123'] = false;     // error, boolean !~> string
+x[123] = false;       // TODO: use the number's value to error here
+x['foo'+'bar'] = 'derp'; // ok since we can't tell
+(x[`foo`]: string);   // error, key doesn't exist
+
+var y : {foo: string} = {foo: 'bar'};
+y['foo'] = 123; // error, number !~> string
+y['bar'] = 'abc'; // error, property not found
+
+(y['hasOwnProperty']: string); // error, prototype method is not a string
diff --git a/tests/objects/unaliased_assign.js b/tests/objects/unaliased_assign.js
new file mode 100644
index 000000000000..c1cebeea5260
--- /dev/null
+++ b/tests/objects/unaliased_assign.js
@@ -0,0 +1,27 @@
+/**
+ * test handling of unaliased value assignment.
+ *
+ * An unaliased object rvalue may be assigned to a supertype lvalue,
+ * because later widening mutations on the rvalue can't break assumptions
+ * made by other lvalues.
+ *
+ * However, upon assignment the rvalue must take on the type of the
+ * lvalue, to avoid both false positives and false negatives
+ * (unsoundness), as shown below.
+ *
+ * @flow
+ */
+
+var glob: { x: string } = { x: "hey" };
+
+function assign_then_alias() {
+  var obj: { x: string | number };
+  obj = { x: "hey" };
+  glob = obj;    // error: subsequent assignment might make glob.x a number
+}
+
+function assign_then_widen() {
+  var obj: { x: string | number };
+  obj = { x: "hey" };
+  obj.x = 10;  // ok, by lvalue's given type
+}
diff --git a/tests/objmap/__snapshots__/jsfmt.spec.js.snap b/tests/objmap/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..59efee2952c0
--- /dev/null
+++ b/tests/objmap/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,37 @@
+exports[`test objmap.js 1`] = `
+"declare function promiseAllByKey<O>(o: O): Promise<$ObjMap<O,typeof $await>>;
+declare function keyMirror<O>(o: O): $ObjMapi<O, <K>(k:K) => K>;
+
+var o = keyMirror({
+  FOO: null,
+  BAR: null,
+});
+
+(o.FOO : \'FOO\'); // ok
+(o.FOO : \'BAR\'); // error, \'FOO\' incompatible with \'BAR\'
+
+promiseAllByKey({
+  foo: Promise.resolve(0),
+  bar: \'bar\',
+}).then(o => {
+  (o.foo: string); // error, number ~> string
+  (o.bar: \'bar\'); // ok
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/objmap/jsfmt.spec.js b/tests/objmap/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/objmap/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/objmap/objmap.js b/tests/objmap/objmap.js
new file mode 100644
index 000000000000..2bdd9fd2ddc9
--- /dev/null
+++ b/tests/objmap/objmap.js
@@ -0,0 +1,18 @@
+declare function promiseAllByKey<O>(o: O): Promise<$ObjMap<O,typeof $await>>;
+declare function keyMirror<O>(o: O): $ObjMapi<O, <K>(k:K) => K>;
+
+var o = keyMirror({
+  FOO: null,
+  BAR: null,
+});
+
+(o.FOO : 'FOO'); // ok
+(o.FOO : 'BAR'); // error, 'FOO' incompatible with 'BAR'
+
+promiseAllByKey({
+  foo: Promise.resolve(0),
+  bar: 'bar',
+}).then(o => {
+  (o.foo: string); // error, number ~> string
+  (o.bar: 'bar'); // ok
+});
diff --git a/tests/optional/__snapshots__/jsfmt.spec.js.snap b/tests/optional/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..df6981ed082c
--- /dev/null
+++ b/tests/optional/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,407 @@
+exports[`test client_optional.js 1`] = `
+"var qux = require(\'./optional\');
+
+qux(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var qux = require(\"./optional\");
+qux(0);
+
+"
+`;
+
+exports[`test default.js 1`] = `
+"function f<T>(foo, bar = foo): [T, T] {
+  return [foo, bar];
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test generic.js 1`] = `
+"function x<T>(x: T = 0) {}
+
+class C {
+  x<T>(x: T = 0) {}
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test maybe.js 1`] = `
+"function foo(x?: string): ?string {
+    return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(x: string): ?string {
+  return x;
+}
+
+"
+`;
+
+exports[`test nullable.js 1`] = `
+"/* @flow */
+
+function optionalNullable1(x: {y?: ?number}) {
+  if (x.y !== null && x.y !== undefined) {
+    x.y++;
+  }
+}
+
+function optionalNullable2(x: {y?: ?number}) {
+  if (x.y !== undefined && x.y !== null) {
+    x.y++;
+  }
+}
+
+function optionalNullable3(x: {y?: ?number}) {
+  if (!(x.y !== null && x.y !== undefined)) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable4(x: {y?: ?number}) {
+  if (!(x.y !== undefined && x.y !== null)) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable5(x: {y?: ?number}) {
+  if (x.y === null || x.y === undefined) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable6(x: {y?: ?number}) {
+  if (x.y === undefined || x.y === null) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable7(x: {y?: ?number}) {
+  if (!(x.y === null || x.y === undefined)) {
+    x.y++;
+  }
+}
+
+function optionalNullable8(x: {y?: ?number}) {
+  if (!(x.y === undefined || x.y === null)) {
+    x.y++;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function optionalNullable1(x: { y?: ?number }) {
+  if (x.y !== null && x.y !== undefined) {
+    x.y++;
+  }
+}
+function optionalNullable2(x: { y?: ?number }) {
+  if (x.y !== undefined && x.y !== null) {
+    x.y++;
+  }
+}
+function optionalNullable3(x: { y?: ?number }) {
+  if (!(x.y !== null && x.y !== undefined)) {
+    x.y++;// should error
+  }
+}
+function optionalNullable4(x: { y?: ?number }) {
+  if (!(x.y !== undefined && x.y !== null)) {
+    x.y++;// should error
+  }
+}
+function optionalNullable5(x: { y?: ?number }) {
+  if (x.y === null || x.y === undefined) {
+    x.y++;// should error
+  }
+}
+function optionalNullable6(x: { y?: ?number }) {
+  if (x.y === undefined || x.y === null) {
+    x.y++;// should error
+  }
+}
+function optionalNullable7(x: { y?: ?number }) {
+  if (!(x.y === null || x.y === undefined)) {
+    x.y++;
+  }
+}
+function optionalNullable8(x: { y?: ?number }) {
+  if (!(x.y === undefined || x.y === null)) {
+    x.y++;
+  }
+}
+
+"
+`;
+
+exports[`test optional.js 1`] = `
+"function bar(x?,y?) { x * 0; }
+bar(0);
+
+var foo:(x?:number)=>void = bar;
+foo();
+
+function qux(x=\"hello\",...y):string { foo(x); return y[0]; }
+
+qux(0,0);
+qux(0,...[\"\",42]);
+
+module.exports = qux;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test optional_param.js 1`] = `
+"/* @flow */
+function foo(x?: string): string {
+    if (x == null) { return \'foo\'; }
+    return x;
+}
+
+function bar(obj: {x?: string}): string {
+    if (obj.x == null) { return \'foo\'; }
+    return obj.x;
+}
+
+function baz(bar?) {
+    if (!bar) { return 1; }
+    return bar.duck
+}
+
+function testOptionalNullable(x?: ?string): string {
+    if (x == null) { return \'foo\'; }
+    return x;
+}
+
+function testOptionalNullableDefault(x?: ?string = \"hi\"): string {
+    if (x == null) { return \'foo\'; }
+    return x;
+}
+
+function testOptionalNullableProperty(obj: {x?: ?string}): string {
+    if (obj.x == null) { return \'foo\'; }
+    return obj.x;
+}
+
+function testOptionalNullableFlowingToNullable(x?: ?string): ?string {
+  var f = function(y: ?string) {};
+  f(x);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo(x: string): string {
+  if (x == null) {
+    return \"foo\";
+  }
+  return x;
+}
+function bar(obj: { x?: string }): string {
+  if (obj.x == null) {
+    return \"foo\";
+  }
+  return obj.x;
+}
+function baz(bar) {
+  if (!bar) {
+    return 1;
+  }
+  return bar.duck;
+}
+function testOptionalNullable(x: ?string): string {
+  if (x == null) {
+    return \"foo\";
+  }
+  return x;
+}
+function testOptionalNullableDefault(x: ?string = \"hi\"): string {
+  if (x == null) {
+    return \"foo\";
+  }
+  return x;
+}
+function testOptionalNullableProperty(obj: { x?: ?string }): string {
+  if (obj.x == null) {
+    return \"foo\";
+  }
+  return obj.x;
+}
+function testOptionalNullableFlowingToNullable(x: ?string): ?string {
+  var f = function(y: ?string) {
+    
+  };
+  f(x);
+}
+
+"
+`;
+
+exports[`test optional_param2.js 1`] = `
+"declare class I<V> {
+    map<M>(
+        mapper: (value?: V) => M
+    ): I<M>;
+}
+var i:I<number> = new I();
+var j:I<number> = i.map(id => id);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1368:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test optional_param3.js 1`] = `
+"function foo(x?: number) {}
+foo(undefined); // ok
+
+function bar(x = \"bar\"): string {
+  return x;
+}
+bar(undefined); // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(x: number) {
+  
+}
+foo(undefined);// ok
+function bar(x = \"bar\"): string {
+  return x;
+}
+bar(undefined);// ok
+
+"
+`;
+
+exports[`test optional_param4.js 1`] = `
+"/* @flow */
+
+function foo(x?: number, ...y: Array<string>): [?number, Array<string>] {
+  return [x, y];
+}
+
+foo(); // OK
+foo(123), // OK
+foo(123, \'hello\'); // OK
+
+
+foo(true); // ERROR boolean ~> number
+foo(123, true); // ERROR boolean ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test undefined.js 1`] = `
+"var x;
+
+function foo(bar? = undefined) {
+    x = bar;
+}
+
+function bar() {
+    return x.duck;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x;
+function foo(bar = undefined) {
+  x = bar;
+}
+function bar() {
+  return x.duck;
+}
+
+"
+`;
+
+exports[`test undefined2.js 1`] = `
+"var x;
+
+function foo(bar?) {
+    x = bar;
+}
+
+function bar() {
+    return x.duck;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x;
+function foo(bar) {
+  x = bar;
+}
+function bar() {
+  return x.duck;
+}
+
+"
+`;
diff --git a/tests/optional/client_optional.js b/tests/optional/client_optional.js
new file mode 100644
index 000000000000..1f7d6b7bb0b1
--- /dev/null
+++ b/tests/optional/client_optional.js
@@ -0,0 +1,3 @@
+var qux = require('./optional');
+
+qux(0);
diff --git a/tests/optional/default.js b/tests/optional/default.js
new file mode 100644
index 000000000000..48d31c63ba77
--- /dev/null
+++ b/tests/optional/default.js
@@ -0,0 +1,3 @@
+function f<T>(foo, bar = foo): [T, T] {
+  return [foo, bar];
+}
diff --git a/tests/optional/generic.js b/tests/optional/generic.js
new file mode 100644
index 000000000000..3fb2a4d6c460
--- /dev/null
+++ b/tests/optional/generic.js
@@ -0,0 +1,5 @@
+function x<T>(x: T = 0) {}
+
+class C {
+  x<T>(x: T = 0) {}
+}
diff --git a/tests/optional/jsfmt.spec.js b/tests/optional/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/optional/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/optional/maybe.js b/tests/optional/maybe.js
new file mode 100644
index 000000000000..d2266e6d22a4
--- /dev/null
+++ b/tests/optional/maybe.js
@@ -0,0 +1,3 @@
+function foo(x?: string): ?string {
+    return x;
+}
diff --git a/tests/optional/nullable.js b/tests/optional/nullable.js
new file mode 100644
index 000000000000..509397894097
--- /dev/null
+++ b/tests/optional/nullable.js
@@ -0,0 +1,49 @@
+/* @flow */
+
+function optionalNullable1(x: {y?: ?number}) {
+  if (x.y !== null && x.y !== undefined) {
+    x.y++;
+  }
+}
+
+function optionalNullable2(x: {y?: ?number}) {
+  if (x.y !== undefined && x.y !== null) {
+    x.y++;
+  }
+}
+
+function optionalNullable3(x: {y?: ?number}) {
+  if (!(x.y !== null && x.y !== undefined)) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable4(x: {y?: ?number}) {
+  if (!(x.y !== undefined && x.y !== null)) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable5(x: {y?: ?number}) {
+  if (x.y === null || x.y === undefined) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable6(x: {y?: ?number}) {
+  if (x.y === undefined || x.y === null) {
+    x.y++; // should error
+  }
+}
+
+function optionalNullable7(x: {y?: ?number}) {
+  if (!(x.y === null || x.y === undefined)) {
+    x.y++;
+  }
+}
+
+function optionalNullable8(x: {y?: ?number}) {
+  if (!(x.y === undefined || x.y === null)) {
+    x.y++;
+  }
+}
diff --git a/tests/optional/optional.js b/tests/optional/optional.js
new file mode 100644
index 000000000000..79fa1d5317b9
--- /dev/null
+++ b/tests/optional/optional.js
@@ -0,0 +1,12 @@
+function bar(x?,y?) { x * 0; }
+bar(0);
+
+var foo:(x?:number)=>void = bar;
+foo();
+
+function qux(x="hello",...y):string { foo(x); return y[0]; }
+
+qux(0,0);
+qux(0,...["",42]);
+
+module.exports = qux;
diff --git a/tests/optional/optional_param.js b/tests/optional/optional_param.js
new file mode 100644
index 000000000000..5ba9b9a660ca
--- /dev/null
+++ b/tests/optional/optional_param.js
@@ -0,0 +1,35 @@
+/* @flow */
+function foo(x?: string): string {
+    if (x == null) { return 'foo'; }
+    return x;
+}
+
+function bar(obj: {x?: string}): string {
+    if (obj.x == null) { return 'foo'; }
+    return obj.x;
+}
+
+function baz(bar?) {
+    if (!bar) { return 1; }
+    return bar.duck
+}
+
+function testOptionalNullable(x?: ?string): string {
+    if (x == null) { return 'foo'; }
+    return x;
+}
+
+function testOptionalNullableDefault(x?: ?string = "hi"): string {
+    if (x == null) { return 'foo'; }
+    return x;
+}
+
+function testOptionalNullableProperty(obj: {x?: ?string}): string {
+    if (obj.x == null) { return 'foo'; }
+    return obj.x;
+}
+
+function testOptionalNullableFlowingToNullable(x?: ?string): ?string {
+  var f = function(y: ?string) {};
+  f(x);
+}
diff --git a/tests/optional/optional_param2.js b/tests/optional/optional_param2.js
new file mode 100644
index 000000000000..c26f546d3e84
--- /dev/null
+++ b/tests/optional/optional_param2.js
@@ -0,0 +1,7 @@
+declare class I<V> {
+    map<M>(
+        mapper: (value?: V) => M
+    ): I<M>;
+}
+var i:I<number> = new I();
+var j:I<number> = i.map(id => id);
diff --git a/tests/optional/optional_param3.js b/tests/optional/optional_param3.js
new file mode 100644
index 000000000000..1171945a726d
--- /dev/null
+++ b/tests/optional/optional_param3.js
@@ -0,0 +1,7 @@
+function foo(x?: number) {}
+foo(undefined); // ok
+
+function bar(x = "bar"): string {
+  return x;
+}
+bar(undefined); // ok
diff --git a/tests/optional/optional_param4.js b/tests/optional/optional_param4.js
new file mode 100644
index 000000000000..c880d64e6fef
--- /dev/null
+++ b/tests/optional/optional_param4.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+function foo(x?: number, ...y: Array<string>): [?number, Array<string>] {
+  return [x, y];
+}
+
+foo(); // OK
+foo(123), // OK
+foo(123, 'hello'); // OK
+
+
+foo(true); // ERROR boolean ~> number
+foo(123, true); // ERROR boolean ~> string
diff --git a/tests/optional/undefined.js b/tests/optional/undefined.js
new file mode 100644
index 000000000000..5a23002c0cab
--- /dev/null
+++ b/tests/optional/undefined.js
@@ -0,0 +1,9 @@
+var x;
+
+function foo(bar? = undefined) {
+    x = bar;
+}
+
+function bar() {
+    return x.duck;
+}
diff --git a/tests/optional/undefined2.js b/tests/optional/undefined2.js
new file mode 100644
index 000000000000..921c7383c757
--- /dev/null
+++ b/tests/optional/undefined2.js
@@ -0,0 +1,9 @@
+var x;
+
+function foo(bar?) {
+    x = bar;
+}
+
+function bar() {
+    return x.duck;
+}
diff --git a/tests/optional_props/__snapshots__/jsfmt.spec.js.snap b/tests/optional_props/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0c27bae9581e
--- /dev/null
+++ b/tests/optional_props/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,199 @@
+exports[`test test.js 1`] = `
+"var x: { } = { foo: 0 };
+var y: { foo?: string } = x; // OK in TypeScript, not OK in Flow
+
+var z: string = y.foo || \"\";
+
+var o = { };
+y = o; // OK; we know that narrowing could not have happened
+o.foo = 0; // future widening is constrained
+
+function bar(config: { foo?: number }) {}
+bar({});
+bar({foo: \"\"});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: {} = { foo: 0 };
+var y: { foo?: string } = x;// OK in TypeScript, not OK in Flow
+var z: string = y.foo || \"\";
+var o = {};
+y = o;// OK; we know that narrowing could not have happened
+o.foo = 0;// future widening is constrained
+function bar(config: { foo?: number }) {
+  
+}
+bar({});
+bar({ foo: \"\" });
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"var a: { foo?: string } = {};
+a.foo = undefined; // This is not an error
+a.foo = null; // But this is an error
+
+var b: { foo?: ?string } = {};
+b.foo = undefined; // This is fine
+b.foo = null; // Also fine
+
+var c: { foo?: string } = { foo: undefined }; // This is not an error
+var d: { foo?: string } = { foo: null }; // But this is an error
+
+var e: { foo?: ?string } = { foo: undefined }; // This is fine
+var f: { foo?: ?string } = { foo: null }; // Also fine
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var a: { foo?: string } = {};
+a.foo = undefined;// This is not an error
+a.foo = null;// But this is an error
+var b: { foo?: ?string } = {};
+b.foo = undefined;// This is fine
+b.foo = null;// Also fine
+var c: { foo?: string } = { foo: undefined };// This is not an error
+var d: { foo?: string } = { foo: null };// But this is an error
+var e: { foo?: ?string } = { foo: undefined };// This is fine
+var f: { foo?: ?string } = { foo: null };// Also fine
+
+"
+`;
+
+exports[`test test3.js 1`] = `
+"// @flow
+
+/*
+   object literals are sealed. this is simply a heuristic
+   decision: most of the time, the rule gives the \'right\'
+   errors.
+
+   an exception is when a literal is used as an initializer
+   for an lvalue whose type specifies optional properties
+   missing from the literal, as below.
+
+   the problem becomes visible when a property assignment
+   is then used to (legitimately) extend the object with an
+   optional property - the variable\'s specific (path-
+   dependent) type has become that of the literal which.
+   without adjustment, will reject the property addition.
+
+   the solution in cases where a sealed object type (as from
+   an object literal) flows to an object type with optional
+   properties, is to have the sealed type acquire the optional
+   properties.
+ */
+
+// x has optional property b.
+// (note that the initializer here does not play into
+// the problem, it\'s just a placeholder. initializers
+// do not narrow the types of annotated variables as do
+// subsequent assignments.)
+//
+var x: { a: number, b?: number } = { a: 0 };
+
+// now assign an object literal lacking property b.
+// the literal\'s type is sealed and has only a at creation.
+// but it then flows, specific ~> general, to x\'s annotation
+// type. at that point, it acquires b as an optional property.
+//
+x = { a: 0 };
+
+// ...which allows this assignment to take place.
+x.b = 1;
+
+// T7810506
+class A {
+    x: { a: number, b?: string };
+    foo() {
+        // Something similar should happen here, but doesn\'t: the problem is
+        // made explicit by adding generics (see test3_failure.js introduced by
+        // D2747512). There is a race between writing b on the object literal
+        // type and adding b as an optional property to it, since in general we
+        // cannot guarantee that the flow from the object literal to the
+        // annotation will be processed before the flow involving the
+        // access. Here we lose the race and get an error on the write.
+        this.x = { a: 123 };
+        this.x.b = \'hello\';
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+/*
+   object literals are sealed. this is simply a heuristic
+   decision: most of the time, the rule gives the \'right\'
+   errors.
+
+   an exception is when a literal is used as an initializer
+   for an lvalue whose type specifies optional properties
+   missing from the literal, as below.
+
+   the problem becomes visible when a property assignment
+   is then used to (legitimately) extend the object with an
+   optional property - the variable\'s specific (path-
+   dependent) type has become that of the literal which.
+   without adjustment, will reject the property addition.
+
+   the solution in cases where a sealed object type (as from
+   an object literal) flows to an object type with optional
+   properties, is to have the sealed type acquire the optional
+   properties.
+ */
+// x has optional property b.
+// (note that the initializer here does not play into
+// the problem, it\'s just a placeholder. initializers
+// do not narrow the types of annotated variables as do
+// subsequent assignments.)
+//
+var x: { a: number, b?: number } = { a: 0 };
+// now assign an object literal lacking property b.
+// the literal\'s type is sealed and has only a at creation.
+// but it then flows, specific ~> general, to x\'s annotation
+// type. at that point, it acquires b as an optional property.
+//
+x = { a: 0 };
+// ...which allows this assignment to take place.
+x.b = 1;
+// T7810506
+class A {
+  x: { a: number, b?: string };
+  foo() {
+    // Something similar should happen here, but doesn\'t: the problem is
+    // made explicit by adding generics (see test3_failure.js introduced by
+    // D2747512). There is a race between writing b on the object literal
+    // type and adding b as an optional property to it, since in general we
+    // cannot guarantee that the flow from the object literal to the
+    // annotation will be processed before the flow involving the
+    // access. Here we lose the race and get an error on the write.
+    this.x = { a: 123 };
+    this.x.b = \"hello\";
+  }
+}
+
+"
+`;
+
+exports[`test test3_failure.js 1`] = `
+"// generalization of failure in test3.js
+
+class A<O: {x: { a: number, b?: string}}> {
+  o: O;
+  foo() {
+    this.o.x = { a: 123 };
+    this.o.x.b = \'hello\'; // this is a spurious error (see test3.js for details)
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/optional_props/jsfmt.spec.js b/tests/optional_props/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/optional_props/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/optional_props/test.js b/tests/optional_props/test.js
new file mode 100644
index 000000000000..ecb039485694
--- /dev/null
+++ b/tests/optional_props/test.js
@@ -0,0 +1,12 @@
+var x: { } = { foo: 0 };
+var y: { foo?: string } = x; // OK in TypeScript, not OK in Flow
+
+var z: string = y.foo || "";
+
+var o = { };
+y = o; // OK; we know that narrowing could not have happened
+o.foo = 0; // future widening is constrained
+
+function bar(config: { foo?: number }) {}
+bar({});
+bar({foo: ""});
diff --git a/tests/optional_props/test2.js b/tests/optional_props/test2.js
new file mode 100644
index 000000000000..827c6f3776ce
--- /dev/null
+++ b/tests/optional_props/test2.js
@@ -0,0 +1,13 @@
+var a: { foo?: string } = {};
+a.foo = undefined; // This is not an error
+a.foo = null; // But this is an error
+
+var b: { foo?: ?string } = {};
+b.foo = undefined; // This is fine
+b.foo = null; // Also fine
+
+var c: { foo?: string } = { foo: undefined }; // This is not an error
+var d: { foo?: string } = { foo: null }; // But this is an error
+
+var e: { foo?: ?string } = { foo: undefined }; // This is fine
+var f: { foo?: ?string } = { foo: null }; // Also fine
diff --git a/tests/optional_props/test3.js b/tests/optional_props/test3.js
new file mode 100644
index 000000000000..2b737ace63fa
--- /dev/null
+++ b/tests/optional_props/test3.js
@@ -0,0 +1,56 @@
+// @flow
+
+/*
+   object literals are sealed. this is simply a heuristic
+   decision: most of the time, the rule gives the 'right'
+   errors.
+
+   an exception is when a literal is used as an initializer
+   for an lvalue whose type specifies optional properties
+   missing from the literal, as below.
+
+   the problem becomes visible when a property assignment
+   is then used to (legitimately) extend the object with an
+   optional property - the variable's specific (path-
+   dependent) type has become that of the literal which.
+   without adjustment, will reject the property addition.
+
+   the solution in cases where a sealed object type (as from
+   an object literal) flows to an object type with optional
+   properties, is to have the sealed type acquire the optional
+   properties.
+ */
+
+// x has optional property b.
+// (note that the initializer here does not play into
+// the problem, it's just a placeholder. initializers
+// do not narrow the types of annotated variables as do
+// subsequent assignments.)
+//
+var x: { a: number, b?: number } = { a: 0 };
+
+// now assign an object literal lacking property b.
+// the literal's type is sealed and has only a at creation.
+// but it then flows, specific ~> general, to x's annotation
+// type. at that point, it acquires b as an optional property.
+//
+x = { a: 0 };
+
+// ...which allows this assignment to take place.
+x.b = 1;
+
+// T7810506
+class A {
+    x: { a: number, b?: string };
+    foo() {
+        // Something similar should happen here, but doesn't: the problem is
+        // made explicit by adding generics (see test3_failure.js introduced by
+        // D2747512). There is a race between writing b on the object literal
+        // type and adding b as an optional property to it, since in general we
+        // cannot guarantee that the flow from the object literal to the
+        // annotation will be processed before the flow involving the
+        // access. Here we lose the race and get an error on the write.
+        this.x = { a: 123 };
+        this.x.b = 'hello';
+    }
+}
diff --git a/tests/optional_props/test3_failure.js b/tests/optional_props/test3_failure.js
new file mode 100644
index 000000000000..f6478197da18
--- /dev/null
+++ b/tests/optional_props/test3_failure.js
@@ -0,0 +1,9 @@
+// generalization of failure in test3.js
+
+class A<O: {x: { a: number, b?: string}}> {
+  o: O;
+  foo() {
+    this.o.x = { a: 123 };
+    this.o.x.b = 'hello'; // this is a spurious error (see test3.js for details)
+  }
+}
diff --git a/tests/overload/__snapshots__/jsfmt.spec.js.snap b/tests/overload/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4998e29a8cec
--- /dev/null
+++ b/tests/overload/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,176 @@
+exports[`test overload.js 1`] = `
+"/**
+ * tests of overload selection
+ *
+ * @flow
+ */
+
+var x1: number = \"\".match(0)[0];
+var x2: number = \"\".match(/pattern/)[0];
+var x3: string = \"\".replace(/pattern/,\"...\");
+var x4: number = \"\".split(/pattern/)[0];
+
+declare class C {
+    foo(x:number): number;
+    foo(x:string): string;
+
+    bar(x: { a: number }): number;
+    bar(x: { a: string }): string;
+}
+
+var a = new C();
+
+a.foo(0); // ok
+a.foo(\"hey\"); // ok
+a.foo(true); // error, function cannot be called on intersection type
+
+a.bar({ a: 0 }); // ok
+a.bar({ a: \"hey\" }); // ok
+a.bar({ a: true }); // error, function cannot be called on intersection type
+
+declare var x: { a: boolean; } & { b: string };
+
+a.bar(x); // error with nested intersection info (outer for bar, inner for x)
+
+/********** tests **************
+interface Dummy<T> {
+    dumb(foo: (x:number) => number):number;
+    dumb(foo: (x:string) => string):string;
+
+    dumber<U>(bar: (x:T) => Array<U>):U;
+    dumber<U>(bar: (x:T) => U):Array<U>;
+}
+
+function foo(x:string):string { return x; }
+var y:number = new Dummy().dumb(foo);
+
+function bar1(x:number):Array<string> { return []; }
+var z1:number = new Dummy().dumber(bar1);
+
+function bar2(x:number):string { return \"...\"; }
+var z2:Array<string> = new Dummy().dumber(bar2);
+*/
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"function foo() {
+  var output = new FakeUint8Array();
+  output.set(new FakeUint8Array(), 0); // matches one of the overloads of set
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo() {
+  var output = new FakeUint8Array();
+  output.set(new FakeUint8Array(), 0);// matches one of the overloads of set
+}
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"declare class Foo {
+  bar(x: \'hmm\'): number;
+  bar(x: string): string;
+}
+var foo = new Foo;
+(foo.bar(\'hmm\'): number); // OK
+(foo.bar(\'hmmm\'): number); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test3.js 1`] = `
+"// passing a union-like thing into an overload is ok
+// if overload handles each branch of union-like thing
+
+// unions
+declare function f(x: string): void;
+declare function f(x: number): void;
+declare var x_f: string | number;
+f(x_f); // ok
+
+// maybe
+declare function g(x: null): void;
+declare function g(x: void): void;
+declare function g(x: string): void;
+declare var x_g: ?string;
+g(x_g); // ok
+
+// optional
+declare function h(x: void): void;
+declare function h(x: string): void;
+declare var x_h: {p?: string};
+h(x_h.p); // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test union.js 1`] = `
+"function foo<U> (x: $Either<Array<U>,U>): Array<U> { return []; }
+
+var x1:number = foo(0)[0];
+var x2:string = foo([\"\"])[0];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/overload/jsfmt.spec.js b/tests/overload/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/overload/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/overload/lib/__snapshots__/jsfmt.spec.js.snap b/tests/overload/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b85798c12da2
--- /dev/null
+++ b/tests/overload/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,23 @@
+exports[`test lib.js 1`] = `
+"declare class FakeUint8Array {
+  set(index: number, value: number): void;
+  set(array: FakeUint8Array | Array<number>, offset?: number): void;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/overload/lib/jsfmt.spec.js b/tests/overload/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/overload/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/overload/lib/lib.js b/tests/overload/lib/lib.js
new file mode 100644
index 000000000000..616d065acbe6
--- /dev/null
+++ b/tests/overload/lib/lib.js
@@ -0,0 +1,4 @@
+declare class FakeUint8Array {
+  set(index: number, value: number): void;
+  set(array: FakeUint8Array | Array<number>, offset?: number): void;
+}
diff --git a/tests/overload/overload.js b/tests/overload/overload.js
new file mode 100644
index 000000000000..ca2d8848bba4
--- /dev/null
+++ b/tests/overload/overload.js
@@ -0,0 +1,51 @@
+/**
+ * tests of overload selection
+ *
+ * @flow
+ */
+
+var x1: number = "".match(0)[0];
+var x2: number = "".match(/pattern/)[0];
+var x3: string = "".replace(/pattern/,"...");
+var x4: number = "".split(/pattern/)[0];
+
+declare class C {
+    foo(x:number): number;
+    foo(x:string): string;
+
+    bar(x: { a: number }): number;
+    bar(x: { a: string }): string;
+}
+
+var a = new C();
+
+a.foo(0); // ok
+a.foo("hey"); // ok
+a.foo(true); // error, function cannot be called on intersection type
+
+a.bar({ a: 0 }); // ok
+a.bar({ a: "hey" }); // ok
+a.bar({ a: true }); // error, function cannot be called on intersection type
+
+declare var x: { a: boolean; } & { b: string };
+
+a.bar(x); // error with nested intersection info (outer for bar, inner for x)
+
+/********** tests **************
+interface Dummy<T> {
+    dumb(foo: (x:number) => number):number;
+    dumb(foo: (x:string) => string):string;
+
+    dumber<U>(bar: (x:T) => Array<U>):U;
+    dumber<U>(bar: (x:T) => U):Array<U>;
+}
+
+function foo(x:string):string { return x; }
+var y:number = new Dummy().dumb(foo);
+
+function bar1(x:number):Array<string> { return []; }
+var z1:number = new Dummy().dumber(bar1);
+
+function bar2(x:number):string { return "..."; }
+var z2:Array<string> = new Dummy().dumber(bar2);
+*/
diff --git a/tests/overload/test.js b/tests/overload/test.js
new file mode 100644
index 000000000000..1dc44ef28277
--- /dev/null
+++ b/tests/overload/test.js
@@ -0,0 +1,4 @@
+function foo() {
+  var output = new FakeUint8Array();
+  output.set(new FakeUint8Array(), 0); // matches one of the overloads of set
+}
diff --git a/tests/overload/test2.js b/tests/overload/test2.js
new file mode 100644
index 000000000000..d3d1fb7f5ba6
--- /dev/null
+++ b/tests/overload/test2.js
@@ -0,0 +1,7 @@
+declare class Foo {
+  bar(x: 'hmm'): number;
+  bar(x: string): string;
+}
+var foo = new Foo;
+(foo.bar('hmm'): number); // OK
+(foo.bar('hmmm'): number); // error
diff --git a/tests/overload/test3.js b/tests/overload/test3.js
new file mode 100644
index 000000000000..4c4fefe6e609
--- /dev/null
+++ b/tests/overload/test3.js
@@ -0,0 +1,21 @@
+// passing a union-like thing into an overload is ok
+// if overload handles each branch of union-like thing
+
+// unions
+declare function f(x: string): void;
+declare function f(x: number): void;
+declare var x_f: string | number;
+f(x_f); // ok
+
+// maybe
+declare function g(x: null): void;
+declare function g(x: void): void;
+declare function g(x: string): void;
+declare var x_g: ?string;
+g(x_g); // ok
+
+// optional
+declare function h(x: void): void;
+declare function h(x: string): void;
+declare var x_h: {p?: string};
+h(x_h.p); // ok
diff --git a/tests/overload/union.js b/tests/overload/union.js
new file mode 100644
index 000000000000..4e707c3feb53
--- /dev/null
+++ b/tests/overload/union.js
@@ -0,0 +1,4 @@
+function foo<U> (x: $Either<Array<U>,U>): Array<U> { return []; }
+
+var x1:number = foo(0)[0];
+var x2:string = foo([""])[0];
diff --git a/tests/parse/__snapshots__/jsfmt.spec.js.snap b/tests/parse/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9a0838ba525a
--- /dev/null
+++ b/tests/parse/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,90 @@
+exports[`test fail.js 1`] = `
+".
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (1:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3592:12)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test fail-flow.js 1`] = `
+"/* @flow */
+
+.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (3:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3592:12)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test fail-flow-2.js 1`] = `
+"/**
+ * @flow */
+
+.
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (4:0)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3592:12)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+    at Parser.parseMaybeAssign (/node_modules/babylon/lib/index.js:5700:20)
+"
+`;
+
+exports[`test no_parse_error.js 1`] = `
+"/*
+@flow
+*/
+
+var x = \'Test\';
+var y = 5 / x;
+
+var z: {
+    type: number,
+    y: string
+} = {type: 1, y: \'hey\'};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+@flow
+*/
+var x = \"Test\";
+var y = 5 / x;
+var z: { type: number, y: string } = { type: 1, y: \"hey\" };
+
+"
+`;
diff --git a/tests/parse/fail-flow-2.js b/tests/parse/fail-flow-2.js
new file mode 100644
index 000000000000..97dfd87f73a3
--- /dev/null
+++ b/tests/parse/fail-flow-2.js
@@ -0,0 +1,4 @@
+/**
+ * @flow */
+
+.
diff --git a/tests/parse/fail-flow.js b/tests/parse/fail-flow.js
new file mode 100644
index 000000000000..762b3652bbfe
--- /dev/null
+++ b/tests/parse/fail-flow.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+.
diff --git a/tests/parse/fail.js b/tests/parse/fail.js
new file mode 100644
index 000000000000..9c558e357c41
--- /dev/null
+++ b/tests/parse/fail.js
@@ -0,0 +1 @@
+.
diff --git a/tests/parse/jsfmt.spec.js b/tests/parse/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/parse/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/parse/no_parse_error.js b/tests/parse/no_parse_error.js
new file mode 100644
index 000000000000..51fd29947373
--- /dev/null
+++ b/tests/parse/no_parse_error.js
@@ -0,0 +1,11 @@
+/*
+@flow
+*/
+
+var x = 'Test';
+var y = 5 / x;
+
+var z: {
+    type: number,
+    y: string
+} = {type: 1, y: 'hey'};
diff --git a/tests/parse_error_haste/Client.js b/tests/parse_error_haste/Client.js
new file mode 100644
index 000000000000..b3827baaa074
--- /dev/null
+++ b/tests/parse_error_haste/Client.js
@@ -0,0 +1,11 @@
+/**
+ * Client imports some but not all modules,
+ * triggering/suppressing parse errors.
+ * @flow
+ */
+
+// non-flow files should not show parse errors
+var A = require("Foo");          // non-Flow file @providesModule Foo
+var B = require("./NoProvides"); // non-Flow file
+
+var C = require("./ParseError"); // Flow file
diff --git a/tests/parse_error_haste/NoProvides.js b/tests/parse_error_haste/NoProvides.js
new file mode 100644
index 000000000000..16817984e83b
--- /dev/null
+++ b/tests/parse_error_haste/NoProvides.js
@@ -0,0 +1,9 @@
+/**
+ * Parse errors, imported, not in flow, no provides module.
+ * No parse errors are raised because it is ignored by flow.
+ */
+function f(s) { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
diff --git a/tests/parse_error_haste/ParseError.js b/tests/parse_error_haste/ParseError.js
new file mode 100644
index 000000000000..6766fa50ec34
--- /dev/null
+++ b/tests/parse_error_haste/ParseError.js
@@ -0,0 +1,6 @@
+// @flow
+
+function foo() { ### // invalid token
+}
+
+module.exports = foo;
diff --git a/tests/parse_error_haste/Provides.js b/tests/parse_error_haste/Provides.js
new file mode 100644
index 000000000000..da8e04dcaba6
--- /dev/null
+++ b/tests/parse_error_haste/Provides.js
@@ -0,0 +1,12 @@
+/**
+ * Parse errors, imported, not in flow, provides module.
+ * Should see a parse error in this file, and module
+ * not found in client.
+ * @providesModule Foo
+ * @noflow
+ */
+function f(s: string): string { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
diff --git a/tests/parse_error_haste/Unimported.js b/tests/parse_error_haste/Unimported.js
new file mode 100644
index 000000000000..177d59e6ab69
--- /dev/null
+++ b/tests/parse_error_haste/Unimported.js
@@ -0,0 +1,10 @@
+/**
+ * Parse errors but not in flow and not imported.
+ * Should see no parse errors for this file.
+ * @providesModule Bar
+ */
+function f(s:string):string { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
diff --git a/tests/parse_error_haste/__snapshots__/jsfmt.spec.js.snap b/tests/parse_error_haste/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0fd5bcf9e3fe
--- /dev/null
+++ b/tests/parse_error_haste/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,142 @@
+exports[`test Client.js 1`] = `
+"/**
+ * Client imports some but not all modules,
+ * triggering/suppressing parse errors.
+ * @flow
+ */
+
+// non-flow files should not show parse errors
+var A = require(\"Foo\");          // non-Flow file @providesModule Foo
+var B = require(\"./NoProvides\"); // non-Flow file
+
+var C = require(\"./ParseError\"); // Flow file
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Client imports some but not all modules,
+ * triggering/suppressing parse errors.
+ * @flow
+ */
+// non-flow files should not show parse errors
+var A = require(\"Foo\");// non-Flow file @providesModule Foo
+var B = require(\"./NoProvides\");// non-Flow file
+var C = require(\"./ParseError\");// Flow file
+
+"
+`;
+
+exports[`test NoProvides.js 1`] = `
+"/**
+ * Parse errors, imported, not in flow, no provides module.
+ * No parse errors are raised because it is ignored by flow.
+ */
+function f(s) { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (5:16)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
+
+exports[`test ParseError.js 1`] = `
+"// @flow
+
+function foo() { ### // invalid token
+}
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (3:17)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
+
+exports[`test Provides.js 1`] = `
+"/**
+ * Parse errors, imported, not in flow, provides module.
+ * Should see a parse error in this file, and module
+ * not found in client.
+ * @providesModule Foo
+ * @noflow
+ */
+function f(s: string): string { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (8:32)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
+
+exports[`test Unimported.js 1`] = `
+"/**
+ * Parse errors but not in flow and not imported.
+ * Should see no parse errors for this file.
+ * @providesModule Bar
+ */
+function f(s:string):string { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (6:30)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
diff --git a/tests/parse_error_haste/jsfmt.spec.js b/tests/parse_error_haste/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/parse_error_haste/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/parse_error_node/Client.js b/tests/parse_error_node/Client.js
new file mode 100644
index 000000000000..45ea11195d28
--- /dev/null
+++ b/tests/parse_error_node/Client.js
@@ -0,0 +1,10 @@
+/**
+ * Client imports some but not all modules,
+ * triggering/suppressing parse errors.
+ * @flow
+ */
+
+// non-flow files should not give parse errors
+var A = require("./Imported");          // non-Flow file @providesModule Foo
+
+var B = require("./ParseError");        // Flow file
diff --git a/tests/parse_error_node/Imported.js b/tests/parse_error_node/Imported.js
new file mode 100644
index 000000000000..16817984e83b
--- /dev/null
+++ b/tests/parse_error_node/Imported.js
@@ -0,0 +1,9 @@
+/**
+ * Parse errors, imported, not in flow, no provides module.
+ * No parse errors are raised because it is ignored by flow.
+ */
+function f(s) { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
diff --git a/tests/parse_error_node/ParseError.js b/tests/parse_error_node/ParseError.js
new file mode 100644
index 000000000000..6766fa50ec34
--- /dev/null
+++ b/tests/parse_error_node/ParseError.js
@@ -0,0 +1,6 @@
+// @flow
+
+function foo() { ### // invalid token
+}
+
+module.exports = foo;
diff --git a/tests/parse_error_node/Unimported.js b/tests/parse_error_node/Unimported.js
new file mode 100644
index 000000000000..177d59e6ab69
--- /dev/null
+++ b/tests/parse_error_node/Unimported.js
@@ -0,0 +1,10 @@
+/**
+ * Parse errors but not in flow and not imported.
+ * Should see no parse errors for this file.
+ * @providesModule Bar
+ */
+function f(s:string):string { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
diff --git a/tests/parse_error_node/__snapshots__/jsfmt.spec.js.snap b/tests/parse_error_node/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bb6c5eb1fac5
--- /dev/null
+++ b/tests/parse_error_node/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,108 @@
+exports[`test Client.js 1`] = `
+"/**
+ * Client imports some but not all modules,
+ * triggering/suppressing parse errors.
+ * @flow
+ */
+
+// non-flow files should not give parse errors
+var A = require(\"./Imported\");          // non-Flow file @providesModule Foo
+
+var B = require(\"./ParseError\");        // Flow file
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Client imports some but not all modules,
+ * triggering/suppressing parse errors.
+ * @flow
+ */
+// non-flow files should not give parse errors
+var A = require(\"./Imported\");// non-Flow file @providesModule Foo
+var B = require(\"./ParseError\");// Flow file
+
+"
+`;
+
+exports[`test Imported.js 1`] = `
+"/**
+ * Parse errors, imported, not in flow, no provides module.
+ * No parse errors are raised because it is ignored by flow.
+ */
+function f(s) { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (5:16)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
+
+exports[`test ParseError.js 1`] = `
+"// @flow
+
+function foo() { ### // invalid token
+}
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (3:17)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
+
+exports[`test Unimported.js 1`] = `
+"/**
+ * Parse errors but not in flow and not imported.
+ * Should see no parse errors for this file.
+ * @providesModule Bar
+ */
+function f(s:string):string { ### // illegal token
+  return s;
+}
+
+module.exports = { f: f }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected character \'#\' (6:30)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.getTokenFromCode (/node_modules/babylon/lib/index.js:1065:10)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:694:19)
+    at Parser.<anonymous> (/node_modules/babylon/lib/index.js:6441:20)
+    at Parser.readToken (/node_modules/babylon/lib/index.js:5376:22)
+    at Parser.nextToken (/node_modules/babylon/lib/index.js:684:19)
+    at Parser.next (/node_modules/babylon/lib/index.js:609:10)
+    at Parser.eat (/node_modules/babylon/lib/index.js:616:12)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:15)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+"
+`;
diff --git a/tests/parse_error_node/jsfmt.spec.js b/tests/parse_error_node/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/parse_error_node/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/path/__snapshots__/jsfmt.spec.js.snap b/tests/path/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a2a3fe378afd
--- /dev/null
+++ b/tests/path/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test while.js 1`] = `
+"var x = 1;
+while(typeof x == "number" || typeof x == "string") {
+    x = x + 1;
+    if (true) x = "";
+}
+var z:number = x;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x = 1;
+while (typeof x == "number" || typeof x == "string") {
+  x = x + 1;
+  if (true)
+    x = "";
+}
+var z: number = x;
+
+"
+`;
diff --git a/tests/path/jsfmt.spec.js b/tests/path/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/path/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/path/while.js b/tests/path/while.js
new file mode 100644
index 000000000000..83c943b5faf5
--- /dev/null
+++ b/tests/path/while.js
@@ -0,0 +1,6 @@
+var x = 1;
+while(typeof x == "number" || typeof x == "string") {
+    x = x + 1;
+    if (true) x = "";
+}
+var z:number = x;
diff --git a/tests/plsummit/__snapshots__/jsfmt.spec.js.snap b/tests/plsummit/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ffd3dd6c2c29
--- /dev/null
+++ b/tests/plsummit/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,132 @@
+exports[`test arrays.js 1`] = `
+"function foo(x) { return [x, x > 0, \"number \" + x]; }
+
+var [n, b, s] = foo(42);
+n * s.length;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function foo(x) {
+  return [ x, x > 0, \"number \" + x ];
+}
+var [ n, b, s ] = foo(42);
+n * s.length;
+
+"
+`;
+
+exports[`test export_class.js 1`] = `
+"class C {
+    x: number;
+    constructor(x: number) { this.x = x; }
+}
+
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  x: number;
+  constructor(x: number) {
+    this.x = x;
+  }
+}
+module.exports = C;
+
+"
+`;
+
+exports[`test generics.js 1`] = `
+"/* @flow */
+
+var r: number = 0;
+function foo<X>(x: X): X { r = x; return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test import_class.js 1`] = `
+"var C = require(\'./export_class\');
+
+var c = new C(\"\");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var C = require(\"./export_class\");
+var c = new C(\"\");
+
+"
+`;
+
+exports[`test locals.js 1`] = `
+"/* @flow */
+
+function foo() {
+    var x = 0;
+    var y = x;
+}
+
+function bar(x: ?string): number {
+    if (x == null) x = \"\";
+    return x.length;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo() {
+  var x = 0;
+  var y = x;
+}
+function bar(x: ?string): number {
+  if (x == null)
+    x = \"\";
+  return x.length;
+}
+
+"
+`;
+
+exports[`test objects.js 1`] = `
+"function C() { this.x = 0; }
+C.prototype.foo = function() { return this.x; }
+
+var c = new C();
+var x: string = c.foo();
+
+function foo() { return this.y; }
+function bar() { return this.foo(); }
+var o = { y: \"\", foo: foo, bar: bar };
+var o2 = { y: 0, foo: foo, bar: bar };
+
+o.bar();
+var y: number = o2.bar();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function C() {
+  this.x = 0;
+}
+C.prototype.foo = function() {
+  return this.x;
+};
+var c = new C();
+var x: string = c.foo();
+function foo() {
+  return this.y;
+}
+function bar() {
+  return this.foo();
+}
+var o = { y: \"\", foo: foo, bar: bar };
+var o2 = { y: 0, foo: foo, bar: bar };
+o.bar();
+var y: number = o2.bar();
+
+"
+`;
diff --git a/tests/plsummit/arrays.js b/tests/plsummit/arrays.js
new file mode 100644
index 000000000000..9ed4c7b22f49
--- /dev/null
+++ b/tests/plsummit/arrays.js
@@ -0,0 +1,4 @@
+function foo(x) { return [x, x > 0, "number " + x]; }
+
+var [n, b, s] = foo(42);
+n * s.length;
diff --git a/tests/plsummit/export_class.js b/tests/plsummit/export_class.js
new file mode 100644
index 000000000000..8f796fb05385
--- /dev/null
+++ b/tests/plsummit/export_class.js
@@ -0,0 +1,6 @@
+class C {
+    x: number;
+    constructor(x: number) { this.x = x; }
+}
+
+module.exports = C;
diff --git a/tests/plsummit/generics.js b/tests/plsummit/generics.js
new file mode 100644
index 000000000000..ec4d476134da
--- /dev/null
+++ b/tests/plsummit/generics.js
@@ -0,0 +1,4 @@
+/* @flow */
+
+var r: number = 0;
+function foo<X>(x: X): X { r = x; return x; }
diff --git a/tests/plsummit/import_class.js b/tests/plsummit/import_class.js
new file mode 100644
index 000000000000..4a361b1515cd
--- /dev/null
+++ b/tests/plsummit/import_class.js
@@ -0,0 +1,3 @@
+var C = require('./export_class');
+
+var c = new C("");
diff --git a/tests/plsummit/jsfmt.spec.js b/tests/plsummit/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/plsummit/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/plsummit/locals.js b/tests/plsummit/locals.js
new file mode 100644
index 000000000000..08f150b95c56
--- /dev/null
+++ b/tests/plsummit/locals.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+function foo() {
+    var x = 0;
+    var y = x;
+}
+
+function bar(x: ?string): number {
+    if (x == null) x = "";
+    return x.length;
+}
diff --git a/tests/plsummit/objects.js b/tests/plsummit/objects.js
new file mode 100644
index 000000000000..29af3f72b10f
--- /dev/null
+++ b/tests/plsummit/objects.js
@@ -0,0 +1,13 @@
+function C() { this.x = 0; }
+C.prototype.foo = function() { return this.x; }
+
+var c = new C();
+var x: string = c.foo();
+
+function foo() { return this.y; }
+function bar() { return this.foo(); }
+var o = { y: "", foo: foo, bar: bar };
+var o2 = { y: 0, foo: foo, bar: bar };
+
+o.bar();
+var y: number = o2.bar();
diff --git a/tests/poly/__snapshots__/jsfmt.spec.js.snap b/tests/poly/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4a4d1b086938
--- /dev/null
+++ b/tests/poly/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,192 @@
+exports[`test annot.js 1`] = `
+"class A<X> { }
+new A; // OK, implicitly inferred type args
+class B extends A { } // OK, same as above
+
+function foo(b): A<any> { // ok but unsafe, caller may assume any type arg
+  return b ? (new A: A<number>): (new A: A<string>);
+}
+
+function bar(): A<*> { // error, * can\'t be {} and {x: string} at the same time
+  return (new A: A<{}>) || (new A: A<{x: string}>);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test implicit_bounded_instantiation.js 1`] = `
+"// @flow
+
+class Base {}
+class Middle extends Base {}
+class Child extends Middle {}
+
+class C<T: Middle> {
+  meth(a: T): T {
+    return a;
+  }
+}
+
+// T is implicitly (bounded by) Middle in constructor call if not provided.
+// Explicit type arg is required in annotation - here a wildcard captures it.
+var a: C<*> = new C();
+
+a.meth(new Middle());
+a.meth(new Child());
+a.meth(42); // Error: number ~> Middle
+a.meth(new Base()); // Error: Base ~> Middle
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1029.js 1`] = `
+"// @flow
+
+// naive unification causes combinatorial explosion here,
+// effectively hangs
+
+declare type Box<T> = {
+  map1<U>(f: (x: T) => U): Box<U>;
+  map2<U>(f: (x: T) => U): Box<U>;
+  map3<U>(f: (x: T) => U): Box<U>;
+  map4<U>(f: (x: T) => U): Box<U>;
+  map5<U>(f: (x: T) => U): Box<U>;
+}
+
+declare var bool: Box<boolean>;
+
+declare function unbox<A>(box: Box<A>): A
+
+unbox(bool);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test poly.js 1`] = `
+"class Foo<T> {
+    x:T;
+    constructor(x:T) { this.x = x; }
+}
+
+function bar<S>(foo:Foo<S>,y:S):Foo<S> { return new Foo(y); }
+
+var P = {
+    bar: bar
+}
+
+declare var Q: {
+    bar<S>(foo:Foo<S>,y:S):Foo<S>;
+}
+
+var foo = new Foo(0);
+var x:string = foo.x;
+var z:Foo<number> = Q.bar(foo,\"\");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"class C {
+  foo<X>(x: X): X { return x; }
+  foo_<X: number>(x: X): number { return x; }
+  bar<X>(x: X): X { return x; }
+  qux(x: number): number { return x; }
+}
+class D extends C {
+  foo(x: number): number { return x; } // error (specialization, see below)
+  foo_(x: number): number { return x; } // OK, but only because the overridden foo accepts no more than number and returns exactly number
+  bar<X>(x: X): X { return x; } // OK
+  qux<X>(x: X): X { return x; } // OK (generalization)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  foo(x: X): X {
+    return x;
+  }
+  foo_(x: X): number {
+    return x;
+  }
+  bar(x: X): X {
+    return x;
+  }
+  qux(x: number): number {
+    return x;
+  }
+}
+class D extends C {
+  foo(x: number): number {
+    return x;
+  }// error (specialization, see below)
+  foo_(x: number): number {
+    return x;
+  }// OK, but only because the overridden foo accepts no more than number and returns exactly number
+  bar(x: X): X {
+    return x;
+  }// OK
+  qux(x: X): X {
+    return x;
+  }// OK (generalization)
+}
+
+"
+`;
diff --git a/tests/poly/annot.js b/tests/poly/annot.js
new file mode 100644
index 000000000000..f5feef466989
--- /dev/null
+++ b/tests/poly/annot.js
@@ -0,0 +1,11 @@
+class A<X> { }
+new A; // OK, implicitly inferred type args
+class B extends A { } // OK, same as above
+
+function foo(b): A<any> { // ok but unsafe, caller may assume any type arg
+  return b ? (new A: A<number>): (new A: A<string>);
+}
+
+function bar(): A<*> { // error, * can't be {} and {x: string} at the same time
+  return (new A: A<{}>) || (new A: A<{x: string}>);
+}
diff --git a/tests/poly/implicit_bounded_instantiation.js b/tests/poly/implicit_bounded_instantiation.js
new file mode 100644
index 000000000000..e684afff4d6b
--- /dev/null
+++ b/tests/poly/implicit_bounded_instantiation.js
@@ -0,0 +1,20 @@
+// @flow
+
+class Base {}
+class Middle extends Base {}
+class Child extends Middle {}
+
+class C<T: Middle> {
+  meth(a: T): T {
+    return a;
+  }
+}
+
+// T is implicitly (bounded by) Middle in constructor call if not provided.
+// Explicit type arg is required in annotation - here a wildcard captures it.
+var a: C<*> = new C();
+
+a.meth(new Middle());
+a.meth(new Child());
+a.meth(42); // Error: number ~> Middle
+a.meth(new Base()); // Error: Base ~> Middle
diff --git a/tests/poly/issue-1029.js b/tests/poly/issue-1029.js
new file mode 100644
index 000000000000..5b7ac33f3823
--- /dev/null
+++ b/tests/poly/issue-1029.js
@@ -0,0 +1,18 @@
+// @flow
+
+// naive unification causes combinatorial explosion here,
+// effectively hangs
+
+declare type Box<T> = {
+  map1<U>(f: (x: T) => U): Box<U>;
+  map2<U>(f: (x: T) => U): Box<U>;
+  map3<U>(f: (x: T) => U): Box<U>;
+  map4<U>(f: (x: T) => U): Box<U>;
+  map5<U>(f: (x: T) => U): Box<U>;
+}
+
+declare var bool: Box<boolean>;
+
+declare function unbox<A>(box: Box<A>): A
+
+unbox(bool);
diff --git a/tests/poly/jsfmt.spec.js b/tests/poly/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/poly/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/poly/poly.js b/tests/poly/poly.js
new file mode 100644
index 000000000000..be8b8014784e
--- /dev/null
+++ b/tests/poly/poly.js
@@ -0,0 +1,18 @@
+class Foo<T> {
+    x:T;
+    constructor(x:T) { this.x = x; }
+}
+
+function bar<S>(foo:Foo<S>,y:S):Foo<S> { return new Foo(y); }
+
+var P = {
+    bar: bar
+}
+
+declare var Q: {
+    bar<S>(foo:Foo<S>,y:S):Foo<S>;
+}
+
+var foo = new Foo(0);
+var x:string = foo.x;
+var z:Foo<number> = Q.bar(foo,"");
diff --git a/tests/poly/test.js b/tests/poly/test.js
new file mode 100644
index 000000000000..9e72bab6ada9
--- /dev/null
+++ b/tests/poly/test.js
@@ -0,0 +1,12 @@
+class C {
+  foo<X>(x: X): X { return x; }
+  foo_<X: number>(x: X): number { return x; }
+  bar<X>(x: X): X { return x; }
+  qux(x: number): number { return x; }
+}
+class D extends C {
+  foo(x: number): number { return x; } // error (specialization, see below)
+  foo_(x: number): number { return x; } // OK, but only because the overridden foo accepts no more than number and returns exactly number
+  bar<X>(x: X): X { return x; } // OK
+  qux<X>(x: X): X { return x; } // OK (generalization)
+}
diff --git a/tests/poly_class_export/A.js b/tests/poly_class_export/A.js
new file mode 100644
index 000000000000..3a6aecfd9ff5
--- /dev/null
+++ b/tests/poly_class_export/A.js
@@ -0,0 +1,7 @@
+// @flow
+
+class A<T> {
+  x: T
+}
+
+module.exports = A;
diff --git a/tests/poly_class_export/B.js b/tests/poly_class_export/B.js
new file mode 100644
index 000000000000..d4282e925827
--- /dev/null
+++ b/tests/poly_class_export/B.js
@@ -0,0 +1,11 @@
+// @flow
+
+let A = require('./A');
+
+class B extends A<string> {
+  constructor() {
+    super();
+  }
+}
+
+module.exports = new B();
diff --git a/tests/poly_class_export/C.js b/tests/poly_class_export/C.js
new file mode 100644
index 000000000000..e017e2c83c91
--- /dev/null
+++ b/tests/poly_class_export/C.js
@@ -0,0 +1,14 @@
+// @flow
+
+// This test exports a function whose return type is the class's `this` type.
+// It should be inferred (no annotation required).
+
+class Foo {
+  foo(): this {
+    return this;
+  }
+}
+
+export function f(x: Foo) {
+  return x.foo();
+}
diff --git a/tests/poly_class_export/__snapshots__/jsfmt.spec.js.snap b/tests/poly_class_export/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..038cb4d4f12d
--- /dev/null
+++ b/tests/poly_class_export/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,88 @@
+exports[`test A.js 1`] = `
+"// @flow
+
+class A<T> {
+  x: T
+}
+
+module.exports = A;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test B.js 1`] = `
+"// @flow
+
+let A = require(\'./A\');
+
+class B extends A<string> {
+  constructor() {
+    super();
+  }
+}
+
+module.exports = new B();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1180:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test C.js 1`] = `
+"// @flow
+
+// This test exports a function whose return type is the class\'s \`this\` type.
+// It should be inferred (no annotation required).
+
+class Foo {
+  foo(): this {
+    return this;
+  }
+}
+
+export function f(x: Foo) {
+  return x.foo();
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// This test exports a function whose return type is the class\'s \`this\` type.
+// It should be inferred (no annotation required).
+class Foo {
+  foo(): this {
+    return this;
+  }
+}
+export function f(x: Foo) {
+  return x.foo();
+}
+
+"
+`;
diff --git a/tests/poly_class_export/jsfmt.spec.js b/tests/poly_class_export/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/poly_class_export/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/poly_overload/decls/__snapshots__/jsfmt.spec.js.snap b/tests/poly_overload/decls/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ada571d251c5
--- /dev/null
+++ b/tests/poly_overload/decls/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,35 @@
+exports[`test typescript-deferred.js 1`] = `
+"interface Some<X> {}
+interface Other<X> { x: X; }
+interface None<Y> {}
+interface Nada<Y> { y: Y }
+interface A<X> {
+  foo<Y>(s: Some<X>, e: None<Y>): A<Y>;
+  foo<Y>(s: Some<X>, e: Nada<Y>): A<Y>;
+  foo<Y>(s: Other<X>, e: None<Y>): A<Y>;
+  foo<Y>(s: Other<X>, e: Nada<Y>): A<Y>;
+}
+interface B<X> extends A<X> {
+  foo<Y>(s: Some<X>, e: None<Y>): B<Y>;
+  foo<Y>(s: Some<X>, e: Nada<Y>): B<Y>;
+  foo<Y>(s: Other<X>, e: None<Y>): B<Y>;
+  foo<Y>(s: Other<X>, e: Nada<Y>): B<Y>;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1384:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/poly_overload/decls/jsfmt.spec.js b/tests/poly_overload/decls/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/poly_overload/decls/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/poly_overload/decls/typescript-deferred.js b/tests/poly_overload/decls/typescript-deferred.js
new file mode 100644
index 000000000000..cf6fe780dc37
--- /dev/null
+++ b/tests/poly_overload/decls/typescript-deferred.js
@@ -0,0 +1,16 @@
+interface Some<X> {}
+interface Other<X> { x: X; }
+interface None<Y> {}
+interface Nada<Y> { y: Y }
+interface A<X> {
+  foo<Y>(s: Some<X>, e: None<Y>): A<Y>;
+  foo<Y>(s: Some<X>, e: Nada<Y>): A<Y>;
+  foo<Y>(s: Other<X>, e: None<Y>): A<Y>;
+  foo<Y>(s: Other<X>, e: Nada<Y>): A<Y>;
+}
+interface B<X> extends A<X> {
+  foo<Y>(s: Some<X>, e: None<Y>): B<Y>;
+  foo<Y>(s: Some<X>, e: Nada<Y>): B<Y>;
+  foo<Y>(s: Other<X>, e: None<Y>): B<Y>;
+  foo<Y>(s: Other<X>, e: Nada<Y>): B<Y>;
+}
diff --git a/tests/predicates-abstract/__snapshots__/jsfmt.spec.js.snap b/tests/predicates-abstract/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9bb9fc127f51
--- /dev/null
+++ b/tests/predicates-abstract/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,278 @@
+exports[`test filter.js 1`] = `
+"// @flow
+
+// Filter the contents of an array
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+declare var arr: Array<mixed>;
+const barr = my_filter(arr, is_string);
+(barr: Array<string>);
+
+function is_string(x): %checks {
+  return typeof x === \"string\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (11:23)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test filter-union.js 1`] = `
+"// @flow
+
+// Filter the contents of an array
+
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+type A = { kind: \'A\', u: number }
+type B = { kind: \'B\', v: string }
+type C = { kind: \'C\', y: boolean }
+type D = { kind: \'D\', x: boolean }
+type E = { kind: \'E\', y: boolean }
+
+declare var ab: Array<A|B|C>;
+
+(my_filter(ab, (x): %checks => x.kind === \'A\'): Array<A>);    // OK
+(my_filter(ab, (x): %checks => x.kind !== \'A\'): Array<B|C>);  // OK
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (16:20)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test refine.js 1`] = `
+"// @flow
+
+/*
+  $Pred<N> is an \"abstract predicate type\", i.e. denotes a (function) type that
+  refines N variables. So if \`cb\` is a function, then it should be refining
+  exactly N argument. It is abstract in that we do not need to specify:
+  (a) which variables are going to be refined (just the number), or (b) what
+  exactly the refinement (predicate) is going to be.
+
+  $Refine<T,P,k> is a refinement type, that refines type T with the k-th
+  argument that gets refined by an abstract preficate type P.
+*/
+declare function refine<T, P: $Pred<1>>(v: T, cb: P): $Refine<T,P,1>;
+// function refine(v, cb)
+// { if (cb(v)) { return v; } else { throw new Error(); } }
+
+/*
+  Use case
+*/
+declare var a: mixed;
+var b = refine(a, is_string);
+(b: string);
+
+declare function refine_fst<T, P: $Pred<2>>(v: T, w: T, cb: P): $Refine<T,P,1>;
+// function refine_fst(v, w, cb)
+// { if (cb(v, w)) { return v; } else { throw new Error(); } }
+
+declare var c: mixed;
+declare var d: mixed;
+
+var e = refine2(c, d, is_string_and_number);
+(e: string);
+
+
+declare function refine2<T, P: $Pred<2>>(v: T, w: T, cb: P): $Refine<T,P,1>;
+
+// function refine_fst(v, w, cb)
+// { if (cb(v, w)) { return w; } else { throw new Error(); } }
+
+function is_string(x): boolean %checks {
+  return typeof x === \"string\";
+}
+
+function is_string_and_number(x, y): %checks {
+  return typeof x === \"string\" && typeof y === \"number\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected { (40:31)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:33)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+    at Parser.pp$3.parseFunctionBody (/node_modules/babylon/lib/index.js:4004:22)
+    at Parser.parseFunctionBody (/node_modules/babylon/lib/index.js:5211:20)
+    at Parser.pp$1.parseFunction (/node_modules/babylon/lib/index.js:2257:8)
+    at Parser.pp$1.parseFunctionStatement (/node_modules/babylon/lib/index.js:1926:15)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1712:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+"
+`;
+
+exports[`test sanity-filter.js 1`] = `
+"// @flow
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+// Sanity check A: filtering the wrong type
+declare var a: Array<mixed>;
+const b = my_filter(a, is_string);
+(b: Array<number>);
+
+
+// Sanity check B: Passing non-predicate function to filter
+declare var c: Array<mixed>;
+const d = my_filter(c, is_string_regular);
+(d: Array<string>);
+
+function is_string(x): boolean %checks {
+  return typeof x === \"string\";
+}
+
+function is_string_regular(x): boolean {
+  return typeof x === \"string\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected { (16:31)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:33)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+    at Parser.pp$3.parseFunctionBody (/node_modules/babylon/lib/index.js:4004:22)
+    at Parser.parseFunctionBody (/node_modules/babylon/lib/index.js:5211:20)
+    at Parser.pp$1.parseFunction (/node_modules/babylon/lib/index.js:2257:8)
+    at Parser.pp$1.parseFunctionStatement (/node_modules/babylon/lib/index.js:1926:15)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1712:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+"
+`;
+
+exports[`test sanity-filter-union.js 1`] = `
+"// @flow
+
+// Filter the contents of an array
+
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+type A = { kind: \'A\', u: number }
+type B = { kind: \'B\', v: string }
+type C = { kind: \'C\', y: boolean }
+type D = { kind: \'D\', x: boolean }
+type E = { kind: \'E\', y: boolean }
+
+declare var ab: Array<A|B|C>;
+
+(my_filter(ab, (x): %checks => x.kind === \'A\'): Array<B>);    // ERROR
+(my_filter(ab, (x): %checks => x.kind !== \'A\'): Array<A|C>);  // ERROR
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (16:20)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test sanity-refine.js 1`] = `
+"// @flow
+
+// Sanity check A: the refinment position index is outside of the allowed range
+declare function refine<T, P: $Pred<1>>(v: T, cb: P): $Refine<T,P,2>;
+
+declare var a: mixed;
+var b = refine(a, is_string);   // ERROR: index out of bounds
+(b: string);
+
+
+// Sanity check B: refine2 expects a function that accepts 3 arguments but
+// it is called with a function that takes 2
+declare var c: mixed;
+declare var d: mixed;
+declare var e: mixed;
+
+declare function refine3<T, P: $Pred<3>>(u: T, v: T, w: T, cb: P): $Refine<T,P,1>;
+
+var e = refine3(c, d, e, is_string_and_number);
+(e: string);
+
+function is_string_and_number(x, y): %checks {
+  return typeof x === \"string\" && typeof y === \"number\";
+}
+
+
+// Sanity check C: expecting a predicate function but passed a non-predicate one
+var e = refine(a, is_string_regular);   // ERROR: is_string_regular is not a
+                                        // predicate function
+(e: number);
+
+////////////////////////////////////////////////////////////////////////////////
+
+function is_string(x): %checks {
+  return typeof x === \"string\";
+}
+
+function is_string_regular(x)  {
+  return typeof x === \"string\";
+}
+
+function is_string_and_number(x, y): %checks {
+  return typeof x === \"string\" && typeof y === \"number\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (22:37)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
diff --git a/tests/predicates-abstract/filter-union.js b/tests/predicates-abstract/filter-union.js
new file mode 100644
index 000000000000..081cd6ebc161
--- /dev/null
+++ b/tests/predicates-abstract/filter-union.js
@@ -0,0 +1,17 @@
+// @flow
+
+// Filter the contents of an array
+
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+type A = { kind: 'A', u: number }
+type B = { kind: 'B', v: string }
+type C = { kind: 'C', y: boolean }
+type D = { kind: 'D', x: boolean }
+type E = { kind: 'E', y: boolean }
+
+declare var ab: Array<A|B|C>;
+
+(my_filter(ab, (x): %checks => x.kind === 'A'): Array<A>);    // OK
+(my_filter(ab, (x): %checks => x.kind !== 'A'): Array<B|C>);  // OK
diff --git a/tests/predicates-abstract/filter.js b/tests/predicates-abstract/filter.js
new file mode 100644
index 000000000000..c14d10737b62
--- /dev/null
+++ b/tests/predicates-abstract/filter.js
@@ -0,0 +1,13 @@
+// @flow
+
+// Filter the contents of an array
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+declare var arr: Array<mixed>;
+const barr = my_filter(arr, is_string);
+(barr: Array<string>);
+
+function is_string(x): %checks {
+  return typeof x === "string";
+}
diff --git a/tests/predicates-abstract/jsfmt.spec.js b/tests/predicates-abstract/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/predicates-abstract/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/predicates-abstract/refine.js b/tests/predicates-abstract/refine.js
new file mode 100644
index 000000000000..bde9c92f3e60
--- /dev/null
+++ b/tests/predicates-abstract/refine.js
@@ -0,0 +1,46 @@
+// @flow
+
+/*
+  $Pred<N> is an "abstract predicate type", i.e. denotes a (function) type that
+  refines N variables. So if `cb` is a function, then it should be refining
+  exactly N argument. It is abstract in that we do not need to specify:
+  (a) which variables are going to be refined (just the number), or (b) what
+  exactly the refinement (predicate) is going to be.
+
+  $Refine<T,P,k> is a refinement type, that refines type T with the k-th
+  argument that gets refined by an abstract preficate type P.
+*/
+declare function refine<T, P: $Pred<1>>(v: T, cb: P): $Refine<T,P,1>;
+// function refine(v, cb)
+// { if (cb(v)) { return v; } else { throw new Error(); } }
+
+/*
+  Use case
+*/
+declare var a: mixed;
+var b = refine(a, is_string);
+(b: string);
+
+declare function refine_fst<T, P: $Pred<2>>(v: T, w: T, cb: P): $Refine<T,P,1>;
+// function refine_fst(v, w, cb)
+// { if (cb(v, w)) { return v; } else { throw new Error(); } }
+
+declare var c: mixed;
+declare var d: mixed;
+
+var e = refine2(c, d, is_string_and_number);
+(e: string);
+
+
+declare function refine2<T, P: $Pred<2>>(v: T, w: T, cb: P): $Refine<T,P,1>;
+
+// function refine_fst(v, w, cb)
+// { if (cb(v, w)) { return w; } else { throw new Error(); } }
+
+function is_string(x): boolean %checks {
+  return typeof x === "string";
+}
+
+function is_string_and_number(x, y): %checks {
+  return typeof x === "string" && typeof y === "number";
+}
diff --git a/tests/predicates-abstract/sanity-filter-union.js b/tests/predicates-abstract/sanity-filter-union.js
new file mode 100644
index 000000000000..a3eb6d03be69
--- /dev/null
+++ b/tests/predicates-abstract/sanity-filter-union.js
@@ -0,0 +1,17 @@
+// @flow
+
+// Filter the contents of an array
+
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+type A = { kind: 'A', u: number }
+type B = { kind: 'B', v: string }
+type C = { kind: 'C', y: boolean }
+type D = { kind: 'D', x: boolean }
+type E = { kind: 'E', y: boolean }
+
+declare var ab: Array<A|B|C>;
+
+(my_filter(ab, (x): %checks => x.kind === 'A'): Array<B>);    // ERROR
+(my_filter(ab, (x): %checks => x.kind !== 'A'): Array<A|C>);  // ERROR
diff --git a/tests/predicates-abstract/sanity-filter.js b/tests/predicates-abstract/sanity-filter.js
new file mode 100644
index 000000000000..52ea0aaf6153
--- /dev/null
+++ b/tests/predicates-abstract/sanity-filter.js
@@ -0,0 +1,22 @@
+// @flow
+
+declare function my_filter<T, P: $Pred<1>>(v: Array<T>, cb: P): Array<$Refine<T,P,1>>;
+
+// Sanity check A: filtering the wrong type
+declare var a: Array<mixed>;
+const b = my_filter(a, is_string);
+(b: Array<number>);
+
+
+// Sanity check B: Passing non-predicate function to filter
+declare var c: Array<mixed>;
+const d = my_filter(c, is_string_regular);
+(d: Array<string>);
+
+function is_string(x): boolean %checks {
+  return typeof x === "string";
+}
+
+function is_string_regular(x): boolean {
+  return typeof x === "string";
+}
diff --git a/tests/predicates-abstract/sanity-refine.js b/tests/predicates-abstract/sanity-refine.js
new file mode 100644
index 000000000000..2edc62b47c8d
--- /dev/null
+++ b/tests/predicates-abstract/sanity-refine.js
@@ -0,0 +1,44 @@
+// @flow
+
+// Sanity check A: the refinment position index is outside of the allowed range
+declare function refine<T, P: $Pred<1>>(v: T, cb: P): $Refine<T,P,2>;
+
+declare var a: mixed;
+var b = refine(a, is_string);   // ERROR: index out of bounds
+(b: string);
+
+
+// Sanity check B: refine2 expects a function that accepts 3 arguments but
+// it is called with a function that takes 2
+declare var c: mixed;
+declare var d: mixed;
+declare var e: mixed;
+
+declare function refine3<T, P: $Pred<3>>(u: T, v: T, w: T, cb: P): $Refine<T,P,1>;
+
+var e = refine3(c, d, e, is_string_and_number);
+(e: string);
+
+function is_string_and_number(x, y): %checks {
+  return typeof x === "string" && typeof y === "number";
+}
+
+
+// Sanity check C: expecting a predicate function but passed a non-predicate one
+var e = refine(a, is_string_regular);   // ERROR: is_string_regular is not a
+                                        // predicate function
+(e: number);
+
+////////////////////////////////////////////////////////////////////////////////
+
+function is_string(x): %checks {
+  return typeof x === "string";
+}
+
+function is_string_regular(x)  {
+  return typeof x === "string";
+}
+
+function is_string_and_number(x, y): %checks {
+  return typeof x === "string" && typeof y === "number";
+}
diff --git a/tests/predicates-declared/__snapshots__/jsfmt.spec.js.snap b/tests/predicates-declared/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5b38e142c50a
--- /dev/null
+++ b/tests/predicates-declared/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,473 @@
+exports[`test function-bind.js 1`] = `
+"// @flow
+
+// Sanity checks:
+//  - use of bind in a position of a function predicate.
+//    (This case should fall through, as method calls
+//    are currently not supported.) The original behavior
+//    (including \`havoc\`) should be retained.
+
+class C {
+  m() {
+    return true;
+  }
+  a: 1;
+
+  n() {
+    if(this.m.bind(this)) {
+      this.a;
+    }
+  }
+}
+
+declare var m: Function;
+const o = { a: 1 };
+
+if (m.bind(o)) {
+  o.a;
+}
+
+
+class D {
+  m: Function;
+
+  n() {
+    if(this.m({})) { }
+  }
+}
+
+declare var m: Function;
+const x = \"\";
+if (m.bind(this)(x)) { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 288, end: 289, loc: [object Object], value: 1, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
+
+exports[`test function-union.js 1`] = `
+"// @flow
+
+declare function f1(x: mixed): boolean %checks(typeof x === \"string\");
+declare function f2(x: mixed): boolean %checks(Array.isArray(x));
+
+declare var cond: boolean;
+
+// Feature check:
+function foo(x: number | string | Array<string>): number {
+
+  var f = (cond) ? f1 : f2;
+
+  if (f(x)) {
+    return x.length;
+  } else {
+    return 1;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:39)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test is-string-decl.js 1`] = `
+"// @flow
+
+declare function is_string(x: mixed): boolean %checks(typeof x === \"string\");
+declare function is_number(x: mixed): boolean %checks(typeof x === \"number\");
+
+// Feature check:
+function foo(x: string | Array<string>): string {
+  if (is_string(x)) {
+    // The use of \`is_string\` as a conditional check
+    // should guarantee the narrowing of the type of \`x\`
+    // to string.
+    return x;
+  } else {
+    // Accordingly the negation of the above check
+    // guarantees that \`x\` here is an Array<string>
+    return x.join();
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:46)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test logical-or.js 1`] = `
+"// @flow
+
+// Sanity check:
+// - conditional functions do not affect behavior of conditional
+//   expressions (e.g. \`||\`)
+
+declare function r(x: string): number;
+var s = \'a\';
+var n = r(s) || 1;
+(n: number);
+
+var x = \"\";
+if (x = r(s) || 1) {
+  (x: number);
+}
+
+declare var dollars: mixed;
+
+function foo(x: mixed) { return 1; }
+(foo(dollars) || 0);
+
+(Number(dollars) || 0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test object-invariant.js 1`] = `
+"// @flow
+
+// Sanity check:
+// - preserving \`havoc\` semantics
+
+type Meeting = {
+  organizer: ?Invitee,
+  es: Array<Invitee>
+}
+
+type Invitee = {
+  fbid: number
+}
+
+function f(_this: { m: ?Meeting }): string {
+  if (!_this.m) {
+    return \"0\";
+  }
+
+  if (_this.m.es.some((a) => a.fbid === 0)) {
+
+  }
+  return \"3\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test orig-string-tag-check.js 1`] = `
+"// @flow
+
+// The original first-order case
+
+function foo(x: string | Array<string>): string {
+  if (typeof x === \"string\") {
+    return x; // [ERROR] x: Array<string> doesn\'t match return type
+  }
+  else {
+    return x.join(); // [ERROR] x: string doesn\'t have .join method
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test sanity-conditional.js 1`] = `
+"// @flow
+
+// ERROR: only allow conditional expressions in \`%checks\`
+
+declare function foo(x: string): mixed %checks(x = \"1\");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (5:39)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test sanity-fall-through.js 1`] = `
+"// @flow
+
+// Sanity check:
+// - we should still be getting an error at the second return statement
+
+declare function pred<T>(x: T): boolean;
+
+function foo(s: Array<string>): string {
+  if (pred(s)) {
+    return \"1\";
+  }
+  return 1;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test sanity-invalid-calls.js 1`] = `
+"// @flow
+
+// Sanity check:
+// - invalid calls at predicate positions
+
+declare function pred<T>(x: T): boolean;
+
+function foo(s: Array<string>): string {
+
+  if ((1)(s)) {
+    return \"1\";
+  }
+
+  if ((pred + 1)(\"s\")) {
+    return \"1\";
+  }
+
+  return \"1\"
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test sanity-is-string-bug.js 1`] = `
+"// @flow
+
+declare function is_string(x: mixed): boolean %checks(typeof x === \"string\");
+declare function is_number(x: mixed): boolean %checks(typeof x === \"number\");
+
+// Sanity check:
+// - Erroneous logic
+
+function bar(x: string | Array<string>): string {
+  if (is_number(x)) {
+    return x;
+  } else {
+    return x.join();    // error: both string and Array<string> can flow to x
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:46)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test sanity-parameter-mismatch.js 1`] = `
+"// @flow
+
+// Sanity check: make sure the parameters are checked as usual
+
+declare function foo(
+  input: mixed,
+  types: string | Array<string>
+): boolean %checks(typeof input === \"string\" || Array.isArray(input));
+
+foo(3, 3);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (8:11)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test sanity-pred-with-body.js 1`] = `
+"// @flow
+
+// Sanity check:
+// - predicate functions cannot have bodies (can only be declarations)
+
+function pred(x: mixed): boolean %checks(typeof x === \"string\") { // error: cannot use pred type here
+  return typeof x === \"string\";
+}
+
+function foo(x: string | Array<string>): string {
+  if (pred(x)) {
+    return x;
+  }
+  return \"1\"
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected { (6:33)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.expect (/node_modules/babylon/lib/index.js:1621:33)
+    at Parser.pp$1.parseBlock (/node_modules/babylon/lib/index.js:2119:8)
+    at Parser.pp$3.parseFunctionBody (/node_modules/babylon/lib/index.js:4004:22)
+    at Parser.parseFunctionBody (/node_modules/babylon/lib/index.js:5211:20)
+    at Parser.pp$1.parseFunction (/node_modules/babylon/lib/index.js:2257:8)
+    at Parser.pp$1.parseFunctionStatement (/node_modules/babylon/lib/index.js:1926:15)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1712:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+"
+`;
+
+exports[`test sanity-return-type.js 1`] = `
+"// @flow
+
+declare function f2(x: mixed): string %checks(Array.isArray(x));
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:38)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
diff --git a/tests/predicates-declared/function-bind.js b/tests/predicates-declared/function-bind.js
new file mode 100644
index 000000000000..ac501bb17518
--- /dev/null
+++ b/tests/predicates-declared/function-bind.js
@@ -0,0 +1,40 @@
+// @flow
+
+// Sanity checks:
+//  - use of bind in a position of a function predicate.
+//    (This case should fall through, as method calls
+//    are currently not supported.) The original behavior
+//    (including `havoc`) should be retained.
+
+class C {
+  m() {
+    return true;
+  }
+  a: 1;
+
+  n() {
+    if(this.m.bind(this)) {
+      this.a;
+    }
+  }
+}
+
+declare var m: Function;
+const o = { a: 1 };
+
+if (m.bind(o)) {
+  o.a;
+}
+
+
+class D {
+  m: Function;
+
+  n() {
+    if(this.m({})) { }
+  }
+}
+
+declare var m: Function;
+const x = "";
+if (m.bind(this)(x)) { }
diff --git a/tests/predicates-declared/function-union.js b/tests/predicates-declared/function-union.js
new file mode 100644
index 000000000000..561c9d1eb8ce
--- /dev/null
+++ b/tests/predicates-declared/function-union.js
@@ -0,0 +1,18 @@
+// @flow
+
+declare function f1(x: mixed): boolean %checks(typeof x === "string");
+declare function f2(x: mixed): boolean %checks(Array.isArray(x));
+
+declare var cond: boolean;
+
+// Feature check:
+function foo(x: number | string | Array<string>): number {
+
+  var f = (cond) ? f1 : f2;
+
+  if (f(x)) {
+    return x.length;
+  } else {
+    return 1;
+  }
+}
diff --git a/tests/predicates-declared/is-string-decl.js b/tests/predicates-declared/is-string-decl.js
new file mode 100644
index 000000000000..11c94296c89f
--- /dev/null
+++ b/tests/predicates-declared/is-string-decl.js
@@ -0,0 +1,18 @@
+// @flow
+
+declare function is_string(x: mixed): boolean %checks(typeof x === "string");
+declare function is_number(x: mixed): boolean %checks(typeof x === "number");
+
+// Feature check:
+function foo(x: string | Array<string>): string {
+  if (is_string(x)) {
+    // The use of `is_string` as a conditional check
+    // should guarantee the narrowing of the type of `x`
+    // to string.
+    return x;
+  } else {
+    // Accordingly the negation of the above check
+    // guarantees that `x` here is an Array<string>
+    return x.join();
+  }
+}
diff --git a/tests/predicates-declared/jsfmt.spec.js b/tests/predicates-declared/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/predicates-declared/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/predicates-declared/logical-or.js b/tests/predicates-declared/logical-or.js
new file mode 100644
index 000000000000..babe5b660fc1
--- /dev/null
+++ b/tests/predicates-declared/logical-or.js
@@ -0,0 +1,22 @@
+// @flow
+
+// Sanity check:
+// - conditional functions do not affect behavior of conditional
+//   expressions (e.g. `||`)
+
+declare function r(x: string): number;
+var s = 'a';
+var n = r(s) || 1;
+(n: number);
+
+var x = "";
+if (x = r(s) || 1) {
+  (x: number);
+}
+
+declare var dollars: mixed;
+
+function foo(x: mixed) { return 1; }
+(foo(dollars) || 0);
+
+(Number(dollars) || 0);
diff --git a/tests/predicates-declared/object-invariant.js b/tests/predicates-declared/object-invariant.js
new file mode 100644
index 000000000000..916f7ead2fdc
--- /dev/null
+++ b/tests/predicates-declared/object-invariant.js
@@ -0,0 +1,24 @@
+// @flow
+
+// Sanity check:
+// - preserving `havoc` semantics
+
+type Meeting = {
+  organizer: ?Invitee,
+  es: Array<Invitee>
+}
+
+type Invitee = {
+  fbid: number
+}
+
+function f(_this: { m: ?Meeting }): string {
+  if (!_this.m) {
+    return "0";
+  }
+
+  if (_this.m.es.some((a) => a.fbid === 0)) {
+
+  }
+  return "3";
+}
diff --git a/tests/predicates-declared/orig-string-tag-check.js b/tests/predicates-declared/orig-string-tag-check.js
new file mode 100644
index 000000000000..3930027f602f
--- /dev/null
+++ b/tests/predicates-declared/orig-string-tag-check.js
@@ -0,0 +1,12 @@
+// @flow
+
+// The original first-order case
+
+function foo(x: string | Array<string>): string {
+  if (typeof x === "string") {
+    return x; // [ERROR] x: Array<string> doesn't match return type
+  }
+  else {
+    return x.join(); // [ERROR] x: string doesn't have .join method
+  }
+}
diff --git a/tests/predicates-declared/sanity-conditional.js b/tests/predicates-declared/sanity-conditional.js
new file mode 100644
index 000000000000..d3d4ced873ad
--- /dev/null
+++ b/tests/predicates-declared/sanity-conditional.js
@@ -0,0 +1,5 @@
+// @flow
+
+// ERROR: only allow conditional expressions in `%checks`
+
+declare function foo(x: string): mixed %checks(x = "1");
diff --git a/tests/predicates-declared/sanity-fall-through.js b/tests/predicates-declared/sanity-fall-through.js
new file mode 100644
index 000000000000..2a4df3867533
--- /dev/null
+++ b/tests/predicates-declared/sanity-fall-through.js
@@ -0,0 +1,13 @@
+// @flow
+
+// Sanity check:
+// - we should still be getting an error at the second return statement
+
+declare function pred<T>(x: T): boolean;
+
+function foo(s: Array<string>): string {
+  if (pred(s)) {
+    return "1";
+  }
+  return 1;
+}
diff --git a/tests/predicates-declared/sanity-invalid-calls.js b/tests/predicates-declared/sanity-invalid-calls.js
new file mode 100644
index 000000000000..1ccb68edb9af
--- /dev/null
+++ b/tests/predicates-declared/sanity-invalid-calls.js
@@ -0,0 +1,19 @@
+// @flow
+
+// Sanity check:
+// - invalid calls at predicate positions
+
+declare function pred<T>(x: T): boolean;
+
+function foo(s: Array<string>): string {
+
+  if ((1)(s)) {
+    return "1";
+  }
+
+  if ((pred + 1)("s")) {
+    return "1";
+  }
+
+  return "1"
+}
diff --git a/tests/predicates-declared/sanity-is-string-bug.js b/tests/predicates-declared/sanity-is-string-bug.js
new file mode 100644
index 000000000000..f96d550bb857
--- /dev/null
+++ b/tests/predicates-declared/sanity-is-string-bug.js
@@ -0,0 +1,15 @@
+// @flow
+
+declare function is_string(x: mixed): boolean %checks(typeof x === "string");
+declare function is_number(x: mixed): boolean %checks(typeof x === "number");
+
+// Sanity check:
+// - Erroneous logic
+
+function bar(x: string | Array<string>): string {
+  if (is_number(x)) {
+    return x;
+  } else {
+    return x.join();    // error: both string and Array<string> can flow to x
+  }
+}
diff --git a/tests/predicates-declared/sanity-parameter-mismatch.js b/tests/predicates-declared/sanity-parameter-mismatch.js
new file mode 100644
index 000000000000..5432bc826ac8
--- /dev/null
+++ b/tests/predicates-declared/sanity-parameter-mismatch.js
@@ -0,0 +1,10 @@
+// @flow
+
+// Sanity check: make sure the parameters are checked as usual
+
+declare function foo(
+  input: mixed,
+  types: string | Array<string>
+): boolean %checks(typeof input === "string" || Array.isArray(input));
+
+foo(3, 3);
diff --git a/tests/predicates-declared/sanity-pred-with-body.js b/tests/predicates-declared/sanity-pred-with-body.js
new file mode 100644
index 000000000000..1a60d83869d4
--- /dev/null
+++ b/tests/predicates-declared/sanity-pred-with-body.js
@@ -0,0 +1,15 @@
+// @flow
+
+// Sanity check:
+// - predicate functions cannot have bodies (can only be declarations)
+
+function pred(x: mixed): boolean %checks(typeof x === "string") { // error: cannot use pred type here
+  return typeof x === "string";
+}
+
+function foo(x: string | Array<string>): string {
+  if (pred(x)) {
+    return x;
+  }
+  return "1"
+}
diff --git a/tests/predicates-declared/sanity-return-type.js b/tests/predicates-declared/sanity-return-type.js
new file mode 100644
index 000000000000..7ee0f6a11980
--- /dev/null
+++ b/tests/predicates-declared/sanity-return-type.js
@@ -0,0 +1,3 @@
+// @flow
+
+declare function f2(x: mixed): string %checks(Array.isArray(x));
diff --git a/tests/predicates-inferred/__snapshots__/jsfmt.spec.js.snap b/tests/predicates-inferred/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a19780c8be50
--- /dev/null
+++ b/tests/predicates-inferred/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,289 @@
+exports[`test sanity.js 1`] = `
+"// @flow
+
+// Sanity check: shouldn\'t be allowed to declare a predicate AND use \`chekcs\`
+
+function check(y): %checks(typeof y === \"string\") {
+  return typeof y === \"number\";
+}
+
+declare var y: number | boolean;
+
+if (check(y)) {
+  (y: number);
+}
+
+// Sanity: disallowed body
+function indirect_is_number(y): %checks {
+  var y = 1;
+  return typeof y === \"number\";
+}
+
+function bak(z: string | number): number {
+  if (indirect_is_number(z)) {
+    return z;
+  } else {
+    return z.length;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:19)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test sanity-multi-params.js 1`] = `
+"// @flow
+
+// Feature: multi params
+function multi_param(w,x,y,z): %checks {
+  return typeof z === \"string\";
+}
+
+function foo(x: string | Array<string>): string {
+  if (multi_param(\"1\", \"2\", x, \"3\")) {
+    return x;
+  } else {
+    return x.join();
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (4:31)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test sanity-ordering.js 1`] = `
+"// @flow
+
+declare var key: string;
+declare var obj: { page: ?Object; };
+
+if (dotAccess(obj)) {
+  (obj.page: Object);
+}
+
+function dotAccess(head, create) {
+  const path = \'path.location\';
+  const stack = path.split(\'.\');
+  do {
+    const key = stack.shift();
+    head = head[key] || create && (head[key] = {});
+  } while (stack.length && head);
+  return head;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:925
+      if (endsWithBrace(doBody))
+          ^
+
+ReferenceError: endsWithBrace is not defined
+    at genericPrintNoParens (/src/printer.js:925:11)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:561:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test sanity-unbound-var.js 1`] = `
+"// @flow
+
+declare var y: mixed;
+
+// Sanity check: this should fail, because the preficate function
+// checks \`y\` instead of \`x\`.
+function err(x): %checks {
+  return typeof y === \"string\";
+}
+
+function foo(x: string | Array<string>): string {
+  if (err(x)) {
+    return x;
+  } else {
+    return x.join();
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (7:17)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test simple-predicate-func.js 1`] = `
+"// @flow
+
+function is_string(y): %checks {
+  return typeof y === \"string\";
+}
+
+function is_bool(y): %checks {
+  return typeof y === \"boolean\";
+}
+
+function is_number(y): %checks {
+  return typeof y === \"number\";
+}
+
+// Feature check:
+function foo(x: string | Array<string>): string {
+  if (is_string(x)) {
+    // The use of \`is_string\` as a conditional check
+    // should guarantee the narrowing of the type of \`x\`
+    // to string.
+    return x;
+  } else {
+    // Accordingly the negation of the above check
+    // guarantees that \`x\` here is an Array<string>
+    return x.join();
+  }
+}
+
+// Same as above but refining an offset
+function bar(z: { f: string | Array<string>}): string {
+  if (is_string(z.f)) {
+    return z.f;
+  } else {
+    return z.f.join();
+  }
+}
+
+function is_number_or_bool(y): %checks {
+  return is_number(y) || is_bool(y);
+}
+
+function baz(z: string | number): number {
+  if (is_number_or_bool(z)) {
+    return z;
+  } else {
+    return z.length;
+  }
+}
+
+// Feature: multi params
+function multi_param(w,x,y,z): %checks {
+  return typeof z === \"string\";
+}
+
+function foo(x: string | Array<string>): string {
+  if (multi_param(\"1\", \"2\", \"3\", x)) {
+    return x;
+  } else {
+    return x.join();
+  }
+}
+
+function foo(a, b) {
+  if (two_strings(a, b)) {
+    from_two_strings(a, b);
+  }
+}
+
+function two_strings(x,y): %checks {
+  return is_string(x) && is_string(y) ;
+}
+
+declare function from_two_strings(x: string, y: string): void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (3:23)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test simple-predicate-func-post.js 1`] = `
+"// @flow
+
+// Feature check:
+// The predicate function is defined after the conditional check
+
+function foo(x: string | Array<string>): string {
+  if (is_string(x)) {
+    // The use of \`is_string\` as a conditional check
+    // should guarantee the narrowing of the type of \`x\`
+    // to string.
+    return x;
+  } else {
+    // Accordingly the negation of the above check
+    // guarantees that \`x\` here is an Array<string>
+    return x.join();
+  }
+}
+
+function is_string(x): %checks {
+  return typeof x === \"string\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (19:23)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
diff --git a/tests/predicates-inferred/jsfmt.spec.js b/tests/predicates-inferred/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/predicates-inferred/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/predicates-inferred/sanity-multi-params.js b/tests/predicates-inferred/sanity-multi-params.js
new file mode 100644
index 000000000000..e08ae04e2c67
--- /dev/null
+++ b/tests/predicates-inferred/sanity-multi-params.js
@@ -0,0 +1,14 @@
+// @flow
+
+// Feature: multi params
+function multi_param(w,x,y,z): %checks {
+  return typeof z === "string";
+}
+
+function foo(x: string | Array<string>): string {
+  if (multi_param("1", "2", x, "3")) {
+    return x;
+  } else {
+    return x.join();
+  }
+}
diff --git a/tests/predicates-inferred/sanity-ordering.js b/tests/predicates-inferred/sanity-ordering.js
new file mode 100644
index 000000000000..741e65fd305f
--- /dev/null
+++ b/tests/predicates-inferred/sanity-ordering.js
@@ -0,0 +1,18 @@
+// @flow
+
+declare var key: string;
+declare var obj: { page: ?Object; };
+
+if (dotAccess(obj)) {
+  (obj.page: Object);
+}
+
+function dotAccess(head, create) {
+  const path = 'path.location';
+  const stack = path.split('.');
+  do {
+    const key = stack.shift();
+    head = head[key] || create && (head[key] = {});
+  } while (stack.length && head);
+  return head;
+}
diff --git a/tests/predicates-inferred/sanity-unbound-var.js b/tests/predicates-inferred/sanity-unbound-var.js
new file mode 100644
index 000000000000..8ff02beb0e9c
--- /dev/null
+++ b/tests/predicates-inferred/sanity-unbound-var.js
@@ -0,0 +1,17 @@
+// @flow
+
+declare var y: mixed;
+
+// Sanity check: this should fail, because the preficate function
+// checks `y` instead of `x`.
+function err(x): %checks {
+  return typeof y === "string";
+}
+
+function foo(x: string | Array<string>): string {
+  if (err(x)) {
+    return x;
+  } else {
+    return x.join();
+  }
+}
diff --git a/tests/predicates-inferred/sanity.js b/tests/predicates-inferred/sanity.js
new file mode 100644
index 000000000000..5a2aa6d59ce6
--- /dev/null
+++ b/tests/predicates-inferred/sanity.js
@@ -0,0 +1,27 @@
+// @flow
+
+// Sanity check: shouldn't be allowed to declare a predicate AND use `chekcs`
+
+function check(y): %checks(typeof y === "string") {
+  return typeof y === "number";
+}
+
+declare var y: number | boolean;
+
+if (check(y)) {
+  (y: number);
+}
+
+// Sanity: disallowed body
+function indirect_is_number(y): %checks {
+  var y = 1;
+  return typeof y === "number";
+}
+
+function bak(z: string | number): number {
+  if (indirect_is_number(z)) {
+    return z;
+  } else {
+    return z.length;
+  }
+}
diff --git a/tests/predicates-inferred/simple-predicate-func-post.js b/tests/predicates-inferred/simple-predicate-func-post.js
new file mode 100644
index 000000000000..ba5f390920dd
--- /dev/null
+++ b/tests/predicates-inferred/simple-predicate-func-post.js
@@ -0,0 +1,21 @@
+// @flow
+
+// Feature check:
+// The predicate function is defined after the conditional check
+
+function foo(x: string | Array<string>): string {
+  if (is_string(x)) {
+    // The use of `is_string` as a conditional check
+    // should guarantee the narrowing of the type of `x`
+    // to string.
+    return x;
+  } else {
+    // Accordingly the negation of the above check
+    // guarantees that `x` here is an Array<string>
+    return x.join();
+  }
+}
+
+function is_string(x): %checks {
+  return typeof x === "string";
+}
diff --git a/tests/predicates-inferred/simple-predicate-func.js b/tests/predicates-inferred/simple-predicate-func.js
new file mode 100644
index 000000000000..bb254dbe5c7c
--- /dev/null
+++ b/tests/predicates-inferred/simple-predicate-func.js
@@ -0,0 +1,73 @@
+// @flow
+
+function is_string(y): %checks {
+  return typeof y === "string";
+}
+
+function is_bool(y): %checks {
+  return typeof y === "boolean";
+}
+
+function is_number(y): %checks {
+  return typeof y === "number";
+}
+
+// Feature check:
+function foo(x: string | Array<string>): string {
+  if (is_string(x)) {
+    // The use of `is_string` as a conditional check
+    // should guarantee the narrowing of the type of `x`
+    // to string.
+    return x;
+  } else {
+    // Accordingly the negation of the above check
+    // guarantees that `x` here is an Array<string>
+    return x.join();
+  }
+}
+
+// Same as above but refining an offset
+function bar(z: { f: string | Array<string>}): string {
+  if (is_string(z.f)) {
+    return z.f;
+  } else {
+    return z.f.join();
+  }
+}
+
+function is_number_or_bool(y): %checks {
+  return is_number(y) || is_bool(y);
+}
+
+function baz(z: string | number): number {
+  if (is_number_or_bool(z)) {
+    return z;
+  } else {
+    return z.length;
+  }
+}
+
+// Feature: multi params
+function multi_param(w,x,y,z): %checks {
+  return typeof z === "string";
+}
+
+function foo(x: string | Array<string>): string {
+  if (multi_param("1", "2", "3", x)) {
+    return x;
+  } else {
+    return x.join();
+  }
+}
+
+function foo(a, b) {
+  if (two_strings(a, b)) {
+    from_two_strings(a, b);
+  }
+}
+
+function two_strings(x,y): %checks {
+  return is_string(x) && is_string(y) ;
+}
+
+declare function from_two_strings(x: string, y: string): void;
diff --git a/tests/predicates-parsing/__snapshots__/jsfmt.spec.js.snap b/tests/predicates-parsing/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f2a3a00e626d
--- /dev/null
+++ b/tests/predicates-parsing/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,224 @@
+exports[`test fail-0.js 1`] = `
+"// @flow
+
+// Error: \'declare\', \'checks\' but missing predicate
+
+declare function f2(x: mixed): boolean %checks;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (5:39)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test fail-1.js 1`] = `
+"// @flow
+
+// Error: no return statement
+
+function f6(x: mixed): %checks (x !== null) {  }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:23)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test fail-2.js 1`] = `
+"// @flow
+
+var a2 = (x: mixed): %checks (x !== null) => {        // Error: body form
+  var x = 1; return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (3:19)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2043:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+"
+`;
+
+exports[`test fail-3.js 1`] = `
+"// @flow
+
+// Cannot declare predicate with a function body is present.
+
+function f5(x: mixed): %checks (x !== null) { return x !== null }
+
+var a2 = (x: mixed): %checks (x !== null) => x !== null;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (5:23)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$7.flowParsePrimaryType (/node_modules/babylon/lib/index.js:5099:8)
+    at Parser.pp$7.flowParsePostfixType (/node_modules/babylon/lib/index.js:5105:19)
+    at Parser.pp$7.flowParsePrefixType (/node_modules/babylon/lib/index.js:5122:17)
+    at Parser.pp$7.flowParseAnonFunctionWithoutParens (/node_modules/babylon/lib/index.js:5127:20)
+    at Parser.pp$7.flowParseIntersectionType (/node_modules/babylon/lib/index.js:5141:19)
+    at Parser.pp$7.flowParseUnionType (/node_modules/babylon/lib/index.js:5151:19)
+    at Parser.pp$7.flowParseType (/node_modules/babylon/lib/index.js:5162:19)
+    at Parser.pp$7.flowParseTypeInitialiser (/node_modules/babylon/lib/index.js:4430:19)
+"
+`;
+
+exports[`test pass.js 1`] = `
+"// @flow
+
+declare function f1(x: mixed): boolean;
+
+declare function f3(x: mixed): boolean %checks (x !== null);
+
+declare function f4(x: mixed): boolean %checks (x !== null);
+
+function f7(x: mixed):  %checks { return x !== null }
+
+var a0 = (x: mixed) => x !== null;
+
+var a1 = (x: mixed): %checks => x !== null;
+
+(x): %checks => x !== null;
+
+const insert_a_really_big_predicated_arrow_function_name_here = (x)
+  : %checks => x !== null;
+
+declare var x;
+(x)
+checks => 123;
+
+type checks = any;
+
+declare function f(x: mixed): checks
+(typeof x === null);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (5:39)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$7.flowParseDeclareFunction (/node_modules/babylon/lib/index.js:4467:8)
+    at Parser.pp$7.flowParseDeclare (/node_modules/babylon/lib/index.js:4476:17)
+    at Parser.parseExpressionStatement (/node_modules/babylon/lib/index.js:5235:25)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1785:17)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+"
+`;
+
+exports[`test unsupported-0.js 1`] = `
+"// @flow
+
+// variables cannot be annotated with a predicate type
+
+var a3: (x: mixed) => boolean %checks (x !== null);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (5:30)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2043:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+"
+`;
+
+exports[`test unsupported-1.js 1`] = `
+"// @flow
+
+// (inited) variables cannot be annotated with a predicate type
+
+var a4: (x: mixed) => boolean %checks = (x: mixed) => x !== null;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (5:30)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2043:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+"
+`;
+
+exports[`test unsupported-2.js 1`] = `
+"// @flow
+
+// Error: no support for checked preds
+
+var a5: (x: mixed) => boolean %checks(x !== null) =
+  (y: mixed) => typeof y !== \"string\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token, expected ; (5:30)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp.semicolon (/node_modules/babylon/lib/index.js:1614:38)
+    at Parser.pp$1.parseVarStatement (/node_modules/babylon/lib/index.js:2043:8)
+    at Parser.pp$1.parseStatement (/node_modules/babylon/lib/index.js:1735:19)
+    at Parser.parseStatement (/node_modules/babylon/lib/index.js:5224:22)
+    at Parser.pp$1.parseBlockBody (/node_modules/babylon/lib/index.js:2139:21)
+    at Parser.pp$1.parseTopLevel (/node_modules/babylon/lib/index.js:1651:8)
+    at Parser.parse (/node_modules/babylon/lib/index.js:1543:17)
+    at Object.parse$1 [as parse] (/node_modules/babylon/lib/index.js:6472:37)
+"
+`;
diff --git a/tests/predicates-parsing/fail-0.js b/tests/predicates-parsing/fail-0.js
new file mode 100644
index 000000000000..93439645deb4
--- /dev/null
+++ b/tests/predicates-parsing/fail-0.js
@@ -0,0 +1,5 @@
+// @flow
+
+// Error: 'declare', 'checks' but missing predicate
+
+declare function f2(x: mixed): boolean %checks;
diff --git a/tests/predicates-parsing/fail-1.js b/tests/predicates-parsing/fail-1.js
new file mode 100644
index 000000000000..ceb1e926e073
--- /dev/null
+++ b/tests/predicates-parsing/fail-1.js
@@ -0,0 +1,5 @@
+// @flow
+
+// Error: no return statement
+
+function f6(x: mixed): %checks (x !== null) {  }
diff --git a/tests/predicates-parsing/fail-2.js b/tests/predicates-parsing/fail-2.js
new file mode 100644
index 000000000000..68260c92aecc
--- /dev/null
+++ b/tests/predicates-parsing/fail-2.js
@@ -0,0 +1,5 @@
+// @flow
+
+var a2 = (x: mixed): %checks (x !== null) => {        // Error: body form
+  var x = 1; return x;
+}
diff --git a/tests/predicates-parsing/fail-3.js b/tests/predicates-parsing/fail-3.js
new file mode 100644
index 000000000000..1cd15ba3f689
--- /dev/null
+++ b/tests/predicates-parsing/fail-3.js
@@ -0,0 +1,7 @@
+// @flow
+
+// Cannot declare predicate with a function body is present.
+
+function f5(x: mixed): %checks (x !== null) { return x !== null }
+
+var a2 = (x: mixed): %checks (x !== null) => x !== null;
diff --git a/tests/predicates-parsing/jsfmt.spec.js b/tests/predicates-parsing/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/predicates-parsing/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/predicates-parsing/pass.js b/tests/predicates-parsing/pass.js
new file mode 100644
index 000000000000..05e5c54ec9c6
--- /dev/null
+++ b/tests/predicates-parsing/pass.js
@@ -0,0 +1,27 @@
+// @flow
+
+declare function f1(x: mixed): boolean;
+
+declare function f3(x: mixed): boolean %checks (x !== null);
+
+declare function f4(x: mixed): boolean %checks (x !== null);
+
+function f7(x: mixed):  %checks { return x !== null }
+
+var a0 = (x: mixed) => x !== null;
+
+var a1 = (x: mixed): %checks => x !== null;
+
+(x): %checks => x !== null;
+
+const insert_a_really_big_predicated_arrow_function_name_here = (x)
+  : %checks => x !== null;
+
+declare var x;
+(x)
+checks => 123;
+
+type checks = any;
+
+declare function f(x: mixed): checks
+(typeof x === null);
diff --git a/tests/predicates-parsing/unsupported-0.js b/tests/predicates-parsing/unsupported-0.js
new file mode 100644
index 000000000000..84ed10e27e21
--- /dev/null
+++ b/tests/predicates-parsing/unsupported-0.js
@@ -0,0 +1,5 @@
+// @flow
+
+// variables cannot be annotated with a predicate type
+
+var a3: (x: mixed) => boolean %checks (x !== null);
diff --git a/tests/predicates-parsing/unsupported-1.js b/tests/predicates-parsing/unsupported-1.js
new file mode 100644
index 000000000000..c9a7af823fd2
--- /dev/null
+++ b/tests/predicates-parsing/unsupported-1.js
@@ -0,0 +1,5 @@
+// @flow
+
+// (inited) variables cannot be annotated with a predicate type
+
+var a4: (x: mixed) => boolean %checks = (x: mixed) => x !== null;
diff --git a/tests/predicates-parsing/unsupported-2.js b/tests/predicates-parsing/unsupported-2.js
new file mode 100644
index 000000000000..d4999b9c36b5
--- /dev/null
+++ b/tests/predicates-parsing/unsupported-2.js
@@ -0,0 +1,6 @@
+// @flow
+
+// Error: no support for checked preds
+
+var a5: (x: mixed) => boolean %checks(x !== null) =
+  (y: mixed) => typeof y !== "string";
diff --git a/tests/private/__snapshots__/jsfmt.spec.js.snap b/tests/private/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..69badd198c90
--- /dev/null
+++ b/tests/private/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,36 @@
+exports[`test private.js 1`] = `
+"class A {
+  x: number;
+  _x: string;
+  __x: number;
+  constructor() { this.x = 0; this._x = ""; this.__x = 0; }
+}
+
+class B extends A {
+  foo() {
+    var x: number = this.x;
+    var _x: string = this._x;
+    var __x: number = this.__x;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {
+  x: number;
+  _x: string;
+  __x: number;
+  constructor() {
+    this.x = 0;
+    this._x = "";
+    this.__x = 0;
+  }
+}
+class B extends A {
+  foo() {
+    var x: number = this.x;
+    var _x: string = this._x;
+    var __x: number = this.__x;
+  }
+}
+
+"
+`;
diff --git a/tests/private/jsfmt.spec.js b/tests/private/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/private/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/private/private.js b/tests/private/private.js
new file mode 100644
index 000000000000..60e209d079fc
--- /dev/null
+++ b/tests/private/private.js
@@ -0,0 +1,14 @@
+class A {
+  x: number;
+  _x: string;
+  __x: number;
+  constructor() { this.x = 0; this._x = ""; this.__x = 0; }
+}
+
+class B extends A {
+  foo() {
+    var x: number = this.x;
+    var _x: string = this._x;
+    var __x: number = this.__x;
+  }
+}
diff --git a/tests/promises/__snapshots__/jsfmt.spec.js.snap b/tests/promises/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7e3ce9ba9dbe
--- /dev/null
+++ b/tests/promises/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,428 @@
+exports[`test all.js 1`] = `
+"// @flow
+
+declare var pstr: Promise<string>;
+declare var pnum: Promise<number>;
+
+Promise.all([
+  pstr,
+  pnum,
+  true, // non-Promise values passed through
+]).then((xs) => {
+  // tuple information is preserved
+  let [a,b,c] = xs;
+  (a: number);  // Error: string ~> number
+  (b: boolean); // Error: number ~> boolean
+  (c: string);  // Error: boolean ~> string
+
+  // array element type is (string | number | boolean)
+  xs.forEach(x => {
+    (x: void);  // Errors: string ~> void, number ~> void, boolean ~> void
+  });
+});
+
+// First argument is required
+Promise.all(); // Error: expected array instead of undefined (too few arguments)
+
+// Mis-typed arg
+Promise.all(0); // Error: expected array instead of number
+
+// Promise.all is a function
+(Promise.all : Function);
+
+// Promise.all supports iterables
+function test(val: Iterable<Promise<number>>) {
+  const r: Promise<Array<number>> = Promise.all(val);
+}
+
+function tes2(val: Map<string, Promise<number>>) {
+  const r: Promise<Array<number>> = Promise.all(val.values());
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test covariance.js 1`] = `
+"/* @flow */
+
+async function testAll() {
+  /* This is a test case from https://github.com/facebook/flow/issues/1143
+   * which was previously an error due to Array\'s invariance and an improper
+   * definition of Promise.all */
+    const x: Array<Promise<?string>> = [];
+    const y: Promise<Array<?string>> = Promise.all(x);
+    const z: Array<?string> = await y;
+}
+
+async function testRace() {
+    const x: Array<Promise<?string>> = [];
+    const y: Promise<?string> = Promise.race(x);
+    const z: ?string = await y;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test promise.js 1`] = `
+"/**
+ * @flow
+ */
+
+//////////////////////////////////////////////////
+// == Promise constructor resolve() function == //
+//////////////////////////////////////////////////
+
+// Promise constructor resolve(T) -> then(T)
+new Promise(function(resolve, reject) {
+  resolve(0);
+}).then(function(num) {
+  var a: number = num;
+
+  // TODO: The error message that results from this is almost useless
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise constructor with arrow function resolve(T) -> then(T)
+new Promise((resolve, reject) => resolve(0))
+  .then(function(num) {
+    var a: number = num;
+
+    // TODO: The error message that results from this is almost useless
+    var b: string = num; // Error: number ~> string
+  });
+
+// Promise constructor resolve(Promise<T>) -> then(T)
+new Promise(function(resolve, reject) {
+  resolve(new Promise(function(resolve, reject) {
+    resolve(0);
+  }));
+}).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise constructor resolve(Promise<Promise<T>>) -> then(T)
+new Promise(function(resolve, reject) {
+  resolve(new Promise(function(resolve, reject) {
+    resolve(new Promise(function(resolve, reject) {
+      resolve(0);
+    }));
+  }));
+}).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise constructor resolve(T); resolve(U); -> then(T|U)
+new Promise(function(resolve, reject) {
+  if (Math.random()) {
+    resolve(42);
+  } else {
+    resolve(\'str\');
+  }
+}).then(function(numOrStr) {
+  if (typeof numOrStr === \'string\') {
+    var a: string = numOrStr;
+  } else {
+    var b: number = numOrStr;
+  }
+  var c: string = numOrStr; // Error: number|string -> string
+});
+
+/////////////////////////////////////////////////
+// == Promise constructor reject() function == //
+/////////////////////////////////////////////////
+
+// TODO: Promise constructor reject(T) -> catch(T)
+new Promise(function(resolve, reject) {
+  reject(0);
+}).catch(function(num) {
+  var a: number = num;
+
+  // TODO
+  var b: string = num; // Error: number ~> string
+});
+
+// TODO: Promise constructor reject(Promise<T>) ~> catch(Promise<T>)
+new Promise(function(resolve, reject) {
+  reject(new Promise(function(resolve, reject) {
+    reject(0);
+  }));
+}).catch(function(num) {
+  var a: Promise<number> = num;
+
+  // TODO
+  var b: number = num; // Error: Promise<Number> ~> number
+});
+
+// TODO: Promise constructor reject(T); reject(U); -> then(T|U)
+new Promise(function(resolve, reject) {
+  if (Math.random()) {
+    reject(42);
+  } else {
+    reject(\'str\');
+  }
+}).catch(function(numOrStr) {
+  if (typeof numOrStr === \'string\') {
+    var a: string = numOrStr;
+  } else {
+    var b: number = numOrStr;
+  }
+
+  // TODO
+  var c: string = numOrStr; // Error: number|string -> string
+});
+
+/////////////////////////////
+// == Promise.resolve() == //
+/////////////////////////////
+
+// Promise.resolve(T) -> then(T)
+Promise.resolve(0).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise.resolve(Promise<T>) -> then(T)
+Promise.resolve(Promise.resolve(0)).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise.resolve(Promise<Promise<T>>) -> then(T)
+Promise.resolve(Promise.resolve(Promise.resolve(0))).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+////////////////////////////
+// == Promise.reject() == //
+////////////////////////////
+
+// TODO: Promise.reject(T) -> catch(T)
+Promise.reject(0).catch(function(num) {
+  var a: number = num;
+
+  // TODO
+  var b: string = num; // Error: number ~> string
+});
+
+// TODO: Promise.reject(Promise<T>) -> catch(Promise<T>)
+Promise.reject(Promise.resolve(0)).then(function(num) {
+  var a: Promise<number> = num;
+
+  // TODO
+  var b: number = num; // Error: Promise<number> ~> number
+});
+
+//////////////////////////////////
+// == Promise.prototype.then == //
+//////////////////////////////////
+
+// resolvedPromise.then():T -> then(T)
+Promise.resolve(0)
+  .then(function(num) { return \'asdf\'; })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// resolvedPromise.then():Promise<T> -> then(T)
+Promise.resolve(0)
+  .then(function(num) { return Promise.resolve(\'asdf\'); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// resolvedPromise.then():Promise<Promise<T>> -> then(T)
+Promise.resolve(0)
+  .then(function(num) { return Promise.resolve(Promise.resolve(\'asdf\')); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// TODO: resolvedPromise.then(<throw(T)>) -> catch(T)
+Promise.resolve(0)
+  .then(function(num) {
+    throw \'str\';
+  })
+  .catch(function(str) {
+    var a: string = str;
+
+    // TODO
+    var b: number = str; // Error: string ~> number
+  });
+
+///////////////////////////////////
+// == Promise.prototype.catch == //
+///////////////////////////////////
+
+// rejectedPromise.catch():U -> then(U)
+Promise.reject(0)
+  .catch(function(num) { return \'asdf\'; })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// rejectedPromise.catch():Promise<U> -> then(U)
+Promise.reject(0)
+  .catch(function(num) { return Promise.resolve(\'asdf\'); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// rejectedPromise.catch():Promise<Promise<U>> -> then(U)
+Promise.reject(0)
+  .catch(function(num) { return Promise.resolve(Promise.resolve(\'asdf\')); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// TODO: resolvedPromise<T> -> catch() -> then():T
+Promise.resolve(0)
+  .catch(function(err) {})
+  .then(function(num) {
+    var a: number = num;
+
+    // TODO
+    var b: string = num; // Error: string ~> number
+  });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test resolve_global.js 1`] = `
+"/**
+ * test Promise name resolution
+ * @flow
+ */
+
+/**
+ * 1. introduce shadowing bindings for important names
+ */
+class Promise {}
+
+/**
+ * 2. implicit refs to Promise during desugaring should be unaffected
+ */
+async function foo(x: boolean) {
+  if (x) {
+    return {bar: \'baz\'};
+  } else {
+    return null;
+  }
+}
+
+async function run() {
+  console.log(await foo(true));
+  console.log(await foo(false));
+}
+
+run();
+
+/**
+ * 3. but explicit name refs from code and annos resolve
+ * using the usual rules
+ */
+// error: \`Promise\` in return expr is the local binding
+async function bar() {
+  return Promise.resolve(0);
+}
+
+// error: return type anno is a ref to the local binding
+async function baz(): Promise<number> {
+  return 0;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test resolve_void.js 1`] = `
+"// @flow
+
+(Promise.resolve(): Promise<number>); // error
+
+(Promise.resolve(undefined): Promise<number>); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/promises/all.js b/tests/promises/all.js
new file mode 100644
index 000000000000..74d02a75eae0
--- /dev/null
+++ b/tests/promises/all.js
@@ -0,0 +1,39 @@
+// @flow
+
+declare var pstr: Promise<string>;
+declare var pnum: Promise<number>;
+
+Promise.all([
+  pstr,
+  pnum,
+  true, // non-Promise values passed through
+]).then((xs) => {
+  // tuple information is preserved
+  let [a,b,c] = xs;
+  (a: number);  // Error: string ~> number
+  (b: boolean); // Error: number ~> boolean
+  (c: string);  // Error: boolean ~> string
+
+  // array element type is (string | number | boolean)
+  xs.forEach(x => {
+    (x: void);  // Errors: string ~> void, number ~> void, boolean ~> void
+  });
+});
+
+// First argument is required
+Promise.all(); // Error: expected array instead of undefined (too few arguments)
+
+// Mis-typed arg
+Promise.all(0); // Error: expected array instead of number
+
+// Promise.all is a function
+(Promise.all : Function);
+
+// Promise.all supports iterables
+function test(val: Iterable<Promise<number>>) {
+  const r: Promise<Array<number>> = Promise.all(val);
+}
+
+function tes2(val: Map<string, Promise<number>>) {
+  const r: Promise<Array<number>> = Promise.all(val.values());
+}
diff --git a/tests/promises/covariance.js b/tests/promises/covariance.js
new file mode 100644
index 000000000000..dbfdd6912d72
--- /dev/null
+++ b/tests/promises/covariance.js
@@ -0,0 +1,16 @@
+/* @flow */
+
+async function testAll() {
+  /* This is a test case from https://github.com/facebook/flow/issues/1143
+   * which was previously an error due to Array's invariance and an improper
+   * definition of Promise.all */
+    const x: Array<Promise<?string>> = [];
+    const y: Promise<Array<?string>> = Promise.all(x);
+    const z: Array<?string> = await y;
+}
+
+async function testRace() {
+    const x: Array<Promise<?string>> = [];
+    const y: Promise<?string> = Promise.race(x);
+    const z: ?string = await y;
+}
diff --git a/tests/promises/jsfmt.spec.js b/tests/promises/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/promises/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/promises/promise.js b/tests/promises/promise.js
new file mode 100644
index 000000000000..1266b018346d
--- /dev/null
+++ b/tests/promises/promise.js
@@ -0,0 +1,228 @@
+/**
+ * @flow
+ */
+
+//////////////////////////////////////////////////
+// == Promise constructor resolve() function == //
+//////////////////////////////////////////////////
+
+// Promise constructor resolve(T) -> then(T)
+new Promise(function(resolve, reject) {
+  resolve(0);
+}).then(function(num) {
+  var a: number = num;
+
+  // TODO: The error message that results from this is almost useless
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise constructor with arrow function resolve(T) -> then(T)
+new Promise((resolve, reject) => resolve(0))
+  .then(function(num) {
+    var a: number = num;
+
+    // TODO: The error message that results from this is almost useless
+    var b: string = num; // Error: number ~> string
+  });
+
+// Promise constructor resolve(Promise<T>) -> then(T)
+new Promise(function(resolve, reject) {
+  resolve(new Promise(function(resolve, reject) {
+    resolve(0);
+  }));
+}).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise constructor resolve(Promise<Promise<T>>) -> then(T)
+new Promise(function(resolve, reject) {
+  resolve(new Promise(function(resolve, reject) {
+    resolve(new Promise(function(resolve, reject) {
+      resolve(0);
+    }));
+  }));
+}).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise constructor resolve(T); resolve(U); -> then(T|U)
+new Promise(function(resolve, reject) {
+  if (Math.random()) {
+    resolve(42);
+  } else {
+    resolve('str');
+  }
+}).then(function(numOrStr) {
+  if (typeof numOrStr === 'string') {
+    var a: string = numOrStr;
+  } else {
+    var b: number = numOrStr;
+  }
+  var c: string = numOrStr; // Error: number|string -> string
+});
+
+/////////////////////////////////////////////////
+// == Promise constructor reject() function == //
+/////////////////////////////////////////////////
+
+// TODO: Promise constructor reject(T) -> catch(T)
+new Promise(function(resolve, reject) {
+  reject(0);
+}).catch(function(num) {
+  var a: number = num;
+
+  // TODO
+  var b: string = num; // Error: number ~> string
+});
+
+// TODO: Promise constructor reject(Promise<T>) ~> catch(Promise<T>)
+new Promise(function(resolve, reject) {
+  reject(new Promise(function(resolve, reject) {
+    reject(0);
+  }));
+}).catch(function(num) {
+  var a: Promise<number> = num;
+
+  // TODO
+  var b: number = num; // Error: Promise<Number> ~> number
+});
+
+// TODO: Promise constructor reject(T); reject(U); -> then(T|U)
+new Promise(function(resolve, reject) {
+  if (Math.random()) {
+    reject(42);
+  } else {
+    reject('str');
+  }
+}).catch(function(numOrStr) {
+  if (typeof numOrStr === 'string') {
+    var a: string = numOrStr;
+  } else {
+    var b: number = numOrStr;
+  }
+
+  // TODO
+  var c: string = numOrStr; // Error: number|string -> string
+});
+
+/////////////////////////////
+// == Promise.resolve() == //
+/////////////////////////////
+
+// Promise.resolve(T) -> then(T)
+Promise.resolve(0).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise.resolve(Promise<T>) -> then(T)
+Promise.resolve(Promise.resolve(0)).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+// Promise.resolve(Promise<Promise<T>>) -> then(T)
+Promise.resolve(Promise.resolve(Promise.resolve(0))).then(function(num) {
+  var a: number = num;
+  var b: string = num; // Error: number ~> string
+});
+
+////////////////////////////
+// == Promise.reject() == //
+////////////////////////////
+
+// TODO: Promise.reject(T) -> catch(T)
+Promise.reject(0).catch(function(num) {
+  var a: number = num;
+
+  // TODO
+  var b: string = num; // Error: number ~> string
+});
+
+// TODO: Promise.reject(Promise<T>) -> catch(Promise<T>)
+Promise.reject(Promise.resolve(0)).then(function(num) {
+  var a: Promise<number> = num;
+
+  // TODO
+  var b: number = num; // Error: Promise<number> ~> number
+});
+
+//////////////////////////////////
+// == Promise.prototype.then == //
+//////////////////////////////////
+
+// resolvedPromise.then():T -> then(T)
+Promise.resolve(0)
+  .then(function(num) { return 'asdf'; })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// resolvedPromise.then():Promise<T> -> then(T)
+Promise.resolve(0)
+  .then(function(num) { return Promise.resolve('asdf'); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// resolvedPromise.then():Promise<Promise<T>> -> then(T)
+Promise.resolve(0)
+  .then(function(num) { return Promise.resolve(Promise.resolve('asdf')); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// TODO: resolvedPromise.then(<throw(T)>) -> catch(T)
+Promise.resolve(0)
+  .then(function(num) {
+    throw 'str';
+  })
+  .catch(function(str) {
+    var a: string = str;
+
+    // TODO
+    var b: number = str; // Error: string ~> number
+  });
+
+///////////////////////////////////
+// == Promise.prototype.catch == //
+///////////////////////////////////
+
+// rejectedPromise.catch():U -> then(U)
+Promise.reject(0)
+  .catch(function(num) { return 'asdf'; })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// rejectedPromise.catch():Promise<U> -> then(U)
+Promise.reject(0)
+  .catch(function(num) { return Promise.resolve('asdf'); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// rejectedPromise.catch():Promise<Promise<U>> -> then(U)
+Promise.reject(0)
+  .catch(function(num) { return Promise.resolve(Promise.resolve('asdf')); })
+  .then(function(str) {
+    var a: string = str;
+    var b: number = str; // Error: string ~> number
+  });
+
+// TODO: resolvedPromise<T> -> catch() -> then():T
+Promise.resolve(0)
+  .catch(function(err) {})
+  .then(function(num) {
+    var a: number = num;
+
+    // TODO
+    var b: string = num; // Error: string ~> number
+  });
diff --git a/tests/promises/resolve_global.js b/tests/promises/resolve_global.js
new file mode 100644
index 000000000000..d53873b74cca
--- /dev/null
+++ b/tests/promises/resolve_global.js
@@ -0,0 +1,41 @@
+/**
+ * test Promise name resolution
+ * @flow
+ */
+
+/**
+ * 1. introduce shadowing bindings for important names
+ */
+class Promise {}
+
+/**
+ * 2. implicit refs to Promise during desugaring should be unaffected
+ */
+async function foo(x: boolean) {
+  if (x) {
+    return {bar: 'baz'};
+  } else {
+    return null;
+  }
+}
+
+async function run() {
+  console.log(await foo(true));
+  console.log(await foo(false));
+}
+
+run();
+
+/**
+ * 3. but explicit name refs from code and annos resolve
+ * using the usual rules
+ */
+// error: `Promise` in return expr is the local binding
+async function bar() {
+  return Promise.resolve(0);
+}
+
+// error: return type anno is a ref to the local binding
+async function baz(): Promise<number> {
+  return 0;
+}
diff --git a/tests/promises/resolve_void.js b/tests/promises/resolve_void.js
new file mode 100644
index 000000000000..c98ec554aa54
--- /dev/null
+++ b/tests/promises/resolve_void.js
@@ -0,0 +1,5 @@
+// @flow
+
+(Promise.resolve(): Promise<number>); // error
+
+(Promise.resolve(undefined): Promise<number>); // error
diff --git a/tests/pure_component/__snapshots__/jsfmt.spec.js.snap b/tests/pure_component/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..80fcdf839ab9
--- /dev/null
+++ b/tests/pure_component/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,16 @@
+exports[`test test.js 1`] = `
+"var React = require('react');
+
+class C extends React.PureComponent {
+  props: { x: number };
+}
+(<C />); // error (\`x\` is a required prop)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var React = require("react");
+class C extends React.PureComponent {
+  props: { x: number };
+}
+<C/>;// error (\`x\` is a required prop)
+
+"
+`;
diff --git a/tests/pure_component/jsfmt.spec.js b/tests/pure_component/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/pure_component/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/pure_component/test.js b/tests/pure_component/test.js
new file mode 100644
index 000000000000..ec8e3daed8ed
--- /dev/null
+++ b/tests/pure_component/test.js
@@ -0,0 +1,6 @@
+var React = require('react');
+
+class C extends React.PureComponent {
+  props: { x: number };
+}
+(<C />); // error (`x` is a required prop)
diff --git a/tests/qualified/__snapshots__/jsfmt.spec.js.snap b/tests/qualified/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..345f03a98111
--- /dev/null
+++ b/tests/qualified/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test qualified.js 1`] = `
+"class C { }
+var M = { C: C };
+
+var x:M.C = 0;
+
+type foo = {bar: number};
+
+declare var of_type_foo: foo;
+type bar = typeof of_type_foo.bar;
+
+var a: bar = 42;
+var b: bar = 'asdf'; // Error: string ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {}
+var M = { C: C };
+var x: M.C = 0;
+type foo = { bar: number };
+declare var of_type_foo: foo;
+type bar = typeof of_type_foo.bar;
+var a: bar = 42;
+var b: bar = "asdf";// Error: string ~> number
+
+"
+`;
diff --git a/tests/qualified/jsfmt.spec.js b/tests/qualified/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/qualified/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/qualified/qualified.js b/tests/qualified/qualified.js
new file mode 100644
index 000000000000..f5fc7616799c
--- /dev/null
+++ b/tests/qualified/qualified.js
@@ -0,0 +1,12 @@
+class C { }
+var M = { C: C };
+
+var x:M.C = 0;
+
+type foo = {bar: number};
+
+declare var of_type_foo: foo;
+type bar = typeof of_type_foo.bar;
+
+var a: bar = 42;
+var b: bar = 'asdf'; // Error: string ~> number
diff --git a/tests/react/ArityError.react.js b/tests/react/ArityError.react.js
new file mode 100644
index 000000000000..531fdc1e980e
--- /dev/null
+++ b/tests/react/ArityError.react.js
@@ -0,0 +1,11 @@
+/**
+ * @providesModule ArityError.react
+ */
+var React = require('react');
+var AudienceInsightsContainer = React.createClass({
+  renderComponent(AudienceInsights: ReactClass<*>) {
+    return <AudienceInsights />;
+  },
+});
+
+module.exports = AudienceInsightsContainer;
diff --git a/tests/react/__snapshots__/jsfmt.spec.js.snap b/tests/react/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4f2dc3ec59f8
--- /dev/null
+++ b/tests/react/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,395 @@
+exports[`test ArityError.react.js 1`] = `
+"/**
+ * @providesModule ArityError.react
+ */
+var React = require(\'react\');
+var AudienceInsightsContainer = React.createClass({
+  renderComponent(AudienceInsights: ReactClass<*>) {
+    return <AudienceInsights />;
+  },
+});
+
+module.exports = AudienceInsightsContainer;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test createElement_string.js 1`] = `
+"// @flow
+import React from \'react\';
+
+class Bar extends React.Component {}
+
+class Foo extends React.Component {
+  render() {
+    const Cmp = Math.random() < 0.5 ? \'div\' : Bar;
+    return (<Cmp/>);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import React from \"react\";
+class Bar extends React.Component {}
+class Foo extends React.Component {
+  render() {
+    const Cmp = (Math.random() < 0.5 ? \"div\" : Bar);
+    return <Cmp/>;
+  }
+}
+
+"
+`;
+
+exports[`test createElementRequiredProp_string.js 1`] = `
+"// @flow
+import React from \'react\';
+
+class Bar extends React.Component {
+  props: {
+    test: number,
+  };
+  render() {
+    return (
+      <div>
+        {this.props.test}
+      </div>
+    )
+  }
+}
+
+class Foo extends React.Component {
+  render() {
+    const Cmp = Math.random() < 0.5 ? \'div\' : Bar;
+    return (<Cmp/>);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import React from \"react\";
+class Bar extends React.Component {
+  props: { test: number };
+  render() {
+    return (
+      <div>
+        {this.props.test}
+      </div>
+    );
+  }
+}
+class Foo extends React.Component {
+  render() {
+    const Cmp = (Math.random() < 0.5 ? \"div\" : Bar);
+    return <Cmp/>;
+  }
+}
+
+"
+`;
+
+exports[`test import_react.js 1`] = `
+"/* @flow */
+
+import react from \"react\";
+import {Component} from \"react\";
+
+var a: Component<*,*,*> = new react.Component();
+var b: number = new react.Component(); // Error: ReactComponent ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test jsx_spread.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Foo = React.createClass({
+  propTypes: {
+    bar: React.PropTypes.string.isRequired,
+  },
+});
+
+var props = {bar: 42};
+var blah = <Foo {...props} />; // error bar, number given string expected
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Foo = React.createClass({
+  propTypes: { bar: React.PropTypes.string.isRequired }
+});
+var props = { bar: 42 };
+var blah = <Foo {...props}/>;// error bar, number given string expected
+
+"
+`;
+
+exports[`test proptype_arrayOf.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Example = React.createClass({
+  propTypes: {
+    arr: React.PropTypes.arrayOf(React.PropTypes.number).isRequired
+  },
+});
+
+var ok_empty = <Example arr={[]} />
+var ok_numbers = <Example arr={[1, 2]} />
+
+var fail_not_array = <Example arr={2} />
+var fail_mistyped_elems = <Example arr={[1, \"foo\"]} />
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Example = React.createClass({
+  propTypes: { arr: React.PropTypes.arrayOf(React.PropTypes.number).isRequired }
+});
+var ok_empty = <Example arr={[  ]}/>;
+var ok_numbers = <Example arr={[ 1, 2 ]}/>;
+var fail_not_array = <Example arr={2}/>;
+var fail_mistyped_elems = <Example arr={[ 1, \"foo\" ]}/>;
+
+"
+`;
+
+exports[`test proptype_func.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Example = React.createClass({
+  propTypes: {
+    func: React.PropTypes.func.isRequired
+  },
+});
+
+var ok_void = <Example func={() => {}} />;
+var ok_args = <Example func={(x) => {}} />;
+var ok_retval = <Example func={() => 1} />
+
+var fail_mistyped = <Example func={2} />
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Example = React.createClass({
+  propTypes: { func: React.PropTypes.func.isRequired }
+});
+var ok_void = <Example func={() => {
+  
+}}/>;
+var ok_args = <Example func={x => {
+  
+}}/>;
+var ok_retval = <Example func={() => 1}/>;
+var fail_mistyped = <Example func={2}/>;
+
+"
+`;
+
+exports[`test proptype_missing.js 1`] = `
+"/* @flow */
+
+/* If you create a react component with createClass() but don\'t specify the
+ * propTypes, what should the type of props be?
+ *
+ * It used to be an empty object, but we didn\'t enforce that correctly, so
+ * people could do whatever they wanted with this.props.
+ *
+ * As of 0.21.0 it started to be an error when people used this.props in a
+ * strict equality situation. It was weird that this was only sometimes
+ * enforced, so glevi changed this.props to be Object by default.
+ *
+ * We may change this back to the empty object at some point and fix the
+ * situations where it didn\'t used to error
+ */
+var React = React.createClass({
+  getID(): string {
+    // So this would have been an error in 0.21.0 if we didn\'t make this.props
+    // Object
+    switch (this.props.name) {
+      case \'a\': return \'Bob\';
+      default: return \'Alice\';
+    }
+  },
+
+  render() {
+    // But this never errored
+    return <div id={this.props.name} />;
+  }
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test proptype_object.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Example = React.createClass({
+  propTypes: {
+    object: React.PropTypes.object.isRequired
+  },
+});
+
+var ok_empty = <Example object={{}} />;
+var ok_props = <Example object={{foo: \"bar\"}} />;
+
+var fail_mistyped = <Example object={2} />
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Example = React.createClass({
+  propTypes: { object: React.PropTypes.object.isRequired }
+});
+var ok_empty = <Example object={{}}/>;
+var ok_props = <Example object={{ foo: \"bar\" }}/>;
+var fail_mistyped = <Example object={2}/>;
+
+"
+`;
+
+exports[`test proptype_objectOf.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Example = React.createClass({
+  propTypes: {
+    obj: React.PropTypes.objectOf(React.PropTypes.number).isRequired
+  },
+});
+
+var ok_empty = <Example obj={{}} />
+var ok_numbers = <Example obj={{foo: 1, bar: 2}} />
+
+var fail_not_object = <Example obj={2} />
+var fail_mistyped_props = <Example obj={{foo: \"foo\"}} />
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Example = React.createClass({
+  propTypes: {
+    obj: React.PropTypes.objectOf(React.PropTypes.number).isRequired
+  }
+});
+var ok_empty = <Example obj={{}}/>;
+var ok_numbers = <Example obj={{ foo: 1, bar: 2 }}/>;
+var fail_not_object = <Example obj={2}/>;
+var fail_mistyped_props = <Example obj={{ foo: \"foo\" }}/>;
+
+"
+`;
+
+exports[`test proptype_oneOf.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Example = React.createClass({
+  propTypes: {
+    literal: React.PropTypes.oneOf([\"foo\"]).isRequired
+  },
+});
+
+var ex1 = <Example literal=\"foo\" />;
+var ex2 = <Example literal=\"bar\" />;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Example = React.createClass({
+  propTypes: { literal: React.PropTypes.oneOf([ \"foo\" ]).isRequired }
+});
+var ex1 = <Example literal=\"foo\"/>;
+var ex2 = <Example literal=\"bar\"/>;
+
+"
+`;
+
+exports[`test proptype_oneOfType.js 1`] = `
+"/* @flow */
+
+var React = require(\'react\');
+var Example = React.createClass({
+  propTypes: {
+    prop: React.PropTypes.oneOfType([
+      React.PropTypes.string,
+      React.PropTypes.number
+    ]).isRequired
+  },
+  render() {
+    if (typeof this.props.prop === \"string\") {
+      return <div>{this.props.prop}</div>
+    } else {
+      return <div>{this.props.prop.toFixed(2)}</div>
+    }
+  }
+});
+
+var ok_number = <Example prop={42} />;
+var ok_string = <Example prop=\"bar\" />;
+
+var fail_bool = <Example prop={true} />
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var React = require(\"react\");
+var Example = React.createClass({
+  propTypes: {
+    prop: React.PropTypes.oneOfType(
+      [ React.PropTypes.string, React.PropTypes.number ]
+    ).isRequired
+  },
+  render() {
+    if (typeof this.props.prop === \"string\") {
+      return <div>{this.props.prop}</div>;
+    } else {
+      return <div>{this.props.prop.toFixed(2)}</div>;
+    }
+  }
+});
+var ok_number = <Example prop={42}/>;
+var ok_string = <Example prop=\"bar\"/>;
+var fail_bool = <Example prop={true}/>;
+
+"
+`;
diff --git a/tests/react/createElementRequiredProp_string.js b/tests/react/createElementRequiredProp_string.js
new file mode 100644
index 000000000000..5793a65c4799
--- /dev/null
+++ b/tests/react/createElementRequiredProp_string.js
@@ -0,0 +1,22 @@
+// @flow
+import React from 'react';
+
+class Bar extends React.Component {
+  props: {
+    test: number,
+  };
+  render() {
+    return (
+      <div>
+        {this.props.test}
+      </div>
+    )
+  }
+}
+
+class Foo extends React.Component {
+  render() {
+    const Cmp = Math.random() < 0.5 ? 'div' : Bar;
+    return (<Cmp/>);
+  }
+}
diff --git a/tests/react/createElement_string.js b/tests/react/createElement_string.js
new file mode 100644
index 000000000000..b6d548afec6a
--- /dev/null
+++ b/tests/react/createElement_string.js
@@ -0,0 +1,11 @@
+// @flow
+import React from 'react';
+
+class Bar extends React.Component {}
+
+class Foo extends React.Component {
+  render() {
+    const Cmp = Math.random() < 0.5 ? 'div' : Bar;
+    return (<Cmp/>);
+  }
+}
diff --git a/tests/react/import_react.js b/tests/react/import_react.js
new file mode 100644
index 000000000000..d608b7c2f16c
--- /dev/null
+++ b/tests/react/import_react.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+import react from "react";
+import {Component} from "react";
+
+var a: Component<*,*,*> = new react.Component();
+var b: number = new react.Component(); // Error: ReactComponent ~> number
diff --git a/tests/react/jsfmt.spec.js b/tests/react/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/react/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/react/jsx_spread.js b/tests/react/jsx_spread.js
new file mode 100644
index 000000000000..d5214d7e40e6
--- /dev/null
+++ b/tests/react/jsx_spread.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+var React = require('react');
+var Foo = React.createClass({
+  propTypes: {
+    bar: React.PropTypes.string.isRequired,
+  },
+});
+
+var props = {bar: 42};
+var blah = <Foo {...props} />; // error bar, number given string expected
diff --git a/tests/react/proptype_arrayOf.js b/tests/react/proptype_arrayOf.js
new file mode 100644
index 000000000000..f6cd3822821b
--- /dev/null
+++ b/tests/react/proptype_arrayOf.js
@@ -0,0 +1,14 @@
+/* @flow */
+
+var React = require('react');
+var Example = React.createClass({
+  propTypes: {
+    arr: React.PropTypes.arrayOf(React.PropTypes.number).isRequired
+  },
+});
+
+var ok_empty = <Example arr={[]} />
+var ok_numbers = <Example arr={[1, 2]} />
+
+var fail_not_array = <Example arr={2} />
+var fail_mistyped_elems = <Example arr={[1, "foo"]} />
diff --git a/tests/react/proptype_func.js b/tests/react/proptype_func.js
new file mode 100644
index 000000000000..52f452d63793
--- /dev/null
+++ b/tests/react/proptype_func.js
@@ -0,0 +1,14 @@
+/* @flow */
+
+var React = require('react');
+var Example = React.createClass({
+  propTypes: {
+    func: React.PropTypes.func.isRequired
+  },
+});
+
+var ok_void = <Example func={() => {}} />;
+var ok_args = <Example func={(x) => {}} />;
+var ok_retval = <Example func={() => 1} />
+
+var fail_mistyped = <Example func={2} />
diff --git a/tests/react/proptype_missing.js b/tests/react/proptype_missing.js
new file mode 100644
index 000000000000..29fa980fab45
--- /dev/null
+++ b/tests/react/proptype_missing.js
@@ -0,0 +1,30 @@
+/* @flow */
+
+/* If you create a react component with createClass() but don't specify the
+ * propTypes, what should the type of props be?
+ *
+ * It used to be an empty object, but we didn't enforce that correctly, so
+ * people could do whatever they wanted with this.props.
+ *
+ * As of 0.21.0 it started to be an error when people used this.props in a
+ * strict equality situation. It was weird that this was only sometimes
+ * enforced, so glevi changed this.props to be Object by default.
+ *
+ * We may change this back to the empty object at some point and fix the
+ * situations where it didn't used to error
+ */
+var React = React.createClass({
+  getID(): string {
+    // So this would have been an error in 0.21.0 if we didn't make this.props
+    // Object
+    switch (this.props.name) {
+      case 'a': return 'Bob';
+      default: return 'Alice';
+    }
+  },
+
+  render() {
+    // But this never errored
+    return <div id={this.props.name} />;
+  }
+});
diff --git a/tests/react/proptype_object.js b/tests/react/proptype_object.js
new file mode 100644
index 000000000000..5a4754df6126
--- /dev/null
+++ b/tests/react/proptype_object.js
@@ -0,0 +1,13 @@
+/* @flow */
+
+var React = require('react');
+var Example = React.createClass({
+  propTypes: {
+    object: React.PropTypes.object.isRequired
+  },
+});
+
+var ok_empty = <Example object={{}} />;
+var ok_props = <Example object={{foo: "bar"}} />;
+
+var fail_mistyped = <Example object={2} />
diff --git a/tests/react/proptype_objectOf.js b/tests/react/proptype_objectOf.js
new file mode 100644
index 000000000000..abead5617f30
--- /dev/null
+++ b/tests/react/proptype_objectOf.js
@@ -0,0 +1,14 @@
+/* @flow */
+
+var React = require('react');
+var Example = React.createClass({
+  propTypes: {
+    obj: React.PropTypes.objectOf(React.PropTypes.number).isRequired
+  },
+});
+
+var ok_empty = <Example obj={{}} />
+var ok_numbers = <Example obj={{foo: 1, bar: 2}} />
+
+var fail_not_object = <Example obj={2} />
+var fail_mistyped_props = <Example obj={{foo: "foo"}} />
diff --git a/tests/react/proptype_oneOf.js b/tests/react/proptype_oneOf.js
new file mode 100644
index 000000000000..f7486afb9a16
--- /dev/null
+++ b/tests/react/proptype_oneOf.js
@@ -0,0 +1,11 @@
+/* @flow */
+
+var React = require('react');
+var Example = React.createClass({
+  propTypes: {
+    literal: React.PropTypes.oneOf(["foo"]).isRequired
+  },
+});
+
+var ex1 = <Example literal="foo" />;
+var ex2 = <Example literal="bar" />;
diff --git a/tests/react/proptype_oneOfType.js b/tests/react/proptype_oneOfType.js
new file mode 100644
index 000000000000..3fa66d947cb6
--- /dev/null
+++ b/tests/react/proptype_oneOfType.js
@@ -0,0 +1,23 @@
+/* @flow */
+
+var React = require('react');
+var Example = React.createClass({
+  propTypes: {
+    prop: React.PropTypes.oneOfType([
+      React.PropTypes.string,
+      React.PropTypes.number
+    ]).isRequired
+  },
+  render() {
+    if (typeof this.props.prop === "string") {
+      return <div>{this.props.prop}</div>
+    } else {
+      return <div>{this.props.prop.toFixed(2)}</div>
+    }
+  }
+});
+
+var ok_number = <Example prop={42} />;
+var ok_string = <Example prop="bar" />;
+
+var fail_bool = <Example prop={true} />
diff --git a/tests/react_functional/__snapshots__/jsfmt.spec.js.snap b/tests/react_functional/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ff19495104e0
--- /dev/null
+++ b/tests/react_functional/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,32 @@
+exports[`test test.js 1`] = `
+"import React from \"react\";
+
+function F(props: { foo: string }) {}
+<F />; // error: missing \`foo\`
+<F foo={0} />; // error: number ~> string
+<F foo=\"\" />; // ok
+
+// props subtyping is property-wise covariant
+function G(props: { foo: string|numner }) {}
+<G foo=\"\" />; // ok
+
+var Z = 0;
+<Z />; // error, expected React component
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/react_functional/jsfmt.spec.js b/tests/react_functional/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/react_functional/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/react_functional/test.js b/tests/react_functional/test.js
new file mode 100644
index 000000000000..acdec6f9409e
--- /dev/null
+++ b/tests/react_functional/test.js
@@ -0,0 +1,13 @@
+import React from "react";
+
+function F(props: { foo: string }) {}
+<F />; // error: missing `foo`
+<F foo={0} />; // error: number ~> string
+<F foo="" />; // ok
+
+// props subtyping is property-wise covariant
+function G(props: { foo: string|numner }) {}
+<G foo="" />; // ok
+
+var Z = 0;
+<Z />; // error, expected React component
diff --git a/tests/react_modules/__snapshots__/jsfmt.spec.js.snap b/tests/react_modules/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2fedbc3a5ef0
--- /dev/null
+++ b/tests/react_modules/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,241 @@
+exports[`test createclass-callsite.js 1`] = `
+"/* @flow */
+var React = require(\'react\');
+var Hello = require(\'./createclass-module\');
+
+var HelloLocal = React.createClass({
+  propTypes: {
+    name: React.PropTypes.string.isRequired,
+  },
+
+  render: function(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+});
+
+var Callsite = React.createClass({
+  render: function(): React.Element<*> {
+    return (
+      <div>
+        <Hello />
+        <HelloLocal />
+      </div>
+    );
+  }
+});
+
+module.exports = Callsite;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test createclass-module.js 1`] = `
+"/* @flow */
+var React = require(\'react\');
+
+var Hello = React.createClass({
+  propTypes: {
+    name: React.PropTypes.string.isRequired,
+  },
+
+  render: function(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+});
+
+module.exports = Hello;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test es6class-proptypes-callsite.js 1`] = `
+"/* @flow */
+import React from \'react\';
+import Hello from \'./es6class-proptypes-module\';
+
+class HelloLocal extends React.Component<void, {name: string}, void> {
+  defaultProps = {};
+  propTypes = {
+    name: React.PropTypes.string.isRequired,
+  };
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+class Callsite extends React.Component<void, {}, void> {
+  render(): React.Element<*> {
+    return (
+      <div>
+        <Hello />
+        <HelloLocal />
+      </div>
+    );
+  }
+}
+
+module.exports = Callsite;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1180:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test es6class-proptypes-module.js 1`] = `
+"/* @flow */
+import React from \'react\';
+
+class Hello extends React.Component<void, {name: string}, void> {
+  defaultProps = {};
+  propTypes = {
+    name: React.PropTypes.string.isRequired,
+  };
+
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+module.exports = Hello;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1180:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test es6class-types-callsite.js 1`] = `
+"/* @flow */
+import React from \'react\';
+import Hello from \'./es6class-types-module\';
+
+type Props = {name: string};
+
+class HelloLocal extends React.Component<void, Props, void> {
+  props: Props;
+
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+class Callsite extends React.Component<void, Props, void> {
+  render(): React.Element<*> {
+    return (
+      <div>
+        <Hello />
+        <HelloLocal />
+      </div>
+    );
+  }
+}
+
+module.exports = Callsite;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1180:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test es6class-types-module.js 1`] = `
+"/* @flow */
+import React from \'react\';
+
+type Props = {name: string};
+
+class Hello extends React.Component<{}, Props, void>{
+  props: Props;
+  static defaultProps: {};
+
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+module.exports = Hello;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1180:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/react_modules/createclass-callsite.js b/tests/react_modules/createclass-callsite.js
new file mode 100644
index 000000000000..5a5f3b175953
--- /dev/null
+++ b/tests/react_modules/createclass-callsite.js
@@ -0,0 +1,26 @@
+/* @flow */
+var React = require('react');
+var Hello = require('./createclass-module');
+
+var HelloLocal = React.createClass({
+  propTypes: {
+    name: React.PropTypes.string.isRequired,
+  },
+
+  render: function(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+});
+
+var Callsite = React.createClass({
+  render: function(): React.Element<*> {
+    return (
+      <div>
+        <Hello />
+        <HelloLocal />
+      </div>
+    );
+  }
+});
+
+module.exports = Callsite;
diff --git a/tests/react_modules/createclass-module.js b/tests/react_modules/createclass-module.js
new file mode 100644
index 000000000000..3b7e25cdd5dc
--- /dev/null
+++ b/tests/react_modules/createclass-module.js
@@ -0,0 +1,14 @@
+/* @flow */
+var React = require('react');
+
+var Hello = React.createClass({
+  propTypes: {
+    name: React.PropTypes.string.isRequired,
+  },
+
+  render: function(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+});
+
+module.exports = Hello;
diff --git a/tests/react_modules/es6class-proptypes-callsite.js b/tests/react_modules/es6class-proptypes-callsite.js
new file mode 100644
index 000000000000..6a50aa90ee7a
--- /dev/null
+++ b/tests/react_modules/es6class-proptypes-callsite.js
@@ -0,0 +1,26 @@
+/* @flow */
+import React from 'react';
+import Hello from './es6class-proptypes-module';
+
+class HelloLocal extends React.Component<void, {name: string}, void> {
+  defaultProps = {};
+  propTypes = {
+    name: React.PropTypes.string.isRequired,
+  };
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+class Callsite extends React.Component<void, {}, void> {
+  render(): React.Element<*> {
+    return (
+      <div>
+        <Hello />
+        <HelloLocal />
+      </div>
+    );
+  }
+}
+
+module.exports = Callsite;
diff --git a/tests/react_modules/es6class-proptypes-module.js b/tests/react_modules/es6class-proptypes-module.js
new file mode 100644
index 000000000000..86e55da1b28f
--- /dev/null
+++ b/tests/react_modules/es6class-proptypes-module.js
@@ -0,0 +1,15 @@
+/* @flow */
+import React from 'react';
+
+class Hello extends React.Component<void, {name: string}, void> {
+  defaultProps = {};
+  propTypes = {
+    name: React.PropTypes.string.isRequired,
+  };
+
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+module.exports = Hello;
diff --git a/tests/react_modules/es6class-types-callsite.js b/tests/react_modules/es6class-types-callsite.js
new file mode 100644
index 000000000000..c5586b682c17
--- /dev/null
+++ b/tests/react_modules/es6class-types-callsite.js
@@ -0,0 +1,26 @@
+/* @flow */
+import React from 'react';
+import Hello from './es6class-types-module';
+
+type Props = {name: string};
+
+class HelloLocal extends React.Component<void, Props, void> {
+  props: Props;
+
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+class Callsite extends React.Component<void, Props, void> {
+  render(): React.Element<*> {
+    return (
+      <div>
+        <Hello />
+        <HelloLocal />
+      </div>
+    );
+  }
+}
+
+module.exports = Callsite;
diff --git a/tests/react_modules/es6class-types-module.js b/tests/react_modules/es6class-types-module.js
new file mode 100644
index 000000000000..d91eeab83f36
--- /dev/null
+++ b/tests/react_modules/es6class-types-module.js
@@ -0,0 +1,15 @@
+/* @flow */
+import React from 'react';
+
+type Props = {name: string};
+
+class Hello extends React.Component<{}, Props, void>{
+  props: Props;
+  static defaultProps: {};
+
+  render(): React.Element<*> {
+    return <div>{this.props.name}</div>;
+  }
+}
+
+module.exports = Hello;
diff --git a/tests/react_modules/jsfmt.spec.js b/tests/react_modules/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/react_modules/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/rec/__snapshots__/jsfmt.spec.js.snap b/tests/rec/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e319f1c39127
--- /dev/null
+++ b/tests/rec/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,226 @@
+exports[`test issue-598.js 1`] = `
+"/* @flow */
+
+type F<A> = { foo<B>(x: A): F<B> }
+declare function foo(x: any): F<any>;
+({ foo }: F<any>);
+
+function bar(y: F<number>): F<string> { return y; }
+function bar1<X>(y: F<X>): F<any> { return y; }
+function bar2<X>(y: F<any>): F<X> { return y; }
+
+type Functor<A> = {
+  map<B>(f: (val: A) => B): Functor<B>
+}
+
+function identity<A>(val: A): Functor<A> {
+  return {
+    map<B>(f: (_: typeof val) => B): Functor<B> { return identity(f(val)) }
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1228.js 1`] = `
+"/* @flow */
+
+type Task <error, value>
+  = { chain<tagged>(next:(input:value) => Task<error, tagged>):
+          Task<error, tagged>
+    }
+
+function id(x: Task<any,any>): Task<any,any> { return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"class P<X> { x: X; } // this is like Promise
+
+type Pstar<X> = X | Pstar<P<X>>; // this is like Promise*
+
+var p: P<number> = new P;
+(p.x: string); // error
+
+var pstar: Pstar<number> = 0; // OK
+(pstar: number); // error, but limit potentially unbounded number of errors!
+                 // e.g., P<number> ~/~ number, P<P<number>> ~/~ number, ...
+
+pstar = p; // OK
+(pstar.x: string); // error
+
+pstar = (new P: P<P<number>>); // OK
+(pstar.x: string); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"var a = []; // Array<X> ~> a
+function bar() {
+  a = a.concat([]); // terminate despite expanding types:
+  // a ~> .concat(Array<Y>)
+  // Array<X> ~> .concat(Array<Y>)
+  // Array<X|Y> ~> a
+  // Array<X|Y> ~> .concat(Array<Y>)
+  // Array<X|Y|Y> ~> a
+};
+
+class A<X> {
+  x: A<A<X>>;
+}
+var a_ = new A;
+function foo0() {
+  a_ = a_.x; // terminate despite expanding types
+}
+
+type T<X> = { y: S<X> };
+type S<X> = T<S<X>>;
+function foo1(b: S<*>) {
+  b = b.y; // terminate despite expanding types, OK
+  // S<*> = { y: S<S<*>> }
+  // Both S<S<*>> and S<*> expand to { y: { y: ... }}.
+}
+
+class D<X> { }
+class B<X> extends D<X> { }
+class C<X> extends B<X> { }
+((new C: C<number>): D<string>) // error: number ~/~ string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test3.js 1`] = `
+"type I<X> = () => I<I<X>>;
+type J<X> = () => J<J<X>>;
+
+function foo(x: I<number>): J<number> {
+  return x; // terminate despite expanding types, OK
+  // I<number> and J<number> both expand to () => () => ...
+}
+
+type Q<X> = { x: X; }
+type P<X> = () => Q<P<X>>;
+
+function bar(x: P<number>): () => P<number> {
+  return x; // terminate despite expanding types, error
+  // P<number> = () => { x: P<number> }
+  // () => P<number> = () => () => { x: P<number> }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test4.js 1`] = `
+"type T = T // cycle in type alias should not cause non-termination
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+type T = T;// cycle in type alias should not cause non-termination
+
+"
+`;
+
+exports[`test test5.js 1`] = `
+"/* @flow */
+
+type NestedArray<T> = Array<T | NestedArray<T>>;
+
+function flatten<T>(arrArg: NestedArray<T>) {
+  let arr = arrArg;
+  while (true) {
+    arr = Array.prototype.concat.apply([], arr);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/rec/issue-1228.js b/tests/rec/issue-1228.js
new file mode 100644
index 000000000000..6eae30ab211c
--- /dev/null
+++ b/tests/rec/issue-1228.js
@@ -0,0 +1,8 @@
+/* @flow */
+
+type Task <error, value>
+  = { chain<tagged>(next:(input:value) => Task<error, tagged>):
+          Task<error, tagged>
+    }
+
+function id(x: Task<any,any>): Task<any,any> { return x; }
diff --git a/tests/rec/issue-598.js b/tests/rec/issue-598.js
new file mode 100644
index 000000000000..b42d9ec635c8
--- /dev/null
+++ b/tests/rec/issue-598.js
@@ -0,0 +1,19 @@
+/* @flow */
+
+type F<A> = { foo<B>(x: A): F<B> }
+declare function foo(x: any): F<any>;
+({ foo }: F<any>);
+
+function bar(y: F<number>): F<string> { return y; }
+function bar1<X>(y: F<X>): F<any> { return y; }
+function bar2<X>(y: F<any>): F<X> { return y; }
+
+type Functor<A> = {
+  map<B>(f: (val: A) => B): Functor<B>
+}
+
+function identity<A>(val: A): Functor<A> {
+  return {
+    map<B>(f: (_: typeof val) => B): Functor<B> { return identity(f(val)) }
+  }
+}
diff --git a/tests/rec/jsfmt.spec.js b/tests/rec/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/rec/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/rec/test.js b/tests/rec/test.js
new file mode 100644
index 000000000000..4b224d0ce984
--- /dev/null
+++ b/tests/rec/test.js
@@ -0,0 +1,16 @@
+class P<X> { x: X; } // this is like Promise
+
+type Pstar<X> = X | Pstar<P<X>>; // this is like Promise*
+
+var p: P<number> = new P;
+(p.x: string); // error
+
+var pstar: Pstar<number> = 0; // OK
+(pstar: number); // error, but limit potentially unbounded number of errors!
+                 // e.g., P<number> ~/~ number, P<P<number>> ~/~ number, ...
+
+pstar = p; // OK
+(pstar.x: string); // error
+
+pstar = (new P: P<P<number>>); // OK
+(pstar.x: string); // error
diff --git a/tests/rec/test2.js b/tests/rec/test2.js
new file mode 100644
index 000000000000..f52df80b5415
--- /dev/null
+++ b/tests/rec/test2.js
@@ -0,0 +1,30 @@
+var a = []; // Array<X> ~> a
+function bar() {
+  a = a.concat([]); // terminate despite expanding types:
+  // a ~> .concat(Array<Y>)
+  // Array<X> ~> .concat(Array<Y>)
+  // Array<X|Y> ~> a
+  // Array<X|Y> ~> .concat(Array<Y>)
+  // Array<X|Y|Y> ~> a
+};
+
+class A<X> {
+  x: A<A<X>>;
+}
+var a_ = new A;
+function foo0() {
+  a_ = a_.x; // terminate despite expanding types
+}
+
+type T<X> = { y: S<X> };
+type S<X> = T<S<X>>;
+function foo1(b: S<*>) {
+  b = b.y; // terminate despite expanding types, OK
+  // S<*> = { y: S<S<*>> }
+  // Both S<S<*>> and S<*> expand to { y: { y: ... }}.
+}
+
+class D<X> { }
+class B<X> extends D<X> { }
+class C<X> extends B<X> { }
+((new C: C<number>): D<string>) // error: number ~/~ string
diff --git a/tests/rec/test3.js b/tests/rec/test3.js
new file mode 100644
index 000000000000..9c2baa21a3b5
--- /dev/null
+++ b/tests/rec/test3.js
@@ -0,0 +1,16 @@
+type I<X> = () => I<I<X>>;
+type J<X> = () => J<J<X>>;
+
+function foo(x: I<number>): J<number> {
+  return x; // terminate despite expanding types, OK
+  // I<number> and J<number> both expand to () => () => ...
+}
+
+type Q<X> = { x: X; }
+type P<X> = () => Q<P<X>>;
+
+function bar(x: P<number>): () => P<number> {
+  return x; // terminate despite expanding types, error
+  // P<number> = () => { x: P<number> }
+  // () => P<number> = () => () => { x: P<number> }
+}
diff --git a/tests/rec/test4.js b/tests/rec/test4.js
new file mode 100644
index 000000000000..7116cd9dbfbc
--- /dev/null
+++ b/tests/rec/test4.js
@@ -0,0 +1 @@
+type T = T // cycle in type alias should not cause non-termination
diff --git a/tests/rec/test5.js b/tests/rec/test5.js
new file mode 100644
index 000000000000..3052dcead8c2
--- /dev/null
+++ b/tests/rec/test5.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+type NestedArray<T> = Array<T | NestedArray<T>>;
+
+function flatten<T>(arrArg: NestedArray<T>) {
+  let arr = arrArg;
+  while (true) {
+    arr = Array.prototype.concat.apply([], arr);
+  }
+}
diff --git a/tests/recheck-haste/A1.js b/tests/recheck-haste/A1.js
new file mode 100644
index 000000000000..638d95f80d1d
--- /dev/null
+++ b/tests/recheck-haste/A1.js
@@ -0,0 +1,4 @@
+/**
+ * @providesModule A
+ * @flow
+ */
diff --git a/tests/recheck-haste/A3.js b/tests/recheck-haste/A3.js
new file mode 100644
index 000000000000..62bd9a77de77
--- /dev/null
+++ b/tests/recheck-haste/A3.js
@@ -0,0 +1,3 @@
+// @flow
+
+require('A');
diff --git a/tests/recheck-haste/__snapshots__/jsfmt.spec.js.snap b/tests/recheck-haste/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9bc3b995516a
--- /dev/null
+++ b/tests/recheck-haste/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,21 @@
+exports[`test A1.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test A3.js 1`] = `
+"// @flow
+
+require('A');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+require("A");
+
+"
+`;
diff --git a/tests/recheck-haste/jsfmt.spec.js b/tests/recheck-haste/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck-haste/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck-haste/tmp1A/A2.js b/tests/recheck-haste/tmp1A/A2.js
new file mode 100644
index 000000000000..cf331fe3deb2
--- /dev/null
+++ b/tests/recheck-haste/tmp1A/A2.js
@@ -0,0 +1,4 @@
+/**
+ * @providesModule B
+ * @flow
+ */
diff --git a/tests/recheck-haste/tmp1A/__snapshots__/jsfmt.spec.js.snap b/tests/recheck-haste/tmp1A/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b200fabe0f33
--- /dev/null
+++ b/tests/recheck-haste/tmp1A/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test A2.js 1`] = `
+"/**
+ * @providesModule B
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
diff --git a/tests/recheck-haste/tmp1A/jsfmt.spec.js b/tests/recheck-haste/tmp1A/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck-haste/tmp1A/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck-haste/tmp2A/A3.js b/tests/recheck-haste/tmp2A/A3.js
new file mode 100644
index 000000000000..c62d55de1472
--- /dev/null
+++ b/tests/recheck-haste/tmp2A/A3.js
@@ -0,0 +1,3 @@
+// @flow
+
+require('B');
diff --git a/tests/recheck-haste/tmp2A/__snapshots__/jsfmt.spec.js.snap b/tests/recheck-haste/tmp2A/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9b95ee207fcb
--- /dev/null
+++ b/tests/recheck-haste/tmp2A/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test A3.js 1`] = `
+"// @flow
+
+require('B');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+require("B");
+
+"
+`;
diff --git a/tests/recheck-haste/tmp2A/jsfmt.spec.js b/tests/recheck-haste/tmp2A/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck-haste/tmp2A/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ef429d1fc181
--- /dev/null
+++ b/tests/recheck/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,352 @@
+exports[`test a1.js 1`] = `
+"// @flow
+
+function foo(x: number): string { return 5; }
+
+foo(0);
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function foo(x: number): string {
+  return 5;
+}
+foo(0);
+module.exports = foo;
+
+"
+`;
+
+exports[`test a2.js 1`] = `
+"// @flow
+
+const foo = require(\'./a1\');
+
+module.exports = foo(\"\");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+const foo = require(\"./a1\");
+module.exports = foo(\"\");
+
+"
+`;
+
+exports[`test a3.js 1`] = `
+"// @flow
+
+const five = require(\'./a2\');
+
+(five + five: string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+const five = require(\"./a2\");
+(five + five: string);
+
+"
+`;
+
+exports[`test b0.js 1`] = `
+"// @flow
+
+class C { x: C; }
+class E { x: C; }
+
+module.exports = { C, E };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class C {
+  x: C;
+}
+class E {
+  x: C;
+}
+module.exports = { C, E };
+
+"
+`;
+
+exports[`test b1.js 1`] = `
+"// @flow
+
+import { C, E } from \"./b0\";
+function foo() { return C; }
+function bar() { return E; }
+let X = foo();
+class F extends X { }
+class D extends F { }
+module.exports = { C, D };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { C, E } from \"./b0\";
+function foo() {
+  return C;
+}
+function bar() {
+  return E;
+}
+let X = foo();
+class F extends X {}
+class D extends F {}
+module.exports = { C, D };
+
+"
+`;
+
+exports[`test b2.js 1`] = `
+"// @flow
+
+module.exports = require(\"./b1\");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+module.exports = require(\"./b1\");
+
+"
+`;
+
+exports[`test b3.js 1`] = `
+"// @flow
+
+import { C, D } from \"./b2\";
+
+(new D: C);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { C, D } from \"./b2\";
+(new D(): C);
+
+"
+`;
+
+exports[`test c1.js 1`] = `
+"// @flow
+
+export function foo(props: { x: number }) { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export function foo(props: { x: number }) {
+  
+}
+
+"
+`;
+
+exports[`test c2.js 1`] = `
+"// @flow
+
+import { foo } from \"./c1\";
+
+export function bar(props: { x: number }) {
+  foo({ x: 0 });
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { foo } from \"./c1\";
+export function bar(props: { x: number }) {
+  foo({ x: 0 });
+}
+
+"
+`;
+
+exports[`test c3.js 1`] = `
+"// @flow
+
+import { bar } from \"./c2\";
+
+bar({ x: 0 });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { bar } from \"./c2\";
+bar({ x: 0 });
+
+"
+`;
+
+exports[`test d1.js 1`] = `
+"// @flow
+
+export class A {}
+export class B {}
+export var x = new A;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export class A {}
+export class B {}
+export var x = new A();
+
+"
+`;
+
+exports[`test d2.js 1`] = `
+"// @flow
+
+import {A, x} from \"./d1\";
+export var y: A = x;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { A, x } from \"./d1\";
+export var y: A = x;
+
+"
+`;
+
+exports[`test e1.js 1`] = `
+"// @flow
+
+export type Action =
+  | { type: \'FOO\' }
+  | { type: \'BAR\' }
+;
+
+export const LIFE = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test e2.js 1`] = `
+"// @flow
+
+import type { Action } from \'./e1\';
+
+const f = (): Action => {
+  return { type: \'FOO\' };
+}
+
+import { LIFE } from \'./e1\';
+
+(LIFE: 42);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 139, end: 141, loc: [object Object], value: 42, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
+
+exports[`test f1.js 1`] = `
+"// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type T = { x: number };
+type S = { x: string };
+declare var a: T;
+declare var b: S;
+declare var c: T;
+module.exports = { a, b, c };
+
+"
+`;
+
+exports[`test f2.js 1`] = `
+"// @flow
+
+var { a, b, c } = require(\'./f1\');
+(c: { x: number });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var { a, b, c } = require(\"./f1\");
+(c: { x: number });
+
+"
+`;
+
+exports[`test g1.js 1`] = `
+"// @flow
+
+export class C { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export class C {}
+
+"
+`;
+
+exports[`test g2.js 1`] = `
+"// @flow
+
+import { C } from \'./g1\';
+
+class D extends C { }
+
+module.exports = { D };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { C } from \"./g1\";
+class D extends C {}
+module.exports = { D };
+
+"
+`;
+
+exports[`test g3.js 1`] = `
+"// @flow
+
+import { C } from \'./g1\';
+import { D } from \'./g2\';
+
+(new D: C)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { C } from \"./g1\";
+import { D } from \"./g2\";
+(new D(): C);
+
+"
+`;
+
+exports[`test h1.js 1`] = `
+"// @flow
+
+export type Foo = number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export type Foo = number;
+
+"
+`;
+
+exports[`test h2.js 1`] = `
+"// @flow
+
+import type { Foo } from \'./h1\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import type { Foo } from \"./h1\";
+
+"
+`;
diff --git a/tests/recheck/a1.js b/tests/recheck/a1.js
new file mode 100644
index 000000000000..2a9c78c41807
--- /dev/null
+++ b/tests/recheck/a1.js
@@ -0,0 +1,7 @@
+// @flow
+
+function foo(x: number): string { return 5; }
+
+foo(0);
+
+module.exports = foo;
diff --git a/tests/recheck/a2.js b/tests/recheck/a2.js
new file mode 100644
index 000000000000..cfb5d1cd21db
--- /dev/null
+++ b/tests/recheck/a2.js
@@ -0,0 +1,5 @@
+// @flow
+
+const foo = require('./a1');
+
+module.exports = foo("");
diff --git a/tests/recheck/a3.js b/tests/recheck/a3.js
new file mode 100644
index 000000000000..93135f1dfd8b
--- /dev/null
+++ b/tests/recheck/a3.js
@@ -0,0 +1,5 @@
+// @flow
+
+const five = require('./a2');
+
+(five + five: string);
diff --git a/tests/recheck/b0.js b/tests/recheck/b0.js
new file mode 100644
index 000000000000..a054df3838fb
--- /dev/null
+++ b/tests/recheck/b0.js
@@ -0,0 +1,6 @@
+// @flow
+
+class C { x: C; }
+class E { x: C; }
+
+module.exports = { C, E };
diff --git a/tests/recheck/b1.js b/tests/recheck/b1.js
new file mode 100644
index 000000000000..02d08fc99ae4
--- /dev/null
+++ b/tests/recheck/b1.js
@@ -0,0 +1,9 @@
+// @flow
+
+import { C, E } from "./b0";
+function foo() { return C; }
+function bar() { return E; }
+let X = foo();
+class F extends X { }
+class D extends F { }
+module.exports = { C, D };
diff --git a/tests/recheck/b2.js b/tests/recheck/b2.js
new file mode 100644
index 000000000000..89602457fce4
--- /dev/null
+++ b/tests/recheck/b2.js
@@ -0,0 +1,3 @@
+// @flow
+
+module.exports = require("./b1");
diff --git a/tests/recheck/b3.js b/tests/recheck/b3.js
new file mode 100644
index 000000000000..948f528d624e
--- /dev/null
+++ b/tests/recheck/b3.js
@@ -0,0 +1,5 @@
+// @flow
+
+import { C, D } from "./b2";
+
+(new D: C);
diff --git a/tests/recheck/c1.js b/tests/recheck/c1.js
new file mode 100644
index 000000000000..34760f1969f4
--- /dev/null
+++ b/tests/recheck/c1.js
@@ -0,0 +1,3 @@
+// @flow
+
+export function foo(props: { x: number }) { }
diff --git a/tests/recheck/c2.js b/tests/recheck/c2.js
new file mode 100644
index 000000000000..5a7549516cf5
--- /dev/null
+++ b/tests/recheck/c2.js
@@ -0,0 +1,7 @@
+// @flow
+
+import { foo } from "./c1";
+
+export function bar(props: { x: number }) {
+  foo({ x: 0 });
+}
diff --git a/tests/recheck/c3.js b/tests/recheck/c3.js
new file mode 100644
index 000000000000..cf0e94248644
--- /dev/null
+++ b/tests/recheck/c3.js
@@ -0,0 +1,5 @@
+// @flow
+
+import { bar } from "./c2";
+
+bar({ x: 0 });
diff --git a/tests/recheck/d1.js b/tests/recheck/d1.js
new file mode 100644
index 000000000000..b5dd060f3f0f
--- /dev/null
+++ b/tests/recheck/d1.js
@@ -0,0 +1,5 @@
+// @flow
+
+export class A {}
+export class B {}
+export var x = new A;
diff --git a/tests/recheck/d2.js b/tests/recheck/d2.js
new file mode 100644
index 000000000000..7dd91ff07f40
--- /dev/null
+++ b/tests/recheck/d2.js
@@ -0,0 +1,4 @@
+// @flow
+
+import {A, x} from "./d1";
+export var y: A = x;
diff --git a/tests/recheck/e1.js b/tests/recheck/e1.js
new file mode 100644
index 000000000000..d0de69b553ef
--- /dev/null
+++ b/tests/recheck/e1.js
@@ -0,0 +1,8 @@
+// @flow
+
+export type Action =
+  | { type: 'FOO' }
+  | { type: 'BAR' }
+;
+
+export const LIFE = 42;
diff --git a/tests/recheck/e2.js b/tests/recheck/e2.js
new file mode 100644
index 000000000000..cb730cc55dc1
--- /dev/null
+++ b/tests/recheck/e2.js
@@ -0,0 +1,11 @@
+// @flow
+
+import type { Action } from './e1';
+
+const f = (): Action => {
+  return { type: 'FOO' };
+}
+
+import { LIFE } from './e1';
+
+(LIFE: 42);
diff --git a/tests/recheck/f1.js b/tests/recheck/f1.js
new file mode 100644
index 000000000000..f367b83232d6
--- /dev/null
+++ b/tests/recheck/f1.js
@@ -0,0 +1,10 @@
+// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c };
diff --git a/tests/recheck/f2.js b/tests/recheck/f2.js
new file mode 100644
index 000000000000..33c925aefac5
--- /dev/null
+++ b/tests/recheck/f2.js
@@ -0,0 +1,4 @@
+// @flow
+
+var { a, b, c } = require('./f1');
+(c: { x: number });
diff --git a/tests/recheck/g1.js b/tests/recheck/g1.js
new file mode 100644
index 000000000000..2db46640d122
--- /dev/null
+++ b/tests/recheck/g1.js
@@ -0,0 +1,3 @@
+// @flow
+
+export class C { }
diff --git a/tests/recheck/g2.js b/tests/recheck/g2.js
new file mode 100644
index 000000000000..5da8b17aff83
--- /dev/null
+++ b/tests/recheck/g2.js
@@ -0,0 +1,7 @@
+// @flow
+
+import { C } from './g1';
+
+class D extends C { }
+
+module.exports = { D };
diff --git a/tests/recheck/g3.js b/tests/recheck/g3.js
new file mode 100644
index 000000000000..a922c8b50bb3
--- /dev/null
+++ b/tests/recheck/g3.js
@@ -0,0 +1,6 @@
+// @flow
+
+import { C } from './g1';
+import { D } from './g2';
+
+(new D: C)
diff --git a/tests/recheck/h1.js b/tests/recheck/h1.js
new file mode 100644
index 000000000000..658225cb3857
--- /dev/null
+++ b/tests/recheck/h1.js
@@ -0,0 +1,3 @@
+// @flow
+
+export type Foo = number;
diff --git a/tests/recheck/h2.js b/tests/recheck/h2.js
new file mode 100644
index 000000000000..27cc789c77ab
--- /dev/null
+++ b/tests/recheck/h2.js
@@ -0,0 +1,3 @@
+// @flow
+
+import type { Foo } from './h1';
diff --git a/tests/recheck/jsfmt.spec.js b/tests/recheck/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1a/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1a/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..35a87e8c321c
--- /dev/null
+++ b/tests/recheck/tmp1a/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test a1.js 1`] = `
+"// @flow
+
+function foo(x: number): number { return 5; }
+
+foo(0);
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function foo(x: number): number {
+  return 5;
+}
+foo(0);
+module.exports = foo;
+
+"
+`;
diff --git a/tests/recheck/tmp1a/a1.js b/tests/recheck/tmp1a/a1.js
new file mode 100644
index 000000000000..6aea0d8312b9
--- /dev/null
+++ b/tests/recheck/tmp1a/a1.js
@@ -0,0 +1,7 @@
+// @flow
+
+function foo(x: number): number { return 5; }
+
+foo(0);
+
+module.exports = foo;
diff --git a/tests/recheck/tmp1a/jsfmt.spec.js b/tests/recheck/tmp1a/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1a/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1b/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1b/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..cd873290ace9
--- /dev/null
+++ b/tests/recheck/tmp1b/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test b1.js 1`] = `
+"// @flow
+
+import { C, E } from "./b0";
+function foo() { return C; }
+function bar() { return E; }
+let X = bar();
+class F extends X { }
+class D extends F { }
+module.exports = { C, D };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { C, E } from "./b0";
+function foo() {
+  return C;
+}
+function bar() {
+  return E;
+}
+let X = bar();
+class F extends X {}
+class D extends F {}
+module.exports = { C, D };
+
+"
+`;
diff --git a/tests/recheck/tmp1b/b1.js b/tests/recheck/tmp1b/b1.js
new file mode 100644
index 000000000000..468f26a53950
--- /dev/null
+++ b/tests/recheck/tmp1b/b1.js
@@ -0,0 +1,9 @@
+// @flow
+
+import { C, E } from "./b0";
+function foo() { return C; }
+function bar() { return E; }
+let X = bar();
+class F extends X { }
+class D extends F { }
+module.exports = { C, D };
diff --git a/tests/recheck/tmp1b/jsfmt.spec.js b/tests/recheck/tmp1b/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1b/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1c/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1c/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..812fec93444b
--- /dev/null
+++ b/tests/recheck/tmp1c/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,17 @@
+exports[`test c2.js 1`] = `
+"// @flow
+
+import { foo } from "./c1";
+
+export function bar(props: { y: number }) {
+  foo({ y: 0 });
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+import { foo } from "./c1";
+export function bar(props: { y: number }) {
+  foo({ y: 0 });
+}
+
+"
+`;
diff --git a/tests/recheck/tmp1c/c2.js b/tests/recheck/tmp1c/c2.js
new file mode 100644
index 000000000000..78f854440217
--- /dev/null
+++ b/tests/recheck/tmp1c/c2.js
@@ -0,0 +1,7 @@
+// @flow
+
+import { foo } from "./c1";
+
+export function bar(props: { y: number }) {
+  foo({ y: 0 });
+}
diff --git a/tests/recheck/tmp1c/jsfmt.spec.js b/tests/recheck/tmp1c/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1c/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1d/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1d/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0bff460b8b4e
--- /dev/null
+++ b/tests/recheck/tmp1d/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,14 @@
+exports[`test d1.js 1`] = `
+"// @flow
+
+export class A {}
+export class B {}
+export var x = new B;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export class A {}
+export class B {}
+export var x = new B();
+
+"
+`;
diff --git a/tests/recheck/tmp1d/d1.js b/tests/recheck/tmp1d/d1.js
new file mode 100644
index 000000000000..bfcfcbdf7f2c
--- /dev/null
+++ b/tests/recheck/tmp1d/d1.js
@@ -0,0 +1,5 @@
+// @flow
+
+export class A {}
+export class B {}
+export var x = new B;
diff --git a/tests/recheck/tmp1d/jsfmt.spec.js b/tests/recheck/tmp1d/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1d/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1e/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1e/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6aea92cc691b
--- /dev/null
+++ b/tests/recheck/tmp1e/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,30 @@
+exports[`test e2.js 1`] = `
+"// @flow
+
+import type { Action } from \'./e1\';
+
+const f = (): Action => {
+  return { type: \'QUX\' };
+}
+
+import { LIFE } from \'./e1\';
+
+(LIFE: 42);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 139, end: 141, loc: [object Object], value: 42, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
diff --git a/tests/recheck/tmp1e/e2.js b/tests/recheck/tmp1e/e2.js
new file mode 100644
index 000000000000..337afa6cfe53
--- /dev/null
+++ b/tests/recheck/tmp1e/e2.js
@@ -0,0 +1,11 @@
+// @flow
+
+import type { Action } from './e1';
+
+const f = (): Action => {
+  return { type: 'QUX' };
+}
+
+import { LIFE } from './e1';
+
+(LIFE: 42);
diff --git a/tests/recheck/tmp1e/jsfmt.spec.js b/tests/recheck/tmp1e/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1e/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1f/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1f/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e93239948127
--- /dev/null
+++ b/tests/recheck/tmp1f/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test f1.js 1`] = `
+"// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: S;
+
+module.exports = { a, b, c };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type T = { x: number };
+type S = { x: string };
+declare var a: T;
+declare var b: S;
+declare var c: S;
+module.exports = { a, b, c };
+
+"
+`;
diff --git a/tests/recheck/tmp1f/f1.js b/tests/recheck/tmp1f/f1.js
new file mode 100644
index 000000000000..4fa64d3756fc
--- /dev/null
+++ b/tests/recheck/tmp1f/f1.js
@@ -0,0 +1,10 @@
+// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: S;
+
+module.exports = { a, b, c };
diff --git a/tests/recheck/tmp1f/jsfmt.spec.js b/tests/recheck/tmp1f/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1f/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1g/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1g/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..124e3714c8f1
--- /dev/null
+++ b/tests/recheck/tmp1g/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,12 @@
+exports[`test g1.js 1`] = `
+"// @flow
+
+export class C { }
+export var extra = null;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export class C {}
+export var extra = null;
+
+"
+`;
diff --git a/tests/recheck/tmp1g/g1.js b/tests/recheck/tmp1g/g1.js
new file mode 100644
index 000000000000..bef8fa52cafa
--- /dev/null
+++ b/tests/recheck/tmp1g/g1.js
@@ -0,0 +1,4 @@
+// @flow
+
+export class C { }
+export var extra = null;
diff --git a/tests/recheck/tmp1g/jsfmt.spec.js b/tests/recheck/tmp1g/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1g/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp1h/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp1h/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..13d5fbb33b30
--- /dev/null
+++ b/tests/recheck/tmp1h/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test h1.js 1`] = `
+"// @flow
+
+export type Bar = number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export type Bar = number;
+
+"
+`;
diff --git a/tests/recheck/tmp1h/h1.js b/tests/recheck/tmp1h/h1.js
new file mode 100644
index 000000000000..ef374d6a5c5c
--- /dev/null
+++ b/tests/recheck/tmp1h/h1.js
@@ -0,0 +1,3 @@
+// @flow
+
+export type Bar = number;
diff --git a/tests/recheck/tmp1h/jsfmt.spec.js b/tests/recheck/tmp1h/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp1h/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp2a/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp2a/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..dd2074794bdf
--- /dev/null
+++ b/tests/recheck/tmp2a/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test a1.js 1`] = `
+"// @flow
+
+function foo(x: number): number { return 5; }
+
+foo("");
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function foo(x: number): number {
+  return 5;
+}
+foo("");
+module.exports = foo;
+
+"
+`;
diff --git a/tests/recheck/tmp2a/a1.js b/tests/recheck/tmp2a/a1.js
new file mode 100644
index 000000000000..16f0c5ce36ca
--- /dev/null
+++ b/tests/recheck/tmp2a/a1.js
@@ -0,0 +1,7 @@
+// @flow
+
+function foo(x: number): number { return 5; }
+
+foo("");
+
+module.exports = foo;
diff --git a/tests/recheck/tmp2a/jsfmt.spec.js b/tests/recheck/tmp2a/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp2a/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp2b/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp2b/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..04d276feff6f
--- /dev/null
+++ b/tests/recheck/tmp2b/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,19 @@
+exports[`test b0.js 1`] = `
+"// @flow
+
+class C { x: C; }
+class E extends C { x: C; }
+
+module.exports = { C, E };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+class C {
+  x: C;
+}
+class E extends C {
+  x: C;
+}
+module.exports = { C, E };
+
+"
+`;
diff --git a/tests/recheck/tmp2b/b0.js b/tests/recheck/tmp2b/b0.js
new file mode 100644
index 000000000000..e6b98e33120f
--- /dev/null
+++ b/tests/recheck/tmp2b/b0.js
@@ -0,0 +1,6 @@
+// @flow
+
+class C { x: C; }
+class E extends C { x: C; }
+
+module.exports = { C, E };
diff --git a/tests/recheck/tmp2b/jsfmt.spec.js b/tests/recheck/tmp2b/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp2b/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp2c/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp2c/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7b20457b536d
--- /dev/null
+++ b/tests/recheck/tmp2c/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,12 @@
+exports[`test c1.js 1`] = `
+"// @flow
+
+export function foo(props: { y: number }) { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+export function foo(props: { y: number }) {
+  
+}
+
+"
+`;
diff --git a/tests/recheck/tmp2c/c1.js b/tests/recheck/tmp2c/c1.js
new file mode 100644
index 000000000000..a2e88ae8f295
--- /dev/null
+++ b/tests/recheck/tmp2c/c1.js
@@ -0,0 +1,3 @@
+// @flow
+
+export function foo(props: { y: number }) { }
diff --git a/tests/recheck/tmp2c/jsfmt.spec.js b/tests/recheck/tmp2c/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp2c/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp2e/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp2e/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6a9b521d85b6
--- /dev/null
+++ b/tests/recheck/tmp2e/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,27 @@
+exports[`test e1.js 1`] = `
+"// @flow
+
+export type Action =
+  | { type: \'QUX\' }
+  | { type: \'BAR\' }
+;
+
+export const LIFE = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/recheck/tmp2e/e1.js b/tests/recheck/tmp2e/e1.js
new file mode 100644
index 000000000000..36a4c56b9b24
--- /dev/null
+++ b/tests/recheck/tmp2e/e1.js
@@ -0,0 +1,8 @@
+// @flow
+
+export type Action =
+  | { type: 'QUX' }
+  | { type: 'BAR' }
+;
+
+export const LIFE = 42;
diff --git a/tests/recheck/tmp2e/jsfmt.spec.js b/tests/recheck/tmp2e/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp2e/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp2f/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp2f/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4ae23f4c5660
--- /dev/null
+++ b/tests/recheck/tmp2f/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test f1.js 1`] = `
+"// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type T = { x: number };
+type S = { x: string };
+declare var a: T;
+declare var b: S;
+declare var c: T;
+module.exports = { a, b, c };
+
+"
+`;
diff --git a/tests/recheck/tmp2f/f1.js b/tests/recheck/tmp2f/f1.js
new file mode 100644
index 000000000000..f367b83232d6
--- /dev/null
+++ b/tests/recheck/tmp2f/f1.js
@@ -0,0 +1,10 @@
+// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c };
diff --git a/tests/recheck/tmp2f/jsfmt.spec.js b/tests/recheck/tmp2f/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp2f/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp3e/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp3e/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2f2da9b320b2
--- /dev/null
+++ b/tests/recheck/tmp3e/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,58 @@
+exports[`test e1.js 1`] = `
+"// @flow
+
+export type Action =
+  | { type: \'QUX\' }
+  | { type: \'BAR\' }
+;
+
+export const LIFE = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test e2.js 1`] = `
+"// @flow
+
+import type { Action } from \'./e1\';
+
+const f = (): Action => {
+  return { type: \'QUX\' };
+}
+
+import { LIFE } from \'./e1\';
+
+(LIFE: 0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 139, end: 140, loc: [object Object], value: 0, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
diff --git a/tests/recheck/tmp3e/e1.js b/tests/recheck/tmp3e/e1.js
new file mode 100644
index 000000000000..244efab277dc
--- /dev/null
+++ b/tests/recheck/tmp3e/e1.js
@@ -0,0 +1,8 @@
+// @flow
+
+export type Action =
+  | { type: 'QUX' }
+  | { type: 'BAR' }
+;
+
+export const LIFE = 0;
diff --git a/tests/recheck/tmp3e/e2.js b/tests/recheck/tmp3e/e2.js
new file mode 100644
index 000000000000..6a7ca1b4fa5c
--- /dev/null
+++ b/tests/recheck/tmp3e/e2.js
@@ -0,0 +1,11 @@
+// @flow
+
+import type { Action } from './e1';
+
+const f = (): Action => {
+  return { type: 'QUX' };
+}
+
+import { LIFE } from './e1';
+
+(LIFE: 0);
diff --git a/tests/recheck/tmp3e/jsfmt.spec.js b/tests/recheck/tmp3e/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp3e/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp3f/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp3f/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f58b33b71daa
--- /dev/null
+++ b/tests/recheck/tmp3f/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test f1.js 1`] = `
+"// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c: a };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type T = { x: number };
+type S = { x: string };
+declare var a: T;
+declare var b: S;
+declare var c: T;
+module.exports = { a, b, c: a };
+
+"
+`;
diff --git a/tests/recheck/tmp3f/f1.js b/tests/recheck/tmp3f/f1.js
new file mode 100644
index 000000000000..40a98b9b68b8
--- /dev/null
+++ b/tests/recheck/tmp3f/f1.js
@@ -0,0 +1,10 @@
+// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c: a };
diff --git a/tests/recheck/tmp3f/jsfmt.spec.js b/tests/recheck/tmp3f/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp3f/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/recheck/tmp4f/__snapshots__/jsfmt.spec.js.snap b/tests/recheck/tmp4f/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c9815810a0ee
--- /dev/null
+++ b/tests/recheck/tmp4f/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,22 @@
+exports[`test f1.js 1`] = `
+"// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c: b };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type T = { x: number };
+type S = { x: string };
+declare var a: T;
+declare var b: S;
+declare var c: T;
+module.exports = { a, b, c: b };
+
+"
+`;
diff --git a/tests/recheck/tmp4f/f1.js b/tests/recheck/tmp4f/f1.js
new file mode 100644
index 000000000000..77954a93f28a
--- /dev/null
+++ b/tests/recheck/tmp4f/f1.js
@@ -0,0 +1,10 @@
+// @flow
+
+type T = { x: number };
+type S = { x: string };
+
+declare var a: T;
+declare var b: S;
+declare var c: T;
+
+module.exports = { a, b, c: b };
diff --git a/tests/recheck/tmp4f/jsfmt.spec.js b/tests/recheck/tmp4f/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/recheck/tmp4f/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/record/__snapshots__/jsfmt.spec.js.snap b/tests/record/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3e4a86f4d980
--- /dev/null
+++ b/tests/record/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,43 @@
+exports[`test test.js 1`] = `
+"type Key1 = \'foo\' | \'bar\'; // make an enum type with known key set
+var o1: {[key: Key1]: number} = {
+  foo: 0,
+  bar: \"\", // error: string ~/~ number
+};
+o1.foo; // OK
+o1.qux; // error: qux not found
+o1.toString(); // ok
+
+type R = {foo: any, bar: any};
+type Key2 = $Keys<R>; // another way to make an enum type, with unknown key set
+var o2: {[key: Key2]: number} = { foo: 0 }; // OK to leave out bar
+o2.bar; // OK to access bar
+o2.qux; // error: qux not found
+
+class C<X> {
+  x: $Subtype<{[key: $Keys<X>]: any}>; // object with larger key set than X\'s
+}
+class D extends C<{foo: number, bar: string}> {
+  x: { foo: number, qux: boolean }; // error: qux not found
+}
+
+type AnyKey = $Keys<Object>;
+var o3: {[key: AnyKey]: number} = { foo: 0 };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/record/jsfmt.spec.js b/tests/record/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/record/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/record/test.js b/tests/record/test.js
new file mode 100644
index 000000000000..b7b1357f13c4
--- /dev/null
+++ b/tests/record/test.js
@@ -0,0 +1,24 @@
+type Key1 = 'foo' | 'bar'; // make an enum type with known key set
+var o1: {[key: Key1]: number} = {
+  foo: 0,
+  bar: "", // error: string ~/~ number
+};
+o1.foo; // OK
+o1.qux; // error: qux not found
+o1.toString(); // ok
+
+type R = {foo: any, bar: any};
+type Key2 = $Keys<R>; // another way to make an enum type, with unknown key set
+var o2: {[key: Key2]: number} = { foo: 0 }; // OK to leave out bar
+o2.bar; // OK to access bar
+o2.qux; // error: qux not found
+
+class C<X> {
+  x: $Subtype<{[key: $Keys<X>]: any}>; // object with larger key set than X's
+}
+class D extends C<{foo: number, bar: string}> {
+  x: { foo: number, qux: boolean }; // error: qux not found
+}
+
+type AnyKey = $Keys<Object>;
+var o3: {[key: AnyKey]: number} = { foo: 0 };
diff --git a/tests/refi/__snapshots__/jsfmt.spec.js.snap b/tests/refi/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a9fd427a869d
--- /dev/null
+++ b/tests/refi/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,1196 @@
+exports[`test bound.js 1`] = `
+"// refinements of bound vars (closed-over locals)
+// should have the same lifetimes as heap objects.
+
+var x : ?string = \"xxx\";
+
+var tests =
+[
+  function() {
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    if (x != null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    if (x == null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    if (x == null)
+      return;
+    var y : string = x;  // ok
+  },
+
+  function() {
+    if (!(x != null)) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  /* TODO we actually allow this currently; fix
+  // requires further remedial work in Env
+  function() {
+    if (x != null) {
+      alert(\"\");
+      var y : string = x;  // not ok
+    }
+  },
+  */
+  function() {
+    if (x != null) {}
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    if (x != null) {
+    } else {
+      var y : string = x;  // not ok
+    }
+  },
+
+  function() {
+    var y : string = x != null ? x : \"\"; // ok
+  },
+
+  function() {
+    var y : string = x || \"\"; // ok
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// refinements of bound vars (closed-over locals)
+// should have the same lifetimes as heap objects.
+var x: ?string = \"xxx\";
+var tests = [
+  function() {
+    var y: string = x;// not ok
+  },
+  function() {
+    if (x != null) {
+      var y: string = x;// ok
+    }
+  },
+  function() {
+    if (x == null) {
+      
+    } else {
+      var y: string = x;// ok
+    }
+  },
+  function() {
+    if (x == null)
+      return;
+    var y: string = x;// ok
+  },
+  function() {
+    if (!(x != null)) {
+      
+    } else {
+      var y: string = x;// ok
+    }
+  },
+  /* TODO we actually allow this currently; fix
+  // requires further remedial work in Env
+  function() {
+    if (x != null) {
+      alert(\"\");
+      var y : string = x;  // not ok
+    }
+  },
+  */
+  function() {
+    if (x != null) {
+      
+    }
+    var y: string = x;// not ok
+  },
+  function() {
+    if (x != null) {
+      
+    } else {
+      var y: string = x;// not ok
+    }
+  },
+  function() {
+    var y: string = (x != null ? x : \"\");// ok
+  },
+  function() {
+    var y: string = x || \"\";// ok
+  }
+];
+
+"
+`;
+
+exports[`test heap.js 1`] = `
+"var tests =
+[
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    var y : string = x.p;  // not ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p == null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p == null)
+      return;
+    var y : string = x.p;  // ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (!(x.p != null)) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {
+      alert(\"\");
+      var y : string = x.p;  // not ok
+    }
+  },
+
+  function () {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {
+      x.p = null;
+      var y : string = x.p;  // not ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {}
+    var y : string = x.p;  // not ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {
+    } else {
+      var y : string = x.p;  // not ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    var y : string = x.p != null ? x.p : \"\"; // ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    var y : string = x.p || \"\"; // ok
+  },
+
+  function() {
+    var x : {p:string | string[]} = {p:[\"xxx\"]};
+    if (Array.isArray(x.p)) {
+      var y : string[] = x.p; // ok
+    } else {
+      var z : string = x.p; // ok
+    }
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (!x.y) {
+      x.y = \"foo\";
+    }
+    (x.y: string);
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (x.y) {
+    } else {
+      x.y = \"foo\";
+    }
+    (x.y: string);
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (!x.y) {
+      x.y = 123; // error
+    }
+    (x.y: string); // error, this got widened to a number
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (x.y) {
+      x.y = \"foo\";
+    } else {
+      x.y = \"bar\";
+    }
+    (x.y : string);
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == \"number\") {
+      x.y = \"foo\";
+    }
+    (x.y : string); // error, could also be boolean
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == \"number\") {
+      x.y = \"foo\";
+    } else if (typeof x.y == \"boolean\") {
+      x.y = \"bar\";
+    }
+    (x.y : boolean); // error, string
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (!x.y) {
+      x.y = \"foo\";
+    }
+    if (x.y) {
+      x.y = null;
+    }
+    (x.y : string); // error
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == \"number\") {
+      x.y = \"foo\";
+    }
+    // now x.y can is string | boolean
+    if (typeof x.y == \"string\") {
+      x.y = false;
+    }
+    // now x.y is only boolean
+    (x.y : string); // error
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == \"number\") {
+      x.y = \"foo\";
+    }
+    // now x.y can is string | boolean
+    if (typeof x.y == \"string\") {
+      x.y = 123;
+    }
+    // now x.y is number | boolean
+    (x.y : string); // error
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    var z : string = \"foo\";
+    if (x.y) {
+      x.y = z;
+    } else {
+      x.y = z;
+    }
+    (x.y : string);
+  },
+
+  function(x: string) {
+    if (x === \'a\') {}
+    (x: \'b\'); // error (but only once, string !~> \'b\'; \'a\' is irrelevant)
+  },
+
+  function(x: mixed) {
+    if (typeof x.bar === \'string\') {} // error, so \`x.bar\` refinement is empty
+    (x: string & number);
+  },
+
+  // --- nested conditionals ---
+  // after a branch, the current scope may have changed. this causes the
+  // subsequent assignment to refine the new scope. these tests make sure that
+  // the scope that gets merged after the if statement is the correct
+  // post-condition scope, not the one that was saved at the beginning of the
+  // if statement.
+
+  function() {
+    let x: { foo: ?string } = { foo: null };
+    if (!x.foo) {
+      if (false) {}
+      x.foo = \"foo\";
+    }
+    (x.foo: string);
+  },
+
+  function() {
+    let x: { foo: ?string } = { foo: null };
+    if (!x.foo) {
+      while(false) {}
+      x.foo = \"foo\";
+    }
+    (x.foo: string);
+  },
+
+  function() {
+    let x: { foo: ?string } = { foo: null };
+    if (!x.foo) {
+      for (var i = 0; i < 0; i++) {}
+      x.foo = \"foo\";
+    }
+    (x.foo: string);
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {
+      var {p} = x; // TODO: annot checked against type of x
+      (p : string); // ok
+    }
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test lex.js 1`] = `
+"function block_scope(x: string | number) {
+  {
+    let x;
+    x = \"\"; // doesn\'t refine outer x
+  }
+  (x : string); // error: number ~> string
+}
+
+function switch_scope(x: string | number) {
+  switch (x) {
+    default:
+      let x;
+      x = \"\"; // doesn\'t refine outer x
+  }
+  (x : string); // error: number ~> string
+}
+
+function try_scope(x: string | number) {
+  try {
+    let x;
+    x = \"\"; // doesn\'t refine outer x
+  } catch (e) {
+    x = \"\"; // refinement would only escape if both sides refined
+  }
+  (x : string); // error: number ~> string
+}
+
+function try_scope_catch(x: string | number) {
+  try {
+    x = \"\"; // refinement would only escape if both sides refined
+  } catch (e) {
+    let x;
+    x = \"\"; // doesn\'t refine outer x
+  }
+  (x : string); // error: number ~> string
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test local.js 1`] = `
+"var paths =
+[
+  function() {
+    var x : ?string = \"xxx\";
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (x != null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (x == null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (x == null)
+      return;
+    var y : string = x;  // ok
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (!(x != null)) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (x != null) {
+      alert(\"\");
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (x != null) {}
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (x != null) {
+    } else {
+      var y : string = x;  // not ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    var y : string = x != null ? x : \"\"; // ok
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    var y : string = x || \"\"; // ok
+  },
+
+  function() {
+    var x : string | string[] = [\"xxx\"];
+    if (Array.isArray(x)) {
+      var y : string[] = x; // ok
+    } else {
+      var z : string = x; // ok
+    }
+  },
+
+  function() {
+    var x : ?string = null;
+    if (!x) {
+      x = \"xxx\";
+    }
+    var y : string = x;
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test null_tests.js 1`] = `
+"var null_tests =
+[
+  // expr != null
+  function() {
+    var x : ?string = \"xxx\";
+    if (x != null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (null != x) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p != null) {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q != null) {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr == null
+  function() {
+    var x : ?string = \"xxx\";
+    if (x == null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p == null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q == null) {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr !== null
+  function() {
+    var x : ?string = \"xxx\";
+    if (x !== null) {
+      var y : string | void = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p !== null) {
+      var y : string | void = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q !== null) {
+      var y : string | void = x.p.q;  // ok
+    }
+  },
+
+  // expr === null
+  function() {
+    var x : ?string = \"xxx\";
+    if (x === null) {} else {
+      var y : string | void = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p === null) {} else {
+      var y : string | void = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q === null) {} else {
+      var y : string | void = x.p.q;  // ok
+    }
+  },
+];
+
+// this.p op null
+class C {
+  p: ?string;
+
+  ensure0(): string {
+    if (this.p != null)
+      return this.p;
+    else
+      return \"\";
+  }
+
+  ensure1(): string {
+    if (this.p == null)
+      return \"\";
+    return this.p;
+  }
+
+  ensure2(): string | void {
+    if (this.p !== null)
+      return this.p;
+    else
+      return \"\";
+  }
+
+  ensure3(): string | void {
+    if (this.p === null)
+      return \"\";
+    return this.p;
+  }
+}
+
+// super.p op null
+class D extends C {
+
+  ensure100(): string {
+    if (super.p != null)
+      return super.p;
+    else
+      return \"\";
+  }
+
+  ensure101(): string {
+    if (super.p == null)
+      return \"\";
+    else
+      return super.p;
+  }
+
+  ensure103(): string {
+    if (super.p != null) {
+      alert(\"\");
+      return super.p;  // not ok
+    }
+    return \"\";
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test switch.js 1`] = `
+"// @flow
+function foo(a,b,c) {
+  switch (c) {
+  case a.x.y: // OK
+  case b.x.y: // OK
+    return;
+  default:
+    return;
+  }
+}
+
+// test refis out of switches that are exhaustive without default case
+
+function exhaustion1(x): number {
+  var foo;
+  switch (x) {
+  case 0: // falls through
+  case 1:
+    foo = 3;
+    break;
+  default:
+    throw new Error(\'Invalid state\');
+  }
+  return foo; // no error
+}
+
+function exhaustion2(x, y): number {
+  var foo;
+  switch (x) {
+  case 0:
+    if (y) {
+      break;  // leaks uninitialized foo out of switch
+    }
+    /**
+     * TODO this shouldn\'t cause an error, because the path that
+     * runs it will always go on to assign a number to foo. But
+     * we\'ll need true isolation in env snapshots to model this.
+     * Currently tvars are always shared between clones - we\'d
+     * have to rework envs pretty extensively to avoid it.
+     *
+    foo = \"\";
+     */
+  case 1:
+    foo = 3;
+    break;
+  default:
+    throw new Error(\'Invalid state\');
+  }
+  return foo; // error, possibly uninitialized
+}
+
+function exhaustion3(x): number {
+  let foo = null;
+  switch (x) {
+  case 0: // falls through
+  case 1:
+    foo = 3;
+    break;
+  default:
+    throw new Error(\'Invalid state\');
+  }
+  return foo; // no error
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test typeof_tests.js 1`] = `
+"var null_tests =
+[
+  // typeof expr == typename
+  function() {
+    var x : ?string = \"xxx\";
+    if (typeof x == \"string\") {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (\"string\" == typeof x) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (typeof x.p == \"string\") {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (typeof x.p.q == \"string\") {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // typeof expr != typename
+  function() {
+    var x : ?string = \"xxx\";
+    if (typeof x != \"string\") {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (typeof x.p != \"string\") {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (typeof x.p.q != \"string\") {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // typeof expr === typename
+  function() {
+    var x : ?string = \"xxx\";
+    if (typeof x === \"string\") {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (typeof x.p === \"string\") {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (typeof x.p.q === \"string\") {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // typeof expr !== typename
+  function() {
+    var x : ?string = \"xxx\";
+    if (typeof x !== \"string\") {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (typeof x.p !== \"string\") {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (typeof x.p.q !== \"string\") {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+];
+
+// typeof this.p op typename
+class A {
+  p: ?string;
+
+  ensure0(): string {
+    if (typeof this.p == \"string\")
+      return this.p;
+    else
+      return \"\";
+  }
+
+  ensure1(): string {
+    if (typeof this.p != \"string\")
+      return \"\";
+    else
+     return this.p;
+  }
+
+  ensure2(): string | void {
+    if (typeof this.p === \"string\")
+      return this.p;
+    else
+      return \"\";
+  }
+
+  ensure3(): string | void {
+    if (typeof this.p !== \"string\")
+      return \"\";
+    else
+      return this.p;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test undef_tests.js 1`] = `
+"var undef_tests =
+[
+  // NOTE: not (yet?) supporting non-strict eq test for undefined
+
+  // expr !== undefined
+  function() {
+    var x : ?string = \"xxx\";
+    if (x !== undefined && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (undefined !== x && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p !== undefined && x.p !== null) {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q !== undefined && x.p.q !== null) {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr === undefined
+  function() {
+    var x : ?string = \"xxx\";
+    if (x === undefined || x === null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p === undefined || x.p === null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q === undefined || x.p.q === null) {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+];
+
+// this.p op undefined
+class A {
+  p: ?string;
+
+  ensure0(): string {
+    if (this.p !== undefined && this.p !== null)
+      return this.p;
+    else
+      return \"\";
+  }
+
+  ensure1(): string {
+    if (this.p === undefined || this.p === null)
+      return \"\";
+    else
+      return this.p;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var undef_tests = [
+  // NOTE: not (yet?) supporting non-strict eq test for undefined
+  // expr !== undefined
+  function() {
+    var x: ?string = \"xxx\";
+    if (x !== undefined && x !== null) {
+      var y: string = x;// ok
+    }
+  },
+  function() {
+    var x: ?string = \"xxx\";
+    if (undefined !== x && x !== null) {
+      var y: string = x;// ok
+    }
+  },
+  function() {
+    var x: { p: ?string } = { p: \"xxx\" };
+    if (x.p !== undefined && x.p !== null) {
+      var y: string = x.p;// ok
+    }
+  },
+  function() {
+    var x: { p: { q: ?string } } = { p: { q: \"xxx\" } };
+    if (x.p.q !== undefined && x.p.q !== null) {
+      var y: string = x.p.q;// ok
+    }
+  },
+  // expr === undefined
+  function() {
+    var x: ?string = \"xxx\";
+    if (x === undefined || x === null) {
+      
+    } else {
+      var y: string = x;// ok
+    }
+  },
+  function() {
+    var x: { p: ?string } = { p: \"xxx\" };
+    if (x.p === undefined || x.p === null) {
+      
+    } else {
+      var y: string = x.p;// ok
+    }
+  },
+  function() {
+    var x: { p: { q: ?string } } = { p: { q: \"xxx\" } };
+    if (x.p.q === undefined || x.p.q === null) {
+      
+    } else {
+      var y: string = x.p.q;// ok
+    }
+  }
+];
+// this.p op undefined
+class A {
+  p: ?string;
+  ensure0(): string {
+    if (this.p !== undefined && this.p !== null)
+      return this.p;
+else
+      return \"\";
+  }
+  ensure1(): string {
+    if (this.p === undefined || this.p === null)
+      return \"\";
+else
+      return this.p;
+  }
+}
+
+"
+`;
+
+exports[`test void_tests.js 1`] = `
+"var void_tests =
+[
+  // NOTE: not (yet?) supporting non-strict eq test for undefined
+
+  // expr !== void(...)
+  function() {
+    var x : ?string = \"xxx\";
+    if (x !== void(0) && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = \"xxx\";
+    if (void(0) !== x && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p !== void(0) && x.p !== null) {
+      var y : string | void = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q !== void(0) && x.p.q !== null) {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr === void(...)
+  function() {
+    var x : ?string = \"xxx\";
+    if (x === void(0) || x === null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:\"xxx\"};
+    if (x.p === void(0) || x.p === null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:\"xxx\"}};
+    if (x.p.q === void(0) || x.p.q === null) {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+];
+
+// this.p op void(...)
+class A {
+  p: ?string;
+
+  ensure0(): string {
+    if (this.p !== void(0) && this.p !== null)
+      return this.p;
+    else
+      return \"\";
+  }
+
+  ensure1(): string {
+    if (this.p === void(0) || this.p === null)
+      return \"\";
+    else
+      return this.p;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/refi/bound.js b/tests/refi/bound.js
new file mode 100644
index 000000000000..2c8381126568
--- /dev/null
+++ b/tests/refi/bound.js
@@ -0,0 +1,64 @@
+// refinements of bound vars (closed-over locals)
+// should have the same lifetimes as heap objects.
+
+var x : ?string = "xxx";
+
+var tests =
+[
+  function() {
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    if (x != null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    if (x == null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    if (x == null)
+      return;
+    var y : string = x;  // ok
+  },
+
+  function() {
+    if (!(x != null)) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  /* TODO we actually allow this currently; fix
+  // requires further remedial work in Env
+  function() {
+    if (x != null) {
+      alert("");
+      var y : string = x;  // not ok
+    }
+  },
+  */
+  function() {
+    if (x != null) {}
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    if (x != null) {
+    } else {
+      var y : string = x;  // not ok
+    }
+  },
+
+  function() {
+    var y : string = x != null ? x : ""; // ok
+  },
+
+  function() {
+    var y : string = x || ""; // ok
+  },
+];
diff --git a/tests/refi/heap.js b/tests/refi/heap.js
new file mode 100644
index 000000000000..16a4c2baaa5c
--- /dev/null
+++ b/tests/refi/heap.js
@@ -0,0 +1,237 @@
+var tests =
+[
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    var y : string = x.p;  // not ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p == null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p == null)
+      return;
+    var y : string = x.p;  // ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (!(x.p != null)) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {
+      alert("");
+      var y : string = x.p;  // not ok
+    }
+  },
+
+  function () {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {
+      x.p = null;
+      var y : string = x.p;  // not ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {}
+    var y : string = x.p;  // not ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {
+    } else {
+      var y : string = x.p;  // not ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    var y : string = x.p != null ? x.p : ""; // ok
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    var y : string = x.p || ""; // ok
+  },
+
+  function() {
+    var x : {p:string | string[]} = {p:["xxx"]};
+    if (Array.isArray(x.p)) {
+      var y : string[] = x.p; // ok
+    } else {
+      var z : string = x.p; // ok
+    }
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (!x.y) {
+      x.y = "foo";
+    }
+    (x.y: string);
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (x.y) {
+    } else {
+      x.y = "foo";
+    }
+    (x.y: string);
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (!x.y) {
+      x.y = 123; // error
+    }
+    (x.y: string); // error, this got widened to a number
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (x.y) {
+      x.y = "foo";
+    } else {
+      x.y = "bar";
+    }
+    (x.y : string);
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == "number") {
+      x.y = "foo";
+    }
+    (x.y : string); // error, could also be boolean
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == "number") {
+      x.y = "foo";
+    } else if (typeof x.y == "boolean") {
+      x.y = "bar";
+    }
+    (x.y : boolean); // error, string
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    if (!x.y) {
+      x.y = "foo";
+    }
+    if (x.y) {
+      x.y = null;
+    }
+    (x.y : string); // error
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == "number") {
+      x.y = "foo";
+    }
+    // now x.y can is string | boolean
+    if (typeof x.y == "string") {
+      x.y = false;
+    }
+    // now x.y is only boolean
+    (x.y : string); // error
+  },
+
+  function() {
+    var x : {y: string | number | boolean} = {y: false};
+    if (typeof x.y == "number") {
+      x.y = "foo";
+    }
+    // now x.y can is string | boolean
+    if (typeof x.y == "string") {
+      x.y = 123;
+    }
+    // now x.y is number | boolean
+    (x.y : string); // error
+  },
+
+  function() {
+    var x : {y: ?string} = {y: null};
+    var z : string = "foo";
+    if (x.y) {
+      x.y = z;
+    } else {
+      x.y = z;
+    }
+    (x.y : string);
+  },
+
+  function(x: string) {
+    if (x === 'a') {}
+    (x: 'b'); // error (but only once, string !~> 'b'; 'a' is irrelevant)
+  },
+
+  function(x: mixed) {
+    if (typeof x.bar === 'string') {} // error, so `x.bar` refinement is empty
+    (x: string & number);
+  },
+
+  // --- nested conditionals ---
+  // after a branch, the current scope may have changed. this causes the
+  // subsequent assignment to refine the new scope. these tests make sure that
+  // the scope that gets merged after the if statement is the correct
+  // post-condition scope, not the one that was saved at the beginning of the
+  // if statement.
+
+  function() {
+    let x: { foo: ?string } = { foo: null };
+    if (!x.foo) {
+      if (false) {}
+      x.foo = "foo";
+    }
+    (x.foo: string);
+  },
+
+  function() {
+    let x: { foo: ?string } = { foo: null };
+    if (!x.foo) {
+      while(false) {}
+      x.foo = "foo";
+    }
+    (x.foo: string);
+  },
+
+  function() {
+    let x: { foo: ?string } = { foo: null };
+    if (!x.foo) {
+      for (var i = 0; i < 0; i++) {}
+      x.foo = "foo";
+    }
+    (x.foo: string);
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {
+      var {p} = x; // TODO: annot checked against type of x
+      (p : string); // ok
+    }
+  },
+];
diff --git a/tests/refi/jsfmt.spec.js b/tests/refi/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/refi/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/refi/lex.js b/tests/refi/lex.js
new file mode 100644
index 000000000000..891931b5412f
--- /dev/null
+++ b/tests/refi/lex.js
@@ -0,0 +1,36 @@
+function block_scope(x: string | number) {
+  {
+    let x;
+    x = ""; // doesn't refine outer x
+  }
+  (x : string); // error: number ~> string
+}
+
+function switch_scope(x: string | number) {
+  switch (x) {
+    default:
+      let x;
+      x = ""; // doesn't refine outer x
+  }
+  (x : string); // error: number ~> string
+}
+
+function try_scope(x: string | number) {
+  try {
+    let x;
+    x = ""; // doesn't refine outer x
+  } catch (e) {
+    x = ""; // refinement would only escape if both sides refined
+  }
+  (x : string); // error: number ~> string
+}
+
+function try_scope_catch(x: string | number) {
+  try {
+    x = ""; // refinement would only escape if both sides refined
+  } catch (e) {
+    let x;
+    x = ""; // doesn't refine outer x
+  }
+  (x : string); // error: number ~> string
+}
diff --git a/tests/refi/local.js b/tests/refi/local.js
new file mode 100644
index 000000000000..372cdfa0d657
--- /dev/null
+++ b/tests/refi/local.js
@@ -0,0 +1,84 @@
+var paths =
+[
+  function() {
+    var x : ?string = "xxx";
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (x != null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (x == null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (x == null)
+      return;
+    var y : string = x;  // ok
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (!(x != null)) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (x != null) {
+      alert("");
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (x != null) {}
+    var y : string = x;  // not ok
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (x != null) {
+    } else {
+      var y : string = x;  // not ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    var y : string = x != null ? x : ""; // ok
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    var y : string = x || ""; // ok
+  },
+
+  function() {
+    var x : string | string[] = ["xxx"];
+    if (Array.isArray(x)) {
+      var y : string[] = x; // ok
+    } else {
+      var z : string = x; // ok
+    }
+  },
+
+  function() {
+    var x : ?string = null;
+    if (!x) {
+      x = "xxx";
+    }
+    var y : string = x;
+  },
+];
diff --git a/tests/refi/null_tests.js b/tests/refi/null_tests.js
new file mode 100644
index 000000000000..f7c6ad7c111f
--- /dev/null
+++ b/tests/refi/null_tests.js
@@ -0,0 +1,154 @@
+var null_tests =
+[
+  // expr != null
+  function() {
+    var x : ?string = "xxx";
+    if (x != null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (null != x) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p != null) {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q != null) {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr == null
+  function() {
+    var x : ?string = "xxx";
+    if (x == null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p == null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q == null) {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr !== null
+  function() {
+    var x : ?string = "xxx";
+    if (x !== null) {
+      var y : string | void = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p !== null) {
+      var y : string | void = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q !== null) {
+      var y : string | void = x.p.q;  // ok
+    }
+  },
+
+  // expr === null
+  function() {
+    var x : ?string = "xxx";
+    if (x === null) {} else {
+      var y : string | void = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p === null) {} else {
+      var y : string | void = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q === null) {} else {
+      var y : string | void = x.p.q;  // ok
+    }
+  },
+];
+
+// this.p op null
+class C {
+  p: ?string;
+
+  ensure0(): string {
+    if (this.p != null)
+      return this.p;
+    else
+      return "";
+  }
+
+  ensure1(): string {
+    if (this.p == null)
+      return "";
+    return this.p;
+  }
+
+  ensure2(): string | void {
+    if (this.p !== null)
+      return this.p;
+    else
+      return "";
+  }
+
+  ensure3(): string | void {
+    if (this.p === null)
+      return "";
+    return this.p;
+  }
+}
+
+// super.p op null
+class D extends C {
+
+  ensure100(): string {
+    if (super.p != null)
+      return super.p;
+    else
+      return "";
+  }
+
+  ensure101(): string {
+    if (super.p == null)
+      return "";
+    else
+      return super.p;
+  }
+
+  ensure103(): string {
+    if (super.p != null) {
+      alert("");
+      return super.p;  // not ok
+    }
+    return "";
+  }
+}
diff --git a/tests/refi/switch.js b/tests/refi/switch.js
new file mode 100644
index 000000000000..f1100fe2cfc8
--- /dev/null
+++ b/tests/refi/switch.js
@@ -0,0 +1,63 @@
+// @flow
+function foo(a,b,c) {
+  switch (c) {
+  case a.x.y: // OK
+  case b.x.y: // OK
+    return;
+  default:
+    return;
+  }
+}
+
+// test refis out of switches that are exhaustive without default case
+
+function exhaustion1(x): number {
+  var foo;
+  switch (x) {
+  case 0: // falls through
+  case 1:
+    foo = 3;
+    break;
+  default:
+    throw new Error('Invalid state');
+  }
+  return foo; // no error
+}
+
+function exhaustion2(x, y): number {
+  var foo;
+  switch (x) {
+  case 0:
+    if (y) {
+      break;  // leaks uninitialized foo out of switch
+    }
+    /**
+     * TODO this shouldn't cause an error, because the path that
+     * runs it will always go on to assign a number to foo. But
+     * we'll need true isolation in env snapshots to model this.
+     * Currently tvars are always shared between clones - we'd
+     * have to rework envs pretty extensively to avoid it.
+     *
+    foo = "";
+     */
+  case 1:
+    foo = 3;
+    break;
+  default:
+    throw new Error('Invalid state');
+  }
+  return foo; // error, possibly uninitialized
+}
+
+function exhaustion3(x): number {
+  let foo = null;
+  switch (x) {
+  case 0: // falls through
+  case 1:
+    foo = 3;
+    break;
+  default:
+    throw new Error('Invalid state');
+  }
+  return foo; // no error
+}
diff --git a/tests/refi/typeof_tests.js b/tests/refi/typeof_tests.js
new file mode 100644
index 000000000000..7eefa8b5c274
--- /dev/null
+++ b/tests/refi/typeof_tests.js
@@ -0,0 +1,130 @@
+var null_tests =
+[
+  // typeof expr == typename
+  function() {
+    var x : ?string = "xxx";
+    if (typeof x == "string") {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if ("string" == typeof x) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (typeof x.p == "string") {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (typeof x.p.q == "string") {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // typeof expr != typename
+  function() {
+    var x : ?string = "xxx";
+    if (typeof x != "string") {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (typeof x.p != "string") {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (typeof x.p.q != "string") {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // typeof expr === typename
+  function() {
+    var x : ?string = "xxx";
+    if (typeof x === "string") {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (typeof x.p === "string") {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (typeof x.p.q === "string") {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // typeof expr !== typename
+  function() {
+    var x : ?string = "xxx";
+    if (typeof x !== "string") {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (typeof x.p !== "string") {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (typeof x.p.q !== "string") {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+];
+
+// typeof this.p op typename
+class A {
+  p: ?string;
+
+  ensure0(): string {
+    if (typeof this.p == "string")
+      return this.p;
+    else
+      return "";
+  }
+
+  ensure1(): string {
+    if (typeof this.p != "string")
+      return "";
+    else
+     return this.p;
+  }
+
+  ensure2(): string | void {
+    if (typeof this.p === "string")
+      return this.p;
+    else
+      return "";
+  }
+
+  ensure3(): string | void {
+    if (typeof this.p !== "string")
+      return "";
+    else
+      return this.p;
+  }
+}
diff --git a/tests/refi/undef_tests.js b/tests/refi/undef_tests.js
new file mode 100644
index 000000000000..c23dfeaa101a
--- /dev/null
+++ b/tests/refi/undef_tests.js
@@ -0,0 +1,74 @@
+var undef_tests =
+[
+  // NOTE: not (yet?) supporting non-strict eq test for undefined
+
+  // expr !== undefined
+  function() {
+    var x : ?string = "xxx";
+    if (x !== undefined && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (undefined !== x && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p !== undefined && x.p !== null) {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q !== undefined && x.p.q !== null) {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr === undefined
+  function() {
+    var x : ?string = "xxx";
+    if (x === undefined || x === null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p === undefined || x.p === null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q === undefined || x.p.q === null) {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+];
+
+// this.p op undefined
+class A {
+  p: ?string;
+
+  ensure0(): string {
+    if (this.p !== undefined && this.p !== null)
+      return this.p;
+    else
+      return "";
+  }
+
+  ensure1(): string {
+    if (this.p === undefined || this.p === null)
+      return "";
+    else
+      return this.p;
+  }
+}
diff --git a/tests/refi/void_tests.js b/tests/refi/void_tests.js
new file mode 100644
index 000000000000..f74e7bcc8260
--- /dev/null
+++ b/tests/refi/void_tests.js
@@ -0,0 +1,74 @@
+var void_tests =
+[
+  // NOTE: not (yet?) supporting non-strict eq test for undefined
+
+  // expr !== void(...)
+  function() {
+    var x : ?string = "xxx";
+    if (x !== void(0) && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : ?string = "xxx";
+    if (void(0) !== x && x !== null) {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p !== void(0) && x.p !== null) {
+      var y : string | void = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q !== void(0) && x.p.q !== null) {
+      var y : string = x.p.q;  // ok
+    }
+  },
+
+  // expr === void(...)
+  function() {
+    var x : ?string = "xxx";
+    if (x === void(0) || x === null) {} else {
+      var y : string = x;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:?string} = {p:"xxx"};
+    if (x.p === void(0) || x.p === null) {} else {
+      var y : string = x.p;  // ok
+    }
+  },
+
+  function() {
+    var x : {p:{q:?string}} = {p:{q:"xxx"}};
+    if (x.p.q === void(0) || x.p.q === null) {} else {
+      var y : string = x.p.q;  // ok
+    }
+  },
+];
+
+// this.p op void(...)
+class A {
+  p: ?string;
+
+  ensure0(): string {
+    if (this.p !== void(0) && this.p !== null)
+      return this.p;
+    else
+      return "";
+  }
+
+  ensure1(): string {
+    if (this.p === void(0) || this.p === null)
+      return "";
+    else
+      return this.p;
+  }
+}
diff --git a/tests/refinements/__snapshots__/jsfmt.spec.js.snap b/tests/refinements/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3cb42ac081d0
--- /dev/null
+++ b/tests/refinements/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,2290 @@
+exports[`test assignment.js 1`] = `
+"/* @flow */
+
+function foo(x : ?number) {
+  var y;
+  if (y = x) {
+    var z = y * 1000;
+  }
+}
+
+type Bar = {
+  parent: ?Bar;
+  doStuff: () => void
+}
+
+function bar0(x : Bar) {
+  while (x = x.parent) { // can\'t assign x to ?Bar
+    x.doStuff();
+  }
+}
+
+function bar1(x : ?Bar) {
+  while (x = x.parent) { // x.parent might be null
+    x.doStuff();
+  }
+}
+
+function bar2(x : Bar) {
+  var y = x;
+  while (y = y.parent) {
+    y.doStuff();
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test ast_node.js 1`] = `
+"type Node1 = {
+  kind: \'Node1\',
+  prop1?: string
+};
+
+type Node2 = {
+  kind: \'Node2\',
+  prop2?: string
+}
+
+export type ASTNode = Node1 | Node2;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test bool.js 1`] = `
+"/* @flow */
+
+function foo(x: ?bool) {
+  if (x === false) {
+    return;
+  }
+
+  if (x === true) {
+    return;
+  }
+
+  x[0]; // error on null and undefined
+}
+
+function bar(x: ?bool) {
+  if (x !== true) {
+    if (x !== false) {
+      x[0]; // error on null and undefined
+    }
+  }
+}
+
+function baz(x: ?bool) {
+  if (100 * false) {
+    return;
+  }
+  if (false * 100) {
+    return;
+  }
+}
+
+let tests = [
+  function(x: { done: true, result: string } | { done: false }) {
+    if (x.done === true) {
+      return x.result;
+    }
+    return x.result; // error
+  },
+
+  function(x: { done: true, result: string } | { done: false }) {
+    if (true === x.done) {
+      return x.result;
+    }
+    return x.result; // error
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test computed_string_literal.js 1`] = `
+"// @flow
+
+type A = {
+  \'b_c\': ?string
+};
+
+function stuff(str: string) {}
+
+function testProperty(a: A) {
+  if (a.b_c) {
+    stuff(a.b_c)
+  }
+}
+
+function testLiteralProperty(a: A) {
+  if (a[\'b_c\']) {
+    stuff(a[\'b_c\'])
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type A = { \"b_c\": ?string };
+function stuff(str: string) {
+  
+}
+function testProperty(a: A) {
+  if (a.b_c) {
+    stuff(a.b_c);
+  }
+}
+function testLiteralProperty(a: A) {
+  if (a[\"b_c\"]) {
+    stuff(a[\"b_c\"]);
+  }
+}
+
+"
+`;
+
+exports[`test cond_prop.js 1`] = `
+"/* @flow */
+
+type Type = Name | ListType | NonNullType;
+type Name = {kind: \'Name\', value: string, type: void };
+type ListType = {kind: \'ListType\', type: Type};
+type NonNullType = {kind: \'NonNullType\', type: Name | ListType | BadType};
+type BadType = {};
+
+function getTypeASTName(typeAST: Type): string {
+  if (!typeAST.type) throw new Error(\'Must be wrapping type\'); // OK
+  return getTypeASTName(typeAST.type); // error, BadType not a subtype of Type
+}
+
+let tests = [
+  function(x: { done: true, result: string } | { done: false }) {
+    if (x.done) {
+      return x.result;
+    }
+    return x.result; // error
+  },
+
+  function(x: { done: true, result: string } | { foo: string }) {
+    if (x.done) {
+      return x.result; // error, consider { foo: \"herp\", done: \"derp\" }
+    }
+    return x.result; // error
+  },
+
+  function() {
+    type T
+      = { foo: Object, bar: string }
+      | { baz: string, quux: string }
+
+    function testAlwaysTruthyProp(t: T) {
+      if (t.foo) {
+        (t.bar: string); // error, consider { baz: \"x\", quux: \"y\", foo: \"boom\" }
+      } else {
+        (t.quux: string); // ok. since foo is an object (always truthy), the
+                          // else case completely rules out the first branch of
+                          // the union.
+      }
+    }
+
+    function testSometimesTruthyProp(t: T) {
+      if (t.bar) {
+        (t.foo: Object); // error, consider { baz: \"x\", quux: \"y\", bar: \"boom\" }
+      } else {
+        (t.quux: string); // error, consider { foo: {}, bar: \"\" }
+      }
+    }
+  },
+]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test constants.js 1`] = `
+"/* @flow */
+
+export const SUCCESS: \'SUCCESS\' = \'SUCCESS\';
+export const ERROR: \'ERROR\' = \'ERROR\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+export const SUCCESS: \"SUCCESS\" = \"SUCCESS\";
+export const ERROR: \"ERROR\" = \"ERROR\";
+
+"
+`;
+
+exports[`test eq.js 1`] = `
+"/* @flow */
+
+let tests = [
+  function(x: string, y: number) {
+    if (x == y) {} // error, string & number are not comparable (unsafe casting)
+    if (x === y) {} // no error, to match \`let z = (x === y)\` which is allowed
+  },
+
+  function(x: string) {
+    if (x == undefined) {} // ok
+    if (x == void 0) {} // ok
+  },
+
+  function(x: string) {
+    if (x == null) {} // ok
+  },
+
+  function(x: { y: \'foo\' } | { y: \'bar\' }) {
+    if (x.y == 123) {} // error
+    if (x.y === 123) {} // ok
+  },
+]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test exists.js 1`] = `
+"declare class Foo {
+  foo: string;
+}
+
+function foo0(x: ?string): string {
+  return x && x || \"\";
+}
+
+function foo1(x: ?Foo): string {
+  return x && x.foo || \"\";
+}
+
+function foo2(x: ?Class<Foo>): string {
+  return x && new x().foo || \"\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test func_call.js 1`] = `
+"// @flow
+
+let tests = [
+  function(x: { y?: string }, z: () => string) {
+    if (x.y) {
+      // make sure we visit the AST in the correct order. if we visit z() before
+      // x.y, then the function call will invalidate the refinement of x.y
+      // incorrectly.
+      x.y.indexOf(z()); // no error
+    }
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test hasOwnProperty.js 1`] = `
+"/* @flow */
+
+function foo(x:{y?:() => void}) {
+  x.y(); // error: could be undefined
+  if (x.hasOwnProperty(\'y\')) {
+    x.y(); // error: still could be undefined
+  }
+  if (x.hasOwnProperty(\'z\')) {
+    x.z(); // error: unreachable, but we don\'t help you here
+  }
+}
+
+function bar(x:Object) {
+  x.y(); // treated as \`any\`, so allowed
+  if (x.hasOwnProperty(\'y\')) {
+    x.y(); // still treated as \`any\`, so allowed
+  }
+  if (x.hasOwnProperty(\'z\')) {
+    x.z(); // also treated as \`any\`, so allowed
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test heap_defassign.js 1`] = `
+"// @flow
+
+type Obj = { p: number | string }
+
+function f () {}
+
+function def_assign_function_havoc(obj: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    f();                        // clears refi
+    var x: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_setprop_havoc(obj: Obj, obj2: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    obj2.p = \'hey\';             // clears refi
+    var x: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_index_havoc(obj: Obj, obj2: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    obj2[\'p\'] = \'hey\';          // clears refi
+    var x: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_within_if(b: boolean, obj: Obj) {
+    if (b) {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    }
+    var y: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_within_while(b: boolean, obj: Obj) {
+    while (b) {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    }
+    var y: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_within_do(b: boolean, obj: Obj) {
+    do {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    } while (b);
+    var y: number = obj.p;      // no error, loop runs at least once
+}
+
+function def_assign_within_try(b: boolean, obj: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    try {
+        f();                    // clears refi and might throw
+        obj.p = \'hey\';
+    } catch (e) {
+        f();                    // clears refi and might throw
+        obj.p = \'hey\';
+    } finally {
+        // NOTE: the values understood to flow to obj.p at this point
+        // include the number 42 written downstream;
+        // so if we did y:string, we would get at least a spurious error
+        // (among other reasonable errors caused by values written upstream)
+        var y: number = obj.p;  // error, string ~/~ number
+        obj.p = 42;
+    }
+    var z:string = obj.p;       // error, number ~/~ string
+}
+
+function def_assign_within_for(b: boolean, obj: Obj) {
+    for (; b; ) {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    }
+    var z: number = obj.p;      // error, (number | string) ~/~ number
+}
+
+// --- name-sensitive havoc ---
+
+type Obj2 = { q: number | string }
+
+function def_assign_setprop_nohavoc(obj: Obj, obj2: Obj2) {
+    obj.p = 10;                 // (obj.p : number)
+    obj2.q = \'hey\';             // doesn\'t clear refi of .p
+    var x: number = obj.p;      // still ok
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test lib.js 1`] = `
+"/* @flow */
+
+declare var BAZ: {stuff?: (x: number) => void} | void;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test missing-property-cond.js 1`] = `
+"// @flow
+
+function foo1(o: { x: number }) {
+  if (o.p1) { // OK, this is an idiomatic way of testing property existence
+    o.x;
+  }
+}
+
+function foo2(o: { x: number }) {
+  if (o.p2) { // OK
+    o.p2.x; // error, since o.p2\'s type is unknown (e.g., could be \`number\`)
+  }
+}
+
+function foo3(o: { x: number }) {
+  o.p3.x; // usual error outside conditional
+}
+
+function foo4(o: $Exact<{ x: number }>) {
+  if (o.p4) { // OK
+    o.p4.x; // currently OK, should be unreachable
+  } else {
+    o.p4.x; // error
+  }
+}
+
+function foo5() {
+  const o = { };
+  _foo5();
+  if (o.p) { o.p(); }
+  function _foo5() {
+    o.p = function() { }
+  }
+}
+
+function foo6(o: mixed) {
+  if (o.bar) {} // error, any lookup on mixed is unsafe
+}
+
+function foo7(o: mixed) {
+  if (typeof o.bar === \'string\') {} // error
+  if (o && typeof o.bar === \'string\') {} // ok
+  if (o != null && typeof o.bar === \'string\') {} // ok
+  if (o !== null && o !== undefined && typeof o.bar === \'string\') {} // ok
+}
+
+function foo8(o: { p: mixed }) {
+  if (o.p && o.p.q) {} // this is ok because o.p is truthy, so o.p.q is safe
+  if (o.p && o.p.q && o.p.q.r) {}
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test mixed.js 1`] = `
+"/* @flow */
+
+function takesNumber(x: number) {}
+function takesString(x: string) {}
+
+function num(x: mixed) {
+  if (typeof x === \"number\") {
+    takesString(x); // error
+    (!x: false); // error: we don\'t know the truthiness of x
+  }
+  if (typeof x === \"number\" && x) {
+    (!x: false); // ok
+  }
+  if (x && typeof x === \"number\") {
+    (!x: false); // ok
+  }
+}
+
+function str(x: mixed) {
+  if (typeof x === \"string\") {
+    takesNumber(x); // error
+    (!x: false); // error: we don\'t know the truthiness of x
+  }
+  if (typeof x === \"string\" && x) {
+    (!x: false); // ok
+  }
+  if (x && typeof x === \"string\") {
+    (!x: false); // ok
+  }
+}
+
+function bool(x: mixed) {
+  if (typeof x === \"boolean\") {
+    takesString(x); // error
+    (x: true); // error: we don\'t know the truthiness of x
+  }
+  if (typeof x === \"boolean\" && x) {
+    (x: true); // ok
+  }
+  if (x && typeof x === \"boolean\") {
+    (x: true); // ok
+  }
+}
+
+function fun(x: mixed) {
+  if (typeof x === \"function\") {
+    takesString(x); // error
+  }
+}
+
+function obj0(x: mixed) {
+  if (typeof x === \"object\") {
+    takesString(x); // error
+  }
+}
+
+function obj1(x: mixed) {
+  if (Array.isArray(x)) {
+    takesString(x); // error
+  }
+}
+
+function undef(x: mixed) {
+  if (typeof x === \"undefined\") {
+    takesString(x); // error
+  }
+}
+
+function null_(x: mixed) {
+  if (x === null) {
+    takesString(x); // error
+  }
+}
+
+function maybe(x: mixed) {
+  if (x == null) {
+    takesString(x); // error
+  }
+}
+
+function true_(x: mixed) {
+  if (x === true) {
+    takesString(x); // error
+  }
+}
+
+function false_(x: mixed) {
+  if (x === false) {
+    takesString(x); // error
+  }
+}
+
+function obj2(x: mixed) {
+  if (typeof x === \"object\") {
+    (x: { [key: string]: mixed } | null);
+    if (x !== null) {
+      (x[\'foo\']: string); // error, mixed
+    }
+  }
+}
+
+function obj2(x: mixed) {
+  if (typeof x === \"object\" && x) {
+    (x: Object);
+  }
+  if (x && typeof x === \"object\") {
+    (x: Object);
+  }
+  if (x != null && typeof x === \"object\") {
+    (x: Object);
+  }
+  if (x !== null && typeof x === \"object\") {
+    (x: Object);
+  }
+}
+
+function arr0(x: mixed) {
+  if (Array.isArray(x)) {
+    takesString(x[0]); // error
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test node1.js 1`] = `
+"module.exports = \'Node1\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+module.exports = \"Node1\";
+
+"
+`;
+
+exports[`test not.js 1`] = `
+"/* @flow */
+
+function foo(x: ?bool) {
+  if (!x) {
+    x++; // should error for null, void and bool (false)
+  }
+}
+
+function bar(x: ?number) {
+  if (!x) {
+    x[0]; // should error for null, void and number (0)
+  }
+}
+
+function baz (x: ?number) {
+  if (x === null || x === undefined) {
+    return;
+  }
+
+  if (!x) {
+    x[0]; // should error for number (0)
+  }
+}
+
+class TestClass {}
+
+let tests = [
+  function() {
+    var y = true;
+    while (y) {
+      y = !y;
+    }
+  },
+  function(x: Function) {
+    (!x: false); // ok, functions are always truthy
+  },
+  function(x: Object) {
+    (!x: false); // ok, objects are always truthy
+  },
+  function(x: string) {
+    (!x: false); // error, strings are not always truthy
+  },
+  function(x: number) {
+    (!x: false); // error, numbers are not always truthy
+  },
+  function(x: boolean) {
+    (!x: false); // error, bools are not always truthy
+  },
+  function(x: TestClass) {
+    (!x: false); // ok, classes are always truthy
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo(x: ?boolean) {
+  if (!x) {
+    x++;// should error for null, void and bool (false)
+  }
+}
+function bar(x: ?number) {
+  if (!x) {
+    x[0];// should error for null, void and number (0)
+  }
+}
+function baz(x: ?number) {
+  if (x === null || x === undefined) {
+    return;
+  }
+  if (!x) {
+    x[0];// should error for number (0)
+  }
+}
+class TestClass {}
+let tests = [
+  function() {
+    var y = true;
+    while (y) {
+      y = !y;
+    }
+  },
+  function(x: Function) {
+    (!x: false);// ok, functions are always truthy
+  },
+  function(x: Object) {
+    (!x: false);// ok, objects are always truthy
+  },
+  function(x: string) {
+    (!x: false);// error, strings are not always truthy
+  },
+  function(x: number) {
+    (!x: false);// error, numbers are not always truthy
+  },
+  function(x: boolean) {
+    (!x: false);// error, bools are not always truthy
+  },
+  function(x: TestClass) {
+    (!x: false);// ok, classes are always truthy
+  }
+];
+
+"
+`;
+
+exports[`test null.js 1`] = `
+"/* @flow */
+
+function null_bogus_comparison() {
+  if (100 * null) {
+    return;
+  }
+  if (null * 100) {
+    return;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function null_bogus_comparison() {
+  if (100 * null) {
+    return;
+  }
+  if (null * 100) {
+    return;
+  }
+}
+
+"
+`;
+
+exports[`test number.js 1`] = `
+"// @flow
+
+type Mode = 0 | 1 | 2;
+
+let tests = [
+  function(x: number) {
+    if (x === 0) {
+      (x: void); // error
+    }
+    (x: 0); // error
+  },
+
+  function(x: number) {
+    if (x !== 0) {
+      (x: 0); // error
+    }
+    (x: void); // error
+  },
+
+  function(x: 1): 0 {
+    if (x === 0) {
+      return x; // unreachable, no error
+    }
+    return 0;
+  },
+
+  function(x: 0): number {
+    if (x === 1) {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: 0) {
+    if (x !== 1) {
+      (x: 0);
+    }
+    (x: 0);
+  },
+
+  function(x: 0): number {
+    if (x === 0) {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: 0 | 1) {
+    if (x === 0) {
+      (x: 0);
+      (x: void); // error
+    }
+    if (x === 1) {
+      (x: 1);
+      (x: void); // error
+    }
+  },
+
+  function(x: { foo: number }): 0 {
+    if (x.foo === 0) {
+      return x.foo;
+    }
+    return x.foo; // error
+  },
+
+  function(
+    x: { kind: 0, foo: number } | { kind: 1, bar: number }
+  ): number {
+    if (x.kind === 0) {
+      return x.foo;
+    } else {
+      return x.bar;
+    }
+  },
+
+  function(num: number, obj: { foo: number }) {
+    if (num === obj.bar) { // ok, typos allowed in conditionals
+    }
+  },
+
+  function(num: number, obj: {[key: string]: number}) {
+    if (num === obj.bar) { // ok
+    }
+  },
+
+  function(n: number): Mode {
+    if (n !== 0 && n !== 1 && n !== 2) {
+      throw new Error(\"Wrong number passed\");
+    }
+    return n;
+  },
+
+  function(s: number): ?Mode {
+    if (s === 0) {
+      return s;
+    } else if (s === 3) {
+      return s; // error
+    }
+  },
+
+  function(mode: Mode) {
+    switch (mode) {
+      case 0:
+        (mode: 0);
+        break;
+
+      case 1:
+      case 2:
+        (mode: 1 | 2);
+        break;
+    }
+  },
+
+  function(x: number): 0 {
+    if (x) {
+      return x; // error
+    } else {
+      return x; // no error, inferred to be 0
+    }
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 22, end: 23, loc: [object Object], value: 0, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
+
+exports[`test property.js 1`] = `
+"/* @flow */
+
+function a(x: {[key: string]: ?string}, y: string): string {
+  if (x[y]) {
+    return x[y];
+  }
+  return \"\";
+}
+
+function b(x: {y: {[key: string]: ?string}}, z: string): string {
+  if (x.y[z]) {
+    return x.y[z];
+  }
+  return \"\";
+}
+
+function c(x: {[key: string]: ?string}, y: {z: string}): string {
+  if (x[y.z]) {
+    return x[y.z];
+  }
+  return \"\";
+}
+
+function d(x: {y: {[key: string]: ?string}}, a: {b: string}): string {
+  if (x.y[a.b]) {
+    return x.y[a.b];
+  }
+  return \"\";
+}
+
+function a_array(x: Array<?string>, y: number): string {
+  if (x[y]) {
+    return x[y];
+  }
+  return \"\";
+}
+
+function b_array(x: {y: Array<?string>}, z: number): string {
+  if (x.y[z]) {
+    return x.y[z];
+  }
+  return \"\";
+}
+
+function c_array(x: Array<?string>, y: {z: number}): string {
+  if (x[y.z]) {
+    return x[y.z];
+  }
+  return \"\";
+}
+
+function d_array(x: {y: Array<?string>}, a: {b: number}): string {
+  if (x.y[a.b]) {
+    return x.y[a.b];
+  }
+  return \"\";
+}
+
+function e_array(x: Array<?string>): string {
+  if (x[0]) {
+    return x[0];
+  }
+  return \"\";
+}
+
+// --- name-sensitive havoc ---
+
+function c2(x: {[key: string]: ?string}, y: {z: string}): string {
+  if (x[y.z]) {
+    y.z = \"HEY\";
+    return x[y.z];  // error
+  }
+  return \"\";
+}
+
+function c3(x: {[key: string]: ?string}, y: {z: string, a: string}): string {
+  if (x[y.z]) {
+    y.a = \"HEY\";
+    return x[y.z];  // ok
+  }
+  return \"\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test refinements.js 1`] = `
+"function foo(b) {
+    var x = b? 0 : null;
+    while (typeof x == \"string\" || typeof x == \"number\") {
+        var y:string = x;
+        x = false;
+    }
+    var z:string = x;
+}
+
+function bar(b) {
+    var x = b? 0 : null;
+    do {
+        var y:string = x;
+        x = false;
+    } while (x === null);
+    var z:string = x;
+}
+
+function maybe_throw() { }
+function qux() {
+    var x = 0;
+    try {
+        maybe_throw();
+        x = \"hello\";
+    } catch (e) {
+        maybe_throw();
+        x = \"hello\";
+    } finally {
+        // NOTE: the values understood to flow to x at this point
+        // include the number 42 written downstream;
+        // so if we did y:string, we would get at least a spurious error
+        // (among other reasonable errors caused by values written upstream)
+        var y:number = x;
+        x = 42;
+    }
+    var z:string = x;
+}
+
+function corge(b) {
+    for (var x = b? 0 : null;
+         typeof x == \"string\" || typeof x == \"number\";
+         x = false) {
+        var y:string = x;
+    }
+    var z:string = x;
+}
+
+function waldo() {
+    var o = {};
+    var x = false;
+    for (x in o) {
+        x = 0; // commenting this out would propagate x:string downstream
+    }
+    var z:number = x;
+}
+
+// regression test: bring a global into scope by testing it.
+// this has no refinement consequences and is error-free.
+// the way we currently cache global lookups causes uneven
+// distribution of the global\'s entries at path merge time,
+// so we need to recognize that it\'s legit rather than an
+// internal error.
+//
+function global_in_conditional0(x: number) {
+    // merge_env
+    if (x != 0) {
+        if (BAZ) {
+        }
+    }
+}
+
+function global_in_conditional2(x: number) {
+    // copy_env
+    for (var i = 0; i < 100; i++) {
+        if (BAZ) {
+        }
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:925
+      if (endsWithBrace(doBody))
+          ^
+
+ReferenceError: endsWithBrace is not defined
+    at genericPrintNoParens (/src/printer.js:925:11)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:561:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test string.js 1`] = `
+"// @flow
+
+type Mode = \"a\" | \"b\" | \"c\";
+
+let tests = [
+  function(x: string) {
+    if (x === \'foo\') {
+      (x: void); // error
+    }
+    (x: \'foo\'); // error
+  },
+
+  function(x: string) {
+    if (x !== \'foo\') {
+      (x: \'foo\'); // error
+    }
+    (x: void); // error
+  },
+
+  function(x: \'bar\'): \'foo\' {
+    if (x === \'foo\') {
+      return x; // unreachable, no error
+    }
+    return \'foo\';
+  },
+
+  function(x: \'foo\'): string {
+    if (x === \'bar\') {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: \'foo\') {
+    if (x !== \'bar\') {
+      (x: \'foo\');
+    }
+    (x: \'foo\');
+  },
+
+  function(x: \'foo\'): string {
+    if (x === \'foo\') {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: \'foo\' | \'bar\') {
+    if (x === \'foo\') {
+      (x: \'foo\');
+      (x: void); // error
+    }
+    if (x === \'bar\') {
+      (x: \'bar\');
+      (x: void); // error
+    }
+  },
+
+  function(x: { foo: string }): \'foo\' {
+    if (x.foo === \'foo\') {
+      return x.foo;
+    }
+    return x.foo; // error
+  },
+
+  function(
+    x: { kind: \'foo\', foo: string } | { kind: \'bar\', bar: string }
+  ): string {
+    if (x.kind === \'foo\') {
+      return x.foo;
+    } else {
+      return x.bar;
+    }
+  },
+
+  function(str: string, obj: { foo: string }) {
+    if (str === obj.bar) { // ok, typos allowed in conditionals
+    }
+  },
+
+  function(str: string, obj: {[key: string]: string}) {
+    if (str === obj.bar) { // ok
+    }
+  },
+
+  function(str: string): Mode {
+    var ch = str[0];
+    if (ch !== \"a\" && ch !== \"b\" && ch !== \"c\") {
+      throw new Error(\"Wrong string passed\");
+    }
+    return ch;
+  },
+
+  function(s: string): ?Mode {
+    if (s === \"a\") {
+      return s;
+    } else if (s === \"d\") {
+      return s; // error
+    }
+  },
+
+  function(mode: Mode) {
+    switch (mode) {
+      case \"a\":
+        (mode: \"a\");
+        break;
+
+      case \"b\":
+      case \"c\":
+        (mode: \"b\" | \"c\");
+        break;
+    }
+  },
+
+  function(x: string): \"\" {
+    if (x) {
+      return x; // error
+    } else {
+      return x; // no error, inferred to be \"\"
+    }
+  },
+
+  // Simple template literals are ok
+  function(x: string): \'foo\' {
+    if (x === \`foo\`) {
+      return x;
+    }
+    if (\`foo\` === x) {
+      return x;
+    }
+    return \'foo\';
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test super_member.js 1`] = `
+"/* @flow */
+
+class A {
+  prop: string;
+  method(): string {
+    return \"A\";
+  }
+}
+
+class B {
+  test(): string {
+    if (super.prop) { // super.prop doesn\'t exist
+      return super.prop; // error, unknown type passed to string expected
+    }
+    return \"B\";
+  }
+}
+
+class C extends A {
+  test(): string {
+    if (super.prop) {
+      return super.prop; // OK
+    }
+    return \"C\";
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class A {
+  prop: string;
+  method(): string {
+    return \"A\";
+  }
+}
+class B {
+  test(): string {
+    if (super.prop) {
+      // super.prop doesn\'t exist
+      return super.prop;// error, unknown type passed to string expected
+    }
+    return \"B\";
+  }
+}
+class C extends A {
+  test(): string {
+    if (super.prop) {
+      return super.prop;// OK
+    }
+    return \"C\";
+  }
+}
+
+"
+`;
+
+exports[`test switch.js 1`] = `
+"/* @flow */
+
+function foo(text: string | number): string {
+  switch (typeof text) {
+　　case \'string\':
+　　　return text;
+    case \'number\':
+      return text; // error, should return string
+　　default:
+　　　return \'wat\';
+　}
+}
+
+function bar(text: string | number): string {
+  switch (typeof text) {
+    case \'string\':
+      return text[0];
+  　default:
+      return (text++) + \'\';
+　}
+}
+
+function baz1(text: string | number): string {
+  switch (typeof text) {
+    case \'number\':
+    case \'string\':
+      return text[0]; // error, [0] on number
+  　default:
+      return \'wat\';
+　}
+}
+
+function baz2(text: string | number): string {
+  switch (typeof text) {
+    case \'string\':
+    case \'number\':
+      return text[0]; // error, [0] on number
+  　default:
+      return \'wat\';
+　}
+}
+
+function corge(text: string | number | Array<string>): string {
+  switch (typeof text) {
+    case \'object\':
+      return text[0];
+    case \'string\':
+    case \'number\':
+      // using ++ since it isn\'t valid on arrays or strings.
+      // should only error for string since Array was filtered out.
+      return (text++) + \'\';
+  　default:
+      return \'wat\';
+　}
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test tagged_union.js 1`] = `
+"// example 1
+
+type Type = Name | ListType;
+type Name = {kind: \'Name\', value: string};
+type ListType = {kind: \'ListType\', name: string};
+
+function getTypeASTName(typeAST: Type): string {
+  if (typeAST.kind === \'Name\') {
+    return typeAST.value; // OK, since typeAST: Name
+  } else {
+    return typeAST.name; // OK, since typeAST: ListType
+  }
+}
+
+// example 2
+import type {ASTNode} from \'./ast_node\';
+var Node = require(\'./node1\'); // Node = \"Node1\"
+function foo(x: ASTNode) {
+  if (x.kind === Node) {
+    return x.prop1.charAt(0); // typeAST: Node1, but x.prop1 may be undefined
+  }
+  return null;
+}
+
+// example 3
+type Apple = { kind: \'Fruit\', taste: \'Bad\' }
+type Orange = { kind: \'Fruit\', taste: \'Good\' }
+type Broccoli = { kind: \'Veg\', taste: \'Bad\', raw: \'No\' }
+type Carrot = { kind: \'Veg\', taste: \'Good\', raw: \'Maybe\' }
+
+type Breakfast = Apple | Orange | Broccoli | Carrot
+
+function bar(x: Breakfast) {
+  if (x.kind === \'Fruit\') { (x.taste: \'Good\'); } // error, Apple.taste = Bad
+  else (x.raw: \'No\'); // error, Carrot.raw = Maybe
+}
+
+function qux(x: Breakfast) {
+  if (x.taste === \'Good\') {
+    (x.raw: \'Yes\' | \'No\'); // 2 errors:
+                           // Orange.raw doesn\'t exist
+                           // Carrot.raw is neither Yes nor No
+  }
+}
+
+// example 4
+function list(n) {
+  if (n > 0) return { kind: \"cons\", next: list(n-1) };
+  return { kind: \"nil\" };
+}
+function length(l) {
+  switch (l.kind) {
+  case \"cons\": return 1 + length(l.next);
+  default: return 0;
+  }
+}
+function check(n) {
+  if (n >= 0) return (n === (length(list(n))));
+  return true;
+}
+
+
+// example 5
+var EnumKind = { A: 1, B: 2, C: 3};
+type A = { kind: 1, A: number };
+type B = { kind: 2, B: number };
+type C = { kind: 3, C: number };
+function kind(x: A | B | C): number {
+  switch (x.kind) {
+  case EnumKind.A: return x.A;
+  case EnumKind.B: return x.B;
+  default: return x.A; // error, x: C and property A not found in type C
+  }
+}
+kind({ kind: EnumKind.A, A: 1 });
+
+// example 6
+type Citizen = { citizen: true };
+type NonCitizen = { citizen: false, nationality: string }
+function nationality(x: Citizen | NonCitizen) {
+  if (x.citizen) return \"Shire\"
+  else return x.nationality;
+}
+
+let tests = [
+  // non-existent props
+  function test7(x: A) {
+    if (x.kindTypo === 1) { // typos are allowed to be tested
+      (x.kindTypo: string); // typos can\'t be used, though
+    }
+  },
+
+  // nested objects
+  function test8(x: {foo: {bar: 1}}) {
+    if (x.foo.bar === 1) {}
+    if (x.fooTypo.bar === 1) {} // error, fooTypo doesn\'t exist
+  },
+
+  // invalid RHS
+  function(x: A) {
+    if (x.kind === (null).toString()) {} // error, method on null
+    if ({kind: 1}.kind === (null).toString()) {} // error, method on null
+  },
+
+  // non-objects on LHS
+  function(
+    x: Array<string>, y: string, z: number, q: boolean,
+    r: Object, s: Function, t: () => void
+  ) {
+    if (x.length === 0) {}
+    if (x.legnth === 0) { // typos are allowed to be tested
+      (x.legnth: number); // inside the block, it\'s a number
+      (x.legnth: string); // error: number literal 0 !~> string
+    }
+    if (y.length === 0) {}
+    if (y.legnth === 0) { // typos are allowed to be tested
+      (y.legnth: number); // inside the block, it\'s a number
+      (y.legnth: string); // error: number literal 0 !~> string
+    }
+    if (z.toString === 0) {}
+    if (z.toStirng === 0) { // typos are allowed to be tested
+      (z.toStirng: number); // inside the block, it\'s a number
+      (z.toStirng: string); // error: number literal 0 !~> string
+    }
+    if (q.valueOf === 0) {}
+    if (q.valeuOf === 0) { // typos are allowed to be tested
+      (q.valeuOf: number); // inside the block, it\'s a number
+      (q.valeuOf: string); // error: number literal 0 !~> string
+    }
+    if (r.toStirng === 0) { // typos are allowed to be tested
+      (r.toStirng: empty); // props on AnyObjT are \`any\`
+    }
+    if (s.call === 0) {}
+    if (s.calll === 0) { // typos are allowed to be tested
+      (t.calll: empty); // ok, props on functions are \`any\` :/
+    }
+    if (t.call === 0) {}
+    if (t.calll === 0) { // typos are allowed to be tested
+      (t.calll: empty); // ok, props on functions are \`any\` :/
+    }
+  },
+
+  // sentinel props become the RHS
+  function(x: { str: string, num: number, bool: boolean }) {
+    if (x.str === \'str\') {
+      (x.str: \'not str\'); // error: \'str\' !~> \'not str\'
+    }
+    if (x.num === 123) {
+      (x.num: 456); // error: 123 !~> 456
+    }
+    if (x.bool === true) {
+      (x.bool: false); // error: true !~> false
+    }
+    // even if it doesn\'t exist...
+    if (x.badStr === \'bad\') {
+      (x.badStr: empty); // error: \'bad\' !~> empty
+    }
+    if (x.badNum === 123) {
+      (x.badNum: empty); // error: 123 !~> empty
+    }
+    if (x.badBool === true) {
+      (x.badBool: empty); // error: true !~> empty
+    }
+  },
+
+  // type mismatch
+  function(x: { foo: 123, y: string } | { foo: \'foo\', z: string }) {
+    if (x.foo === 123) {
+      (x.y: string);
+      x.z; // error
+    } else {
+      (x.z: string);
+      x.y; // error
+    }
+    if (x.foo === \'foo\') {
+      (x.z: string);
+      x.y; // error
+    } else {
+      (x.y: string);
+      x.z; // error
+    }
+  },
+
+  // type mismatch, but one is not a literal
+  function(x: { foo: number, y: string } | { foo: \'foo\', z: string }) {
+    if (x.foo === 123) {
+      (x.y: string); // ok, because 123 !== \'foo\'
+      x.z; // error
+    } else {
+      x.y; // error: x.foo could be a string
+      x.z; // error: could still be either case (if foo was a different number)
+    }
+
+    if (x.foo === \'foo\') {
+      (x.z: string);
+      x.y; // error
+    } else {
+      (x.y: string);
+      x.z; // error
+    }
+  },
+
+  // type mismatch, neither is a literal
+  function(x: { foo: number, y: string } | { foo: string, z: string }) {
+    if (x.foo === 123) {
+      (x.y: string); // ok, because 123 !== string
+      x.z; // error
+    } else {
+      x.y; // error: x.foo could be a string
+      x.z; // error: could still be either case (if foo was a different number)
+    }
+
+    if (x.foo === \'foo\') {
+      (x.z: string);
+      x.y; // error
+    } else {
+      x.y; // error: x.foo could be a different string
+      x.z; // error: x.foo could be a number
+    }
+  },
+
+  // type mismatch, neither is a literal, test is not a literal either
+  function(
+    x: { foo: number, y: string } | { foo: string, z: string },
+    num: number
+  ) {
+    if (x.foo === num) {
+      x.y; // error: flow isn\'t smart enough to figure this out yet
+      x.z; // error
+    }
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test tagged_union_import.js 1`] = `
+"/* @flow */
+
+import { SUCCESS, ERROR } from \'./constants\'
+
+type Success = {
+  type: typeof SUCCESS,
+  message: string
+}
+
+type Error = {
+  type: typeof ERROR,
+  error: string
+}
+
+function handleStatus(status: Success | Error) {
+  switch(status.type) {
+    case SUCCESS:
+      console.log(\`Successful: \${status.message}\`);
+      break;
+    default:
+      console.log(\`Errored: \${status.error}\`);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test typeof.js 1`] = `
+"/* @flow */
+
+function foo(x: bool | number) {
+  if (typeof x === \"boolean\") {
+    x[0]; // error for boolean, not number
+  }
+}
+
+function bar(): number {
+  var x = null;
+  if (typeof x === \"object\") {
+    return x; // error, null
+  }
+  return 0;
+}
+
+/* refining globals */
+function fn0() {
+  if (typeof BAZ !== \'undefined\' &&
+      typeof BAZ.stuff === \'function\') {
+    BAZ.stuff(123);
+  }
+  BAZ.stuff(123); // error, refinement is gone
+}
+function fn1() {
+  BAZ.stuff; // error, could be undefined
+  if (typeof BAZ !== \'undefined\' &&
+      typeof BAZ.stuff === \'function\') {
+    BAZ.stuff(123); // ok
+    BAZ.stuff(123); // error, refinement is gone
+  }
+}
+
+function anyfun(x: number | Function): number {
+  if (typeof x === \"function\") {
+    return 0;
+  }
+  return x; // OK, x refined to \`number\`
+}
+
+function anyobj(x: number | Object): number {
+  if (typeof x === \"object\") {
+    return 0;
+  }
+  return x; // OK, x refined to \`number\`
+}
+
+function testInvalidValue(x: mixed) {
+  if (typeof x === \"foo\") { // error
+    return 0;
+  }
+}
+
+function testTemplateLiteral(x: string | number) {
+  if (typeof x === \`string\`) {
+    return x.length;
+  }
+}
+
+function testInvalidTemplateLiteral(x: string | number) {
+  if (typeof x === \`foo\`) { // error
+    return 0;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test undef.js 1`] = `
+"/* @flow */
+
+function undef_var(x: ?number) {
+  if (x !== null && x !== undefined) {
+    var y = x * 1000;
+  }
+}
+
+function undef_var_rev(x: ?number) {
+  if (x === null || x === undefined) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function undef_prop(x: { x: ?number }) {
+  if (x.x !== null && x.x !== undefined) {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_prop_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === undefined) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_var_fail(x: ?number) {
+  if (x !== undefined) {
+    var y = x * 1000;
+  }
+}
+
+function undef_var_fail_rev(x: ?number) {
+  if (x === undefined) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function undef_prop_fail(x: { x: ?number }) {
+  if (x.x !== undefined) {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_prop_fail_rev(x: { x: ?number }) {
+  if (x.x === undefined) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_unreachable(x: number) {
+  if (x === undefined) {
+    var y = x * 1000; // unreachable
+  }
+  if (x == undefined) {
+    var z = x * 1000; // unreachable
+  }
+}
+
+function undef_var_nonstrict(x: ?number, y: ?number) {
+  if (x != undefined) {
+    var a = x * 1000;
+  }
+  if (y == undefined){
+    var b = y * 1000; // error
+  }
+}
+
+function undef_bogus_comparison() {
+  if (100 * undefined) {
+    return;
+  }
+  if (undefined * 100) {
+    return;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function undef_var(x: ?number) {
+  if (x !== null && x !== undefined) {
+    var y = x * 1000;
+  }
+}
+function undef_var_rev(x: ?number) {
+  if (x === null || x === undefined) {
+    
+  } else {
+    var y = x * 1000;
+  }
+}
+function undef_prop(x: { x: ?number }) {
+  if (x.x !== null && x.x !== undefined) {
+    var y = x.x * 1000;
+  }
+}
+function undef_prop_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === undefined) {
+    
+  } else {
+    var y = x.x * 1000;
+  }
+}
+function undef_var_fail(x: ?number) {
+  if (x !== undefined) {
+    var y = x * 1000;
+  }
+}
+function undef_var_fail_rev(x: ?number) {
+  if (x === undefined) {
+    
+  } else {
+    var y = x * 1000;
+  }
+}
+function undef_prop_fail(x: { x: ?number }) {
+  if (x.x !== undefined) {
+    var y = x.x * 1000;
+  }
+}
+function undef_prop_fail_rev(x: { x: ?number }) {
+  if (x.x === undefined) {
+    
+  } else {
+    var y = x.x * 1000;
+  }
+}
+function undef_unreachable(x: number) {
+  if (x === undefined) {
+    var y = x * 1000;// unreachable
+  }
+  if (x == undefined) {
+    var z = x * 1000;// unreachable
+  }
+}
+function undef_var_nonstrict(x: ?number, y: ?number) {
+  if (x != undefined) {
+    var a = x * 1000;
+  }
+  if (y == undefined) {
+    var b = y * 1000;// error
+  }
+}
+function undef_bogus_comparison() {
+  if (100 * undefined) {
+    return;
+  }
+  if (undefined * 100) {
+    return;
+  }
+}
+
+"
+`;
+
+exports[`test union.js 1`] = `
+"/* @flow */
+
+type thing = number | bool
+
+function foo(x: thing) {
+  if (x === true) {
+    x[0]; // error on boolean
+  }
+}
+
+function bar(x: thing) {
+  if (x !== true && x !== false) {
+    x[0]; // error on number
+  }
+}
+
+function baz(x: ?thing) {
+  if (x && x !== true) {
+    x[0]; // error on number
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test void.js 1`] = `
+"/* @flow */
+
+function void_var(x: ?number) {
+  if (x !== null && x !== void(0)) {
+    var y = x * 1000;
+  }
+}
+
+function void_var_rev(x: ?number) {
+  if (x === null || x === void(0)) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function void_pro(x: { x: ?number }) {
+  if (x.x !== null && x.x !== void(0)) {
+    var y = x.x * 1000;
+  }
+}
+
+function void_pro_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === void(0)) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function void_var_fail(x: ?number) {
+  if (x !== void(0)) {
+    var y = x * 1000;
+  }
+}
+
+function void_var_fail_rev(x: ?number) {
+  if (x === void(0)) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function void_pro_fail(x: { x: ?number }) {
+  if (x.x !== void(0)) {
+    var y = x.x * 1000;
+  }
+}
+
+function void_pro_fail_rev(x: { x: ?number }) {
+  if (x.x === void(0)) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function void_var_side_effect(x: ?number) {
+  if (x !== null && x !== void(x * 1000)) {
+    var y = x * 1000;
+  }
+}
+
+function void_var_side_effect_rev(x: ?number) {
+  if (x === null || x === void(x * 1000)) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function void_prop_side_effect(x: { x: ?number }) {
+  if (x.x !== null && x.x !== void(x.x * 1000)) {
+    var y = x.x * 1000;
+  }
+}
+
+function void_prop_side_effect_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === void(x.x * 1000)) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function void_bogus_comparison() {
+  if (100 * void(0)) {
+    return;
+  }
+  if (void(0) * 100) {
+    return;
+  }
+}
+
+function void_redefined_undefined(x: ?number) {
+  var undefined = \"foo\";
+  if (x !== null && x !== void(0)) {
+    var y = x * 1000;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function void_var(x: ?number) {
+  if (x !== null && x !== void 0) {
+    var y = x * 1000;
+  }
+}
+function void_var_rev(x: ?number) {
+  if (x === null || x === void 0) {
+    
+  } else {
+    var y = x * 1000;
+  }
+}
+function void_pro(x: { x: ?number }) {
+  if (x.x !== null && x.x !== void 0) {
+    var y = x.x * 1000;
+  }
+}
+function void_pro_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === void 0) {
+    
+  } else {
+    var y = x.x * 1000;
+  }
+}
+function void_var_fail(x: ?number) {
+  if (x !== void 0) {
+    var y = x * 1000;
+  }
+}
+function void_var_fail_rev(x: ?number) {
+  if (x === void 0) {
+    
+  } else {
+    var y = x * 1000;
+  }
+}
+function void_pro_fail(x: { x: ?number }) {
+  if (x.x !== void 0) {
+    var y = x.x * 1000;
+  }
+}
+function void_pro_fail_rev(x: { x: ?number }) {
+  if (x.x === void 0) {
+    
+  } else {
+    var y = x.x * 1000;
+  }
+}
+function void_var_side_effect(x: ?number) {
+  if (x !== null && x !== void (x * 1000)) {
+    var y = x * 1000;
+  }
+}
+function void_var_side_effect_rev(x: ?number) {
+  if (x === null || x === void (x * 1000)) {
+    
+  } else {
+    var y = x * 1000;
+  }
+}
+function void_prop_side_effect(x: { x: ?number }) {
+  if (x.x !== null && x.x !== void (x.x * 1000)) {
+    var y = x.x * 1000;
+  }
+}
+function void_prop_side_effect_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === void (x.x * 1000)) {
+    
+  } else {
+    var y = x.x * 1000;
+  }
+}
+function void_bogus_comparison() {
+  if (100 * void 0) {
+    return;
+  }
+  if (void 0 * 100) {
+    return;
+  }
+}
+function void_redefined_undefined(x: ?number) {
+  var undefined = \"foo\";
+  if (x !== null && x !== void 0) {
+    var y = x * 1000;
+  }
+}
+
+"
+`;
diff --git a/tests/refinements/assignment.js b/tests/refinements/assignment.js
new file mode 100644
index 000000000000..a331d6d3e271
--- /dev/null
+++ b/tests/refinements/assignment.js
@@ -0,0 +1,32 @@
+/* @flow */
+
+function foo(x : ?number) {
+  var y;
+  if (y = x) {
+    var z = y * 1000;
+  }
+}
+
+type Bar = {
+  parent: ?Bar;
+  doStuff: () => void
+}
+
+function bar0(x : Bar) {
+  while (x = x.parent) { // can't assign x to ?Bar
+    x.doStuff();
+  }
+}
+
+function bar1(x : ?Bar) {
+  while (x = x.parent) { // x.parent might be null
+    x.doStuff();
+  }
+}
+
+function bar2(x : Bar) {
+  var y = x;
+  while (y = y.parent) {
+    y.doStuff();
+  }
+}
diff --git a/tests/refinements/ast_node.js b/tests/refinements/ast_node.js
new file mode 100644
index 000000000000..396d466e1d94
--- /dev/null
+++ b/tests/refinements/ast_node.js
@@ -0,0 +1,11 @@
+type Node1 = {
+  kind: 'Node1',
+  prop1?: string
+};
+
+type Node2 = {
+  kind: 'Node2',
+  prop2?: string
+}
+
+export type ASTNode = Node1 | Node2;
diff --git a/tests/refinements/bool.js b/tests/refinements/bool.js
new file mode 100644
index 000000000000..5730681c83a7
--- /dev/null
+++ b/tests/refinements/bool.js
@@ -0,0 +1,46 @@
+/* @flow */
+
+function foo(x: ?bool) {
+  if (x === false) {
+    return;
+  }
+
+  if (x === true) {
+    return;
+  }
+
+  x[0]; // error on null and undefined
+}
+
+function bar(x: ?bool) {
+  if (x !== true) {
+    if (x !== false) {
+      x[0]; // error on null and undefined
+    }
+  }
+}
+
+function baz(x: ?bool) {
+  if (100 * false) {
+    return;
+  }
+  if (false * 100) {
+    return;
+  }
+}
+
+let tests = [
+  function(x: { done: true, result: string } | { done: false }) {
+    if (x.done === true) {
+      return x.result;
+    }
+    return x.result; // error
+  },
+
+  function(x: { done: true, result: string } | { done: false }) {
+    if (true === x.done) {
+      return x.result;
+    }
+    return x.result; // error
+  },
+];
diff --git a/tests/refinements/computed_string_literal.js b/tests/refinements/computed_string_literal.js
new file mode 100644
index 000000000000..93fa0716cec4
--- /dev/null
+++ b/tests/refinements/computed_string_literal.js
@@ -0,0 +1,19 @@
+// @flow
+
+type A = {
+  'b_c': ?string
+};
+
+function stuff(str: string) {}
+
+function testProperty(a: A) {
+  if (a.b_c) {
+    stuff(a.b_c)
+  }
+}
+
+function testLiteralProperty(a: A) {
+  if (a['b_c']) {
+    stuff(a['b_c'])
+  }
+}
diff --git a/tests/refinements/cond_prop.js b/tests/refinements/cond_prop.js
new file mode 100644
index 000000000000..7bab5dfef721
--- /dev/null
+++ b/tests/refinements/cond_prop.js
@@ -0,0 +1,52 @@
+/* @flow */
+
+type Type = Name | ListType | NonNullType;
+type Name = {kind: 'Name', value: string, type: void };
+type ListType = {kind: 'ListType', type: Type};
+type NonNullType = {kind: 'NonNullType', type: Name | ListType | BadType};
+type BadType = {};
+
+function getTypeASTName(typeAST: Type): string {
+  if (!typeAST.type) throw new Error('Must be wrapping type'); // OK
+  return getTypeASTName(typeAST.type); // error, BadType not a subtype of Type
+}
+
+let tests = [
+  function(x: { done: true, result: string } | { done: false }) {
+    if (x.done) {
+      return x.result;
+    }
+    return x.result; // error
+  },
+
+  function(x: { done: true, result: string } | { foo: string }) {
+    if (x.done) {
+      return x.result; // error, consider { foo: "herp", done: "derp" }
+    }
+    return x.result; // error
+  },
+
+  function() {
+    type T
+      = { foo: Object, bar: string }
+      | { baz: string, quux: string }
+
+    function testAlwaysTruthyProp(t: T) {
+      if (t.foo) {
+        (t.bar: string); // error, consider { baz: "x", quux: "y", foo: "boom" }
+      } else {
+        (t.quux: string); // ok. since foo is an object (always truthy), the
+                          // else case completely rules out the first branch of
+                          // the union.
+      }
+    }
+
+    function testSometimesTruthyProp(t: T) {
+      if (t.bar) {
+        (t.foo: Object); // error, consider { baz: "x", quux: "y", bar: "boom" }
+      } else {
+        (t.quux: string); // error, consider { foo: {}, bar: "" }
+      }
+    }
+  },
+]
diff --git a/tests/refinements/constants.js b/tests/refinements/constants.js
new file mode 100644
index 000000000000..c845d58c24db
--- /dev/null
+++ b/tests/refinements/constants.js
@@ -0,0 +1,4 @@
+/* @flow */
+
+export const SUCCESS: 'SUCCESS' = 'SUCCESS';
+export const ERROR: 'ERROR' = 'ERROR';
diff --git a/tests/refinements/eq.js b/tests/refinements/eq.js
new file mode 100644
index 000000000000..24fdaab5a448
--- /dev/null
+++ b/tests/refinements/eq.js
@@ -0,0 +1,22 @@
+/* @flow */
+
+let tests = [
+  function(x: string, y: number) {
+    if (x == y) {} // error, string & number are not comparable (unsafe casting)
+    if (x === y) {} // no error, to match `let z = (x === y)` which is allowed
+  },
+
+  function(x: string) {
+    if (x == undefined) {} // ok
+    if (x == void 0) {} // ok
+  },
+
+  function(x: string) {
+    if (x == null) {} // ok
+  },
+
+  function(x: { y: 'foo' } | { y: 'bar' }) {
+    if (x.y == 123) {} // error
+    if (x.y === 123) {} // ok
+  },
+]
diff --git a/tests/refinements/exists.js b/tests/refinements/exists.js
new file mode 100644
index 000000000000..b26e29a5b980
--- /dev/null
+++ b/tests/refinements/exists.js
@@ -0,0 +1,15 @@
+declare class Foo {
+  foo: string;
+}
+
+function foo0(x: ?string): string {
+  return x && x || "";
+}
+
+function foo1(x: ?Foo): string {
+  return x && x.foo || "";
+}
+
+function foo2(x: ?Class<Foo>): string {
+  return x && new x().foo || "";
+}
diff --git a/tests/refinements/func_call.js b/tests/refinements/func_call.js
new file mode 100644
index 000000000000..693c3c44e929
--- /dev/null
+++ b/tests/refinements/func_call.js
@@ -0,0 +1,12 @@
+// @flow
+
+let tests = [
+  function(x: { y?: string }, z: () => string) {
+    if (x.y) {
+      // make sure we visit the AST in the correct order. if we visit z() before
+      // x.y, then the function call will invalidate the refinement of x.y
+      // incorrectly.
+      x.y.indexOf(z()); // no error
+    }
+  },
+];
diff --git a/tests/refinements/hasOwnProperty.js b/tests/refinements/hasOwnProperty.js
new file mode 100644
index 000000000000..1545a554df94
--- /dev/null
+++ b/tests/refinements/hasOwnProperty.js
@@ -0,0 +1,21 @@
+/* @flow */
+
+function foo(x:{y?:() => void}) {
+  x.y(); // error: could be undefined
+  if (x.hasOwnProperty('y')) {
+    x.y(); // error: still could be undefined
+  }
+  if (x.hasOwnProperty('z')) {
+    x.z(); // error: unreachable, but we don't help you here
+  }
+}
+
+function bar(x:Object) {
+  x.y(); // treated as `any`, so allowed
+  if (x.hasOwnProperty('y')) {
+    x.y(); // still treated as `any`, so allowed
+  }
+  if (x.hasOwnProperty('z')) {
+    x.z(); // also treated as `any`, so allowed
+  }
+}
diff --git a/tests/refinements/heap_defassign.js b/tests/refinements/heap_defassign.js
new file mode 100644
index 000000000000..09a760588469
--- /dev/null
+++ b/tests/refinements/heap_defassign.js
@@ -0,0 +1,84 @@
+// @flow
+
+type Obj = { p: number | string }
+
+function f () {}
+
+function def_assign_function_havoc(obj: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    f();                        // clears refi
+    var x: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_setprop_havoc(obj: Obj, obj2: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    obj2.p = 'hey';             // clears refi
+    var x: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_index_havoc(obj: Obj, obj2: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    obj2['p'] = 'hey';          // clears refi
+    var x: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_within_if(b: boolean, obj: Obj) {
+    if (b) {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    }
+    var y: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_within_while(b: boolean, obj: Obj) {
+    while (b) {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    }
+    var y: number = obj.p;      // error, obj.p : number | string
+}
+
+function def_assign_within_do(b: boolean, obj: Obj) {
+    do {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    } while (b);
+    var y: number = obj.p;      // no error, loop runs at least once
+}
+
+function def_assign_within_try(b: boolean, obj: Obj) {
+    obj.p = 10;                 // (obj.p : number)
+    try {
+        f();                    // clears refi and might throw
+        obj.p = 'hey';
+    } catch (e) {
+        f();                    // clears refi and might throw
+        obj.p = 'hey';
+    } finally {
+        // NOTE: the values understood to flow to obj.p at this point
+        // include the number 42 written downstream;
+        // so if we did y:string, we would get at least a spurious error
+        // (among other reasonable errors caused by values written upstream)
+        var y: number = obj.p;  // error, string ~/~ number
+        obj.p = 42;
+    }
+    var z:string = obj.p;       // error, number ~/~ string
+}
+
+function def_assign_within_for(b: boolean, obj: Obj) {
+    for (; b; ) {
+        obj.p = 10;             // (obj.p : number)
+        var x: number = obj.p   // ok by def assign
+    }
+    var z: number = obj.p;      // error, (number | string) ~/~ number
+}
+
+// --- name-sensitive havoc ---
+
+type Obj2 = { q: number | string }
+
+function def_assign_setprop_nohavoc(obj: Obj, obj2: Obj2) {
+    obj.p = 10;                 // (obj.p : number)
+    obj2.q = 'hey';             // doesn't clear refi of .p
+    var x: number = obj.p;      // still ok
+}
diff --git a/tests/refinements/jsfmt.spec.js b/tests/refinements/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/refinements/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/refinements/lib.js b/tests/refinements/lib.js
new file mode 100644
index 000000000000..211648743a38
--- /dev/null
+++ b/tests/refinements/lib.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+declare var BAZ: {stuff?: (x: number) => void} | void;
diff --git a/tests/refinements/missing-property-cond.js b/tests/refinements/missing-property-cond.js
new file mode 100644
index 000000000000..944bd0f99d7d
--- /dev/null
+++ b/tests/refinements/missing-property-cond.js
@@ -0,0 +1,50 @@
+// @flow
+
+function foo1(o: { x: number }) {
+  if (o.p1) { // OK, this is an idiomatic way of testing property existence
+    o.x;
+  }
+}
+
+function foo2(o: { x: number }) {
+  if (o.p2) { // OK
+    o.p2.x; // error, since o.p2's type is unknown (e.g., could be `number`)
+  }
+}
+
+function foo3(o: { x: number }) {
+  o.p3.x; // usual error outside conditional
+}
+
+function foo4(o: $Exact<{ x: number }>) {
+  if (o.p4) { // OK
+    o.p4.x; // currently OK, should be unreachable
+  } else {
+    o.p4.x; // error
+  }
+}
+
+function foo5() {
+  const o = { };
+  _foo5();
+  if (o.p) { o.p(); }
+  function _foo5() {
+    o.p = function() { }
+  }
+}
+
+function foo6(o: mixed) {
+  if (o.bar) {} // error, any lookup on mixed is unsafe
+}
+
+function foo7(o: mixed) {
+  if (typeof o.bar === 'string') {} // error
+  if (o && typeof o.bar === 'string') {} // ok
+  if (o != null && typeof o.bar === 'string') {} // ok
+  if (o !== null && o !== undefined && typeof o.bar === 'string') {} // ok
+}
+
+function foo8(o: { p: mixed }) {
+  if (o.p && o.p.q) {} // this is ok because o.p is truthy, so o.p.q is safe
+  if (o.p && o.p.q && o.p.q.r) {}
+}
diff --git a/tests/refinements/mixed.js b/tests/refinements/mixed.js
new file mode 100644
index 000000000000..5c12b32c541e
--- /dev/null
+++ b/tests/refinements/mixed.js
@@ -0,0 +1,121 @@
+/* @flow */
+
+function takesNumber(x: number) {}
+function takesString(x: string) {}
+
+function num(x: mixed) {
+  if (typeof x === "number") {
+    takesString(x); // error
+    (!x: false); // error: we don't know the truthiness of x
+  }
+  if (typeof x === "number" && x) {
+    (!x: false); // ok
+  }
+  if (x && typeof x === "number") {
+    (!x: false); // ok
+  }
+}
+
+function str(x: mixed) {
+  if (typeof x === "string") {
+    takesNumber(x); // error
+    (!x: false); // error: we don't know the truthiness of x
+  }
+  if (typeof x === "string" && x) {
+    (!x: false); // ok
+  }
+  if (x && typeof x === "string") {
+    (!x: false); // ok
+  }
+}
+
+function bool(x: mixed) {
+  if (typeof x === "boolean") {
+    takesString(x); // error
+    (x: true); // error: we don't know the truthiness of x
+  }
+  if (typeof x === "boolean" && x) {
+    (x: true); // ok
+  }
+  if (x && typeof x === "boolean") {
+    (x: true); // ok
+  }
+}
+
+function fun(x: mixed) {
+  if (typeof x === "function") {
+    takesString(x); // error
+  }
+}
+
+function obj0(x: mixed) {
+  if (typeof x === "object") {
+    takesString(x); // error
+  }
+}
+
+function obj1(x: mixed) {
+  if (Array.isArray(x)) {
+    takesString(x); // error
+  }
+}
+
+function undef(x: mixed) {
+  if (typeof x === "undefined") {
+    takesString(x); // error
+  }
+}
+
+function null_(x: mixed) {
+  if (x === null) {
+    takesString(x); // error
+  }
+}
+
+function maybe(x: mixed) {
+  if (x == null) {
+    takesString(x); // error
+  }
+}
+
+function true_(x: mixed) {
+  if (x === true) {
+    takesString(x); // error
+  }
+}
+
+function false_(x: mixed) {
+  if (x === false) {
+    takesString(x); // error
+  }
+}
+
+function obj2(x: mixed) {
+  if (typeof x === "object") {
+    (x: { [key: string]: mixed } | null);
+    if (x !== null) {
+      (x['foo']: string); // error, mixed
+    }
+  }
+}
+
+function obj2(x: mixed) {
+  if (typeof x === "object" && x) {
+    (x: Object);
+  }
+  if (x && typeof x === "object") {
+    (x: Object);
+  }
+  if (x != null && typeof x === "object") {
+    (x: Object);
+  }
+  if (x !== null && typeof x === "object") {
+    (x: Object);
+  }
+}
+
+function arr0(x: mixed) {
+  if (Array.isArray(x)) {
+    takesString(x[0]); // error
+  }
+}
diff --git a/tests/refinements/node1.js b/tests/refinements/node1.js
new file mode 100644
index 000000000000..97afd3f36556
--- /dev/null
+++ b/tests/refinements/node1.js
@@ -0,0 +1 @@
+module.exports = 'Node1';
diff --git a/tests/refinements/not.js b/tests/refinements/not.js
new file mode 100644
index 000000000000..dafd50927609
--- /dev/null
+++ b/tests/refinements/not.js
@@ -0,0 +1,52 @@
+/* @flow */
+
+function foo(x: ?bool) {
+  if (!x) {
+    x++; // should error for null, void and bool (false)
+  }
+}
+
+function bar(x: ?number) {
+  if (!x) {
+    x[0]; // should error for null, void and number (0)
+  }
+}
+
+function baz (x: ?number) {
+  if (x === null || x === undefined) {
+    return;
+  }
+
+  if (!x) {
+    x[0]; // should error for number (0)
+  }
+}
+
+class TestClass {}
+
+let tests = [
+  function() {
+    var y = true;
+    while (y) {
+      y = !y;
+    }
+  },
+  function(x: Function) {
+    (!x: false); // ok, functions are always truthy
+  },
+  function(x: Object) {
+    (!x: false); // ok, objects are always truthy
+  },
+  function(x: string) {
+    (!x: false); // error, strings are not always truthy
+  },
+  function(x: number) {
+    (!x: false); // error, numbers are not always truthy
+  },
+  function(x: boolean) {
+    (!x: false); // error, bools are not always truthy
+  },
+  function(x: TestClass) {
+    (!x: false); // ok, classes are always truthy
+  },
+];
diff --git a/tests/refinements/null.js b/tests/refinements/null.js
new file mode 100644
index 000000000000..f21881abda93
--- /dev/null
+++ b/tests/refinements/null.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+function null_bogus_comparison() {
+  if (100 * null) {
+    return;
+  }
+  if (null * 100) {
+    return;
+  }
+}
diff --git a/tests/refinements/number.js b/tests/refinements/number.js
new file mode 100644
index 000000000000..4c192b8e428e
--- /dev/null
+++ b/tests/refinements/number.js
@@ -0,0 +1,121 @@
+// @flow
+
+type Mode = 0 | 1 | 2;
+
+let tests = [
+  function(x: number) {
+    if (x === 0) {
+      (x: void); // error
+    }
+    (x: 0); // error
+  },
+
+  function(x: number) {
+    if (x !== 0) {
+      (x: 0); // error
+    }
+    (x: void); // error
+  },
+
+  function(x: 1): 0 {
+    if (x === 0) {
+      return x; // unreachable, no error
+    }
+    return 0;
+  },
+
+  function(x: 0): number {
+    if (x === 1) {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: 0) {
+    if (x !== 1) {
+      (x: 0);
+    }
+    (x: 0);
+  },
+
+  function(x: 0): number {
+    if (x === 0) {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: 0 | 1) {
+    if (x === 0) {
+      (x: 0);
+      (x: void); // error
+    }
+    if (x === 1) {
+      (x: 1);
+      (x: void); // error
+    }
+  },
+
+  function(x: { foo: number }): 0 {
+    if (x.foo === 0) {
+      return x.foo;
+    }
+    return x.foo; // error
+  },
+
+  function(
+    x: { kind: 0, foo: number } | { kind: 1, bar: number }
+  ): number {
+    if (x.kind === 0) {
+      return x.foo;
+    } else {
+      return x.bar;
+    }
+  },
+
+  function(num: number, obj: { foo: number }) {
+    if (num === obj.bar) { // ok, typos allowed in conditionals
+    }
+  },
+
+  function(num: number, obj: {[key: string]: number}) {
+    if (num === obj.bar) { // ok
+    }
+  },
+
+  function(n: number): Mode {
+    if (n !== 0 && n !== 1 && n !== 2) {
+      throw new Error("Wrong number passed");
+    }
+    return n;
+  },
+
+  function(s: number): ?Mode {
+    if (s === 0) {
+      return s;
+    } else if (s === 3) {
+      return s; // error
+    }
+  },
+
+  function(mode: Mode) {
+    switch (mode) {
+      case 0:
+        (mode: 0);
+        break;
+
+      case 1:
+      case 2:
+        (mode: 1 | 2);
+        break;
+    }
+  },
+
+  function(x: number): 0 {
+    if (x) {
+      return x; // error
+    } else {
+      return x; // no error, inferred to be 0
+    }
+  },
+];
diff --git a/tests/refinements/property.js b/tests/refinements/property.js
new file mode 100644
index 000000000000..6513e1deb340
--- /dev/null
+++ b/tests/refinements/property.js
@@ -0,0 +1,82 @@
+/* @flow */
+
+function a(x: {[key: string]: ?string}, y: string): string {
+  if (x[y]) {
+    return x[y];
+  }
+  return "";
+}
+
+function b(x: {y: {[key: string]: ?string}}, z: string): string {
+  if (x.y[z]) {
+    return x.y[z];
+  }
+  return "";
+}
+
+function c(x: {[key: string]: ?string}, y: {z: string}): string {
+  if (x[y.z]) {
+    return x[y.z];
+  }
+  return "";
+}
+
+function d(x: {y: {[key: string]: ?string}}, a: {b: string}): string {
+  if (x.y[a.b]) {
+    return x.y[a.b];
+  }
+  return "";
+}
+
+function a_array(x: Array<?string>, y: number): string {
+  if (x[y]) {
+    return x[y];
+  }
+  return "";
+}
+
+function b_array(x: {y: Array<?string>}, z: number): string {
+  if (x.y[z]) {
+    return x.y[z];
+  }
+  return "";
+}
+
+function c_array(x: Array<?string>, y: {z: number}): string {
+  if (x[y.z]) {
+    return x[y.z];
+  }
+  return "";
+}
+
+function d_array(x: {y: Array<?string>}, a: {b: number}): string {
+  if (x.y[a.b]) {
+    return x.y[a.b];
+  }
+  return "";
+}
+
+function e_array(x: Array<?string>): string {
+  if (x[0]) {
+    return x[0];
+  }
+  return "";
+}
+
+// --- name-sensitive havoc ---
+
+function c2(x: {[key: string]: ?string}, y: {z: string}): string {
+  if (x[y.z]) {
+    y.z = "HEY";
+    return x[y.z];  // error
+  }
+  return "";
+}
+
+function c3(x: {[key: string]: ?string}, y: {z: string, a: string}): string {
+  if (x[y.z]) {
+    y.a = "HEY";
+    return x[y.z];  // ok
+  }
+  return "";
+}
diff --git a/tests/refinements/refinements.js b/tests/refinements/refinements.js
new file mode 100644
index 000000000000..76da9e52058a
--- /dev/null
+++ b/tests/refinements/refinements.js
@@ -0,0 +1,78 @@
+function foo(b) {
+    var x = b? 0 : null;
+    while (typeof x == "string" || typeof x == "number") {
+        var y:string = x;
+        x = false;
+    }
+    var z:string = x;
+}
+
+function bar(b) {
+    var x = b? 0 : null;
+    do {
+        var y:string = x;
+        x = false;
+    } while (x === null);
+    var z:string = x;
+}
+
+function maybe_throw() { }
+function qux() {
+    var x = 0;
+    try {
+        maybe_throw();
+        x = "hello";
+    } catch (e) {
+        maybe_throw();
+        x = "hello";
+    } finally {
+        // NOTE: the values understood to flow to x at this point
+        // include the number 42 written downstream;
+        // so if we did y:string, we would get at least a spurious error
+        // (among other reasonable errors caused by values written upstream)
+        var y:number = x;
+        x = 42;
+    }
+    var z:string = x;
+}
+
+function corge(b) {
+    for (var x = b? 0 : null;
+         typeof x == "string" || typeof x == "number";
+         x = false) {
+        var y:string = x;
+    }
+    var z:string = x;
+}
+
+function waldo() {
+    var o = {};
+    var x = false;
+    for (x in o) {
+        x = 0; // commenting this out would propagate x:string downstream
+    }
+    var z:number = x;
+}
+
+// regression test: bring a global into scope by testing it.
+// this has no refinement consequences and is error-free.
+// the way we currently cache global lookups causes uneven
+// distribution of the global's entries at path merge time,
+// so we need to recognize that it's legit rather than an
+// internal error.
+//
+function global_in_conditional0(x: number) {
+    // merge_env
+    if (x != 0) {
+        if (BAZ) {
+        }
+    }
+}
+
+function global_in_conditional2(x: number) {
+    // copy_env
+    for (var i = 0; i < 100; i++) {
+        if (BAZ) {
+        }
+    }
+}
diff --git a/tests/refinements/string.js b/tests/refinements/string.js
new file mode 100644
index 000000000000..62873deda8e4
--- /dev/null
+++ b/tests/refinements/string.js
@@ -0,0 +1,133 @@
+// @flow
+
+type Mode = "a" | "b" | "c";
+
+let tests = [
+  function(x: string) {
+    if (x === 'foo') {
+      (x: void); // error
+    }
+    (x: 'foo'); // error
+  },
+
+  function(x: string) {
+    if (x !== 'foo') {
+      (x: 'foo'); // error
+    }
+    (x: void); // error
+  },
+
+  function(x: 'bar'): 'foo' {
+    if (x === 'foo') {
+      return x; // unreachable, no error
+    }
+    return 'foo';
+  },
+
+  function(x: 'foo'): string {
+    if (x === 'bar') {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: 'foo') {
+    if (x !== 'bar') {
+      (x: 'foo');
+    }
+    (x: 'foo');
+  },
+
+  function(x: 'foo'): string {
+    if (x === 'foo') {
+      return x;
+    }
+    return x;
+  },
+
+  function(x: 'foo' | 'bar') {
+    if (x === 'foo') {
+      (x: 'foo');
+      (x: void); // error
+    }
+    if (x === 'bar') {
+      (x: 'bar');
+      (x: void); // error
+    }
+  },
+
+  function(x: { foo: string }): 'foo' {
+    if (x.foo === 'foo') {
+      return x.foo;
+    }
+    return x.foo; // error
+  },
+
+  function(
+    x: { kind: 'foo', foo: string } | { kind: 'bar', bar: string }
+  ): string {
+    if (x.kind === 'foo') {
+      return x.foo;
+    } else {
+      return x.bar;
+    }
+  },
+
+  function(str: string, obj: { foo: string }) {
+    if (str === obj.bar) { // ok, typos allowed in conditionals
+    }
+  },
+
+  function(str: string, obj: {[key: string]: string}) {
+    if (str === obj.bar) { // ok
+    }
+  },
+
+  function(str: string): Mode {
+    var ch = str[0];
+    if (ch !== "a" && ch !== "b" && ch !== "c") {
+      throw new Error("Wrong string passed");
+    }
+    return ch;
+  },
+
+  function(s: string): ?Mode {
+    if (s === "a") {
+      return s;
+    } else if (s === "d") {
+      return s; // error
+    }
+  },
+
+  function(mode: Mode) {
+    switch (mode) {
+      case "a":
+        (mode: "a");
+        break;
+
+      case "b":
+      case "c":
+        (mode: "b" | "c");
+        break;
+    }
+  },
+
+  function(x: string): "" {
+    if (x) {
+      return x; // error
+    } else {
+      return x; // no error, inferred to be ""
+    }
+  },
+
+  // Simple template literals are ok
+  function(x: string): 'foo' {
+    if (x === `foo`) {
+      return x;
+    }
+    if (`foo` === x) {
+      return x;
+    }
+    return 'foo';
+  },
+];
diff --git a/tests/refinements/super_member.js b/tests/refinements/super_member.js
new file mode 100644
index 000000000000..3aa941b12d8f
--- /dev/null
+++ b/tests/refinements/super_member.js
@@ -0,0 +1,26 @@
+/* @flow */
+
+class A {
+  prop: string;
+  method(): string {
+    return "A";
+  }
+}
+
+class B {
+  test(): string {
+    if (super.prop) { // super.prop doesn't exist
+      return super.prop; // error, unknown type passed to string expected
+    }
+    return "B";
+  }
+}
+
+class C extends A {
+  test(): string {
+    if (super.prop) {
+      return super.prop; // OK
+    }
+    return "C";
+  }
+}
diff --git a/tests/refinements/switch.js b/tests/refinements/switch.js
new file mode 100644
index 000000000000..f5e41cd22cac
--- /dev/null
+++ b/tests/refinements/switch.js
@@ -0,0 +1,55 @@
+/* @flow */
+
+function foo(text: string | number): string {
+  switch (typeof text) {
+　　case 'string':
+　　　return text;
+    case 'number':
+      return text; // error, should return string
+　　default:
+　　　return 'wat';
+　}
+}
+
+function bar(text: string | number): string {
+  switch (typeof text) {
+    case 'string':
+      return text[0];
+  　default:
+      return (text++) + '';
+　}
+}
+
+function baz1(text: string | number): string {
+  switch (typeof text) {
+    case 'number':
+    case 'string':
+      return text[0]; // error, [0] on number
+  　default:
+      return 'wat';
+　}
+}
+
+function baz2(text: string | number): string {
+  switch (typeof text) {
+    case 'string':
+    case 'number':
+      return text[0]; // error, [0] on number
+  　default:
+      return 'wat';
+　}
+}
+
+function corge(text: string | number | Array<string>): string {
+  switch (typeof text) {
+    case 'object':
+      return text[0];
+    case 'string':
+    case 'number':
+      // using ++ since it isn't valid on arrays or strings.
+      // should only error for string since Array was filtered out.
+      return (text++) + '';
+  　default:
+      return 'wat';
+　}
+}
diff --git a/tests/refinements/tagged_union.js b/tests/refinements/tagged_union.js
new file mode 100644
index 000000000000..19c5c185fb45
--- /dev/null
+++ b/tests/refinements/tagged_union.js
@@ -0,0 +1,232 @@
+// example 1
+
+type Type = Name | ListType;
+type Name = {kind: 'Name', value: string};
+type ListType = {kind: 'ListType', name: string};
+
+function getTypeASTName(typeAST: Type): string {
+  if (typeAST.kind === 'Name') {
+    return typeAST.value; // OK, since typeAST: Name
+  } else {
+    return typeAST.name; // OK, since typeAST: ListType
+  }
+}
+
+// example 2
+import type {ASTNode} from './ast_node';
+var Node = require('./node1'); // Node = "Node1"
+function foo(x: ASTNode) {
+  if (x.kind === Node) {
+    return x.prop1.charAt(0); // typeAST: Node1, but x.prop1 may be undefined
+  }
+  return null;
+}
+
+// example 3
+type Apple = { kind: 'Fruit', taste: 'Bad' }
+type Orange = { kind: 'Fruit', taste: 'Good' }
+type Broccoli = { kind: 'Veg', taste: 'Bad', raw: 'No' }
+type Carrot = { kind: 'Veg', taste: 'Good', raw: 'Maybe' }
+
+type Breakfast = Apple | Orange | Broccoli | Carrot
+
+function bar(x: Breakfast) {
+  if (x.kind === 'Fruit') { (x.taste: 'Good'); } // error, Apple.taste = Bad
+  else (x.raw: 'No'); // error, Carrot.raw = Maybe
+}
+
+function qux(x: Breakfast) {
+  if (x.taste === 'Good') {
+    (x.raw: 'Yes' | 'No'); // 2 errors:
+                           // Orange.raw doesn't exist
+                           // Carrot.raw is neither Yes nor No
+  }
+}
+
+// example 4
+function list(n) {
+  if (n > 0) return { kind: "cons", next: list(n-1) };
+  return { kind: "nil" };
+}
+function length(l) {
+  switch (l.kind) {
+  case "cons": return 1 + length(l.next);
+  default: return 0;
+  }
+}
+function check(n) {
+  if (n >= 0) return (n === (length(list(n))));
+  return true;
+}
+
+
+// example 5
+var EnumKind = { A: 1, B: 2, C: 3};
+type A = { kind: 1, A: number };
+type B = { kind: 2, B: number };
+type C = { kind: 3, C: number };
+function kind(x: A | B | C): number {
+  switch (x.kind) {
+  case EnumKind.A: return x.A;
+  case EnumKind.B: return x.B;
+  default: return x.A; // error, x: C and property A not found in type C
+  }
+}
+kind({ kind: EnumKind.A, A: 1 });
+
+// example 6
+type Citizen = { citizen: true };
+type NonCitizen = { citizen: false, nationality: string }
+function nationality(x: Citizen | NonCitizen) {
+  if (x.citizen) return "Shire"
+  else return x.nationality;
+}
+
+let tests = [
+  // non-existent props
+  function test7(x: A) {
+    if (x.kindTypo === 1) { // typos are allowed to be tested
+      (x.kindTypo: string); // typos can't be used, though
+    }
+  },
+
+  // nested objects
+  function test8(x: {foo: {bar: 1}}) {
+    if (x.foo.bar === 1) {}
+    if (x.fooTypo.bar === 1) {} // error, fooTypo doesn't exist
+  },
+
+  // invalid RHS
+  function(x: A) {
+    if (x.kind === (null).toString()) {} // error, method on null
+    if ({kind: 1}.kind === (null).toString()) {} // error, method on null
+  },
+
+  // non-objects on LHS
+  function(
+    x: Array<string>, y: string, z: number, q: boolean,
+    r: Object, s: Function, t: () => void
+  ) {
+    if (x.length === 0) {}
+    if (x.legnth === 0) { // typos are allowed to be tested
+      (x.legnth: number); // inside the block, it's a number
+      (x.legnth: string); // error: number literal 0 !~> string
+    }
+    if (y.length === 0) {}
+    if (y.legnth === 0) { // typos are allowed to be tested
+      (y.legnth: number); // inside the block, it's a number
+      (y.legnth: string); // error: number literal 0 !~> string
+    }
+    if (z.toString === 0) {}
+    if (z.toStirng === 0) { // typos are allowed to be tested
+      (z.toStirng: number); // inside the block, it's a number
+      (z.toStirng: string); // error: number literal 0 !~> string
+    }
+    if (q.valueOf === 0) {}
+    if (q.valeuOf === 0) { // typos are allowed to be tested
+      (q.valeuOf: number); // inside the block, it's a number
+      (q.valeuOf: string); // error: number literal 0 !~> string
+    }
+    if (r.toStirng === 0) { // typos are allowed to be tested
+      (r.toStirng: empty); // props on AnyObjT are `any`
+    }
+    if (s.call === 0) {}
+    if (s.calll === 0) { // typos are allowed to be tested
+      (t.calll: empty); // ok, props on functions are `any` :/
+    }
+    if (t.call === 0) {}
+    if (t.calll === 0) { // typos are allowed to be tested
+      (t.calll: empty); // ok, props on functions are `any` :/
+    }
+  },
+
+  // sentinel props become the RHS
+  function(x: { str: string, num: number, bool: boolean }) {
+    if (x.str === 'str') {
+      (x.str: 'not str'); // error: 'str' !~> 'not str'
+    }
+    if (x.num === 123) {
+      (x.num: 456); // error: 123 !~> 456
+    }
+    if (x.bool === true) {
+      (x.bool: false); // error: true !~> false
+    }
+    // even if it doesn't exist...
+    if (x.badStr === 'bad') {
+      (x.badStr: empty); // error: 'bad' !~> empty
+    }
+    if (x.badNum === 123) {
+      (x.badNum: empty); // error: 123 !~> empty
+    }
+    if (x.badBool === true) {
+      (x.badBool: empty); // error: true !~> empty
+    }
+  },
+
+  // type mismatch
+  function(x: { foo: 123, y: string } | { foo: 'foo', z: string }) {
+    if (x.foo === 123) {
+      (x.y: string);
+      x.z; // error
+    } else {
+      (x.z: string);
+      x.y; // error
+    }
+    if (x.foo === 'foo') {
+      (x.z: string);
+      x.y; // error
+    } else {
+      (x.y: string);
+      x.z; // error
+    }
+  },
+
+  // type mismatch, but one is not a literal
+  function(x: { foo: number, y: string } | { foo: 'foo', z: string }) {
+    if (x.foo === 123) {
+      (x.y: string); // ok, because 123 !== 'foo'
+      x.z; // error
+    } else {
+      x.y; // error: x.foo could be a string
+      x.z; // error: could still be either case (if foo was a different number)
+    }
+
+    if (x.foo === 'foo') {
+      (x.z: string);
+      x.y; // error
+    } else {
+      (x.y: string);
+      x.z; // error
+    }
+  },
+
+  // type mismatch, neither is a literal
+  function(x: { foo: number, y: string } | { foo: string, z: string }) {
+    if (x.foo === 123) {
+      (x.y: string); // ok, because 123 !== string
+      x.z; // error
+    } else {
+      x.y; // error: x.foo could be a string
+      x.z; // error: could still be either case (if foo was a different number)
+    }
+
+    if (x.foo === 'foo') {
+      (x.z: string);
+      x.y; // error
+    } else {
+      x.y; // error: x.foo could be a different string
+      x.z; // error: x.foo could be a number
+    }
+  },
+
+  // type mismatch, neither is a literal, test is not a literal either
+  function(
+    x: { foo: number, y: string } | { foo: string, z: string },
+    num: number
+  ) {
+    if (x.foo === num) {
+      x.y; // error: flow isn't smart enough to figure this out yet
+      x.z; // error
+    }
+  }
+];
diff --git a/tests/refinements/tagged_union_import.js b/tests/refinements/tagged_union_import.js
new file mode 100644
index 000000000000..e6c39c83ade0
--- /dev/null
+++ b/tests/refinements/tagged_union_import.js
@@ -0,0 +1,23 @@
+/* @flow */
+
+import { SUCCESS, ERROR } from './constants'
+
+type Success = {
+  type: typeof SUCCESS,
+  message: string
+}
+
+type Error = {
+  type: typeof ERROR,
+  error: string
+}
+
+function handleStatus(status: Success | Error) {
+  switch(status.type) {
+    case SUCCESS:
+      console.log(`Successful: ${status.message}`);
+      break;
+    default:
+      console.log(`Errored: ${status.error}`);
+  }
+}
diff --git a/tests/refinements/typeof.js b/tests/refinements/typeof.js
new file mode 100644
index 000000000000..0b1f0da2f72c
--- /dev/null
+++ b/tests/refinements/typeof.js
@@ -0,0 +1,64 @@
+/* @flow */
+
+function foo(x: bool | number) {
+  if (typeof x === "boolean") {
+    x[0]; // error for boolean, not number
+  }
+}
+
+function bar(): number {
+  var x = null;
+  if (typeof x === "object") {
+    return x; // error, null
+  }
+  return 0;
+}
+
+/* refining globals */
+function fn0() {
+  if (typeof BAZ !== 'undefined' &&
+      typeof BAZ.stuff === 'function') {
+    BAZ.stuff(123);
+  }
+  BAZ.stuff(123); // error, refinement is gone
+}
+function fn1() {
+  BAZ.stuff; // error, could be undefined
+  if (typeof BAZ !== 'undefined' &&
+      typeof BAZ.stuff === 'function') {
+    BAZ.stuff(123); // ok
+    BAZ.stuff(123); // error, refinement is gone
+  }
+}
+
+function anyfun(x: number | Function): number {
+  if (typeof x === "function") {
+    return 0;
+  }
+  return x; // OK, x refined to `number`
+}
+
+function anyobj(x: number | Object): number {
+  if (typeof x === "object") {
+    return 0;
+  }
+  return x; // OK, x refined to `number`
+}
+
+function testInvalidValue(x: mixed) {
+  if (typeof x === "foo") { // error
+    return 0;
+  }
+}
+
+function testTemplateLiteral(x: string | number) {
+  if (typeof x === `string`) {
+    return x.length;
+  }
+}
+
+function testInvalidTemplateLiteral(x: string | number) {
+  if (typeof x === `foo`) { // error
+    return 0;
+  }
+}
diff --git a/tests/refinements/undef.js b/tests/refinements/undef.js
new file mode 100644
index 000000000000..14d1b92309ff
--- /dev/null
+++ b/tests/refinements/undef.js
@@ -0,0 +1,80 @@
+/* @flow */
+
+function undef_var(x: ?number) {
+  if (x !== null && x !== undefined) {
+    var y = x * 1000;
+  }
+}
+
+function undef_var_rev(x: ?number) {
+  if (x === null || x === undefined) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function undef_prop(x: { x: ?number }) {
+  if (x.x !== null && x.x !== undefined) {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_prop_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === undefined) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_var_fail(x: ?number) {
+  if (x !== undefined) {
+    var y = x * 1000;
+  }
+}
+
+function undef_var_fail_rev(x: ?number) {
+  if (x === undefined) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function undef_prop_fail(x: { x: ?number }) {
+  if (x.x !== undefined) {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_prop_fail_rev(x: { x: ?number }) {
+  if (x.x === undefined) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function undef_unreachable(x: number) {
+  if (x === undefined) {
+    var y = x * 1000; // unreachable
+  }
+  if (x == undefined) {
+    var z = x * 1000; // unreachable
+  }
+}
+
+function undef_var_nonstrict(x: ?number, y: ?number) {
+  if (x != undefined) {
+    var a = x * 1000;
+  }
+  if (y == undefined){
+    var b = y * 1000; // error
+  }
+}
+
+function undef_bogus_comparison() {
+  if (100 * undefined) {
+    return;
+  }
+  if (undefined * 100) {
+    return;
+  }
+}
diff --git a/tests/refinements/union.js b/tests/refinements/union.js
new file mode 100644
index 000000000000..145df02c3bfd
--- /dev/null
+++ b/tests/refinements/union.js
@@ -0,0 +1,21 @@
+/* @flow */
+
+type thing = number | bool
+
+function foo(x: thing) {
+  if (x === true) {
+    x[0]; // error on boolean
+  }
+}
+
+function bar(x: thing) {
+  if (x !== true && x !== false) {
+    x[0]; // error on number
+  }
+}
+
+function baz(x: ?thing) {
+  if (x && x !== true) {
+    x[0]; // error on number
+  }
+}
diff --git a/tests/refinements/void.js b/tests/refinements/void.js
new file mode 100644
index 000000000000..87d3a8af8644
--- /dev/null
+++ b/tests/refinements/void.js
@@ -0,0 +1,95 @@
+/* @flow */
+
+function void_var(x: ?number) {
+  if (x !== null && x !== void(0)) {
+    var y = x * 1000;
+  }
+}
+
+function void_var_rev(x: ?number) {
+  if (x === null || x === void(0)) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function void_pro(x: { x: ?number }) {
+  if (x.x !== null && x.x !== void(0)) {
+    var y = x.x * 1000;
+  }
+}
+
+function void_pro_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === void(0)) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function void_var_fail(x: ?number) {
+  if (x !== void(0)) {
+    var y = x * 1000;
+  }
+}
+
+function void_var_fail_rev(x: ?number) {
+  if (x === void(0)) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function void_pro_fail(x: { x: ?number }) {
+  if (x.x !== void(0)) {
+    var y = x.x * 1000;
+  }
+}
+
+function void_pro_fail_rev(x: { x: ?number }) {
+  if (x.x === void(0)) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function void_var_side_effect(x: ?number) {
+  if (x !== null && x !== void(x * 1000)) {
+    var y = x * 1000;
+  }
+}
+
+function void_var_side_effect_rev(x: ?number) {
+  if (x === null || x === void(x * 1000)) {
+  } else {
+    var y = x * 1000;
+  }
+}
+
+function void_prop_side_effect(x: { x: ?number }) {
+  if (x.x !== null && x.x !== void(x.x * 1000)) {
+    var y = x.x * 1000;
+  }
+}
+
+function void_prop_side_effect_rev(x: { x: ?number }) {
+  if (x.x === null || x.x === void(x.x * 1000)) {
+  } else {
+    var y = x.x * 1000;
+  }
+}
+
+function void_bogus_comparison() {
+  if (100 * void(0)) {
+    return;
+  }
+  if (void(0) * 100) {
+    return;
+  }
+}
+
+function void_redefined_undefined(x: ?number) {
+  var undefined = "foo";
+  if (x !== null && x !== void(0)) {
+    var y = x * 1000;
+  }
+}
diff --git a/tests/reflection/__snapshots__/jsfmt.spec.js.snap b/tests/reflection/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..370bc1f8b9fb
--- /dev/null
+++ b/tests/reflection/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,18 @@
+exports[`test type.js 1`] = `
+"declare var a: number;
+var b: typeof a = "...";
+var c: typeof a = "...";
+
+type T = number;
+var x:T = "...";
+
+// what about recursive unions?
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare var a: number;
+var b: typeof a = "...";
+var c: typeof a = "...";
+type T = number;
+var x: T = "...";// what about recursive unions?
+
+"
+`;
diff --git a/tests/reflection/jsfmt.spec.js b/tests/reflection/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/reflection/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/reflection/type.js b/tests/reflection/type.js
new file mode 100644
index 000000000000..de8cd6ed4804
--- /dev/null
+++ b/tests/reflection/type.js
@@ -0,0 +1,8 @@
+declare var a: number;
+var b: typeof a = "...";
+var c: typeof a = "...";
+
+type T = number;
+var x:T = "...";
+
+// what about recursive unions?
diff --git a/tests/regexp/__snapshots__/jsfmt.spec.js.snap b/tests/regexp/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..d61d4407d641
--- /dev/null
+++ b/tests/regexp/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,9 @@
+exports[`test regexp.js 1`] = `
+"var patt=/Hello/g
+var match:number = patt.test("Hello world!");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var patt = /Hello/g;
+var match: number = patt.test("Hello world!");
+
+"
+`;
diff --git a/tests/regexp/jsfmt.spec.js b/tests/regexp/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/regexp/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/regexp/regexp.js b/tests/regexp/regexp.js
new file mode 100644
index 000000000000..c8b2340ac812
--- /dev/null
+++ b/tests/regexp/regexp.js
@@ -0,0 +1,2 @@
+var patt=/Hello/g
+var match:number = patt.test("Hello world!");
diff --git a/tests/replace/__snapshots__/jsfmt.spec.js.snap b/tests/replace/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..62ba462c75d7
--- /dev/null
+++ b/tests/replace/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,15 @@
+exports[`test test.js 1`] = `
+"var a = 0;
+
+function foo(x) { }
+
+foo("");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var a = 0;
+function foo(x) {
+  
+}
+foo("");
+
+"
+`;
diff --git a/tests/replace/jsfmt.spec.js b/tests/replace/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/replace/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/replace/test.js b/tests/replace/test.js
new file mode 100644
index 000000000000..8a4904c12fa7
--- /dev/null
+++ b/tests/replace/test.js
@@ -0,0 +1,5 @@
+var a = 0;
+
+function foo(x) { }
+
+foo("");
diff --git a/tests/require/B.js b/tests/require/B.js
new file mode 100644
index 000000000000..e4d0f1b41f44
--- /dev/null
+++ b/tests/require/B.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+exports.numberValue = 42;
diff --git a/tests/require/C.js b/tests/require/C.js
new file mode 100644
index 000000000000..e667c4717b69
--- /dev/null
+++ b/tests/require/C.js
@@ -0,0 +1 @@
+/* @flow */
diff --git a/tests/require/E.js b/tests/require/E.js
new file mode 100644
index 000000000000..7d408be6436e
--- /dev/null
+++ b/tests/require/E.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+// Local `exports` var is just a ref to module.exports, so mutating the original
+// value will affect the exports object but re-binding it makes it useless and
+// does not affect the exports value.
+module.exports = {
+  numberValue: 42
+};
+
+exports = {stringValue: ''};
diff --git a/tests/require/ProvidesModuleA.js b/tests/require/ProvidesModuleA.js
new file mode 100644
index 000000000000..3c651145d2f5
--- /dev/null
+++ b/tests/require/ProvidesModuleA.js
@@ -0,0 +1,6 @@
+/**
+ * @providesModule A
+ * @flow
+ */
+
+exports.numberValue = 42;
diff --git a/tests/require/ProvidesModuleD.js b/tests/require/ProvidesModuleD.js
new file mode 100644
index 000000000000..a4d5ee842062
--- /dev/null
+++ b/tests/require/ProvidesModuleD.js
@@ -0,0 +1,4 @@
+/**
+ * @providesModule D
+ * @flow
+ */
diff --git a/tests/require/__snapshots__/jsfmt.spec.js.snap b/tests/require/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..0ce3d84b8ecb
--- /dev/null
+++ b/tests/require/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,168 @@
+exports[`test B.js 1`] = `
+"/* @flow */
+
+exports.numberValue = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+exports.numberValue = 42;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"/* @flow */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test E.js 1`] = `
+"/* @flow */
+
+// Local \`exports\` var is just a ref to module.exports, so mutating the original
+// value will affect the exports object but re-binding it makes it useless and
+// does not affect the exports value.
+module.exports = {
+  numberValue: 42
+};
+
+exports = {stringValue: ''};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// Local \`exports\` var is just a ref to module.exports, so mutating the original
+// value will affect the exports object but re-binding it makes it useless and
+// does not affect the exports value.
+module.exports = { numberValue: 42 };
+exports = { stringValue: "" };
+
+"
+`;
+
+exports[`test ProvidesModuleA.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+
+exports.numberValue = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule A
+ * @flow
+ */
+exports.numberValue = 42;
+
+"
+`;
+
+exports[`test ProvidesModuleD.js 1`] = `
+"/**
+ * @providesModule D
+ * @flow
+ */
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+"
+`;
+
+exports[`test not_builtin_require.js 1`] = `
+"// @flow
+
+function require() {}
+require("not a module name");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function require() {
+  
+}
+require("not a module name");
+
+"
+`;
+
+exports[`test not_builtin_require2.js 1`] = `
+"// @flow
+
+type require = number;
+var a: require = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+type require = number;
+var a: require = 42;
+
+"
+`;
+
+exports[`test require.js 1`] = `
+"/* @flow */
+
+function takesANumber(num: number): void {}
+function takesAString(str: string): void {}
+
+// @providesModule
+var A = require("A");
+takesANumber(A.numberValue);
+takesAString(A.numberValue);
+
+// File path
+var B = require("./B");
+takesANumber(B.numberValue);
+takesAString(B.numberValue);
+
+// C.js exists, but not as a providesModule
+require("C");
+
+// @providesModule D exists, but not as a filename
+require("./D");
+
+// E exports an object with a numVal property
+var E = require('./E');
+var e_1: number = E.numberValue;
+E.stringValue; // Error: The E exports obj has no 'stringValue' property
+
+// We require that the param passed to require() be a string literal to support
+// guaranteed static extraction
+var a = './E';
+require(a); // Error: Param must be string literal
+require(\`./E\`); // template literals are ok...
+require(\`\${'./E'}\`); // error: but only if they have no expressions
+
+// require.call is allowed but circumverts Flow's static analysis
+require.call(null, "DoesNotExist");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function takesANumber(num: number): void {
+  
+}
+function takesAString(str: string): void {
+  
+}
+// @providesModule
+var A = require("A");
+takesANumber(A.numberValue);
+takesAString(A.numberValue);
+// File path
+var B = require("./B");
+takesANumber(B.numberValue);
+takesAString(B.numberValue);
+// C.js exists, but not as a providesModule
+require("C");
+// @providesModule D exists, but not as a filename
+require("./D");
+// E exports an object with a numVal property
+var E = require("./E");
+var e_1: number = E.numberValue;
+E.stringValue;// Error: The E exports obj has no 'stringValue' property
+// We require that the param passed to require() be a string literal to support
+// guaranteed static extraction
+var a = "./E";
+require(a);// Error: Param must be string literal
+require(\`./E\`);// template literals are ok...
+require(\`\${"./E"}\`);// error: but only if they have no expressions
+// require.call is allowed but circumverts Flow's static analysis
+require.call(null, "DoesNotExist");
+
+"
+`;
diff --git a/tests/require/jsfmt.spec.js b/tests/require/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/require/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/require/not_builtin_require.js b/tests/require/not_builtin_require.js
new file mode 100644
index 000000000000..3671905918bb
--- /dev/null
+++ b/tests/require/not_builtin_require.js
@@ -0,0 +1,4 @@
+// @flow
+
+function require() {}
+require("not a module name");
diff --git a/tests/require/not_builtin_require2.js b/tests/require/not_builtin_require2.js
new file mode 100644
index 000000000000..682bd304ecb4
--- /dev/null
+++ b/tests/require/not_builtin_require2.js
@@ -0,0 +1,4 @@
+// @flow
+
+type require = number;
+var a: require = 42;
diff --git a/tests/require/require.js b/tests/require/require.js
new file mode 100644
index 000000000000..1628df536d39
--- /dev/null
+++ b/tests/require/require.js
@@ -0,0 +1,35 @@
+/* @flow */
+
+function takesANumber(num: number): void {}
+function takesAString(str: string): void {}
+
+// @providesModule
+var A = require("A");
+takesANumber(A.numberValue);
+takesAString(A.numberValue);
+
+// File path
+var B = require("./B");
+takesANumber(B.numberValue);
+takesAString(B.numberValue);
+
+// C.js exists, but not as a providesModule
+require("C");
+
+// @providesModule D exists, but not as a filename
+require("./D");
+
+// E exports an object with a numVal property
+var E = require('./E');
+var e_1: number = E.numberValue;
+E.stringValue; // Error: The E exports obj has no 'stringValue' property
+
+// We require that the param passed to require() be a string literal to support
+// guaranteed static extraction
+var a = './E';
+require(a); // Error: Param must be string literal
+require(`./E`); // template literals are ok...
+require(`${'./E'}`); // error: but only if they have no expressions
+
+// require.call is allowed but circumverts Flow's static analysis
+require.call(null, "DoesNotExist");
diff --git a/tests/requireLazy/A.js b/tests/requireLazy/A.js
new file mode 100644
index 000000000000..37d71689d456
--- /dev/null
+++ b/tests/requireLazy/A.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule A
+ * @flow
+ */
+
+module.exports = {
+  numberValueA: 1,
+  stringValueA: "someString"
+};
diff --git a/tests/requireLazy/B.js b/tests/requireLazy/B.js
new file mode 100644
index 000000000000..d125081a8a9b
--- /dev/null
+++ b/tests/requireLazy/B.js
@@ -0,0 +1,9 @@
+/**
+ * @providesModule B
+ * @flow
+ */
+
+module.exports = {
+  numberValueB: 1,
+  stringValueB: "someString"
+};
diff --git a/tests/requireLazy/__snapshots__/jsfmt.spec.js.snap b/tests/requireLazy/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..c3f58bdfdcc6
--- /dev/null
+++ b/tests/requireLazy/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,93 @@
+exports[`test A.js 1`] = `
+"/**
+ * @providesModule A
+ * @flow
+ */
+
+module.exports = {
+  numberValueA: 1,
+  stringValueA: "someString"
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule A
+ * @flow
+ */
+module.exports = { numberValueA: 1, stringValueA: "someString" };
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"/**
+ * @providesModule B
+ * @flow
+ */
+
+module.exports = {
+  numberValueB: 1,
+  stringValueB: "someString"
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule B
+ * @flow
+ */
+module.exports = { numberValueB: 1, stringValueB: "someString" };
+
+"
+`;
+
+exports[`test requireLazy.js 1`] = `
+"/**
+ * @flow
+ */
+
+requireLazy(['A', 'B'], function(A, B) {
+  var num1: number = A.numberValueA;
+  var str1: string = A.stringValueA;
+  var num2: number = A.stringValueA; // Error: string ~> number
+  var str2: string = A.numberValueA; // Error: number ~> string
+
+  var num3: number = B.numberValueB;
+  var str3: string = B.stringValueB;
+  var num4: number = B.stringValueB; // Error: string ~> number
+  var str4: string = B.numberValueB; // Error: number ~> string
+});
+
+var notA: Object = A;
+var notB: Object = B;
+
+requireLazy(); // Error: No args
+requireLazy([nope], function() {}); // Error: Non-stringliteral args
+requireLazy(['A']); // Error: No calback expression
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+requireLazy(
+  [ "A", "B" ],
+  function(A, B) {
+    var num1: number = A.numberValueA;
+    var str1: string = A.stringValueA;
+    var num2: number = A.stringValueA;// Error: string ~> number
+    var str2: string = A.numberValueA;// Error: number ~> string
+    var num3: number = B.numberValueB;
+    var str3: string = B.stringValueB;
+    var num4: number = B.stringValueB;// Error: string ~> number
+    var str4: string = B.numberValueB;// Error: number ~> string
+  }
+);
+var notA: Object = A;
+var notB: Object = B;
+requireLazy();// Error: No args
+requireLazy(
+  [ nope ],
+  function() {
+    
+  }
+);// Error: Non-stringliteral args
+requireLazy([ "A" ]);// Error: No calback expression
+
+"
+`;
diff --git a/tests/requireLazy/jsfmt.spec.js b/tests/requireLazy/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/requireLazy/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/requireLazy/requireLazy.js b/tests/requireLazy/requireLazy.js
new file mode 100644
index 000000000000..4bc44c3a87df
--- /dev/null
+++ b/tests/requireLazy/requireLazy.js
@@ -0,0 +1,22 @@
+/**
+ * @flow
+ */
+
+requireLazy(['A', 'B'], function(A, B) {
+  var num1: number = A.numberValueA;
+  var str1: string = A.stringValueA;
+  var num2: number = A.stringValueA; // Error: string ~> number
+  var str2: string = A.numberValueA; // Error: number ~> string
+
+  var num3: number = B.numberValueB;
+  var str3: string = B.stringValueB;
+  var num4: number = B.stringValueB; // Error: string ~> number
+  var str4: string = B.numberValueB; // Error: number ~> string
+});
+
+var notA: Object = A;
+var notB: Object = B;
+
+requireLazy(); // Error: No args
+requireLazy([nope], function() {}); // Error: Non-stringliteral args
+requireLazy(['A']); // Error: No calback expression
diff --git a/tests/return/__snapshots__/jsfmt.spec.js.snap b/tests/return/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a71e2ce54cd6
--- /dev/null
+++ b/tests/return/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,104 @@
+exports[`test function_return.js 1`] = `
+"class C {
+    foo() { }
+    bar() { return; }
+    fn(x:number) { return x; }
+}
+
+function f(x): number {
+  if (x > 1) {
+    return 42;
+  }
+}
+
+function g(x): ?number {
+  if (x > 1) {
+    return 42;
+  }
+}
+
+function h(x): number {
+  if (x > 1) {
+    return 42;
+  }
+  return;
+}
+
+function i(x): ?number {
+  if (x > 1) {
+    return 42;
+  }
+  return;
+}
+
+module.exports = C;
+
+//function fn(x:number) { return x; }
+//module.exports = fn;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  foo() {
+    
+  }
+  bar() {
+    return;
+  }
+  fn(x: number) {
+    return x;
+  }
+}
+function f(x): number {
+  if (x > 1) {
+    return 42;
+  }
+}
+function g(x): ?number {
+  if (x > 1) {
+    return 42;
+  }
+}
+function h(x): number {
+  if (x > 1) {
+    return 42;
+  }
+  return;
+}
+function i(x): ?number {
+  if (x > 1) {
+    return 42;
+  }
+  return;
+}
+module.exports = C;//function fn(x:number) { return x; }//module.exports = fn;
+
+"
+`;
+
+exports[`test void.js 1`] = `
+"/* This is a regression test. At one point we incorrectly inferred the return
+   type of functions that have an explicit \`undefined\` to be only \`undefined\` --
+   ignoring other possible exits. */
+function f(b) {
+  if (b) {
+    return undefined;
+  } else {
+    return "nope";
+  }
+}
+
+(f(true): void); // error: string ~> void
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* This is a regression test. At one point we incorrectly inferred the return
+   type of functions that have an explicit \`undefined\` to be only \`undefined\` --
+   ignoring other possible exits. */
+function f(b) {
+  if (b) {
+    return undefined;
+  } else {
+    return "nope";
+  }
+}
+(f(true): void);// error: string ~> void
+
+"
+`;
diff --git a/tests/return/function_return.js b/tests/return/function_return.js
new file mode 100644
index 000000000000..3667ad5d982e
--- /dev/null
+++ b/tests/return/function_return.js
@@ -0,0 +1,36 @@
+class C {
+    foo() { }
+    bar() { return; }
+    fn(x:number) { return x; }
+}
+
+function f(x): number {
+  if (x > 1) {
+    return 42;
+  }
+}
+
+function g(x): ?number {
+  if (x > 1) {
+    return 42;
+  }
+}
+
+function h(x): number {
+  if (x > 1) {
+    return 42;
+  }
+  return;
+}
+
+function i(x): ?number {
+  if (x > 1) {
+    return 42;
+  }
+  return;
+}
+
+module.exports = C;
+
+//function fn(x:number) { return x; }
+//module.exports = fn;
diff --git a/tests/return/jsfmt.spec.js b/tests/return/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/return/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/return/void.js b/tests/return/void.js
new file mode 100644
index 000000000000..6bfe74a3f6ce
--- /dev/null
+++ b/tests/return/void.js
@@ -0,0 +1,12 @@
+/* This is a regression test. At one point we incorrectly inferred the return
+   type of functions that have an explicit `undefined` to be only `undefined` --
+   ignoring other possible exits. */
+function f(b) {
+  if (b) {
+    return undefined;
+  } else {
+    return "nope";
+  }
+}
+
+(f(true): void); // error: string ~> void
diff --git a/tests/return_new/__snapshots__/jsfmt.spec.js.snap b/tests/return_new/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f4fda93a6822
--- /dev/null
+++ b/tests/return_new/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,65 @@
+exports[`test test.js 1`] = `
+"function Foo() { return {}; }
+var foo: number = new Foo(); // error (returns object literal above)
+
+function Bar() { return 0; }
+var bar: number = new Bar(); // error (returns new object)
+
+function Qux() { }
+var qux: number = new Qux(); // error (returns new object)
+
+class A { }
+function B() { return new A(); }
+var a: A = new B(); // OK (returns new A)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function Foo() {
+  return {};
+}
+var foo: number = new Foo();// error (returns object literal above)
+function Bar() {
+  return 0;
+}
+var bar: number = new Bar();// error (returns new object)
+function Qux() {
+  
+}
+var qux: number = new Qux();// error (returns new object)
+class A {}
+function B() {
+  return new A();
+}
+var a: A = new B();// OK (returns new A)
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"declare class D {
+  constructor(): { x: number }; // OK
+  y: any;
+}
+
+var d = new D();
+d.x = \"\"; // error, string ~/~ number (but property x is found)
+
+(new D: D); // error, new D is an object, D not in proto chain
+
+module.exports = D;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/return_new/jsfmt.spec.js b/tests/return_new/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/return_new/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/return_new/test.js b/tests/return_new/test.js
new file mode 100644
index 000000000000..ba0f36f87353
--- /dev/null
+++ b/tests/return_new/test.js
@@ -0,0 +1,12 @@
+function Foo() { return {}; }
+var foo: number = new Foo(); // error (returns object literal above)
+
+function Bar() { return 0; }
+var bar: number = new Bar(); // error (returns new object)
+
+function Qux() { }
+var qux: number = new Qux(); // error (returns new object)
+
+class A { }
+function B() { return new A(); }
+var a: A = new B(); // OK (returns new A)
diff --git a/tests/return_new/test2.js b/tests/return_new/test2.js
new file mode 100644
index 000000000000..8e961a2addd5
--- /dev/null
+++ b/tests/return_new/test2.js
@@ -0,0 +1,11 @@
+declare class D {
+  constructor(): { x: number }; // OK
+  y: any;
+}
+
+var d = new D();
+d.x = ""; // error, string ~/~ number (but property x is found)
+
+(new D: D); // error, new D is an object, D not in proto chain
+
+module.exports = D;
diff --git a/tests/seal/__snapshots__/jsfmt.spec.js.snap b/tests/seal/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8a555f736668
--- /dev/null
+++ b/tests/seal/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,33 @@
+exports[`test imp.js 1`] = `
+"/* @flow */
+
+var imp = require('./obj_annot');
+imp({ name: "imp" });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var imp = require("./obj_annot");
+imp({ name: "imp" });
+
+"
+`;
+
+exports[`test obj_annot.js 1`] = `
+"/* @flow */
+
+function foo(param: { name: string; }): number {
+    return param.id;
+}
+
+foo({ name: "test" });
+
+module.exports = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo(param: { name: string }): number {
+  return param.id;
+}
+foo({ name: "test" });
+module.exports = foo;
+
+"
+`;
diff --git a/tests/seal/imp.js b/tests/seal/imp.js
new file mode 100644
index 000000000000..caae6a1bc613
--- /dev/null
+++ b/tests/seal/imp.js
@@ -0,0 +1,4 @@
+/* @flow */
+
+var imp = require('./obj_annot');
+imp({ name: "imp" });
diff --git a/tests/seal/jsfmt.spec.js b/tests/seal/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/seal/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/seal/obj_annot.js b/tests/seal/obj_annot.js
new file mode 100644
index 000000000000..7df3e9ee6615
--- /dev/null
+++ b/tests/seal/obj_annot.js
@@ -0,0 +1,9 @@
+/* @flow */
+
+function foo(param: { name: string; }): number {
+    return param.id;
+}
+
+foo({ name: "test" });
+
+module.exports = foo;
diff --git a/tests/sealed/__snapshots__/jsfmt.spec.js.snap b/tests/sealed/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9583e539e32b
--- /dev/null
+++ b/tests/sealed/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,88 @@
+exports[`test function.js 1`] = `
+"/* @flow */
+
+function Bar(x: number) {
+  this.x = x;
+}
+Bar.prototype.getX = function() { return this.x; }
+Bar.prototype.getY = function(): string { return this.y; }
+
+module.exports = Bar;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function Bar(x: number) {
+  this.x = x;
+}
+Bar.prototype.getX = function() {
+  return this.x;
+};
+Bar.prototype.getY = function(): string {
+  return this.y;
+};
+module.exports = Bar;
+
+"
+`;
+
+exports[`test proto.js 1`] = `
+"function Foo() { }
+var o = new Foo();
+var x:number = o.x;
+
+Foo.prototype.m = function() { return this.x; }
+
+var y:number = o.m();
+o.x = "...";
+
+Foo.prototype = { m: function() { return false; } }
+
+var export_o: { x:any; } = o; // awkward type cast
+
+module.exports = export_o;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function Foo() {
+  
+}
+var o = new Foo();
+var x: number = o.x;
+Foo.prototype.m = function() {
+  return this.x;
+};
+var y: number = o.m();
+o.x = "...";
+Foo.prototype = {
+  m: function() {
+    return false;
+  }
+};
+var export_o: { x: any } = o;// awkward type cast
+module.exports = export_o;
+
+"
+`;
+
+exports[`test sealed.js 1`] = `
+"var o = require('./proto');
+
+o.z = 0;
+var x:string = o.x;
+
+var Bar = require('./function');
+var a = new Bar(234);
+a.x = 123;
+a.y = 'abc'; // error, needs to be declared in Bar's constructor
+(a.getX(): number);
+(a.getY(): string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = require("./proto");
+o.z = 0;
+var x: string = o.x;
+var Bar = require("./function");
+var a = new Bar(234);
+a.x = 123;
+a.y = "abc";// error, needs to be declared in Bar's constructor
+(a.getX(): number);
+(a.getY(): string);
+
+"
+`;
diff --git a/tests/sealed/function.js b/tests/sealed/function.js
new file mode 100644
index 000000000000..ebfacc5c5e0c
--- /dev/null
+++ b/tests/sealed/function.js
@@ -0,0 +1,9 @@
+/* @flow */
+
+function Bar(x: number) {
+  this.x = x;
+}
+Bar.prototype.getX = function() { return this.x; }
+Bar.prototype.getY = function(): string { return this.y; }
+
+module.exports = Bar;
diff --git a/tests/sealed/jsfmt.spec.js b/tests/sealed/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/sealed/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/sealed/proto.js b/tests/sealed/proto.js
new file mode 100644
index 000000000000..c14fa9e28891
--- /dev/null
+++ b/tests/sealed/proto.js
@@ -0,0 +1,14 @@
+function Foo() { }
+var o = new Foo();
+var x:number = o.x;
+
+Foo.prototype.m = function() { return this.x; }
+
+var y:number = o.m();
+o.x = "...";
+
+Foo.prototype = { m: function() { return false; } }
+
+var export_o: { x:any; } = o; // awkward type cast
+
+module.exports = export_o;
diff --git a/tests/sealed/sealed.js b/tests/sealed/sealed.js
new file mode 100644
index 000000000000..82c955333c94
--- /dev/null
+++ b/tests/sealed/sealed.js
@@ -0,0 +1,11 @@
+var o = require('./proto');
+
+o.z = 0;
+var x:string = o.x;
+
+var Bar = require('./function');
+var a = new Bar(234);
+a.x = 123;
+a.y = 'abc'; // error, needs to be declared in Bar's constructor
+(a.getX(): number);
+(a.getY(): string);
diff --git a/tests/sealed_objects/__snapshots__/jsfmt.spec.js.snap b/tests/sealed_objects/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..bba2a19de525
--- /dev/null
+++ b/tests/sealed_objects/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,40 @@
+exports[`test test.js 1`] = `
+"var o1 = { x: 0 };
+var s1: string = o1.y; // error
+
+var o2: { x: number; y?: string; } = { x: 0 };
+var s2: string = o2.y || ""; // ok
+
+var o3: { x: number; y?: string; } = ({ x: 0, y: 0 }: { x: number; });
+var s3: string = o3.y || ""; // error
+
+var o4: { x: number; y?: string; } = ({ x: 0 }: { x: number; [_:any]:any});
+var s4: string = o4.y || ""; // ok
+
+var o5 = { x: 0, ...{} };
+var s5: string = o5.y; // ok (spreads make object types extensible)
+
+var o6: { x: number; [_:any]:any } = { x: 0 };
+var s6: string = o6.y; // ok  (indexers make object types extensible)
+
+var o7: { x: number; y?: string; } = ({ x: 0, y: 0 }: { x: number; [_:any]:number}); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o1 = { x: 0 };
+var s1: string = o1.y;// error
+var o2: { x: number, y?: string } = { x: 0 };
+var s2: string = o2.y || "";// ok
+var o3: { x: number, y?: string } = ({ x: 0, y: 0 }: { x: number });
+var s3: string = o3.y || "";// error
+var o4: { x: number, y?: string } = ({ x: 0 }: { [_: any]: any, x: number });
+var s4: string = o4.y || "";// ok
+var o5 = { x: 0, ...{} };
+var s5: string = o5.y;// ok (spreads make object types extensible)
+var o6: { [_: any]: any, x: number } = { x: 0 };
+var s6: string = o6.y;// ok  (indexers make object types extensible)
+var o7: { x: number, y?: string } = ({ x: 0, y: 0 }: {
+  [_: any]: number,
+  x: number
+});// error
+
+"
+`;
diff --git a/tests/sealed_objects/jsfmt.spec.js b/tests/sealed_objects/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/sealed_objects/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/sealed_objects/test.js b/tests/sealed_objects/test.js
new file mode 100644
index 000000000000..746ef5d81951
--- /dev/null
+++ b/tests/sealed_objects/test.js
@@ -0,0 +1,19 @@
+var o1 = { x: 0 };
+var s1: string = o1.y; // error
+
+var o2: { x: number; y?: string; } = { x: 0 };
+var s2: string = o2.y || ""; // ok
+
+var o3: { x: number; y?: string; } = ({ x: 0, y: 0 }: { x: number; });
+var s3: string = o3.y || ""; // error
+
+var o4: { x: number; y?: string; } = ({ x: 0 }: { x: number; [_:any]:any});
+var s4: string = o4.y || ""; // ok
+
+var o5 = { x: 0, ...{} };
+var s5: string = o5.y; // ok (spreads make object types extensible)
+
+var o6: { x: number; [_:any]:any } = { x: 0 };
+var s6: string = o6.y; // ok  (indexers make object types extensible)
+
+var o7: { x: number; y?: string; } = ({ x: 0, y: 0 }: { x: number; [_:any]:number}); // error
diff --git a/tests/shape/__snapshots__/jsfmt.spec.js.snap b/tests/shape/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6797d7f4a419
--- /dev/null
+++ b/tests/shape/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,26 @@
+exports[`test test.js 1`] = `
+"type Foo = {
+  field: number,
+}
+
+var x: {field?: number} = {};
+var y: $Shape<Foo> = x;
+(y.field: number)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/shape/jsfmt.spec.js b/tests/shape/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/shape/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/shape/test.js b/tests/shape/test.js
new file mode 100644
index 000000000000..c71770f50278
--- /dev/null
+++ b/tests/shape/test.js
@@ -0,0 +1,7 @@
+type Foo = {
+  field: number,
+}
+
+var x: {field?: number} = {};
+var y: $Shape<Foo> = x;
+(y.field: number)
diff --git a/tests/simple_arrays/__snapshots__/jsfmt.spec.js.snap b/tests/simple_arrays/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..53a54ba638f7
--- /dev/null
+++ b/tests/simple_arrays/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,77 @@
+exports[`test array.js 1`] = `
+"/* @flow */
+var a = [];
+for (var i = 0; i < 10; ++i) {
+    if (i % 2 == 0) { a[i] = 0; }
+    else { a[i] = ''; };
+}
+
+// \`i\` never gets a lower bound, so the array access is stalled until the
+// function is called.
+function foo(i): string { return a[i]; }
+
+// here, because we call \`bar\`, we the array access constraint is discharged and
+// we realize a type error.
+function bar(i): string { return a[i]; }
+bar(0);
+
+// annotations suffice to unblock the access constraint as well, so only
+// uncalled internal functions will not find a type error, which is acceptable
+// behavior as such functions are dead code.
+function baz(i:number): string { return a[i]; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var a = [  ];
+for (var i = 0; i < 10; ++i) {
+  if (i % 2 == 0) {
+    a[i] = 0;
+  } else {
+    a[i] = "";
+  }
+}
+// \`i\` never gets a lower bound, so the array access is stalled until the
+// function is called.
+function foo(i): string {
+  return a[i];
+}
+// here, because we call \`bar\`, we the array access constraint is discharged and
+// we realize a type error.
+function bar(i): string {
+  return a[i];
+}
+bar(0);
+// annotations suffice to unblock the access constraint as well, so only
+// uncalled internal functions will not find a type error, which is acceptable
+// behavior as such functions are dead code.
+function baz(i: number): string {
+  return a[i];
+}
+
+"
+`;
+
+exports[`test array2.js 1`] = `
+"/* @flow */
+var a = [];
+for (var i = 0; i < 10; ++i) {
+    if (i % 2 == 0) { a[i] = 0; }
+    else { a[i] = ''; };
+}
+
+function foo(i: number): string { return a[i]; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var a = [  ];
+for (var i = 0; i < 10; ++i) {
+  if (i % 2 == 0) {
+    a[i] = 0;
+  } else {
+    a[i] = "";
+  }
+}
+function foo(i: number): string {
+  return a[i];
+}
+
+"
+`;
diff --git a/tests/simple_arrays/array.js b/tests/simple_arrays/array.js
new file mode 100644
index 000000000000..c44a1442b19c
--- /dev/null
+++ b/tests/simple_arrays/array.js
@@ -0,0 +1,20 @@
+/* @flow */
+var a = [];
+for (var i = 0; i < 10; ++i) {
+    if (i % 2 == 0) { a[i] = 0; }
+    else { a[i] = ''; };
+}
+
+// `i` never gets a lower bound, so the array access is stalled until the
+// function is called.
+function foo(i): string { return a[i]; }
+
+// here, because we call `bar`, we the array access constraint is discharged and
+// we realize a type error.
+function bar(i): string { return a[i]; }
+bar(0);
+
+// annotations suffice to unblock the access constraint as well, so only
+// uncalled internal functions will not find a type error, which is acceptable
+// behavior as such functions are dead code.
+function baz(i:number): string { return a[i]; }
diff --git a/tests/simple_arrays/array2.js b/tests/simple_arrays/array2.js
new file mode 100644
index 000000000000..b42ec500eac3
--- /dev/null
+++ b/tests/simple_arrays/array2.js
@@ -0,0 +1,8 @@
+/* @flow */
+var a = [];
+for (var i = 0; i < 10; ++i) {
+    if (i % 2 == 0) { a[i] = 0; }
+    else { a[i] = ''; };
+}
+
+function foo(i: number): string { return a[i]; }
diff --git a/tests/simple_arrays/jsfmt.spec.js b/tests/simple_arrays/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/simple_arrays/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/singleton/__snapshots__/jsfmt.spec.js.snap b/tests/singleton/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..882d3227ca6f
--- /dev/null
+++ b/tests/singleton/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,117 @@
+exports[`test boolean.js 1`] = `
+"/* @flow */
+
+function veryOptimistic(isThisAwesome: true): boolean {
+  return isThisAwesome;
+}
+
+var x : boolean = veryOptimistic(true);
+var y : boolean = veryOptimistic(false); // error
+
+function veryPessimistic(isThisAwesome: true): boolean {
+  return !isThisAwesome; // test bool conversion
+}
+
+var x : boolean = veryPessimistic(true);
+var y : boolean = veryPessimistic(false); // error
+
+type MyOwnBooleanLOL = true | false
+
+function bar(x: MyOwnBooleanLOL): false {
+  if (x) {
+    return x;
+  } else {
+    return !x;
+  }
+}
+
+bar(true);
+bar(false);
+bar(1); // error
+
+function alwaysFalsy(x: boolean): false {
+  if (x) {
+    return !x;
+  } else {
+    return x;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test number.js 1`] = `
+"/* @flow */
+
+function highlander(howMany: 1): number {
+  return howMany; // there can be only one!
+}
+
+highlander(1);
+highlander(2); // error
+
+
+type Foo = 1 | 2
+
+function bar(num: Foo): number {
+  return num + 1;
+}
+
+bar(1);
+bar(2);
+bar(3); // error
+
+type ComparatorResult = -1 | 0 | 1
+function sort(fn: (x: any, y: any) => ComparatorResult) {}
+sort((x, y) => -1);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 42, end: 43, loc: [object Object], value: 1, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
+
+exports[`test string.js 1`] = `
+"/* @flow */
+
+type NoSpaces = \"foobar\"
+(\"foobar\": NoSpaces);
+
+type HasSpaces = \"foo bar\"
+(\"foo bar\": HasSpaces);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+type NoSpaces = \"foobar\";
+(\"foobar\": NoSpaces);
+type HasSpaces = \"foo bar\";
+(\"foo bar\": HasSpaces);
+
+"
+`;
diff --git a/tests/singleton/boolean.js b/tests/singleton/boolean.js
new file mode 100644
index 000000000000..dede9679e160
--- /dev/null
+++ b/tests/singleton/boolean.js
@@ -0,0 +1,37 @@
+/* @flow */
+
+function veryOptimistic(isThisAwesome: true): boolean {
+  return isThisAwesome;
+}
+
+var x : boolean = veryOptimistic(true);
+var y : boolean = veryOptimistic(false); // error
+
+function veryPessimistic(isThisAwesome: true): boolean {
+  return !isThisAwesome; // test bool conversion
+}
+
+var x : boolean = veryPessimistic(true);
+var y : boolean = veryPessimistic(false); // error
+
+type MyOwnBooleanLOL = true | false
+
+function bar(x: MyOwnBooleanLOL): false {
+  if (x) {
+    return x;
+  } else {
+    return !x;
+  }
+}
+
+bar(true);
+bar(false);
+bar(1); // error
+
+function alwaysFalsy(x: boolean): false {
+  if (x) {
+    return !x;
+  } else {
+    return x;
+  }
+}
diff --git a/tests/singleton/jsfmt.spec.js b/tests/singleton/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/singleton/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/singleton/number.js b/tests/singleton/number.js
new file mode 100644
index 000000000000..160e9223d340
--- /dev/null
+++ b/tests/singleton/number.js
@@ -0,0 +1,23 @@
+/* @flow */
+
+function highlander(howMany: 1): number {
+  return howMany; // there can be only one!
+}
+
+highlander(1);
+highlander(2); // error
+
+
+type Foo = 1 | 2
+
+function bar(num: Foo): number {
+  return num + 1;
+}
+
+bar(1);
+bar(2);
+bar(3); // error
+
+type ComparatorResult = -1 | 0 | 1
+function sort(fn: (x: any, y: any) => ComparatorResult) {}
+sort((x, y) => -1);
diff --git a/tests/singleton/string.js b/tests/singleton/string.js
new file mode 100644
index 000000000000..aac4a5c70372
--- /dev/null
+++ b/tests/singleton/string.js
@@ -0,0 +1,7 @@
+/* @flow */
+
+type NoSpaces = "foobar"
+("foobar": NoSpaces);
+
+type HasSpaces = "foo bar"
+("foo bar": HasSpaces);
diff --git a/tests/spread/__snapshots__/jsfmt.spec.js.snap b/tests/spread/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6267c1718017
--- /dev/null
+++ b/tests/spread/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,225 @@
+exports[`test test.js 1`] = `
+"function parseTimestamp(timestamp: string): number {
+    return 0;
+}
+
+function parseCounter(line: string): number {
+    return 0;
+}
+
+function parseGroup(lines: Array<string>): {
+    counter: number;
+    begin: number;
+    end: number;
+    text: string;
+} {
+    var counter = parseCounter(lines[0]);
+    var timeframe = parseTimeframe(lines[1]);
+    return {
+        counter,
+        ...timeframe,
+        text: lines[2]
+    };
+}
+
+function parseTimeframe(line: string): { begin: number; end: number } {
+    var timestamps = line.split(\'-->\');
+    return {
+        begin: parseTimestamp(timestamps[0].trim()),
+        end: parseTimestamp(timestamps[1].trim())
+    };
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"/**
+ * @flow
+ */
+
+function foo(o) {
+    bar({...o});
+}
+function bar(_: {foo:number}) { }
+foo({foo: 42});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+function foo(o) {
+  bar({ ...o });
+}
+function bar(_: { foo: number }) {
+  
+}
+foo({ foo: 42 });
+
+"
+`;
+
+exports[`test test3.js 1`] = `
+"var p = { y: \"\" };
+var q = { z: \"\" };
+var o = {
+  x: 5,
+  ...p,
+  ...q,
+};
+var y: number = o.y;
+var z: number = o.z;
+
+// test conflicting keys (they get unioned)
+var r = { y: 123 };
+var s = {
+  ...p,
+  ...r,
+};
+var t: boolean = s.y; // error, string or number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var p = { y: \"\" };
+var q = { z: \"\" };
+var o = { x: 5, ...p, ...q };
+var y: number = o.y;
+var z: number = o.z;
+// test conflicting keys (they get unioned)
+var r = { y: 123 };
+var s = { ...p, ...r };
+var t: boolean = s.y;// error, string or number
+
+"
+`;
+
+exports[`test test4.js 1`] = `
+"/* @flow */
+function test(...nums: Array<number>) {}
+
+test(0, ...[1, 2, 3]);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function test(...nums) {
+  
+}
+test(0, ...[ 1, 2, 3 ]);
+
+"
+`;
+
+exports[`test test5.js 1`] = `
+"/* @flow */
+
+declare function map<Tv, TNext>(
+  obj: {[key: string]: Tv},
+  iterator:((obj: Tv) => TNext),
+): Array<TNext>;
+
+/**
+ * Tests overriding a property via a spread, where the value is a tvar. the
+ * type of the prop from the object that is being overridden (\`x.kind\` in the
+ * case below) should //not// feed back into the tvar (\`value\`), since the
+ * result is a new object.
+ */
+function test(
+  x: {kind: ?string},
+  kinds: {[key: string]: string}
+): Array<{kind: ?string}> {
+  return map(kinds, (value) => {
+    (value: string); // OK
+    return {
+      ...x,
+      kind: value,
+    };
+  });
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1368:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test6.js 1`] = `
+"var o = {
+  foo: \'bar\'
+};
+o = {...o};
+(o: {foo: string});
+
+var p = {
+  foo: \'bar\'
+};
+(p: {foo: string; abc: string}); // error, p doesn\'t have \`abc\` yet
+p = {...p, abc: \'def\'};
+(p: {foo: string; abc: string});
+
+var q = {
+  foo: \'bar\'
+};
+for (var i = 0; i < 10; i++) {
+  q = {...q};
+}
+(q: {foo: string});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = { foo: \"bar\" };
+o = { ...o };
+(o: { foo: string });
+var p = { foo: \"bar\" };
+(p: { foo: string, abc: string });// error, p doesn\'t have \`abc\` yet
+p = { ...p, abc: \"def\" };
+(p: { foo: string, abc: string });
+var q = { foo: \"bar\" };
+for (var i = 0; i < 10; i++) {
+  q = { ...q };
+}
+(q: { foo: string });
+
+"
+`;
+
+exports[`test test7.js 1`] = `
+"// @flow
+
+let tests = [
+  function(x: Object) {
+    ({...x}: Object);
+    ({...x}: void); // error, Object
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  function(x: Object) {
+    ({ ...x }: Object);
+    ({ ...x }: void);// error, Object
+  }
+];
+
+"
+`;
diff --git a/tests/spread/jsfmt.spec.js b/tests/spread/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/spread/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/spread/test.js b/tests/spread/test.js
new file mode 100644
index 000000000000..19c223947226
--- /dev/null
+++ b/tests/spread/test.js
@@ -0,0 +1,30 @@
+function parseTimestamp(timestamp: string): number {
+    return 0;
+}
+
+function parseCounter(line: string): number {
+    return 0;
+}
+
+function parseGroup(lines: Array<string>): {
+    counter: number;
+    begin: number;
+    end: number;
+    text: string;
+} {
+    var counter = parseCounter(lines[0]);
+    var timeframe = parseTimeframe(lines[1]);
+    return {
+        counter,
+        ...timeframe,
+        text: lines[2]
+    };
+}
+
+function parseTimeframe(line: string): { begin: number; end: number } {
+    var timestamps = line.split('-->');
+    return {
+        begin: parseTimestamp(timestamps[0].trim()),
+        end: parseTimestamp(timestamps[1].trim())
+    };
+}
diff --git a/tests/spread/test2.js b/tests/spread/test2.js
new file mode 100644
index 000000000000..d2efac4f66b4
--- /dev/null
+++ b/tests/spread/test2.js
@@ -0,0 +1,9 @@
+/**
+ * @flow
+ */
+
+function foo(o) {
+    bar({...o});
+}
+function bar(_: {foo:number}) { }
+foo({foo: 42});
diff --git a/tests/spread/test3.js b/tests/spread/test3.js
new file mode 100644
index 000000000000..85c1194be5b1
--- /dev/null
+++ b/tests/spread/test3.js
@@ -0,0 +1,17 @@
+var p = { y: "" };
+var q = { z: "" };
+var o = {
+  x: 5,
+  ...p,
+  ...q,
+};
+var y: number = o.y;
+var z: number = o.z;
+
+// test conflicting keys (they get unioned)
+var r = { y: 123 };
+var s = {
+  ...p,
+  ...r,
+};
+var t: boolean = s.y; // error, string or number
diff --git a/tests/spread/test4.js b/tests/spread/test4.js
new file mode 100644
index 000000000000..6b58cbdc7dac
--- /dev/null
+++ b/tests/spread/test4.js
@@ -0,0 +1,4 @@
+/* @flow */
+function test(...nums: Array<number>) {}
+
+test(0, ...[1, 2, 3]);
diff --git a/tests/spread/test5.js b/tests/spread/test5.js
new file mode 100644
index 000000000000..500a78f203c0
--- /dev/null
+++ b/tests/spread/test5.js
@@ -0,0 +1,25 @@
+/* @flow */
+
+declare function map<Tv, TNext>(
+  obj: {[key: string]: Tv},
+  iterator:((obj: Tv) => TNext),
+): Array<TNext>;
+
+/**
+ * Tests overriding a property via a spread, where the value is a tvar. the
+ * type of the prop from the object that is being overridden (`x.kind` in the
+ * case below) should //not// feed back into the tvar (`value`), since the
+ * result is a new object.
+ */
+function test(
+  x: {kind: ?string},
+  kinds: {[key: string]: string}
+): Array<{kind: ?string}> {
+  return map(kinds, (value) => {
+    (value: string); // OK
+    return {
+      ...x,
+      kind: value,
+    };
+  });
+}
diff --git a/tests/spread/test6.js b/tests/spread/test6.js
new file mode 100644
index 000000000000..54613a74d78c
--- /dev/null
+++ b/tests/spread/test6.js
@@ -0,0 +1,20 @@
+var o = {
+  foo: 'bar'
+};
+o = {...o};
+(o: {foo: string});
+
+var p = {
+  foo: 'bar'
+};
+(p: {foo: string; abc: string}); // error, p doesn't have `abc` yet
+p = {...p, abc: 'def'};
+(p: {foo: string; abc: string});
+
+var q = {
+  foo: 'bar'
+};
+for (var i = 0; i < 10; i++) {
+  q = {...q};
+}
+(q: {foo: string});
diff --git a/tests/spread/test7.js b/tests/spread/test7.js
new file mode 100644
index 000000000000..a0c090fc7874
--- /dev/null
+++ b/tests/spread/test7.js
@@ -0,0 +1,8 @@
+// @flow
+
+let tests = [
+  function(x: Object) {
+    ({...x}: Object);
+    ({...x}: void); // error, Object
+  },
+];
diff --git a/tests/static_overload/__snapshots__/jsfmt.spec.js.snap b/tests/static_overload/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5f11981fdd11
--- /dev/null
+++ b/tests/static_overload/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,7 @@
+exports[`test test.js 1`] = `
+"var x: number = StaticOverload.foo(0);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var x: number = StaticOverload.foo(0);
+
+"
+`;
diff --git a/tests/static_overload/jsfmt.spec.js b/tests/static_overload/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/static_overload/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/static_overload/lib/__snapshots__/jsfmt.spec.js.snap b/tests/static_overload/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3e5e45e624ec
--- /dev/null
+++ b/tests/static_overload/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,23 @@
+exports[`test lib.js 1`] = `
+"declare class StaticOverload {
+  static foo(x: number): number;
+  static foo(x: string): string;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/static_overload/lib/jsfmt.spec.js b/tests/static_overload/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/static_overload/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/static_overload/lib/lib.js b/tests/static_overload/lib/lib.js
new file mode 100644
index 000000000000..61179705b9d2
--- /dev/null
+++ b/tests/static_overload/lib/lib.js
@@ -0,0 +1,4 @@
+declare class StaticOverload {
+  static foo(x: number): number;
+  static foo(x: string): string;
+}
diff --git a/tests/static_overload/test.js b/tests/static_overload/test.js
new file mode 100644
index 000000000000..f72428ff8ccd
--- /dev/null
+++ b/tests/static_overload/test.js
@@ -0,0 +1 @@
+var x: number = StaticOverload.foo(0);
diff --git a/tests/statics/__snapshots__/jsfmt.spec.js.snap b/tests/statics/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..342379db62a2
--- /dev/null
+++ b/tests/statics/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,47 @@
+exports[`test class_statics.js 1`] = `
+"class C {
+  static f(x:number) { }
+  static x:string;
+}
+
+C.g = function(x:string) { C.f(x); };
+C.g(0);
+
+var x:number = C.x;
+C.x = 0;~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  f(x: number) {
+    
+  }
+  static x: string;
+}
+C.g = function(x: string) {
+  C.f(x);
+};
+C.g(0);
+var x: number = C.x;
+C.x = 0;
+
+"
+`;
+
+exports[`test funstatics.js 1`] = `
+"function C() { }
+C.prototype.f = function() { return C.g(0); }
+C.g = function(x) { return x; };
+
+var x:string = new C().f();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function C() {
+  
+}
+C.prototype.f = function() {
+  return C.g(0);
+};
+C.g = function(x) {
+  return x;
+};
+var x: string = new C().f();
+
+"
+`;
diff --git a/tests/statics/class_statics.js b/tests/statics/class_statics.js
new file mode 100644
index 000000000000..fc9a02a2b7b1
--- /dev/null
+++ b/tests/statics/class_statics.js
@@ -0,0 +1,10 @@
+class C {
+  static f(x:number) { }
+  static x:string;
+}
+
+C.g = function(x:string) { C.f(x); };
+C.g(0);
+
+var x:number = C.x;
+C.x = 0;
\ No newline at end of file
diff --git a/tests/statics/funstatics.js b/tests/statics/funstatics.js
new file mode 100644
index 000000000000..0e50eca1213c
--- /dev/null
+++ b/tests/statics/funstatics.js
@@ -0,0 +1,5 @@
+function C() { }
+C.prototype.f = function() { return C.g(0); }
+C.g = function(x) { return x; };
+
+var x:string = new C().f();
diff --git a/tests/statics/jsfmt.spec.js b/tests/statics/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/statics/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/strict/__snapshots__/jsfmt.spec.js.snap b/tests/strict/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..82c4b9ed76a8
--- /dev/null
+++ b/tests/strict/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,83 @@
+exports[`test annot.js 1`] = `
+"var A = require('./unknown_class');
+
+class B extends A {
+  foo(x:A):A { return x; }
+  bar(x) { }
+  qux<X,Y>(x:X,y:Y):X { return x;}
+}
+
+module.exports = B;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var A = require("./unknown_class");
+class B extends A {
+  foo(x: A): A {
+    return x;
+  }
+  bar(x) {
+    
+  }
+  qux(x: X, y: Y): X {
+    return x;
+  }
+}
+module.exports = B;
+
+"
+`;
+
+exports[`test fun.js 1`] = `
+"/**
+ * @flow
+ */
+
+// progressively annotate:
+
+//function f(x) { return x; }
+function f(x:number) { return x; }
+//function f(x:number):string { return x; }
+
+var x:string = f(0);
+
+module.exports = f;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+// progressively annotate:
+//function f(x) { return x; }
+function f(x: number) {
+  return x;
+}
+//function f(x:number):string { return x; }
+var x: string = f(0);
+module.exports = f;
+
+"
+`;
+
+exports[`test obj.js 1`] = `
+"/**
+ * @flow
+ */
+
+// progressively annotate:
+
+var o = { x: 0 }
+//var o: {x: number;} = { x: 0 }
+
+var x:string = o.x;
+
+module.exports = o;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+// progressively annotate:
+var o = { x: 0 };
+//var o: {x: number;} = { x: 0 }
+var x: string = o.x;
+module.exports = o;
+
+"
+`;
diff --git a/tests/strict/annot.js b/tests/strict/annot.js
new file mode 100644
index 000000000000..69e385f2ca2c
--- /dev/null
+++ b/tests/strict/annot.js
@@ -0,0 +1,9 @@
+var A = require('./unknown_class');
+
+class B extends A {
+  foo(x:A):A { return x; }
+  bar(x) { }
+  qux<X,Y>(x:X,y:Y):X { return x;}
+}
+
+module.exports = B;
diff --git a/tests/strict/fun.js b/tests/strict/fun.js
new file mode 100644
index 000000000000..b09992315b1e
--- /dev/null
+++ b/tests/strict/fun.js
@@ -0,0 +1,13 @@
+/**
+ * @flow
+ */
+
+// progressively annotate:
+
+//function f(x) { return x; }
+function f(x:number) { return x; }
+//function f(x:number):string { return x; }
+
+var x:string = f(0);
+
+module.exports = f;
diff --git a/tests/strict/jsfmt.spec.js b/tests/strict/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/strict/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/strict/obj.js b/tests/strict/obj.js
new file mode 100644
index 000000000000..0add7bed5bb1
--- /dev/null
+++ b/tests/strict/obj.js
@@ -0,0 +1,12 @@
+/**
+ * @flow
+ */
+
+// progressively annotate:
+
+var o = { x: 0 }
+//var o: {x: number;} = { x: 0 }
+
+var x:string = o.x;
+
+module.exports = o;
diff --git a/tests/strict_requires/A.js b/tests/strict_requires/A.js
new file mode 100644
index 000000000000..0df880dc9718
--- /dev/null
+++ b/tests/strict_requires/A.js
@@ -0,0 +1,2 @@
+/* @flow */
+module.exports = 0;
diff --git a/tests/strict_requires/B.js b/tests/strict_requires/B.js
new file mode 100644
index 000000000000..e954bc64a74b
--- /dev/null
+++ b/tests/strict_requires/B.js
@@ -0,0 +1,2 @@
+/* @flow */
+module.exports = { foo: "" }
diff --git a/tests/strict_requires/C.js b/tests/strict_requires/C.js
new file mode 100644
index 000000000000..991ad5a6ca64
--- /dev/null
+++ b/tests/strict_requires/C.js
@@ -0,0 +1,6 @@
+/* @flow */
+var o = {
+    A: require('./A'),
+    ...require('./B'),
+};
+module.exports = o;
diff --git a/tests/strict_requires/D.js b/tests/strict_requires/D.js
new file mode 100644
index 000000000000..53659ea52004
--- /dev/null
+++ b/tests/strict_requires/D.js
@@ -0,0 +1,5 @@
+/* @flow */
+var C = require('./C');
+var x: number = C.foo;
+var y: string = C.A;
+C.A = false;
diff --git a/tests/strict_requires/__snapshots__/jsfmt.spec.js.snap b/tests/strict_requires/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a9e678089e60
--- /dev/null
+++ b/tests/strict_requires/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,50 @@
+exports[`test A.js 1`] = `
+"/* @flow */
+module.exports = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports = 0;
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"/* @flow */
+module.exports = { foo: "" }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+module.exports = { foo: "" };
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"/* @flow */
+var o = {
+    A: require('./A'),
+    ...require('./B'),
+};
+module.exports = o;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var o = { A: require("./A"), ...require("./B") };
+module.exports = o;
+
+"
+`;
+
+exports[`test D.js 1`] = `
+"/* @flow */
+var C = require('./C');
+var x: number = C.foo;
+var y: string = C.A;
+C.A = false;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var C = require("./C");
+var x: number = C.foo;
+var y: string = C.A;
+C.A = false;
+
+"
+`;
diff --git a/tests/strict_requires/jsfmt.spec.js b/tests/strict_requires/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/strict_requires/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/strings/__snapshots__/jsfmt.spec.js.snap b/tests/strings/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6ec2f5384a0a
--- /dev/null
+++ b/tests/strings/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,42 @@
+exports[`test strings.js 1`] = `
+"\"abc\"
+\'abc\'
+
+\'\\\'\'
+
+\'\"\'
+\'\\\"\'
+\'\\\\\"\'
+
+\"\'\"
+\"\\\'\"
+\"\\\\\'\"
+
+\"\'\\\"\"
+\'\\\'\"\'
+
+\'\\\\\'
+\"\\\\\"
+
+\'\\0\'
+\'🐶\'
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\"abc\";
+\"abc\";
+\"\\\\\'\";
+\"\\\"\";
+\"\\\\\\\"\";
+\"\\\\\\\\\\\"\";
+\"\'\";
+\"\\\\\'\";
+\"\\\\\\\\\'\";
+\"\'\\\\\\\"\";
+\"\\\\\'\\\"\";
+\"\\\\\\\\\";
+\"\\\\\\\\\";
+\"\\\\0\";
+\"🐶\";
+
+
+"
+`;
diff --git a/tests/strings/jsfmt.spec.js b/tests/strings/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/strings/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/strings/strings.js b/tests/strings/strings.js
new file mode 100644
index 000000000000..b296b144d398
--- /dev/null
+++ b/tests/strings/strings.js
@@ -0,0 +1,21 @@
+"abc"
+'abc'
+
+'\''
+
+'"'
+'\"'
+'\\"'
+
+"'"
+"\'"
+"\\'"
+
+"'\""
+'\'"'
+
+'\\'
+"\\"
+
+'\0'
+'🐶'
diff --git a/tests/structural_subtyping/__snapshots__/jsfmt.spec.js.snap b/tests/structural_subtyping/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..e216003a5a18
--- /dev/null
+++ b/tests/structural_subtyping/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,146 @@
+exports[`test builtin.js 1`] = `
+"/**
+ * @flow
+ */
+
+interface IHasLength {
+  length: number;
+}
+
+var lengthTest1: IHasLength = [];
+var lengthTest2: IHasLength = \'hello\';
+var lengthTest3: IHasLength = 123; // number doesn\'t have length
+var lengthTest4: IHasLength = true; // bool doesn\'t have length
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test class.js 1`] = `
+"/**
+ * @flow
+ */
+
+class ClassWithXString {
+  x: string;
+}
+
+interface IHasXString {
+  x: string;
+}
+
+interface IHasXNumber {
+  x: number;
+}
+
+interface IHasYString {
+  y: string;
+}
+
+var testInstance1: IHasXString = new ClassWithXString();
+var testInstance2: IHasXNumber = new ClassWithXString(); // Error wrong type
+var testInstance3: IHasYString = new ClassWithXString(); // Error missing prop
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test obj.js 1`] = `
+"/**
+ * @flow
+ */
+
+interface IHasXString {
+  x: string;
+}
+
+var propTest1: IHasXString = { x: \'hello\' };
+var propTest2: IHasXString = { x: 123 }; // Error string != number
+var propTest3: IHasXString = {}; // Property not found
+var propTest4: IHasXString = ({}: Object);
+
+function propTest5(y: {[key: string]: string}) {
+  (y: IHasXString); // OK
+}
+
+function propTest6(y: {[key: string]: number}) {
+  (y: IHasXString); // error: string != number
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test optional.js 1`] = `
+"/* @flow */
+
+interface HasOptional {
+  a: string,
+  b?: number,
+};
+
+var test1: HasOptional = { a: \"hello\" }
+
+var test2: HasOptional = {}; // Error: missing property a
+
+var test3: HasOptional = { a: \"hello\", b: true }; // Error: boolean ~> number
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
diff --git a/tests/structural_subtyping/builtin.js b/tests/structural_subtyping/builtin.js
new file mode 100644
index 000000000000..ebc0b2de9c27
--- /dev/null
+++ b/tests/structural_subtyping/builtin.js
@@ -0,0 +1,12 @@
+/**
+ * @flow
+ */
+
+interface IHasLength {
+  length: number;
+}
+
+var lengthTest1: IHasLength = [];
+var lengthTest2: IHasLength = 'hello';
+var lengthTest3: IHasLength = 123; // number doesn't have length
+var lengthTest4: IHasLength = true; // bool doesn't have length
diff --git a/tests/structural_subtyping/class.js b/tests/structural_subtyping/class.js
new file mode 100644
index 000000000000..9fa9d3039674
--- /dev/null
+++ b/tests/structural_subtyping/class.js
@@ -0,0 +1,23 @@
+/**
+ * @flow
+ */
+
+class ClassWithXString {
+  x: string;
+}
+
+interface IHasXString {
+  x: string;
+}
+
+interface IHasXNumber {
+  x: number;
+}
+
+interface IHasYString {
+  y: string;
+}
+
+var testInstance1: IHasXString = new ClassWithXString();
+var testInstance2: IHasXNumber = new ClassWithXString(); // Error wrong type
+var testInstance3: IHasYString = new ClassWithXString(); // Error missing prop
diff --git a/tests/structural_subtyping/jsfmt.spec.js b/tests/structural_subtyping/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/structural_subtyping/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/structural_subtyping/obj.js b/tests/structural_subtyping/obj.js
new file mode 100644
index 000000000000..6a9189ac0f62
--- /dev/null
+++ b/tests/structural_subtyping/obj.js
@@ -0,0 +1,20 @@
+/**
+ * @flow
+ */
+
+interface IHasXString {
+  x: string;
+}
+
+var propTest1: IHasXString = { x: 'hello' };
+var propTest2: IHasXString = { x: 123 }; // Error string != number
+var propTest3: IHasXString = {}; // Property not found
+var propTest4: IHasXString = ({}: Object);
+
+function propTest5(y: {[key: string]: string}) {
+  (y: IHasXString); // OK
+}
+
+function propTest6(y: {[key: string]: number}) {
+  (y: IHasXString); // error: string != number
+}
diff --git a/tests/structural_subtyping/optional.js b/tests/structural_subtyping/optional.js
new file mode 100644
index 000000000000..102a511ef7a2
--- /dev/null
+++ b/tests/structural_subtyping/optional.js
@@ -0,0 +1,12 @@
+/* @flow */
+
+interface HasOptional {
+  a: string,
+  b?: number,
+};
+
+var test1: HasOptional = { a: "hello" }
+
+var test2: HasOptional = {}; // Error: missing property a
+
+var test3: HasOptional = { a: "hello", b: true }; // Error: boolean ~> number
diff --git a/tests/suggest/__snapshots__/jsfmt.spec.js.snap b/tests/suggest/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9b7010ce1817
--- /dev/null
+++ b/tests/suggest/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,39 @@
+exports[`test lib.js 1`] = `
+"/* @flow */
+
+function bar(w: number): number { return w; }
+
+module.exports = bar;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function bar(w: number): number {
+  return w;
+}
+module.exports = bar;
+
+"
+`;
+
+exports[`test suggest.js 1`] = `
+"/* @flow */
+
+var bar = require('./lib');
+
+function foo(z: number) { return bar(z); }
+
+var array = ["foo", "bar"];
+array;
+
+module.exports = {foo:foo};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+var bar = require("./lib");
+function foo(z: number) {
+  return bar(z);
+}
+var array = [ "foo", "bar" ];
+array;
+module.exports = { foo: foo };
+
+"
+`;
diff --git a/tests/suggest/jsfmt.spec.js b/tests/suggest/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/suggest/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/suggest/lib.js b/tests/suggest/lib.js
new file mode 100644
index 000000000000..f89c80bf62c5
--- /dev/null
+++ b/tests/suggest/lib.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+function bar(w: number): number { return w; }
+
+module.exports = bar;
diff --git a/tests/suggest/suggest.js b/tests/suggest/suggest.js
new file mode 100644
index 000000000000..e2b005194721
--- /dev/null
+++ b/tests/suggest/suggest.js
@@ -0,0 +1,10 @@
+/* @flow */
+
+var bar = require('./lib');
+
+function foo(z: number) { return bar(z); }
+
+var array = ["foo", "bar"];
+array;
+
+module.exports = {foo:foo};
diff --git a/tests/super/__snapshots__/jsfmt.spec.js.snap b/tests/super/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3173dd9a56b6
--- /dev/null
+++ b/tests/super/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,263 @@
+exports[`test constructor.js 1`] = `
+"class A { x: number; }
+
+class B {
+  x: number;
+  constructor() {
+    this.x; // OK
+  }
+}
+
+class C extends A { }
+
+class D extends A {
+  y: number;
+  constructor() {
+    this.y; // error (no super call)
+    this.x; // error (no super call)
+  }
+}
+
+class E extends A {
+  y: number;
+  constructor() {
+    super();
+    this.y; // OK
+    this.x; // OK
+  }
+}
+
+function leak(f) {
+  f.y; // error
+  f.x; // error
+}
+class F extends A {
+  y: number;
+  constructor() {
+    leak(this); // error (no super call yet)
+    super();
+    this.y;
+    this.x;
+  }
+}
+
+class G extends A {
+  constructor(b) {
+    super.x; // error (no super call)
+  }
+}
+
+class H extends A {
+  y: number;
+  constructor() {
+    if (Math.random() < 0.5)
+      super();
+    else
+      super();
+    this.y; // OK
+    this.x; // OK
+  }
+}
+
+class I_ {
+  constructor(leaked_this) {
+    leaked_this.foo()
+  }
+  foo() { }
+}
+class I extends I_ {
+  constructor() {
+    super(this); // error (no super call yet)
+  }
+}
+
+class J__ { }
+class J_ extends J__ {
+  constructor(closure_leaking_this) {
+    closure_leaking_this();
+    super();
+  }
+  foo() { }
+}
+class J extends J_ {
+  constructor() {
+    super(() => this.foo()); // error (no super call yet)
+    // The reason for this error is that super constructor could call the
+    // closure and therefore access this before calling its own super
+    // constructor (as shown above). The only safe thing to do in the super
+    // constructor is to save the closure so that it can be called later, after
+    // initialization is done (as shown below).
+  }
+}
+
+class K_ {
+  closure_leaking_this: () => void;
+  constructor(closure_leaking_this) {
+    this.closure_leaking_this = closure_leaking_this;
+  }
+  foo() { }
+}
+class K extends K_ {
+  constructor() {
+    super(() => { if (_this) _this.foo() }); // OK
+    var _this = this;
+    this.closure_leaking_this();
+  }
+}
+
+// even though super() calls the parent\'s constructor(), it does not do the same
+// conversion on non-objects. so \`new L_()\` returns an instance of \`L_\` because
+// the constructor returns false (a non-object), but \`super()\` returns false,
+// which then similarly causes \`new L()\` to return an instance of \`L\`.
+class L_ {
+  constructor() {
+    return false;
+  }
+}
+class L extends L_ {
+  constructor() {
+    let x: boolean = super();
+    return x;
+  }
+}
+(new L_(): L_);
+(new L(): L);
+
+// similarly, the converse is true: if the parent\'s constructor returns an
+// object, then the child does too.
+class M_ {
+  constructor() {
+    return {foo: \'foo\'};
+  }
+}
+class M extends M_ {
+  constructor() {
+    return super();
+  }
+}
+(new M_(): {foo: string});
+(new M(): {foo: string});
+
+// however! super() calls the parent constructor with the subclass as its \`this\`
+// value (essentially \`super.constructor.call(this)\`).
+class N_ {
+  constructor(): this {
+    let x = this;
+    return x;
+  }
+}
+class N extends N_ {
+  constructor() {
+    return super();
+  }
+}
+(new N_(): N_);
+(new N(): N);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test import.js 1`] = `
+"class D {
+  foo(): number { return 0; }
+}
+module.exports = D;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class D {
+  foo(): number {
+    return 0;
+  }
+}
+module.exports = D;
+
+"
+`;
+
+exports[`test super.js 1`] = `
+"
+class A {
+  constructor(x:number) { }
+  static staticMethod(x:string): string { return x; }
+  f(x:string) { }
+}
+
+class B extends A {
+  constructor(x:string,y:number) {
+    super(x);
+  }
+
+  static anotherStatic() {
+    (super.staticMethod(\'foo\'): number); // error, string !~> number
+    (super.doesntExist()); // error, A doesn\'t have a doesntExist method
+  }
+
+  g() {
+    super.f(0);
+    return super.g;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {
+  constructor(x: number) {
+    
+  }
+  staticMethod(x: string): string {
+    return x;
+  }
+  f(x: string) {
+    
+  }
+}
+class B extends A {
+  constructor(x: string, y: number) {
+    super(x);
+  }
+  anotherStatic() {
+    (super.staticMethod(\"foo\"): number);// error, string !~> number
+    super.doesntExist();// error, A doesn\'t have a doesntExist method
+  }
+  g() {
+    super.f(0);
+    return super.g;
+  }
+}
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"var D = require(\'./import\');
+class C extends D {
+  constructor() { return super(); }
+  foo() { return super.foo(); }
+}
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var D = require(\"./import\");
+class C extends D {
+  constructor() {
+    return super();
+  }
+  foo() {
+    return super.foo();
+  }
+}
+module.exports = C;
+
+"
+`;
diff --git a/tests/super/constructor.js b/tests/super/constructor.js
new file mode 100644
index 000000000000..3e11a1dfdb03
--- /dev/null
+++ b/tests/super/constructor.js
@@ -0,0 +1,154 @@
+class A { x: number; }
+
+class B {
+  x: number;
+  constructor() {
+    this.x; // OK
+  }
+}
+
+class C extends A { }
+
+class D extends A {
+  y: number;
+  constructor() {
+    this.y; // error (no super call)
+    this.x; // error (no super call)
+  }
+}
+
+class E extends A {
+  y: number;
+  constructor() {
+    super();
+    this.y; // OK
+    this.x; // OK
+  }
+}
+
+function leak(f) {
+  f.y; // error
+  f.x; // error
+}
+class F extends A {
+  y: number;
+  constructor() {
+    leak(this); // error (no super call yet)
+    super();
+    this.y;
+    this.x;
+  }
+}
+
+class G extends A {
+  constructor(b) {
+    super.x; // error (no super call)
+  }
+}
+
+class H extends A {
+  y: number;
+  constructor() {
+    if (Math.random() < 0.5)
+      super();
+    else
+      super();
+    this.y; // OK
+    this.x; // OK
+  }
+}
+
+class I_ {
+  constructor(leaked_this) {
+    leaked_this.foo()
+  }
+  foo() { }
+}
+class I extends I_ {
+  constructor() {
+    super(this); // error (no super call yet)
+  }
+}
+
+class J__ { }
+class J_ extends J__ {
+  constructor(closure_leaking_this) {
+    closure_leaking_this();
+    super();
+  }
+  foo() { }
+}
+class J extends J_ {
+  constructor() {
+    super(() => this.foo()); // error (no super call yet)
+    // The reason for this error is that super constructor could call the
+    // closure and therefore access this before calling its own super
+    // constructor (as shown above). The only safe thing to do in the super
+    // constructor is to save the closure so that it can be called later, after
+    // initialization is done (as shown below).
+  }
+}
+
+class K_ {
+  closure_leaking_this: () => void;
+  constructor(closure_leaking_this) {
+    this.closure_leaking_this = closure_leaking_this;
+  }
+  foo() { }
+}
+class K extends K_ {
+  constructor() {
+    super(() => { if (_this) _this.foo() }); // OK
+    var _this = this;
+    this.closure_leaking_this();
+  }
+}
+
+// even though super() calls the parent's constructor(), it does not do the same
+// conversion on non-objects. so `new L_()` returns an instance of `L_` because
+// the constructor returns false (a non-object), but `super()` returns false,
+// which then similarly causes `new L()` to return an instance of `L`.
+class L_ {
+  constructor() {
+    return false;
+  }
+}
+class L extends L_ {
+  constructor() {
+    let x: boolean = super();
+    return x;
+  }
+}
+(new L_(): L_);
+(new L(): L);
+
+// similarly, the converse is true: if the parent's constructor returns an
+// object, then the child does too.
+class M_ {
+  constructor() {
+    return {foo: 'foo'};
+  }
+}
+class M extends M_ {
+  constructor() {
+    return super();
+  }
+}
+(new M_(): {foo: string});
+(new M(): {foo: string});
+
+// however! super() calls the parent constructor with the subclass as its `this`
+// value (essentially `super.constructor.call(this)`).
+class N_ {
+  constructor(): this {
+    let x = this;
+    return x;
+  }
+}
+class N extends N_ {
+  constructor() {
+    return super();
+  }
+}
+(new N_(): N_);
+(new N(): N);
diff --git a/tests/super/import.js b/tests/super/import.js
new file mode 100644
index 000000000000..4ca97a19d780
--- /dev/null
+++ b/tests/super/import.js
@@ -0,0 +1,4 @@
+class D {
+  foo(): number { return 0; }
+}
+module.exports = D;
diff --git a/tests/super/jsfmt.spec.js b/tests/super/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/super/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/super/super.js b/tests/super/super.js
new file mode 100644
index 000000000000..1bdae53e2366
--- /dev/null
+++ b/tests/super/super.js
@@ -0,0 +1,22 @@
+
+class A {
+  constructor(x:number) { }
+  static staticMethod(x:string): string { return x; }
+  f(x:string) { }
+}
+
+class B extends A {
+  constructor(x:string,y:number) {
+    super(x);
+  }
+
+  static anotherStatic() {
+    (super.staticMethod('foo'): number); // error, string !~> number
+    (super.doesntExist()); // error, A doesn't have a doesntExist method
+  }
+
+  g() {
+    super.f(0);
+    return super.g;
+  }
+}
diff --git a/tests/super/test.js b/tests/super/test.js
new file mode 100644
index 000000000000..3a9a3c3654d7
--- /dev/null
+++ b/tests/super/test.js
@@ -0,0 +1,6 @@
+var D = require('./import');
+class C extends D {
+  constructor() { return super(); }
+  foo() { return super.foo(); }
+}
+module.exports = C;
diff --git a/tests/suppress/A.js b/tests/suppress/A.js
new file mode 100644
index 000000000000..3411f3e65e0a
--- /dev/null
+++ b/tests/suppress/A.js
@@ -0,0 +1,24 @@
+// $FlowFixMe
+var test1: string = 123; // This error should be suppressed
+
+// $FlowIssue
+var test2: string = 123; // This error should be suppressed
+
+function getNum() {
+  return 123;
+}
+
+// $FlowFixMe This was the second loc in the error
+var test3: string = getNum(); // This error should be suppressed
+
+// $FlowFixMe Error unused suppression
+
+var test4: string = 123; // This error is NOT suppressed
+
+                         // $FlowFixMe Indentation shouldn't matter
+var test5: string = 123; // This error should be suppressed
+
+/*
+ * $FlowNewLine
+ */
+var test6: string = 123;
diff --git a/tests/suppress/B.js b/tests/suppress/B.js
new file mode 100644
index 000000000000..b4f41e62eb69
--- /dev/null
+++ b/tests/suppress/B.js
@@ -0,0 +1,2 @@
+// $FlowFixMe
+var test1: string = library_num;
diff --git a/tests/suppress/C.js b/tests/suppress/C.js
new file mode 100644
index 000000000000..80c35d500c6e
--- /dev/null
+++ b/tests/suppress/C.js
@@ -0,0 +1,8 @@
+function takesAString(x: string): void {}
+
+function runTest(y: number): void {
+  takesAString(
+    /* $FlowFixMe - suppressing the error op location should also work */
+    y,
+  );
+}
diff --git a/tests/suppress/__snapshots__/jsfmt.spec.js.snap b/tests/suppress/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..4b43391295c6
--- /dev/null
+++ b/tests/suppress/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,86 @@
+exports[`test A.js 1`] = `
+"// $FlowFixMe
+var test1: string = 123; // This error should be suppressed
+
+// $FlowIssue
+var test2: string = 123; // This error should be suppressed
+
+function getNum() {
+  return 123;
+}
+
+// $FlowFixMe This was the second loc in the error
+var test3: string = getNum(); // This error should be suppressed
+
+// $FlowFixMe Error unused suppression
+
+var test4: string = 123; // This error is NOT suppressed
+
+                         // $FlowFixMe Indentation shouldn't matter
+var test5: string = 123; // This error should be suppressed
+
+/*
+ * $FlowNewLine
+ */
+var test6: string = 123;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// $FlowFixMe
+var test1: string = 123;// This error should be suppressed
+// $FlowIssue
+var test2: string = 123;// This error should be suppressed
+function getNum() {
+  return 123;
+}
+// $FlowFixMe This was the second loc in the error
+var test3: string = getNum();// This error should be suppressed
+// $FlowFixMe Error unused suppression
+var test4: string = 123;// This error is NOT suppressed// $FlowFixMe Indentation shouldn't matter
+var test5: string = 123;// This error should be suppressed
+/*
+ * $FlowNewLine
+ */
+var test6: string = 123;
+
+"
+`;
+
+exports[`test B.js 1`] = `
+"// $FlowFixMe
+var test1: string = library_num;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// $FlowFixMe
+var test1: string = library_num;
+
+"
+`;
+
+exports[`test C.js 1`] = `
+"function takesAString(x: string): void {}
+
+function runTest(y: number): void {
+  takesAString(
+    /* $FlowFixMe - suppressing the error op location should also work */
+    y,
+  );
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function takesAString(x: string): void {
+  
+}
+function runTest(y: number): void {
+  takesAString(
+    /* $FlowFixMe - suppressing the error op location should also work */
+    y
+  );
+}
+
+"
+`;
+
+exports[`test lib.js 1`] = `
+"declare var library_num: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare var library_num: number;
+
+"
+`;
diff --git a/tests/suppress/jsfmt.spec.js b/tests/suppress/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/suppress/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/suppress/lib.js b/tests/suppress/lib.js
new file mode 100644
index 000000000000..21cfa88e53e5
--- /dev/null
+++ b/tests/suppress/lib.js
@@ -0,0 +1 @@
+declare var library_num: number;
diff --git a/tests/suppress_incremental/__snapshots__/jsfmt.spec.js.snap b/tests/suppress_incremental/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..16a23d3be09a
--- /dev/null
+++ b/tests/suppress_incremental/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+(123: number); // no errors
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+(123: number);// no errors
+
+"
+`;
diff --git a/tests/suppress_incremental/jsfmt.spec.js b/tests/suppress_incremental/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/suppress_incremental/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/suppress_incremental/test.js b/tests/suppress_incremental/test.js
new file mode 100644
index 000000000000..8f4e80213ed3
--- /dev/null
+++ b/tests/suppress_incremental/test.js
@@ -0,0 +1,3 @@
+// @flow
+
+(123: number); // no errors
diff --git a/tests/suppress_traces/__snapshots__/jsfmt.spec.js.snap b/tests/suppress_traces/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..32292e7511df
--- /dev/null
+++ b/tests/suppress_traces/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,34 @@
+exports[`test traces.js 1`] = `
+"/*
+ * The location marked with the FlowFixMe does not show up in the original
+ * error but shows up in the flow check --traces 10 result. This test makes
+ * sure that we don't suppress the error due to a location that only shows up
+ * when --traces is turned on.
+ */
+
+// $FlowFixMe - Error unused suppression
+function bar(): number { return 5; }
+
+function foo(x: string) {
+  return bar();
+}
+
+var a: string = foo('hi'); // error number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+ * The location marked with the FlowFixMe does not show up in the original
+ * error but shows up in the flow check --traces 10 result. This test makes
+ * sure that we don't suppress the error due to a location that only shows up
+ * when --traces is turned on.
+ */
+// $FlowFixMe - Error unused suppression
+function bar(): number {
+  return 5;
+}
+function foo(x: string) {
+  return bar();
+}
+var a: string = foo("hi");// error number ~> string
+
+"
+`;
diff --git a/tests/suppress_traces/jsfmt.spec.js b/tests/suppress_traces/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/suppress_traces/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/suppress_traces/traces.js b/tests/suppress_traces/traces.js
new file mode 100644
index 000000000000..1a34c3771dc6
--- /dev/null
+++ b/tests/suppress_traces/traces.js
@@ -0,0 +1,15 @@
+/*
+ * The location marked with the FlowFixMe does not show up in the original
+ * error but shows up in the flow check --traces 10 result. This test makes
+ * sure that we don't suppress the error due to a location that only shows up
+ * when --traces is turned on.
+ */
+
+// $FlowFixMe - Error unused suppression
+function bar(): number { return 5; }
+
+function foo(x: string) {
+  return bar();
+}
+
+var a: string = foo('hi'); // error number ~> string
diff --git a/tests/switch/__snapshots__/jsfmt.spec.js.snap b/tests/switch/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ba9fd1e81846
--- /dev/null
+++ b/tests/switch/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,262 @@
+exports[`test more_switch.js 1`] = `
+"/* @flow */
+
+function foo(x): number {
+    switch (x) {
+      case 0:
+      case 1: return 1;
+      default: throw new Error(\'hi\');
+    }
+}
+
+function bar(x) {
+    switch (x) {
+      case 0: break;
+      default: return;
+    }
+    1;
+}
+
+function baz(x): number {
+  switch (x) {
+    case 0: break;
+    case 1: return 1;
+    default: throw new Error(\'hi\');
+  }
+  return 2;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test switch.js 1`] = `
+"/**
+ * @flow
+ */
+function foo(
+): number {
+    switch (\'foo\') {
+    case \'foo\':
+        return 1;
+    }
+    return 2;
+}
+
+function bar() {
+    switch (\'bar\') {
+    case \'bar\':
+        break;
+    default:
+        break;
+    }
+}
+
+function qux(b) {
+    var x = b? 0: \"\";
+    switch(\'qux\') {
+    case \'\':
+        x = 0;
+    case \'qux\':
+        x = x*x;
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test switch_default_fallthrough.js 1`] = `
+"/**
+ * @flow
+ */
+function foo(x : mixed): string {
+    var a = \"\";
+    var b = \"\";
+
+    switch (x) {
+      case \"foo\":
+        a = 0;
+      default:
+        b = 0;
+    }
+
+    // a is now string | number
+    (a : string); // error, string | number ~/> string
+    (a : number); // error, string | number ~/> number
+
+    // b is now number
+    (b : number); // ok
+    return b; // error, number ~/> string
+}
+
+function baz(x: mixed): number {
+    var a = \"\";
+    var b = \"\";
+
+    switch (x) {
+      case \"baz\":
+        a = 0;
+        break;
+      case \"bar\":
+        a = \"\";
+      default:
+        b = 0;
+    }
+
+    // a is now string | number
+    (a : string); // error, string | number ~/> string
+    (a : number); // error, string | number ~/> number
+
+    // b is now string | number
+    (b : string); // error, string | number ~/> string
+    (b : number); // error, string | number ~/> number
+
+    return a+b; // error, string ~/> number
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test trailing_cases.js 1`] = `
+"/**
+ * trailing cases are allowed - spot checks that we handle them as usual
+ * @flow
+ */
+function f1(i) {
+  var x;
+
+  switch (i) {
+  case 0:
+    x = 0;
+    break;
+  case 1:
+    x = 1;
+    break;
+  default:
+    x = -1;
+    break;
+  case 2:
+    x = \"2\";
+    break;
+  }
+
+  var y:number = x; // error, number | string ~/> number
+}
+
+function f2(i) {
+  var x;
+
+  switch (i) {
+  case 0:
+  case 1:
+  default:
+    x = 1;
+    break;
+  case 2:
+    // does not fall through default
+  }
+
+  var y:number = x; // error, number | uninitialized ~/> number
+}
+
+function f3(i) {
+  var x;
+
+  switch (i) {
+  case 0:
+  case 1:
+  default:
+    // falls through to subsequent cases
+  case 2:
+    x = 1;
+  }
+
+  var y:number = x; // no error
+}
+
+function foo(x): number {
+    switch (x) {
+      case 0:
+      default: throw new Error(\'hi\');
+      case 1: return 1;
+    }
+}
+
+function bar(x) {
+    switch (x) {
+      default: return;
+      case 0: break;
+    }
+    1;
+}
+
+function baz(x): number {
+  switch (x) {
+    case 0: break;
+    default: throw new Error(\'hi\');
+    case 1: return 1;
+  }
+  return 2;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1020
+        }, \"consequent\").indent(options.tabWidth));
+                         ^
+
+TypeError: path.call(...).indent is not a function
+    at genericPrintNoParens (/src/printer.js:1020:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1005:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/switch/jsfmt.spec.js b/tests/switch/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/switch/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/switch/more_switch.js b/tests/switch/more_switch.js
new file mode 100644
index 000000000000..1b478e4a708e
--- /dev/null
+++ b/tests/switch/more_switch.js
@@ -0,0 +1,26 @@
+/* @flow */
+
+function foo(x): number {
+    switch (x) {
+      case 0:
+      case 1: return 1;
+      default: throw new Error('hi');
+    }
+}
+
+function bar(x) {
+    switch (x) {
+      case 0: break;
+      default: return;
+    }
+    1;
+}
+
+function baz(x): number {
+  switch (x) {
+    case 0: break;
+    case 1: return 1;
+    default: throw new Error('hi');
+  }
+  return 2;
+}
diff --git a/tests/switch/switch.js b/tests/switch/switch.js
new file mode 100644
index 000000000000..7431b929b4ea
--- /dev/null
+++ b/tests/switch/switch.js
@@ -0,0 +1,30 @@
+/**
+ * @flow
+ */
+function foo(
+): number {
+    switch ('foo') {
+    case 'foo':
+        return 1;
+    }
+    return 2;
+}
+
+function bar() {
+    switch ('bar') {
+    case 'bar':
+        break;
+    default:
+        break;
+    }
+}
+
+function qux(b) {
+    var x = b? 0: "";
+    switch('qux') {
+    case '':
+        x = 0;
+    case 'qux':
+        x = x*x;
+    }
+}
diff --git a/tests/switch/switch_default_fallthrough.js b/tests/switch/switch_default_fallthrough.js
new file mode 100644
index 000000000000..2b79bada2503
--- /dev/null
+++ b/tests/switch/switch_default_fallthrough.js
@@ -0,0 +1,47 @@
+/**
+ * @flow
+ */
+function foo(x : mixed): string {
+    var a = "";
+    var b = "";
+
+    switch (x) {
+      case "foo":
+        a = 0;
+      default:
+        b = 0;
+    }
+
+    // a is now string | number
+    (a : string); // error, string | number ~/> string
+    (a : number); // error, string | number ~/> number
+
+    // b is now number
+    (b : number); // ok
+    return b; // error, number ~/> string
+}
+
+function baz(x: mixed): number {
+    var a = "";
+    var b = "";
+
+    switch (x) {
+      case "baz":
+        a = 0;
+        break;
+      case "bar":
+        a = "";
+      default:
+        b = 0;
+    }
+
+    // a is now string | number
+    (a : string); // error, string | number ~/> string
+    (a : number); // error, string | number ~/> number
+
+    // b is now string | number
+    (b : string); // error, string | number ~/> string
+    (b : number); // error, string | number ~/> number
+
+    return a+b; // error, string ~/> number
+}
diff --git a/tests/switch/trailing_cases.js b/tests/switch/trailing_cases.js
new file mode 100644
index 000000000000..72f60aa92c28
--- /dev/null
+++ b/tests/switch/trailing_cases.js
@@ -0,0 +1,80 @@
+/**
+ * trailing cases are allowed - spot checks that we handle them as usual
+ * @flow
+ */
+function f1(i) {
+  var x;
+
+  switch (i) {
+  case 0:
+    x = 0;
+    break;
+  case 1:
+    x = 1;
+    break;
+  default:
+    x = -1;
+    break;
+  case 2:
+    x = "2";
+    break;
+  }
+
+  var y:number = x; // error, number | string ~/> number
+}
+
+function f2(i) {
+  var x;
+
+  switch (i) {
+  case 0:
+  case 1:
+  default:
+    x = 1;
+    break;
+  case 2:
+    // does not fall through default
+  }
+
+  var y:number = x; // error, number | uninitialized ~/> number
+}
+
+function f3(i) {
+  var x;
+
+  switch (i) {
+  case 0:
+  case 1:
+  default:
+    // falls through to subsequent cases
+  case 2:
+    x = 1;
+  }
+
+  var y:number = x; // no error
+}
+
+function foo(x): number {
+    switch (x) {
+      case 0:
+      default: throw new Error('hi');
+      case 1: return 1;
+    }
+}
+
+function bar(x) {
+    switch (x) {
+      default: return;
+      case 0: break;
+    }
+    1;
+}
+
+function baz(x): number {
+  switch (x) {
+    case 0: break;
+    default: throw new Error('hi');
+    case 1: return 1;
+  }
+  return 2;
+}
diff --git a/tests/symbol/__snapshots__/jsfmt.spec.js.snap b/tests/symbol/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6d9d2d58fbdd
--- /dev/null
+++ b/tests/symbol/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,14 @@
+exports[`test symbol.js 1`] = `
+"var FOO = Symbol();
+var BAR = Symbol('bar');
+
+// TODO: Expected error
+var WAT = Symbol('foo', 'bar');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var FOO = Symbol();
+var BAR = Symbol("bar");
+// TODO: Expected error
+var WAT = Symbol("foo", "bar");
+
+"
+`;
diff --git a/tests/symbol/jsfmt.spec.js b/tests/symbol/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/symbol/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/symbol/symbol.js b/tests/symbol/symbol.js
new file mode 100644
index 000000000000..f8c625d14c95
--- /dev/null
+++ b/tests/symbol/symbol.js
@@ -0,0 +1,5 @@
+var FOO = Symbol();
+var BAR = Symbol('bar');
+
+// TODO: Expected error
+var WAT = Symbol('foo', 'bar');
diff --git a/tests/symlink/__snapshots__/jsfmt.spec.js.snap b/tests/symlink/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..6a3e902ee7d4
--- /dev/null
+++ b/tests/symlink/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,25 @@
+exports[`test bar.js 1`] = `
+"export type Foo = { x: number; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+export type Foo = { x: number };
+
+"
+`;
+
+exports[`test foo.js 1`] = `
+"export type Foo = { x: number; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+export type Foo = { x: number };
+
+"
+`;
+
+exports[`test qux.js 1`] = `
+"import type { Foo } from './bar.js';
+({ x: "" }: Foo);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+import type { Foo } from "./bar.js";
+({ x: "" }: Foo);
+
+"
+`;
diff --git a/tests/symlink/bar.js b/tests/symlink/bar.js
new file mode 100644
index 000000000000..41044c7c6ca9
--- /dev/null
+++ b/tests/symlink/bar.js
@@ -0,0 +1 @@
+export type Foo = { x: number; }
diff --git a/tests/symlink/foo.js b/tests/symlink/foo.js
new file mode 100644
index 000000000000..41044c7c6ca9
--- /dev/null
+++ b/tests/symlink/foo.js
@@ -0,0 +1 @@
+export type Foo = { x: number; }
diff --git a/tests/symlink/jsfmt.spec.js b/tests/symlink/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/symlink/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/symlink/qux.js b/tests/symlink/qux.js
new file mode 100644
index 000000000000..1595d2426a9d
--- /dev/null
+++ b/tests/symlink/qux.js
@@ -0,0 +1,2 @@
+import type { Foo } from './bar.js';
+({ x: "" }: Foo);
diff --git a/tests/tagged-unions/__snapshots__/jsfmt.spec.js.snap b/tests/tagged-unions/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..f1954cc1a99c
--- /dev/null
+++ b/tests/tagged-unions/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,242 @@
+exports[`test classes.js 1`] = `
+"// @flow
+
+class Foo {
+  type: \'foo\';
+  foo: string;
+}
+
+class Bar {
+  type: \'bar\';
+  bar: string;
+}
+
+type Foobar = Foo | Bar;
+
+function foobar(x: Foobar): string {
+  if (x.type === \'foo\') {
+    return foo(x);
+  } else if (x.type === \'bar\') {
+    return bar(x);
+  } else {
+    return \'unknown\';
+  }
+}
+
+function foo(x: Foo): string {
+  return x.foo;
+}
+
+function bar(x: Bar): string {
+  return x.bar;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test interfaces-neg.js 1`] = `
+"/* @flow */
+
+declare interface IDataBase {
+  id: string,
+  name: string,
+}
+
+declare interface IUserData extends IDataBase {
+  kind: \"user\",
+}
+
+declare interface ISystemData extends IDataBase {
+  kind: \"system\",
+}
+
+declare type IData = IUserData | ISystemData;
+
+const data: IData = {
+  id: \"\",
+  name: \"\",
+  kind: \"system\",
+}
+
+if (data.kind === \"user\") {
+  (data: ISystemData);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test interfaces-pos.js 1`] = `
+"/* @flow */
+
+declare interface IDataBase {
+  id: string,
+  name: string,
+}
+
+declare interface IUserData extends IDataBase {
+  kind: \"user\",
+}
+
+declare interface ISystemData extends IDataBase {
+  kind: \"system\",
+}
+
+declare type IData = IUserData | ISystemData;
+
+const data: IData = {
+  id: \"\",
+  name: \"\",
+  kind: \"system\",
+}
+
+if (data.kind === \"system\") {
+  (data: ISystemData);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test type-decls-neg.js 1`] = `
+"/* @flow */
+
+type DataBase = {
+  id: string,
+  name: string,
+};
+
+type UserData = {
+  id: string,
+  name: string,
+  kind: \"user\",
+}
+
+type SystemData = {
+  id: string,
+  name: string,
+  kind: \"system\",
+}
+
+declare type Data = UserData | SystemData;
+
+const data: Data = {
+  id: \"\",
+  name: \"\",
+  kind: \"system\",
+}
+
+if (data.kind === \"user\") {
+  (data: SystemData);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test type-decls-pos.js 1`] = `
+"/* @flow */
+
+type DataBase = {
+  id: string,
+  name: string,
+};
+
+type UserData = {
+  id: string,
+  name: string,
+  kind: \"user\",
+}
+
+type SystemData = {
+  id: string,
+  name: string,
+  kind: \"system\",
+}
+
+declare type Data = UserData | SystemData;
+
+const data: Data = {
+  id: \"\",
+  name: \"\",
+  kind: \"system\",
+}
+
+if (data.kind === \"system\") {
+  (data: SystemData);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/tagged-unions/classes.js b/tests/tagged-unions/classes.js
new file mode 100644
index 000000000000..0a1a0853dfbf
--- /dev/null
+++ b/tests/tagged-unions/classes.js
@@ -0,0 +1,31 @@
+// @flow
+
+class Foo {
+  type: 'foo';
+  foo: string;
+}
+
+class Bar {
+  type: 'bar';
+  bar: string;
+}
+
+type Foobar = Foo | Bar;
+
+function foobar(x: Foobar): string {
+  if (x.type === 'foo') {
+    return foo(x);
+  } else if (x.type === 'bar') {
+    return bar(x);
+  } else {
+    return 'unknown';
+  }
+}
+
+function foo(x: Foo): string {
+  return x.foo;
+}
+
+function bar(x: Bar): string {
+  return x.bar;
+}
diff --git a/tests/tagged-unions/interfaces-neg.js b/tests/tagged-unions/interfaces-neg.js
new file mode 100644
index 000000000000..c9909d06ccad
--- /dev/null
+++ b/tests/tagged-unions/interfaces-neg.js
@@ -0,0 +1,26 @@
+/* @flow */
+
+declare interface IDataBase {
+  id: string,
+  name: string,
+}
+
+declare interface IUserData extends IDataBase {
+  kind: "user",
+}
+
+declare interface ISystemData extends IDataBase {
+  kind: "system",
+}
+
+declare type IData = IUserData | ISystemData;
+
+const data: IData = {
+  id: "",
+  name: "",
+  kind: "system",
+}
+
+if (data.kind === "user") {
+  (data: ISystemData);
+}
diff --git a/tests/tagged-unions/interfaces-pos.js b/tests/tagged-unions/interfaces-pos.js
new file mode 100644
index 000000000000..533dfe171e7b
--- /dev/null
+++ b/tests/tagged-unions/interfaces-pos.js
@@ -0,0 +1,26 @@
+/* @flow */
+
+declare interface IDataBase {
+  id: string,
+  name: string,
+}
+
+declare interface IUserData extends IDataBase {
+  kind: "user",
+}
+
+declare interface ISystemData extends IDataBase {
+  kind: "system",
+}
+
+declare type IData = IUserData | ISystemData;
+
+const data: IData = {
+  id: "",
+  name: "",
+  kind: "system",
+}
+
+if (data.kind === "system") {
+  (data: ISystemData);
+}
diff --git a/tests/tagged-unions/jsfmt.spec.js b/tests/tagged-unions/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/tagged-unions/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/tagged-unions/type-decls-neg.js b/tests/tagged-unions/type-decls-neg.js
new file mode 100644
index 000000000000..c7fbd789d1c5
--- /dev/null
+++ b/tests/tagged-unions/type-decls-neg.js
@@ -0,0 +1,30 @@
+/* @flow */
+
+type DataBase = {
+  id: string,
+  name: string,
+};
+
+type UserData = {
+  id: string,
+  name: string,
+  kind: "user",
+}
+
+type SystemData = {
+  id: string,
+  name: string,
+  kind: "system",
+}
+
+declare type Data = UserData | SystemData;
+
+const data: Data = {
+  id: "",
+  name: "",
+  kind: "system",
+}
+
+if (data.kind === "user") {
+  (data: SystemData);
+}
diff --git a/tests/tagged-unions/type-decls-pos.js b/tests/tagged-unions/type-decls-pos.js
new file mode 100644
index 000000000000..dec1ed6a0c0a
--- /dev/null
+++ b/tests/tagged-unions/type-decls-pos.js
@@ -0,0 +1,30 @@
+/* @flow */
+
+type DataBase = {
+  id: string,
+  name: string,
+};
+
+type UserData = {
+  id: string,
+  name: string,
+  kind: "user",
+}
+
+type SystemData = {
+  id: string,
+  name: string,
+  kind: "system",
+}
+
+declare type Data = UserData | SystemData;
+
+const data: Data = {
+  id: "",
+  name: "",
+  kind: "system",
+}
+
+if (data.kind === "system") {
+  (data: SystemData);
+}
diff --git a/tests/taint/__snapshots__/jsfmt.spec.js.snap b/tests/taint/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7acccb220455
--- /dev/null
+++ b/tests/taint/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,453 @@
+exports[`test adder.js 1`] = `
+"// @flow
+
+function f(x : $Tainted<number>, y : $Tainted<number>) {
+  var z : $Tainted<number> = x + y;
+}
+function f1(x : $Tainted<number>, y : number) {
+  var z : $Tainted<number> = x + y;
+}
+function f2(x : number, y : $Tainted<number>) {
+  var z : $Tainted<number> = x + y;
+}
+// This should cause an error.
+function f3(x : $Tainted<number>, y : number) {
+  var z : number = x + y;
+}
+// This should cause an error.
+function f4(x : number, y : $Tainted<number>) {
+  var z : number = x + y;
+}
+// This should cause an error.
+function f5(x : number, y : $Tainted<number>) {
+  var z : string = x + y;
+}
+// This should cause an error.
+function f6(x : string, y : $Tainted<number>) {
+  var z : string = x + y;
+}
+// This should cause an error.
+function f7(x : $Tainted<string>, y : $Tainted<number>) {
+  var z : string = x + y;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test any_object.js 1`] = `
+"// @flow
+
+let tests = [
+  // setting a property
+  function(x: $Tainted<string>, y: string) {
+    let obj: Object = {};
+    obj.foo = x; // error, taint ~> any
+    obj[y] = x; // error, taint ~> any
+  },
+
+  // getting a property
+  function() {
+    let obj: Object = { foo: \'foo\' };
+    (obj.foo: $Tainted<string>); // ok
+  },
+
+  // calling a method
+  function(x: $Tainted<string>) {
+    let obj: Object = {};
+    obj.foo(x); // error, taint ~> any
+
+    let foo = obj.foo;
+    foo(x); // error, taint ~> any
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test call-object-property.js 1`] = `
+"// @flow
+
+function foo(x : $Tainted<string>, o : Object) {
+  // Error
+  o.f(x);
+}
+function foo1(x : $Tainted<string>, o : {f : (y : $Tainted<string>) => void}) {
+  o.f(x);
+}
+function foo2(o1 : Object, o2 : {t : $Tainted<string>}) {
+  o1.f(o2.t);
+}
+function foo3<T>(x : $Tainted<T>, o : {f : (y : $Tainted<T>) => void}) {
+  o.f(x);
+}
+function f_foo1(x : $Tainted<string>, f : Function) {
+  // Error
+  f(x);
+}
+function f_foo2(f1 : Function, o : {t : $Tainted<string>}) {
+  f1(o.t);
+}
+function f_foo3(f1 : Function, o1 : Object, o2 : {t : $Tainted<string>}) {
+  (f1(o1))(o2.t);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test comparator.js 1`] = `
+"// @flow
+// Should cause an error.
+function f(x : $Tainted<string>, y : $Tainted<number>) {
+  var z : $Tainted<bool> = x < y;
+}
+// Should cause an error.
+function f1(x : string, y : $Tainted<number>) {
+  var z : $Tainted<bool> = x < y;
+}
+// Should cause an error.
+function f2(x : $Tainted<string>, y : number) {
+  var z : $Tainted<bool> = x < y;
+}
+// Note: We allow removing Taint when two tainted
+// values are compared.
+function f3(x : $Tainted<string>, y : string) {
+  var z : bool = x < y;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test function.js 1`] = `
+"// @flow
+
+let tests = [
+  // flows any to each param
+  function(x: any, y: $Tainted<string>) {
+    x(y); // error, taint ~> any
+  },
+
+  // calling \`any\` returns \`any\`
+  function(x: any, y: $Tainted<string>) {
+    let z = x();
+    z(y);
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test globals.js 1`] = `
+"// @flow
+
+class A {
+  f(x : $Tainted<FakeLocation>) {
+    fakeDocument.location = x; // error
+    doStuff(x); // ok
+  }
+  f1(x : $Tainted<FakeLocation>) {
+    // TODO(rcastano): should cause an error.
+    window.fakeLocation = x;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test lib.js 1`] = `
+"declare class FakeLocation {
+  assign(url: string): void;
+}
+
+declare class FakeDocument {
+  location: FakeLocation;
+}
+
+declare function doStuff(x: $Tainted<any>): void;
+
+declare var fakeDocument: FakeDocument;
+declare var fakeLocation: FakeLocation;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test taint1.js 1`] = `
+"/*
+ *
+ * @flow
+ */
+class A {
+  f(tainted : $Tainted<string>) {
+    // This shouldn\'t give a warning (both are tainted)
+    var also_tainted : $Tainted<string> = tainted;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test taint2.js 1`] = `
+"/*
+ *
+ * @flow
+ */
+class A {
+  f(tainted : $Tainted<string>) {
+    // This *should* give a warning.
+    fakeDocument.location.assign(tainted);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test taint3.js 1`] = `
+"/*
+ *
+ * @flow
+ */
+class A {
+  f(tainted : $Tainted<string>) {
+    // The Tainted annotation should still flow.
+    var safe = tainted;
+    // This should give a warning.
+    var loc : string = safe;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test taint4.js 1`] = `
+"/*
+ *
+ * @flow
+ */
+
+var safe : string = \"safe\";
+// This should be allowed.
+var tainted : $Tainted<string> = safe
+
+function f(x : $Tainted<any>) {
+  // Should cause error.
+  var y : any = x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test use-types.js 1`] = `
+"/*
+ * @flow
+ */
+
+// Should cause an error.
+function foo (x : $Tainted<number>) {
+  var should_fail : number = x * 42;
+}
+// Should cause an error.
+function foo1 (x : $Tainted<{f: number}>) {
+  var ok : number = x.f;
+}
+// Should cause an error.
+function foo2 (o : {f (y:number):number}, t: $Tainted<number>) {
+  return o.f(t);
+}
+
+function foo3 (x : $Tainted<{f: number}>) {
+  var also_tainted : $Tainted<number> = x.f;
+}
+// Should cause an error.
+function foo4 (a : $Tainted<Array<string>>) {
+  var trusted : string = a[0];
+}
+// Type error.
+function foo5 (a : $Tainted<Array<string>>) {
+  var trusted_number : number = a[0];
+}
+
+function foo6 (a : $Tainted<Array<string>>) {
+  var trusted : $Tainted<string> = a[0];
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/taint/adder.js b/tests/taint/adder.js
new file mode 100644
index 000000000000..50dbaf2edae3
--- /dev/null
+++ b/tests/taint/adder.js
@@ -0,0 +1,31 @@
+// @flow
+
+function f(x : $Tainted<number>, y : $Tainted<number>) {
+  var z : $Tainted<number> = x + y;
+}
+function f1(x : $Tainted<number>, y : number) {
+  var z : $Tainted<number> = x + y;
+}
+function f2(x : number, y : $Tainted<number>) {
+  var z : $Tainted<number> = x + y;
+}
+// This should cause an error.
+function f3(x : $Tainted<number>, y : number) {
+  var z : number = x + y;
+}
+// This should cause an error.
+function f4(x : number, y : $Tainted<number>) {
+  var z : number = x + y;
+}
+// This should cause an error.
+function f5(x : number, y : $Tainted<number>) {
+  var z : string = x + y;
+}
+// This should cause an error.
+function f6(x : string, y : $Tainted<number>) {
+  var z : string = x + y;
+}
+// This should cause an error.
+function f7(x : $Tainted<string>, y : $Tainted<number>) {
+  var z : string = x + y;
+}
diff --git a/tests/taint/any_object.js b/tests/taint/any_object.js
new file mode 100644
index 000000000000..6569b7b61069
--- /dev/null
+++ b/tests/taint/any_object.js
@@ -0,0 +1,25 @@
+// @flow
+
+let tests = [
+  // setting a property
+  function(x: $Tainted<string>, y: string) {
+    let obj: Object = {};
+    obj.foo = x; // error, taint ~> any
+    obj[y] = x; // error, taint ~> any
+  },
+
+  // getting a property
+  function() {
+    let obj: Object = { foo: 'foo' };
+    (obj.foo: $Tainted<string>); // ok
+  },
+
+  // calling a method
+  function(x: $Tainted<string>) {
+    let obj: Object = {};
+    obj.foo(x); // error, taint ~> any
+
+    let foo = obj.foo;
+    foo(x); // error, taint ~> any
+  },
+];
diff --git a/tests/taint/call-object-property.js b/tests/taint/call-object-property.js
new file mode 100644
index 000000000000..7cece3014cf2
--- /dev/null
+++ b/tests/taint/call-object-property.js
@@ -0,0 +1,25 @@
+// @flow
+
+function foo(x : $Tainted<string>, o : Object) {
+  // Error
+  o.f(x);
+}
+function foo1(x : $Tainted<string>, o : {f : (y : $Tainted<string>) => void}) {
+  o.f(x);
+}
+function foo2(o1 : Object, o2 : {t : $Tainted<string>}) {
+  o1.f(o2.t);
+}
+function foo3<T>(x : $Tainted<T>, o : {f : (y : $Tainted<T>) => void}) {
+  o.f(x);
+}
+function f_foo1(x : $Tainted<string>, f : Function) {
+  // Error
+  f(x);
+}
+function f_foo2(f1 : Function, o : {t : $Tainted<string>}) {
+  f1(o.t);
+}
+function f_foo3(f1 : Function, o1 : Object, o2 : {t : $Tainted<string>}) {
+  (f1(o1))(o2.t);
+}
diff --git a/tests/taint/comparator.js b/tests/taint/comparator.js
new file mode 100644
index 000000000000..defe902f0c6f
--- /dev/null
+++ b/tests/taint/comparator.js
@@ -0,0 +1,18 @@
+// @flow
+// Should cause an error.
+function f(x : $Tainted<string>, y : $Tainted<number>) {
+  var z : $Tainted<bool> = x < y;
+}
+// Should cause an error.
+function f1(x : string, y : $Tainted<number>) {
+  var z : $Tainted<bool> = x < y;
+}
+// Should cause an error.
+function f2(x : $Tainted<string>, y : number) {
+  var z : $Tainted<bool> = x < y;
+}
+// Note: We allow removing Taint when two tainted
+// values are compared.
+function f3(x : $Tainted<string>, y : string) {
+  var z : bool = x < y;
+}
diff --git a/tests/taint/function.js b/tests/taint/function.js
new file mode 100644
index 000000000000..f007468ba5f8
--- /dev/null
+++ b/tests/taint/function.js
@@ -0,0 +1,14 @@
+// @flow
+
+let tests = [
+  // flows any to each param
+  function(x: any, y: $Tainted<string>) {
+    x(y); // error, taint ~> any
+  },
+
+  // calling `any` returns `any`
+  function(x: any, y: $Tainted<string>) {
+    let z = x();
+    z(y);
+  }
+];
diff --git a/tests/taint/globals.js b/tests/taint/globals.js
new file mode 100644
index 000000000000..18efa6515d2e
--- /dev/null
+++ b/tests/taint/globals.js
@@ -0,0 +1,12 @@
+// @flow
+
+class A {
+  f(x : $Tainted<FakeLocation>) {
+    fakeDocument.location = x; // error
+    doStuff(x); // ok
+  }
+  f1(x : $Tainted<FakeLocation>) {
+    // TODO(rcastano): should cause an error.
+    window.fakeLocation = x;
+  }
+}
diff --git a/tests/taint/jsfmt.spec.js b/tests/taint/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/taint/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/taint/lib.js b/tests/taint/lib.js
new file mode 100644
index 000000000000..3ca07bf6f6a4
--- /dev/null
+++ b/tests/taint/lib.js
@@ -0,0 +1,12 @@
+declare class FakeLocation {
+  assign(url: string): void;
+}
+
+declare class FakeDocument {
+  location: FakeLocation;
+}
+
+declare function doStuff(x: $Tainted<any>): void;
+
+declare var fakeDocument: FakeDocument;
+declare var fakeLocation: FakeLocation;
diff --git a/tests/taint/taint1.js b/tests/taint/taint1.js
new file mode 100644
index 000000000000..29b1260e0865
--- /dev/null
+++ b/tests/taint/taint1.js
@@ -0,0 +1,10 @@
+/*
+ *
+ * @flow
+ */
+class A {
+  f(tainted : $Tainted<string>) {
+    // This shouldn't give a warning (both are tainted)
+    var also_tainted : $Tainted<string> = tainted;
+  }
+}
diff --git a/tests/taint/taint2.js b/tests/taint/taint2.js
new file mode 100644
index 000000000000..7322d8fe84c6
--- /dev/null
+++ b/tests/taint/taint2.js
@@ -0,0 +1,10 @@
+/*
+ *
+ * @flow
+ */
+class A {
+  f(tainted : $Tainted<string>) {
+    // This *should* give a warning.
+    fakeDocument.location.assign(tainted);
+  }
+}
diff --git a/tests/taint/taint3.js b/tests/taint/taint3.js
new file mode 100644
index 000000000000..1e3cb105a7dd
--- /dev/null
+++ b/tests/taint/taint3.js
@@ -0,0 +1,12 @@
+/*
+ *
+ * @flow
+ */
+class A {
+  f(tainted : $Tainted<string>) {
+    // The Tainted annotation should still flow.
+    var safe = tainted;
+    // This should give a warning.
+    var loc : string = safe;
+  }
+}
diff --git a/tests/taint/taint4.js b/tests/taint/taint4.js
new file mode 100644
index 000000000000..61f2ee45b90f
--- /dev/null
+++ b/tests/taint/taint4.js
@@ -0,0 +1,13 @@
+/*
+ *
+ * @flow
+ */
+
+var safe : string = "safe";
+// This should be allowed.
+var tainted : $Tainted<string> = safe
+
+function f(x : $Tainted<any>) {
+  // Should cause error.
+  var y : any = x;
+}
diff --git a/tests/taint/use-types.js b/tests/taint/use-types.js
new file mode 100644
index 000000000000..07f081fec69e
--- /dev/null
+++ b/tests/taint/use-types.js
@@ -0,0 +1,32 @@
+/*
+ * @flow
+ */
+
+// Should cause an error.
+function foo (x : $Tainted<number>) {
+  var should_fail : number = x * 42;
+}
+// Should cause an error.
+function foo1 (x : $Tainted<{f: number}>) {
+  var ok : number = x.f;
+}
+// Should cause an error.
+function foo2 (o : {f (y:number):number}, t: $Tainted<number>) {
+  return o.f(t);
+}
+
+function foo3 (x : $Tainted<{f: number}>) {
+  var also_tainted : $Tainted<number> = x.f;
+}
+// Should cause an error.
+function foo4 (a : $Tainted<Array<string>>) {
+  var trusted : string = a[0];
+}
+// Type error.
+function foo5 (a : $Tainted<Array<string>>) {
+  var trusted_number : number = a[0];
+}
+
+function foo6 (a : $Tainted<Array<string>>) {
+  var trusted : $Tainted<string> = a[0];
+}
diff --git a/tests/template/__snapshots__/jsfmt.spec.js.snap b/tests/template/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..ad3180202c4f
--- /dev/null
+++ b/tests/template/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,64 @@
+exports[`test template.js 1`] = `
+"/* @flow */
+
+(\`foo\`: string); // ok
+(\`bar\`: 'bar'); // ok
+(\`baz\`: number); // error
+
+\`foo \${123} bar\`; // ok, number can be appended to string
+\`foo \${{bar: 123}} baz\`; // error, object can't be appended
+
+let tests = [
+  function(x: string) {
+    \`foo \${x}\`; // ok
+    \`\${x} bar\`; // ok
+    \`foo \${'bar'} \${x}\`; // ok
+  },
+  function(x: number) {
+    \`foo \${x}\`; // ok
+    \`\${x} bar\`; // ok
+    \`foo \${'bar'} \${x}\`; // ok
+  },
+  function(x: boolean) {
+    \`foo \${x}\`; // error
+    \`\${x} bar\`; // error
+    \`foo \${'bar'} \${x}\`; // error
+  },
+  function(x: mixed) {
+    \`foo \${x}\`; // error
+    \`\${x} bar\`; // error
+    \`foo \${'bar'} \${x}\`; // error
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+(\`foo\`: string);// ok
+(\`bar\`: "bar");// ok
+(\`baz\`: number);// error
+\`foo \${123} bar\`;// ok, number can be appended to string
+\`foo \${{ bar: 123 }} baz\`;// error, object can't be appended
+let tests = [
+  function(x: string) {
+    \`foo \${x}\`;// ok
+    \`\${x} bar\`;// ok
+    \`foo \${"bar"} \${x}\`;// ok
+  },
+  function(x: number) {
+    \`foo \${x}\`;// ok
+    \`\${x} bar\`;// ok
+    \`foo \${"bar"} \${x}\`;// ok
+  },
+  function(x: boolean) {
+    \`foo \${x}\`;// error
+    \`\${x} bar\`;// error
+    \`foo \${"bar"} \${x}\`;// error
+  },
+  function(x: mixed) {
+    \`foo \${x}\`;// error
+    \`\${x} bar\`;// error
+    \`foo \${"bar"} \${x}\`;// error
+  }
+];
+
+"
+`;
diff --git a/tests/template/jsfmt.spec.js b/tests/template/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/template/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/template/template.js b/tests/template/template.js
new file mode 100644
index 000000000000..5db2b3976cd3
--- /dev/null
+++ b/tests/template/template.js
@@ -0,0 +1,31 @@
+/* @flow */
+
+(`foo`: string); // ok
+(`bar`: 'bar'); // ok
+(`baz`: number); // error
+
+`foo ${123} bar`; // ok, number can be appended to string
+`foo ${{bar: 123}} baz`; // error, object can't be appended
+
+let tests = [
+  function(x: string) {
+    `foo ${x}`; // ok
+    `${x} bar`; // ok
+    `foo ${'bar'} ${x}`; // ok
+  },
+  function(x: number) {
+    `foo ${x}`; // ok
+    `${x} bar`; // ok
+    `foo ${'bar'} ${x}`; // ok
+  },
+  function(x: boolean) {
+    `foo ${x}`; // error
+    `${x} bar`; // error
+    `foo ${'bar'} ${x}`; // error
+  },
+  function(x: mixed) {
+    `foo ${x}`; // error
+    `${x} bar`; // error
+    `foo ${'bar'} ${x}`; // error
+  },
+];
diff --git a/tests/this/This.js b/tests/this/This.js
new file mode 100644
index 000000000000..6656c4ae0463
--- /dev/null
+++ b/tests/this/This.js
@@ -0,0 +1,60 @@
+/* @providesModule This */
+
+function F() { this.x = 0; }
+F.prototype.m = function() { this.y = 0; }
+
+function foo(p:string) { }
+
+var o1 = new F(); // sets o1.x to 0
+o1.x = "";
+foo(o1.x); // ok by definite assignment
+
+var o2 = new F();
+o1.y = 0;
+o2.y = "";
+foo(o2.y); // setting o1.y to 0 has no effect on o2.y
+
+var o3 = new F();
+o3.m(); // sets o3.y to 0
+o3.y = "";
+foo(o3.y); // ok by definite assignment
+foo(o2.y); // setting o3.y to 0 has no effect on o2.y
+
+/*
+ * this bindings:
+ */
+
+/* standard functions may rebind this */
+function f1() : number {
+  return this.x
+}
+
+var f1_1 = f1.bind({x: 0})();            // ok
+var f1_2 : string = f1.bind({x: 0})();   // error, number -> string
+var f1_3 = f1.bind({x: ""})();           // error, string -> number
+// TODO make this error blame the call site, rather than the function body
+var f1_4 = f1();                         // error, (global object).x
+
+/* arrow functions bind this at point of definition */
+/* top level arrow functions bind this to global object */
+var a1 = () => {
+  return this.x
+}
+
+var ax = a1();                          // error, (this:mixed).x
+
+/* nested arrows bind enclosing this (which may itself rebind) */
+function f2() : number {
+    var a2 = () => { return this.x };
+    return a2()
+}
+
+var f2_1 = f2.bind({x: 0})();            // ok
+var f2_2 : string = f2.bind({x: 0})();   // error, number -> string
+var f2_3 = f2.bind({x: ""})();           // error, string -> number
+// TODO make this error blame the call site, rather than the function body
+var f2_4 = f2();                         // error, (global object).x
+
+(this: void);
+
+module.exports = true;
diff --git a/tests/this/__snapshots__/jsfmt.spec.js.snap b/tests/this/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9541761fed9f
--- /dev/null
+++ b/tests/this/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,184 @@
+exports[`test This.js 1`] = `
+"/* @providesModule This */
+
+function F() { this.x = 0; }
+F.prototype.m = function() { this.y = 0; }
+
+function foo(p:string) { }
+
+var o1 = new F(); // sets o1.x to 0
+o1.x = "";
+foo(o1.x); // ok by definite assignment
+
+var o2 = new F();
+o1.y = 0;
+o2.y = "";
+foo(o2.y); // setting o1.y to 0 has no effect on o2.y
+
+var o3 = new F();
+o3.m(); // sets o3.y to 0
+o3.y = "";
+foo(o3.y); // ok by definite assignment
+foo(o2.y); // setting o3.y to 0 has no effect on o2.y
+
+/*
+ * this bindings:
+ */
+
+/* standard functions may rebind this */
+function f1() : number {
+  return this.x
+}
+
+var f1_1 = f1.bind({x: 0})();            // ok
+var f1_2 : string = f1.bind({x: 0})();   // error, number -> string
+var f1_3 = f1.bind({x: ""})();           // error, string -> number
+// TODO make this error blame the call site, rather than the function body
+var f1_4 = f1();                         // error, (global object).x
+
+/* arrow functions bind this at point of definition */
+/* top level arrow functions bind this to global object */
+var a1 = () => {
+  return this.x
+}
+
+var ax = a1();                          // error, (this:mixed).x
+
+/* nested arrows bind enclosing this (which may itself rebind) */
+function f2() : number {
+    var a2 = () => { return this.x };
+    return a2()
+}
+
+var f2_1 = f2.bind({x: 0})();            // ok
+var f2_2 : string = f2.bind({x: 0})();   // error, number -> string
+var f2_3 = f2.bind({x: ""})();           // error, string -> number
+// TODO make this error blame the call site, rather than the function body
+var f2_4 = f2();                         // error, (global object).x
+
+(this: void);
+
+module.exports = true;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule This */
+function F() {
+  this.x = 0;
+}
+F.prototype.m = function() {
+  this.y = 0;
+};
+function foo(p: string) {
+  
+}
+var o1 = new F();// sets o1.x to 0
+o1.x = "";
+foo(o1.x);// ok by definite assignment
+var o2 = new F();
+o1.y = 0;
+o2.y = "";
+foo(o2.y);// setting o1.y to 0 has no effect on o2.y
+var o3 = new F();
+o3.m();// sets o3.y to 0
+o3.y = "";
+foo(o3.y);// ok by definite assignment
+foo(o2.y);// setting o3.y to 0 has no effect on o2.y
+/*
+ * this bindings:
+ */
+/* standard functions may rebind this */
+function f1(): number {
+  return this.x;
+}
+var f1_1 = f1.bind({ x: 0 })();// ok
+var f1_2: string = f1.bind({ x: 0 })();// error, number -> string
+var f1_3 = f1.bind({ x: "" })();// error, string -> number
+// TODO make this error blame the call site, rather than the function body
+var f1_4 = f1();// error, (global object).x
+/* arrow functions bind this at point of definition */
+/* top level arrow functions bind this to global object */
+var a1 = () => {
+  return this.x;
+};
+var ax = a1();// error, (this:mixed).x
+/* nested arrows bind enclosing this (which may itself rebind) */
+function f2(): number {
+  var a2 = () => {
+    return this.x;
+  };
+  return a2();
+}
+var f2_1 = f2.bind({ x: 0 })();// ok
+var f2_2: string = f2.bind({ x: 0 })();// error, number -> string
+var f2_3 = f2.bind({ x: "" })();// error, string -> number
+// TODO make this error blame the call site, rather than the function body
+var f2_4 = f2();// error, (global object).x
+(this: void);
+module.exports = true;
+
+"
+`;
+
+exports[`test arrows.js 1`] = `
+"class C {
+  foo() {
+    return () => { return this.bar(); }; // OK, since this: C
+  }
+  bar() { return this; } // return type is C
+}
+var c = new C;
+var f = c.foo();
+var i = f(); // OK
+(i: C); // OK
+
+class D extends C { }
+var d = new D;
+var g = d.foo();
+var j = g(); // OK
+(j: D); // error, since return type of bar is C, not the type of \`this\`
+
+class E {
+  foo(x: number) { }
+}
+class F extends E {
+  foo() { // OK to override with generalization
+    (() => {
+      super.foo(""); // find super method, error due to incorrect arg
+    })();
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  foo() {
+    return () => {
+      return this.bar();
+    };// OK, since this: C
+  }
+  bar() {
+    return this;
+  }// return type is C
+}
+var c = new C();
+var f = c.foo();
+var i = f();// OK
+(i: C);// OK
+class D extends C {}
+var d = new D();
+var g = d.foo();
+var j = g();// OK
+(j: D);// error, since return type of bar is C, not the type of \`this\`
+class E {
+  foo(x: number) {
+    
+  }
+}
+class F extends E {
+  foo() {
+    // OK to override with generalization
+    (() => {
+      super.foo("");// find super method, error due to incorrect arg
+    })();
+  }
+}
+
+"
+`;
diff --git a/tests/this/arrows.js b/tests/this/arrows.js
new file mode 100644
index 000000000000..2217bf0b7d56
--- /dev/null
+++ b/tests/this/arrows.js
@@ -0,0 +1,27 @@
+class C {
+  foo() {
+    return () => { return this.bar(); }; // OK, since this: C
+  }
+  bar() { return this; } // return type is C
+}
+var c = new C;
+var f = c.foo();
+var i = f(); // OK
+(i: C); // OK
+
+class D extends C { }
+var d = new D;
+var g = d.foo();
+var j = g(); // OK
+(j: D); // error, since return type of bar is C, not the type of `this`
+
+class E {
+  foo(x: number) { }
+}
+class F extends E {
+  foo() { // OK to override with generalization
+    (() => {
+      super.foo(""); // find super method, error due to incorrect arg
+    })();
+  }
+}
diff --git a/tests/this/jsfmt.spec.js b/tests/this/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/this/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/this_ctor/__snapshots__/jsfmt.spec.js.snap b/tests/this_ctor/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2c702518c36a
--- /dev/null
+++ b/tests/this_ctor/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,36 @@
+exports[`test test.js 1`] = `
+"class A {
+  n: number;
+  constructor(n: number) {
+    this.n = n;
+  }
+  clone(): A {
+    return new this.constructor(this.n);
+  }
+  badClone(): number {
+    return new this.constructor(this.n); // Error A ~> number
+  }
+}
+
+var a1 = new A(1);
+var a2: A = new a1.constructor(2);
+var a3: A = a2.clone();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {
+  n: number;
+  constructor(n: number) {
+    this.n = n;
+  }
+  clone(): A {
+    return new this.constructor(this.n);
+  }
+  badClone(): number {
+    return new this.constructor(this.n);// Error A ~> number
+  }
+}
+var a1 = new A(1);
+var a2: A = new a1.constructor(2);
+var a3: A = a2.clone();
+
+"
+`;
diff --git a/tests/this_ctor/jsfmt.spec.js b/tests/this_ctor/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/this_ctor/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/this_ctor/test.js b/tests/this_ctor/test.js
new file mode 100644
index 000000000000..cbcc6e218d1f
--- /dev/null
+++ b/tests/this_ctor/test.js
@@ -0,0 +1,16 @@
+class A {
+  n: number;
+  constructor(n: number) {
+    this.n = n;
+  }
+  clone(): A {
+    return new this.constructor(this.n);
+  }
+  badClone(): number {
+    return new this.constructor(this.n); // Error A ~> number
+  }
+}
+
+var a1 = new A(1);
+var a2: A = new a1.constructor(2);
+var a3: A = a2.clone();
diff --git a/tests/this_type/__snapshots__/jsfmt.spec.js.snap b/tests/this_type/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..887bf7880742
--- /dev/null
+++ b/tests/this_type/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,474 @@
+exports[`test class_expr.js 1`] = `
+"/* @flow */
+// issue #1191
+
+const Thing = class Thing {
+  zark() {
+    this.x = 123; // error: property not found (must be declared)
+  }
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// issue #1191
+const Thing = class Thing {
+  zark() {
+    this.x = 123;// error: property not found (must be declared)
+  }
+};
+
+"
+`;
+
+exports[`test contra.js 1`] = `
+"// Counterexample with contravariant this type
+
+class C {
+  next: this; // error (see below for exploit): \`this\` should only appear in
+              // covariant positions
+}
+
+class D extends C { }
+
+var d = new D();
+(d: C).next = new C;
+(d.next: D); // sneaky
+
+class A {
+  foo<X: this>(that: X) { } // error: can\'t hide contravariance using a bound
+}
+
+class B extends A {
+  foo<Y: this>(that: Y) { } // error (see above, catches hidden override)
+}
+
+// covariance checks on this type in invariant positions
+
+class Invariant {
+  out_object(): { _: this } { return { _: this }; }
+  in_object(_: { _: this }) { }
+  inout_object: { _: this };
+
+  out_array(): Array<this> { return [this]; }
+  in_array(_: Array<this>) { }
+  inout_array: Array<this>;
+}
+
+// covariance checks on this type as type args
+
+class Misc {
+  // Set<X> has invariant X
+  out_set(): Set<this> { return new Set().add(this); }
+  in_set(_: Set<this>) { }
+  inout_set: Set<this>;
+
+  // Promise<X> has covariant X
+  async out_promise(): Promise<this> { return this; }
+  in_promise(_: Promise<this>) { }
+  inout_promise: Promise<this>;
+
+  // Generator<X,Y,Z> has covariant X, covariant Y, contravariant Z
+  *out_generator(): Generator<this,this,this> {
+    yield this;
+    return this;
+  }
+  in_generator(_: Generator<this,this,this>) { }
+  inout_generator: Generator<this,this,this>;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test export.js 1`] = `
+"export class A1 {
+  foo(): this { return this; }
+  bar(): this { return this; }
+}
+
+export class A2<X> {
+  foo(): this { return this; }
+  bar(): this { return this; }
+  qux(x: X): X { return x; }
+}
+
+export class A3<X> extends A2<X> {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test generics.js 1`] = `
+"class Generic<X> {
+  clone(): Generic<X> { return this; }
+}
+
+class Implicit<X> { arg: X; val: X; }
+class ImplicitNumber extends Implicit { arg: number; }
+
+(new ImplicitNumber().val: string) // error: number ~> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test import.js 1`] = `
+"// Check that imports are handled properly with this types
+
+import { A1 } from \'./export\';
+import type { A2 } from \'./export\';
+import { A3 } from \'./export\';
+
+class B1 extends A1 {
+  foo(): B1 { return new B1(); } // error
+}
+
+(new B1().bar(): B1); // OK
+
+class B3<X> extends A3<X> {
+  foo(): B3<X> { return new B3(); } // error
+}
+
+(new B3().bar(): B3<*>); // OK
+(new B3().qux(0): string); // error
+
+(new B3().bar(): A2<*>); // OK
+((new B3().bar(): B3<string>): A2<number>); // error
+((new B3(): A2<number>).qux(0): string); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test interface.js 1`] = `
+"interface I { xs: Array<this>; }
+interface J { f(): J; }
+class C {
+  xs: Array<C>;
+  f(): C { return this; }
+}
+function foo(c: C): I { return c; }
+function bar(c: C): J { return c; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
+
+exports[`test lib_client.js 1`] = `
+"(new DoublyLinkedList().prev(): DoublyLinkedList);
+(new DoublyLinkedList().next(): DoublyLinkedList)
+
+var MiniImmutable = require(\"mini-immutable\");
+class C {
+  map: MiniImmutable.OrderedMap<number,string>;
+  update() {
+    this.map = this.map.set(0,\"\");
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test self.js 1`] = `
+"class A {
+  foo() { return this; } // return of foo is not annotated to get around
+                         // substituting this below
+  bar(): this { return new A().foo(); } // same as returning : A, so error
+  qux(): this { return this.bar(); } // OK (don\'t cascade errors)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class A {
+  foo() {
+    return this;
+  }// return of foo is not annotated to get around// substituting this below
+  bar(): this {
+    return new A().foo();
+  }// same as returning : A, so error
+  qux(): this {
+    return this.bar();
+  }// OK (don\'t cascade errors)
+}
+
+"
+`;
+
+exports[`test statics.js 1`] = `
+"// supporting \`this\` type in statics
+
+class A {
+  static make(): this { // factory method, whose return type \`this\` (still)
+                        // describes instances of A or subclasses of A: the
+                        // meaning of the \`this\` type is not changed simply by
+                        // switching into a static context
+    return new this; // but in a static context, the value \`this\` is bound to
+                     // the class, instead of instances of the class
+  }
+}
+class B extends A { } // inherits statics method too, with \`this\` bound to the class
+
+(A.make(): A); // OK
+(B.make(): B); // OK
+(B.make(): A); // OK
+(A.make(): B); // error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// supporting \`this\` type in statics
+class A {
+  make(): this {
+    // factory method, whose return type \`this\` (still)
+    // describes instances of A or subclasses of A: the
+    // meaning of the \`this\` type is not changed simply by
+    // switching into a static context
+    return new this();// but in a static context, the value \`this\` is bound to// the class, instead of instances of the class
+  }
+}
+class B extends A {}// inherits statics method too, with \`this\` bound to the class
+(A.make(): A);// OK
+(B.make(): B);// OK
+(B.make(): A);// OK
+(A.make(): B);// error
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"// Examples without \`this\` types (compare with examples below)
+
+class Base {
+  foo() { return this; }
+  qux() { return new Base; }
+
+  bar() { return this; }
+  bar_caller() { return this.bar(); }
+}
+
+class Inherit extends Base { }
+
+class Override extends Base {
+  foo() { return this; } // OK
+  qux() { return this; } // OK, too
+
+  bar() { return new Override; } // OK (cf. error below)
+}
+
+class InheritOverride extends Override { }
+
+(new Inherit().foo(): Base);
+(new Inherit().foo(): Inherit); // error (cf. OK below)
+((new Inherit(): Base).foo(): Base);
+(new Override().foo(): Base);
+(new Override().foo(): Override); // OK
+((new Override(): Base).foo(): Base);
+
+(new InheritOverride().bar_caller(): InheritOverride); // error
+                                                       // blame flips below
+
+// Examples with \`this\` types (compare with examples above)
+
+class Base2 {
+  foo(): this { return this; }
+  qux(): Base2 { return new Base2; }
+
+  bar(): this { return this; }
+  bar_caller(): this { return this.bar(); }
+
+  corge(that: this) { }
+  grault(that: Base2) { }
+}
+
+class Inherit2 extends Base2 { }
+
+class Override2 extends Base2 {
+  foo(): this { return this; } // OK
+  qux(): this { return this; } // OK, too
+
+  bar(): Override2 { return new Override2; } // error (cf. OK above)
+                                             // see exploit below
+
+  corge(that: this) { } // error
+                        // see exploit below
+  grault(that: this) { } // error, too
+}
+
+class InheritOverride2 extends Override2 { }
+
+(new Inherit2().foo(): Base2);
+(new Inherit2().foo(): Inherit2); // OK (cf. error above)
+((new Inherit2(): Base2).foo(): Base2);
+(new Override2().foo(): Base2);
+(new Override2().foo(): Override2); // OK
+((new Override2(): Base2).foo(): Base2);
+
+(new InheritOverride2().bar_caller(): InheritOverride2); // exploits error above
+
+(new Override2(): Base2).corge(new Base2()); // exploits error above
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// Examples without \`this\` types (compare with examples below)
+class Base {
+  foo() {
+    return this;
+  }
+  qux() {
+    return new Base();
+  }
+  bar() {
+    return this;
+  }
+  bar_caller() {
+    return this.bar();
+  }
+}
+class Inherit extends Base {}
+class Override extends Base {
+  foo() {
+    return this;
+  }// OK
+  qux() {
+    return this;
+  }// OK, too
+  bar() {
+    return new Override();
+  }// OK (cf. error below)
+}
+class InheritOverride extends Override {}
+(new Inherit().foo(): Base);
+(new Inherit().foo(): Inherit);// error (cf. OK below)
+((new Inherit(): Base).foo(): Base);
+(new Override().foo(): Base);
+(new Override().foo(): Override);// OK
+((new Override(): Base).foo(): Base);
+(new InheritOverride().bar_caller(): InheritOverride);// error// blame flips below
+// Examples with \`this\` types (compare with examples above)
+class Base2 {
+  foo(): this {
+    return this;
+  }
+  qux(): Base2 {
+    return new Base2();
+  }
+  bar(): this {
+    return this;
+  }
+  bar_caller(): this {
+    return this.bar();
+  }
+  corge(that: this) {
+    
+  }
+  grault(that: Base2) {
+    
+  }
+}
+class Inherit2 extends Base2 {}
+class Override2 extends Base2 {
+  foo(): this {
+    return this;
+  }// OK
+  qux(): this {
+    return this;
+  }// OK, too
+  bar(): Override2 {
+    return new Override2();
+  }// error (cf. OK above)// see exploit below
+  corge(that: this) {
+    
+  }// error// see exploit below
+  grault(that: this) {
+    
+  }// error, too
+}
+class InheritOverride2 extends Override2 {}
+(new Inherit2().foo(): Base2);
+(new Inherit2().foo(): Inherit2);// OK (cf. error above)
+((new Inherit2(): Base2).foo(): Base2);
+(new Override2().foo(): Base2);
+(new Override2().foo(): Override2);// OK
+((new Override2(): Base2).foo(): Base2);
+(new InheritOverride2().bar_caller(): InheritOverride2);// exploits error above
+(new Override2(): Base2).corge(new Base2());// exploits error above
+
+"
+`;
diff --git a/tests/this_type/class_expr.js b/tests/this_type/class_expr.js
new file mode 100644
index 000000000000..9001dfc7b639
--- /dev/null
+++ b/tests/this_type/class_expr.js
@@ -0,0 +1,8 @@
+/* @flow */
+// issue #1191
+
+const Thing = class Thing {
+  zark() {
+    this.x = 123; // error: property not found (must be declared)
+  }
+};
diff --git a/tests/this_type/contra.js b/tests/this_type/contra.js
new file mode 100644
index 000000000000..1bb3c3397614
--- /dev/null
+++ b/tests/this_type/contra.js
@@ -0,0 +1,54 @@
+// Counterexample with contravariant this type
+
+class C {
+  next: this; // error (see below for exploit): `this` should only appear in
+              // covariant positions
+}
+
+class D extends C { }
+
+var d = new D();
+(d: C).next = new C;
+(d.next: D); // sneaky
+
+class A {
+  foo<X: this>(that: X) { } // error: can't hide contravariance using a bound
+}
+
+class B extends A {
+  foo<Y: this>(that: Y) { } // error (see above, catches hidden override)
+}
+
+// covariance checks on this type in invariant positions
+
+class Invariant {
+  out_object(): { _: this } { return { _: this }; }
+  in_object(_: { _: this }) { }
+  inout_object: { _: this };
+
+  out_array(): Array<this> { return [this]; }
+  in_array(_: Array<this>) { }
+  inout_array: Array<this>;
+}
+
+// covariance checks on this type as type args
+
+class Misc {
+  // Set<X> has invariant X
+  out_set(): Set<this> { return new Set().add(this); }
+  in_set(_: Set<this>) { }
+  inout_set: Set<this>;
+
+  // Promise<X> has covariant X
+  async out_promise(): Promise<this> { return this; }
+  in_promise(_: Promise<this>) { }
+  inout_promise: Promise<this>;
+
+  // Generator<X,Y,Z> has covariant X, covariant Y, contravariant Z
+  *out_generator(): Generator<this,this,this> {
+    yield this;
+    return this;
+  }
+  in_generator(_: Generator<this,this,this>) { }
+  inout_generator: Generator<this,this,this>;
+}
diff --git a/tests/this_type/export.js b/tests/this_type/export.js
new file mode 100644
index 000000000000..57303de679e7
--- /dev/null
+++ b/tests/this_type/export.js
@@ -0,0 +1,12 @@
+export class A1 {
+  foo(): this { return this; }
+  bar(): this { return this; }
+}
+
+export class A2<X> {
+  foo(): this { return this; }
+  bar(): this { return this; }
+  qux(x: X): X { return x; }
+}
+
+export class A3<X> extends A2<X> {}
diff --git a/tests/this_type/generics.js b/tests/this_type/generics.js
new file mode 100644
index 000000000000..0514ed85ae1f
--- /dev/null
+++ b/tests/this_type/generics.js
@@ -0,0 +1,8 @@
+class Generic<X> {
+  clone(): Generic<X> { return this; }
+}
+
+class Implicit<X> { arg: X; val: X; }
+class ImplicitNumber extends Implicit { arg: number; }
+
+(new ImplicitNumber().val: string) // error: number ~> string
diff --git a/tests/this_type/import.js b/tests/this_type/import.js
new file mode 100644
index 000000000000..b742e07d7a68
--- /dev/null
+++ b/tests/this_type/import.js
@@ -0,0 +1,22 @@
+// Check that imports are handled properly with this types
+
+import { A1 } from './export';
+import type { A2 } from './export';
+import { A3 } from './export';
+
+class B1 extends A1 {
+  foo(): B1 { return new B1(); } // error
+}
+
+(new B1().bar(): B1); // OK
+
+class B3<X> extends A3<X> {
+  foo(): B3<X> { return new B3(); } // error
+}
+
+(new B3().bar(): B3<*>); // OK
+(new B3().qux(0): string); // error
+
+(new B3().bar(): A2<*>); // OK
+((new B3().bar(): B3<string>): A2<number>); // error
+((new B3(): A2<number>).qux(0): string); // error
diff --git a/tests/this_type/interface.js b/tests/this_type/interface.js
new file mode 100644
index 000000000000..0c1de6a4c9a2
--- /dev/null
+++ b/tests/this_type/interface.js
@@ -0,0 +1,8 @@
+interface I { xs: Array<this>; }
+interface J { f(): J; }
+class C {
+  xs: Array<C>;
+  f(): C { return this; }
+}
+function foo(c: C): I { return c; }
+function bar(c: C): J { return c; }
diff --git a/tests/this_type/jsfmt.spec.js b/tests/this_type/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/this_type/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/this_type/lib/__snapshots__/jsfmt.spec.js.snap b/tests/this_type/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..04cd629de70f
--- /dev/null
+++ b/tests/this_type/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,38 @@
+exports[`test decl.js 1`] = `
+"// The following declare classes use \`this\` types effectively to avoid type
+// errors in ../lib_client.js. If support for \`this\` types in declare classes
+// is disabled for perf reasons, these will produce warnings.
+
+declare class LinkedList {
+  next(): this;
+}
+declare class DoublyLinkedList extends LinkedList {
+  prev(): this;
+}
+
+declare module \"mini-immutable\" {
+  declare class Map<K,V> {
+    set(key: K, value: V): this; // more precise than Map<K,V> (see below)
+  }
+  declare class OrderedMap<K,V> extends Map<K,V> {
+    // inherits set method returning OrderedMap<K,V> instead of Map<K,V>
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/this_type/lib/decl.js b/tests/this_type/lib/decl.js
new file mode 100644
index 000000000000..f3f3e398a68e
--- /dev/null
+++ b/tests/this_type/lib/decl.js
@@ -0,0 +1,19 @@
+// The following declare classes use `this` types effectively to avoid type
+// errors in ../lib_client.js. If support for `this` types in declare classes
+// is disabled for perf reasons, these will produce warnings.
+
+declare class LinkedList {
+  next(): this;
+}
+declare class DoublyLinkedList extends LinkedList {
+  prev(): this;
+}
+
+declare module "mini-immutable" {
+  declare class Map<K,V> {
+    set(key: K, value: V): this; // more precise than Map<K,V> (see below)
+  }
+  declare class OrderedMap<K,V> extends Map<K,V> {
+    // inherits set method returning OrderedMap<K,V> instead of Map<K,V>
+  }
+}
diff --git a/tests/this_type/lib/jsfmt.spec.js b/tests/this_type/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/this_type/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/this_type/lib_client.js b/tests/this_type/lib_client.js
new file mode 100644
index 000000000000..e646c7d721ab
--- /dev/null
+++ b/tests/this_type/lib_client.js
@@ -0,0 +1,10 @@
+(new DoublyLinkedList().prev(): DoublyLinkedList);
+(new DoublyLinkedList().next(): DoublyLinkedList)
+
+var MiniImmutable = require("mini-immutable");
+class C {
+  map: MiniImmutable.OrderedMap<number,string>;
+  update() {
+    this.map = this.map.set(0,"");
+  }
+}
diff --git a/tests/this_type/self.js b/tests/this_type/self.js
new file mode 100644
index 000000000000..68a8db1e0f2d
--- /dev/null
+++ b/tests/this_type/self.js
@@ -0,0 +1,6 @@
+class A {
+  foo() { return this; } // return of foo is not annotated to get around
+                         // substituting this below
+  bar(): this { return new A().foo(); } // same as returning : A, so error
+  qux(): this { return this.bar(); } // OK (don't cascade errors)
+}
diff --git a/tests/this_type/statics.js b/tests/this_type/statics.js
new file mode 100644
index 000000000000..c2ed665599c6
--- /dev/null
+++ b/tests/this_type/statics.js
@@ -0,0 +1,17 @@
+// supporting `this` type in statics
+
+class A {
+  static make(): this { // factory method, whose return type `this` (still)
+                        // describes instances of A or subclasses of A: the
+                        // meaning of the `this` type is not changed simply by
+                        // switching into a static context
+    return new this; // but in a static context, the value `this` is bound to
+                     // the class, instead of instances of the class
+  }
+}
+class B extends A { } // inherits statics method too, with `this` bound to the class
+
+(A.make(): A); // OK
+(B.make(): B); // OK
+(B.make(): A); // OK
+(A.make(): B); // error
diff --git a/tests/this_type/test.js b/tests/this_type/test.js
new file mode 100644
index 000000000000..a47b3ca57ca8
--- /dev/null
+++ b/tests/this_type/test.js
@@ -0,0 +1,70 @@
+// Examples without `this` types (compare with examples below)
+
+class Base {
+  foo() { return this; }
+  qux() { return new Base; }
+
+  bar() { return this; }
+  bar_caller() { return this.bar(); }
+}
+
+class Inherit extends Base { }
+
+class Override extends Base {
+  foo() { return this; } // OK
+  qux() { return this; } // OK, too
+
+  bar() { return new Override; } // OK (cf. error below)
+}
+
+class InheritOverride extends Override { }
+
+(new Inherit().foo(): Base);
+(new Inherit().foo(): Inherit); // error (cf. OK below)
+((new Inherit(): Base).foo(): Base);
+(new Override().foo(): Base);
+(new Override().foo(): Override); // OK
+((new Override(): Base).foo(): Base);
+
+(new InheritOverride().bar_caller(): InheritOverride); // error
+                                                       // blame flips below
+
+// Examples with `this` types (compare with examples above)
+
+class Base2 {
+  foo(): this { return this; }
+  qux(): Base2 { return new Base2; }
+
+  bar(): this { return this; }
+  bar_caller(): this { return this.bar(); }
+
+  corge(that: this) { }
+  grault(that: Base2) { }
+}
+
+class Inherit2 extends Base2 { }
+
+class Override2 extends Base2 {
+  foo(): this { return this; } // OK
+  qux(): this { return this; } // OK, too
+
+  bar(): Override2 { return new Override2; } // error (cf. OK above)
+                                             // see exploit below
+
+  corge(that: this) { } // error
+                        // see exploit below
+  grault(that: this) { } // error, too
+}
+
+class InheritOverride2 extends Override2 { }
+
+(new Inherit2().foo(): Base2);
+(new Inherit2().foo(): Inherit2); // OK (cf. error above)
+((new Inherit2(): Base2).foo(): Base2);
+(new Override2().foo(): Base2);
+(new Override2().foo(): Override2); // OK
+((new Override2(): Base2).foo(): Base2);
+
+(new InheritOverride2().bar_caller(): InheritOverride2); // exploits error above
+
+(new Override2(): Base2).corge(new Base2()); // exploits error above
diff --git a/tests/throw/__snapshots__/jsfmt.spec.js.snap b/tests/throw/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..14240dc16502
--- /dev/null
+++ b/tests/throw/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,46 @@
+exports[`test test.js 1`] = `
+"/**
+ * @flow
+ */
+
+function f(): number {
+    throw new Error(); // OK to not return
+}
+
+function g(a: ?string) {
+    if (a == null) {
+        throw new Error();
+    }
+    return a*1; // a is not null
+}
+
+function h(x: number): string {
+  if (x) {
+    return 'foo';
+  } else {
+    throw new Error();
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+function f(): number {
+  throw new Error();// OK to not return
+}
+function g(a: ?string) {
+  if (a == null) {
+    throw new Error();
+  }
+  return a * 1;// a is not null
+}
+function h(x: number): string {
+  if (x) {
+    return "foo";
+  } else {
+    throw new Error();
+  }
+}
+
+"
+`;
diff --git a/tests/throw/jsfmt.spec.js b/tests/throw/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/throw/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/throw/test.js b/tests/throw/test.js
new file mode 100644
index 000000000000..a77bd4752c38
--- /dev/null
+++ b/tests/throw/test.js
@@ -0,0 +1,22 @@
+/**
+ * @flow
+ */
+
+function f(): number {
+    throw new Error(); // OK to not return
+}
+
+function g(a: ?string) {
+    if (a == null) {
+        throw new Error();
+    }
+    return a*1; // a is not null
+}
+
+function h(x: number): string {
+  if (x) {
+    return 'foo';
+  } else {
+    throw new Error();
+  }
+}
diff --git a/tests/traces/Traces.js b/tests/traces/Traces.js
new file mode 100644
index 000000000000..50dc2194f4c5
--- /dev/null
+++ b/tests/traces/Traces.js
@@ -0,0 +1,20 @@
+// arg/param type mismatch on arg 0
+function g0(y:string) { }
+function f0(x) { g0(x) }
+f0(0);
+
+// ...on arg n
+function g1(a:string, b:string) { }
+function f1(x, y) { g1(x, y) }
+f1("hey", 0);
+
+// h/o call with function expr
+function g2(ylam: (s:string) => number) { }
+function f2(xlam) { g2(xlam) }
+f2(function(x) { return x * x });
+
+// h/o call with function def
+function g3(ylam: (s:string) => number) { }
+function f3(xlam) { g3(xlam) }
+function double(n) { return n * 2 }
+f3(double);
diff --git a/tests/traces/Traces2.js b/tests/traces/Traces2.js
new file mode 100644
index 000000000000..89089d9a4f2f
--- /dev/null
+++ b/tests/traces/Traces2.js
@@ -0,0 +1,19 @@
+// @flow
+
+var React = require('react');
+
+var A = React.createClass({
+  propTypes: { foo: React.PropTypes.string.isRequired }
+});
+
+var B = React.createClass({
+  propTypes: { bar: React.PropTypes.string.isRequired }
+});
+
+function f(b): React.Element<*> {
+  if (b) {
+    return <A foo="hey"/>;
+  } else {
+    return <B bar="hey"/>;
+  }
+}
diff --git a/tests/traces/__snapshots__/jsfmt.spec.js.snap b/tests/traces/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..18c2d489deab
--- /dev/null
+++ b/tests/traces/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,78 @@
+exports[`test Traces.js 1`] = `
+"// arg/param type mismatch on arg 0
+function g0(y:string) { }
+function f0(x) { g0(x) }
+f0(0);
+
+// ...on arg n
+function g1(a:string, b:string) { }
+function f1(x, y) { g1(x, y) }
+f1(\"hey\", 0);
+
+// h/o call with function expr
+function g2(ylam: (s:string) => number) { }
+function f2(xlam) { g2(xlam) }
+f2(function(x) { return x * x });
+
+// h/o call with function def
+function g3(ylam: (s:string) => number) { }
+function f3(xlam) { g3(xlam) }
+function double(n) { return n * 2 }
+f3(double);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test Traces2.js 1`] = `
+"// @flow
+
+var React = require(\'react\');
+
+var A = React.createClass({
+  propTypes: { foo: React.PropTypes.string.isRequired }
+});
+
+var B = React.createClass({
+  propTypes: { bar: React.PropTypes.string.isRequired }
+});
+
+function f(b): React.Element<*> {
+  if (b) {
+    return <A foo=\"hey\"/>;
+  } else {
+    return <B bar=\"hey\"/>;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/traces/jsfmt.spec.js b/tests/traces/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/traces/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/traits/__snapshots__/jsfmt.spec.js.snap b/tests/traits/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..65e29e8fc244
--- /dev/null
+++ b/tests/traits/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,54 @@
+exports[`test test.js 1`] = `
+"declare class Foo extends Qux<string> mixins Bar<number> {
+  // KeyedCollection <: Collection
+  // ...KeyedIterable
+}
+declare class Bar<T> extends Baz<T> {
+  // KeyedIterable <: Iterable
+  y: T
+}
+declare class Qux<T> extends Baz<T> {
+  // Collection <: Iterable
+  y: T, z: T
+}
+declare class Baz<T> {
+  // Iterable
+  x: T
+}
+
+((new Foo).x: number); // error: Qux wins
+((new Foo).y: string); // error: Bar wins
+((new Foo).z: number); // error: Qux wins
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare class Foo {}
+declare class Bar { // KeyedIterable <: Iterable y: T }
+declare class Qux { // Collection <: Iterable y: T, z: T }
+declare class Baz { // Iterable x: T }
+(new Foo().x: number);// error: Qux wins
+(new Foo().y: string);// error: Bar wins
+(new Foo().z: number);// error: Qux wins
+
+"
+`;
+
+exports[`test test2.js 1`] = `
+"declare interface I { }
+declare class C mixins I { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1391
+          fromString(\", \").join(path.map(print, \"extends\"))
+                           ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1391:28)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at /src/printer.js:1601:18
+    at FastPath.map (/src/fast-path.js:167:19)
+    at printStatementSequence (/src/printer.js:1586:8)
+    at /src/printer.js:238:16
+    at FastPath.call (/src/fast-path.js:113:16)
+"
+`;
diff --git a/tests/traits/jsfmt.spec.js b/tests/traits/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/traits/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/traits/test.js b/tests/traits/test.js
new file mode 100644
index 000000000000..569907ac1a9c
--- /dev/null
+++ b/tests/traits/test.js
@@ -0,0 +1,20 @@
+declare class Foo extends Qux<string> mixins Bar<number> {
+  // KeyedCollection <: Collection
+  // ...KeyedIterable
+}
+declare class Bar<T> extends Baz<T> {
+  // KeyedIterable <: Iterable
+  y: T
+}
+declare class Qux<T> extends Baz<T> {
+  // Collection <: Iterable
+  y: T, z: T
+}
+declare class Baz<T> {
+  // Iterable
+  x: T
+}
+
+((new Foo).x: number); // error: Qux wins
+((new Foo).y: string); // error: Bar wins
+((new Foo).z: number); // error: Qux wins
diff --git a/tests/traits/test2.js b/tests/traits/test2.js
new file mode 100644
index 000000000000..244d25a93ed5
--- /dev/null
+++ b/tests/traits/test2.js
@@ -0,0 +1,2 @@
+declare interface I { }
+declare class C mixins I { }
diff --git a/tests/try/__snapshots__/jsfmt.spec.js.snap b/tests/try/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1174df0a3b97
--- /dev/null
+++ b/tests/try/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,567 @@
+exports[`test abnormals.js 1`] = `
+"/* @flow */
+
+/* This test documents an issue we used to have with merging the environment of
+ * the try block and the catch block. The error variable, when inspected and in
+ * the presence of an abnormal, would sometimes kind of leak. It would hit an
+ * abnormal. It was weird.
+ */
+function foo() {
+  try {
+  } catch(error) {
+    if (error.foo === 4) {
+      throw error;
+    }
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+/* This test documents an issue we used to have with merging the environment of
+ * the try block and the catch block. The error variable, when inspected and in
+ * the presence of an abnormal, would sometimes kind of leak. It would hit an
+ * abnormal. It was weird.
+ */
+function foo() {
+  try {
+    
+  } catch (error) {
+    if (error.foo === 4) {
+      throw error;
+    }
+  }
+}
+
+"
+`;
+
+exports[`test init.js 1`] = `
+"/***
+ * test initialization tracking of hoisted stuff
+ * @flow
+ */
+
+// for illustrative purposes only - Flow considers a throw possible
+// anywhere within a block
+function might_throw() {}
+
+// local use of annotated var within try is ok
+function f() {
+  try {
+    var x:number = 0;
+    var y:number = x;
+  } catch (e) {
+  }
+}
+
+// and within catch
+function f() {
+  try {
+  } catch (e) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// but not across try/catch
+function f() {
+  try {
+    might_throw();
+    var x:number = 0;
+  } catch (e) {
+    var y:number = x; // error
+  }
+}
+
+// or try/finally
+function f() {
+  try {
+    might_throw();
+    var x:number = 0;
+  } finally {
+    var y:number = x; // error
+  }
+}
+
+// or catch/finally
+function f() {
+  try {
+  } catch (e) {
+    var x:number = 0;
+  } finally {
+    var y:number = x; // error
+  }
+}
+
+// or try/catch/finally if init doesn't dominate
+function f() {
+  try {
+    var x:number = 0;
+  } catch (e) {
+    might_throw();
+    var x:number = 0;
+  } finally {
+    var y:number = x; // error
+  }
+}
+
+// post-use ok because init dominates here
+function f() {
+  try {
+    var x:number = 0;
+  } catch (e) {
+    might_throw();  // ...but if so, suffix is not reached
+    var x:number = 0;
+  }
+  var y:number = x;
+}
+
+// and here
+function f() {
+  try {
+  } catch (e) {
+  } finally {
+    might_throw();  // ...but if so, suffix is not reached
+    var x:number = 0;
+  }
+  var y:number = x;
+}
+
+// and here
+function f() {
+  try {
+    var x:number;
+  } catch (e) {
+  } finally {
+    might_throw();  // ...but if so, suffix is not reached
+    x = 0;
+  }
+  var y:number = x;
+}
+
+// and here, thank you JS for the wonder that is hoisting
+function f() {
+  try {
+  } catch (e) {
+    var x:number;
+  } finally {
+    might_throw();  // ...but if so, suffix is not reached
+    x = 0;
+  }
+  var y:number = x;
+}
+
+// error if used prior to init
+function f() {
+  var y:number = x; // error
+  try {
+    var x:number = 0;
+  } catch (e) {
+  }
+}
+
+// another non-dominated post
+function f() {
+  try {
+    var x:number = 0;
+  } catch (e) {
+  }
+  var y:number = x; // error
+}
+
+// ditto
+function f() {
+  try {
+  } catch (e) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// ditto
+function f(b) {
+  try {
+    var x:number;
+    if (b) {
+      throw new Error();
+    }
+    x = 0;
+  } catch (e) {
+  }
+  var y:number = x; // error
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/***
+ * test initialization tracking of hoisted stuff
+ * @flow
+ */
+// for illustrative purposes only - Flow considers a throw possible
+// anywhere within a block
+function might_throw() {
+  
+}
+// local use of annotated var within try is ok
+function f() {
+  try {
+    var x: number = 0;
+    var y: number = x;
+  } catch (e) {
+    
+  }
+}
+// and within catch
+function f() {
+  try {
+    
+  } catch (e) {
+    var x: number = 0;
+    var y: number = x;
+  }
+}
+// but not across try/catch
+function f() {
+  try {
+    might_throw();
+    var x: number = 0;
+  } catch (e) {
+    var y: number = x;// error
+  }
+}
+// or try/finally
+function f() {
+  try {
+    might_throw();
+    var x: number = 0;
+  } finally {
+    var y: number = x;// error
+  }
+}
+// or catch/finally
+function f() {
+  try {
+    
+  } catch (e) {
+    var x: number = 0;
+  } finally {
+    var y: number = x;// error
+  }
+}
+// or try/catch/finally if init doesn't dominate
+function f() {
+  try {
+    var x: number = 0;
+  } catch (e) {
+    might_throw();
+    var x: number = 0;
+  } finally {
+    var y: number = x;// error
+  }
+}
+// post-use ok because init dominates here
+function f() {
+  try {
+    var x: number = 0;
+  } catch (e) {
+    might_throw();// ...but if so, suffix is not reached
+    var x: number = 0;
+  }
+  var y: number = x;
+}
+// and here
+function f() {
+  try {
+    
+  } catch (e) {
+    
+  } finally {
+    might_throw();// ...but if so, suffix is not reached
+    var x: number = 0;
+  }
+  var y: number = x;
+}
+// and here
+function f() {
+  try {
+    var x: number;
+  } catch (e) {
+    
+  } finally {
+    might_throw();// ...but if so, suffix is not reached
+    x = 0;
+  }
+  var y: number = x;
+}
+// and here, thank you JS for the wonder that is hoisting
+function f() {
+  try {
+    
+  } catch (e) {
+    var x: number;
+  } finally {
+    might_throw();// ...but if so, suffix is not reached
+    x = 0;
+  }
+  var y: number = x;
+}
+// error if used prior to init
+function f() {
+  var y: number = x;// error
+  try {
+    var x: number = 0;
+  } catch (e) {
+    
+  }
+}
+// another non-dominated post
+function f() {
+  try {
+    var x: number = 0;
+  } catch (e) {
+    
+  }
+  var y: number = x;// error
+}
+// ditto
+function f() {
+  try {
+    
+  } catch (e) {
+    var x: number = 0;
+  }
+  var y: number = x;// error
+}
+// ditto
+function f(b) {
+  try {
+    var x: number;
+    if (b) {
+      throw new Error();
+    }
+    x = 0;
+  } catch (e) {
+    
+  }
+  var y: number = x;// error
+}
+
+"
+`;
+
+exports[`test return.js 1`] = `
+"/**
+ * @flow
+ */
+
+function foo(x: ?number): string {
+    try {
+    } catch (e) {
+        return 'bar';
+    }
+    console.log();
+    return 'foo';
+}
+
+function bar(): string {
+  try {
+    return 'foo';
+  } catch (e) {
+    return 'bar';
+  }
+}
+
+function baz(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    return "foo";
+  }
+  return "bar"; // unreachable
+}
+
+function qux(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+  }
+  console.log();
+  return 'bar';
+}
+
+function quux(): string {
+  try {
+    return qux();
+  } catch (e) {
+  }
+  return 'bar';
+}
+
+function bliffl(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    return "foo";
+  } finally {
+    return "bar";
+  }
+}
+
+function corge(): string {
+  try {
+    return 'foo';
+  } catch (e) {
+    throw new Error('bar');
+  }
+  bar(); // unreachable
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+function foo(x: ?number): string {
+  try {
+    
+  } catch (e) {
+    return "bar";
+  }
+  console.log();
+  return "foo";
+}
+function bar(): string {
+  try {
+    return "foo";
+  } catch (e) {
+    return "bar";
+  }
+}
+function baz(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    return "foo";
+  }
+  return "bar";// unreachable
+}
+function qux(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    
+  }
+  console.log();
+  return "bar";
+}
+function quux(): string {
+  try {
+    return qux();
+  } catch (e) {
+    
+  }
+  return "bar";
+}
+function bliffl(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    return "foo";
+  } finally {
+    return "bar";
+  }
+}
+function corge(): string {
+  try {
+    return "foo";
+  } catch (e) {
+    throw new Error("bar");
+  }
+  bar();// unreachable
+}
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"/***
+ * test env state tracking thru try/catch/finally
+ * @flow
+ */
+
+function foo() {
+    var x = 0;
+    var y;
+    try {
+        x = "";
+    } catch(e) {
+        x = false;
+        throw -1;
+    } finally {
+        y = {};
+    }
+    // here via [try; finally] only.
+    x(); // string ~/> function call (no num or bool error)
+    y(); // object ~/> function call (no uninitialized error)
+}
+
+function bar(response) {
+    var payload;
+    try {
+        payload = JSON.parse(response);
+    } catch (e) {
+        throw new Error('...');
+    }
+    // here via [try] only.
+    if (payload.error) {    // ok
+        // ...
+    }
+}
+
+function qux() {
+    var x = 5;
+    try {
+        throw -1;
+    } finally {
+    }
+    x(); // unreachable
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/***
+ * test env state tracking thru try/catch/finally
+ * @flow
+ */
+function foo() {
+  var x = 0;
+  var y;
+  try {
+    x = "";
+  } catch (e) {
+    x = false;
+    throw -1;
+  } finally {
+    y = {};
+  }
+  // here via [try; finally] only.
+  x();// string ~/> function call (no num or bool error)
+  y();// object ~/> function call (no uninitialized error)
+}
+function bar(response) {
+  var payload;
+  try {
+    payload = JSON.parse(response);
+  } catch (e) {
+    throw new Error("...");
+  }
+  // here via [try] only.
+  if (payload.error) {
+    
+  }
+}
+function qux() {
+  var x = 5;
+  try {
+    throw -1;
+  } finally {
+    
+  }
+  x();// unreachable
+}
+
+"
+`;
diff --git a/tests/try/abnormals.js b/tests/try/abnormals.js
new file mode 100644
index 000000000000..93f26579bfb6
--- /dev/null
+++ b/tests/try/abnormals.js
@@ -0,0 +1,15 @@
+/* @flow */
+
+/* This test documents an issue we used to have with merging the environment of
+ * the try block and the catch block. The error variable, when inspected and in
+ * the presence of an abnormal, would sometimes kind of leak. It would hit an
+ * abnormal. It was weird.
+ */
+function foo() {
+  try {
+  } catch(error) {
+    if (error.foo === 4) {
+      throw error;
+    }
+  }
+}
diff --git a/tests/try/init.js b/tests/try/init.js
new file mode 100644
index 000000000000..be19b23e1b52
--- /dev/null
+++ b/tests/try/init.js
@@ -0,0 +1,154 @@
+/***
+ * test initialization tracking of hoisted stuff
+ * @flow
+ */
+
+// for illustrative purposes only - Flow considers a throw possible
+// anywhere within a block
+function might_throw() {}
+
+// local use of annotated var within try is ok
+function f() {
+  try {
+    var x:number = 0;
+    var y:number = x;
+  } catch (e) {
+  }
+}
+
+// and within catch
+function f() {
+  try {
+  } catch (e) {
+    var x:number = 0;
+    var y:number = x;
+  }
+}
+
+// but not across try/catch
+function f() {
+  try {
+    might_throw();
+    var x:number = 0;
+  } catch (e) {
+    var y:number = x; // error
+  }
+}
+
+// or try/finally
+function f() {
+  try {
+    might_throw();
+    var x:number = 0;
+  } finally {
+    var y:number = x; // error
+  }
+}
+
+// or catch/finally
+function f() {
+  try {
+  } catch (e) {
+    var x:number = 0;
+  } finally {
+    var y:number = x; // error
+  }
+}
+
+// or try/catch/finally if init doesn't dominate
+function f() {
+  try {
+    var x:number = 0;
+  } catch (e) {
+    might_throw();
+    var x:number = 0;
+  } finally {
+    var y:number = x; // error
+  }
+}
+
+// post-use ok because init dominates here
+function f() {
+  try {
+    var x:number = 0;
+  } catch (e) {
+    might_throw();  // ...but if so, suffix is not reached
+    var x:number = 0;
+  }
+  var y:number = x;
+}
+
+// and here
+function f() {
+  try {
+  } catch (e) {
+  } finally {
+    might_throw();  // ...but if so, suffix is not reached
+    var x:number = 0;
+  }
+  var y:number = x;
+}
+
+// and here
+function f() {
+  try {
+    var x:number;
+  } catch (e) {
+  } finally {
+    might_throw();  // ...but if so, suffix is not reached
+    x = 0;
+  }
+  var y:number = x;
+}
+
+// and here, thank you JS for the wonder that is hoisting
+function f() {
+  try {
+  } catch (e) {
+    var x:number;
+  } finally {
+    might_throw();  // ...but if so, suffix is not reached
+    x = 0;
+  }
+  var y:number = x;
+}
+
+// error if used prior to init
+function f() {
+  var y:number = x; // error
+  try {
+    var x:number = 0;
+  } catch (e) {
+  }
+}
+
+// another non-dominated post
+function f() {
+  try {
+    var x:number = 0;
+  } catch (e) {
+  }
+  var y:number = x; // error
+}
+
+// ditto
+function f() {
+  try {
+  } catch (e) {
+    var x:number = 0;
+  }
+  var y:number = x; // error
+}
+
+// ditto
+function f(b) {
+  try {
+    var x:number;
+    if (b) {
+      throw new Error();
+    }
+    x = 0;
+  } catch (e) {
+  }
+  var y:number = x; // error
+}
diff --git a/tests/try/jsfmt.spec.js b/tests/try/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/try/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/try/return.js b/tests/try/return.js
new file mode 100644
index 000000000000..eafe017bb3e7
--- /dev/null
+++ b/tests/try/return.js
@@ -0,0 +1,65 @@
+/**
+ * @flow
+ */
+
+function foo(x: ?number): string {
+    try {
+    } catch (e) {
+        return 'bar';
+    }
+    console.log();
+    return 'foo';
+}
+
+function bar(): string {
+  try {
+    return 'foo';
+  } catch (e) {
+    return 'bar';
+  }
+}
+
+function baz(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    return "foo";
+  }
+  return "bar"; // unreachable
+}
+
+function qux(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+  }
+  console.log();
+  return 'bar';
+}
+
+function quux(): string {
+  try {
+    return qux();
+  } catch (e) {
+  }
+  return 'bar';
+}
+
+function bliffl(): string {
+  try {
+    throw new Error("foo");
+  } catch (e) {
+    return "foo";
+  } finally {
+    return "bar";
+  }
+}
+
+function corge(): string {
+  try {
+    return 'foo';
+  } catch (e) {
+    throw new Error('bar');
+  }
+  bar(); // unreachable
+}
diff --git a/tests/try/test.js b/tests/try/test.js
new file mode 100644
index 000000000000..8ed40eec4766
--- /dev/null
+++ b/tests/try/test.js
@@ -0,0 +1,42 @@
+/***
+ * test env state tracking thru try/catch/finally
+ * @flow
+ */
+
+function foo() {
+    var x = 0;
+    var y;
+    try {
+        x = "";
+    } catch(e) {
+        x = false;
+        throw -1;
+    } finally {
+        y = {};
+    }
+    // here via [try; finally] only.
+    x(); // string ~/> function call (no num or bool error)
+    y(); // object ~/> function call (no uninitialized error)
+}
+
+function bar(response) {
+    var payload;
+    try {
+        payload = JSON.parse(response);
+    } catch (e) {
+        throw new Error('...');
+    }
+    // here via [try] only.
+    if (payload.error) {    // ok
+        // ...
+    }
+}
+
+function qux() {
+    var x = 5;
+    try {
+        throw -1;
+    } finally {
+    }
+    x(); // unreachable
+}
diff --git a/tests/tuples/__snapshots__/jsfmt.spec.js.snap b/tests/tuples/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..1e62f945a534
--- /dev/null
+++ b/tests/tuples/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,105 @@
+exports[`test array.js 1`] = `
+"// @flow
+
+function foo(x: Array<number>): [number, ?number] {
+  return x; // Error, can\'t enforce arity when flowing array to tuple
+}
+
+function foo(x: Array<number>): [number, ?number] {
+  return [x[0], x[1]]; // OK. This is unsound, but at least arity is enforced
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test optional.js 1`] = `
+"// @flow
+
+([0, undefined]: [number, ?string]); // Ok, correct arity
+([0]: [number, ?string]); // Error, arity is enforced
+
+([]: [?number, string]); // error, since second element is not marked optional
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test too-few.js 1`] = `
+"/* @flow */
+
+function foo(a: [Object, Object]) {}
+
+foo([ {} ]); // error, too few elements in array passed to a tuple
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test tuples.js 1`] = `
+"var a: [] = [];
+var b: [] = [123]; // Error - arity mismatch
+var c: [number] = []; // nope
+var d: [number, string] = [123,\'duck\'];
+var e: [number, string,] = [123,\'duck\'];
+var f: [number, string] = [123, 456];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/tuples/array.js b/tests/tuples/array.js
new file mode 100644
index 000000000000..08f7a4c0a972
--- /dev/null
+++ b/tests/tuples/array.js
@@ -0,0 +1,9 @@
+// @flow
+
+function foo(x: Array<number>): [number, ?number] {
+  return x; // Error, can't enforce arity when flowing array to tuple
+}
+
+function foo(x: Array<number>): [number, ?number] {
+  return [x[0], x[1]]; // OK. This is unsound, but at least arity is enforced
+}
diff --git a/tests/tuples/jsfmt.spec.js b/tests/tuples/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/tuples/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/tuples/optional.js b/tests/tuples/optional.js
new file mode 100644
index 000000000000..46764c0fff06
--- /dev/null
+++ b/tests/tuples/optional.js
@@ -0,0 +1,6 @@
+// @flow
+
+([0, undefined]: [number, ?string]); // Ok, correct arity
+([0]: [number, ?string]); // Error, arity is enforced
+
+([]: [?number, string]); // error, since second element is not marked optional
diff --git a/tests/tuples/too-few.js b/tests/tuples/too-few.js
new file mode 100644
index 000000000000..cb8b2d62a094
--- /dev/null
+++ b/tests/tuples/too-few.js
@@ -0,0 +1,5 @@
+/* @flow */
+
+function foo(a: [Object, Object]) {}
+
+foo([ {} ]); // error, too few elements in array passed to a tuple
diff --git a/tests/tuples/tuples.js b/tests/tuples/tuples.js
new file mode 100644
index 000000000000..f44f9c75f7fb
--- /dev/null
+++ b/tests/tuples/tuples.js
@@ -0,0 +1,6 @@
+var a: [] = [];
+var b: [] = [123]; // Error - arity mismatch
+var c: [number] = []; // nope
+var d: [number, string] = [123,'duck'];
+var e: [number, string,] = [123,'duck'];
+var f: [number, string] = [123, 456];
diff --git a/tests/type-at-pos/__snapshots__/jsfmt.spec.js.snap b/tests/type-at-pos/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..08d61143e1bd
--- /dev/null
+++ b/tests/type-at-pos/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,275 @@
+exports[`test destructuring.js 1`] = `
+"// @flow
+
+let [x, y] = [1, 2];
+
+/**
+ * Test what happens when the destructuring is unevaluated. In this case,
+ * \`this\` in a function is unbound, so we never actually find out the type of
+ * \`this.returnsATuple()\` is; thus, we never evaluate \`b\` and so type-at-pos
+ * returns EmptyT.
+ */
+export const X = {
+  returnsATuple: function(): [number, number] {
+    return [1, 2];
+  },
+
+  test: function() {
+    let [a, b] = this.returnsATuple();
+  }
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test function_expressions.js 1`] = `
+"// @flow
+
+// TODO: type-at-pos between the ()\'s should be () => void
+// class X {
+//   foo(): void {}
+// }
+
+const y = {
+  bar(): void {}
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+// TODO: type-at-pos between the ()\'s should be () => void
+// class X {
+//   foo(): void {}
+// }
+const y = {
+  bar(): void {
+    
+  }
+};
+
+"
+`;
+
+exports[`test generics.js 1`] = `
+"// @flow
+
+class C<X> { }
+var cn: C<number> = new C;
+cn;
+
+function foo() { return C; }
+var D = foo();
+var dn: D<number> = new C;
+dn;
+
+type E<X> = C<X>;
+var en: E<number> = new C;
+en;
+
+type F<X> = C<void>;
+var fn: F<number> = new C;
+fn;
+
+type O<X> = { x: X };
+var on: O<number> = { x: 0 };
+on;
+
+type Mono = C<void>;
+var mn: Mono<number> = new C; // error: application of non-poly type
+mn;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test import.js 1`] = `
+"// @flow
+var num = 42;
+function bar() { }
+bar();
+module.exports = num;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+var num = 42;
+function bar() {
+  
+}
+bar();
+module.exports = num;
+
+"
+`;
+
+exports[`test object_special_cases.js 1`] = `
+"/* @flow */
+
+let tests = [
+  function() {
+    let x = {};
+    Object.defineProperty(x, \'foo\', { value: \'\' });
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+let tests = [
+  function() {
+    let x = {};
+    Object.defineProperty(x, \"foo\", { value: \"\" });
+  }
+];
+
+"
+`;
+
+exports[`test optional.js 1`] = `
+"// @flow
+
+function foo(x?: string) {
+  return x;
+}
+
+foo();
+
+function bar(obj: { x?: string }) {
+  return obj.x;
+}
+
+function qux(x?) {
+  return x;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+function foo(x: string) {
+  return x;
+}
+foo();
+function bar(obj: { x?: string }) {
+  return obj.x;
+}
+function qux(x) {
+  return x;
+}
+
+"
+`;
+
+exports[`test predicates.js 1`] = `
+"/* @flow */
+
+let x = 0;
+if (x == null) {}
+if (x == undefined) {}
+if (Array.isArray(x)) {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+let x = 0;
+if (x == null) {
+  
+}
+if (x == undefined) {
+  
+}
+if (Array.isArray(x)) {
+  
+}
+
+"
+`;
+
+exports[`test react.js 1`] = `
+"import React from \"react\";
+React.createElement;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+import React from \"react\";
+React.createElement;
+
+"
+`;
+
+exports[`test templates.js 1`] = `
+"/* @flow */
+\`foo bar\`;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+\`foo bar\`;
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"// @flow
+var str = require(\'./import\');
+function foo() { }
+foo();
+str
+
+type Point = [number, string];
+const x:Point = [1, \"foo\"];
+type MyStr = \"cool\";
+const y:MyStr = \"cool\";
+type MyBool = true;
+const z:MyBool = true;
+type MyNum = 42;
+const w:MyNum = 42;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1237
+      throw new Error(\"unprintable type: \" + JSON.stringify(n.type));
+      ^
+
+Error: unprintable type: \"TupleTypeAnnotation\"
+    at genericPrintNoParens (/src/printer.js:1237:13)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test trycatch.js 1`] = `
+"// @flow
+
+try {
+  throw \"foo\";
+} catch (e) {}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+try {
+  throw \"foo\";
+} catch (e) {
+  
+}
+
+"
+`;
diff --git a/tests/type-at-pos/destructuring.js b/tests/type-at-pos/destructuring.js
new file mode 100644
index 000000000000..103545e77005
--- /dev/null
+++ b/tests/type-at-pos/destructuring.js
@@ -0,0 +1,19 @@
+// @flow
+
+let [x, y] = [1, 2];
+
+/**
+ * Test what happens when the destructuring is unevaluated. In this case,
+ * `this` in a function is unbound, so we never actually find out the type of
+ * `this.returnsATuple()` is; thus, we never evaluate `b` and so type-at-pos
+ * returns EmptyT.
+ */
+export const X = {
+  returnsATuple: function(): [number, number] {
+    return [1, 2];
+  },
+
+  test: function() {
+    let [a, b] = this.returnsATuple();
+  }
+};
diff --git a/tests/type-at-pos/function_expressions.js b/tests/type-at-pos/function_expressions.js
new file mode 100644
index 000000000000..81df45793802
--- /dev/null
+++ b/tests/type-at-pos/function_expressions.js
@@ -0,0 +1,10 @@
+// @flow
+
+// TODO: type-at-pos between the ()'s should be () => void
+// class X {
+//   foo(): void {}
+// }
+
+const y = {
+  bar(): void {}
+};
diff --git a/tests/type-at-pos/generics.js b/tests/type-at-pos/generics.js
new file mode 100644
index 000000000000..a08506b22101
--- /dev/null
+++ b/tests/type-at-pos/generics.js
@@ -0,0 +1,26 @@
+// @flow
+
+class C<X> { }
+var cn: C<number> = new C;
+cn;
+
+function foo() { return C; }
+var D = foo();
+var dn: D<number> = new C;
+dn;
+
+type E<X> = C<X>;
+var en: E<number> = new C;
+en;
+
+type F<X> = C<void>;
+var fn: F<number> = new C;
+fn;
+
+type O<X> = { x: X };
+var on: O<number> = { x: 0 };
+on;
+
+type Mono = C<void>;
+var mn: Mono<number> = new C; // error: application of non-poly type
+mn;
diff --git a/tests/type-at-pos/import.js b/tests/type-at-pos/import.js
new file mode 100644
index 000000000000..9a49778fd59d
--- /dev/null
+++ b/tests/type-at-pos/import.js
@@ -0,0 +1,5 @@
+// @flow
+var num = 42;
+function bar() { }
+bar();
+module.exports = num;
diff --git a/tests/type-at-pos/jsfmt.spec.js b/tests/type-at-pos/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type-at-pos/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type-at-pos/object_special_cases.js b/tests/type-at-pos/object_special_cases.js
new file mode 100644
index 000000000000..d34326b96596
--- /dev/null
+++ b/tests/type-at-pos/object_special_cases.js
@@ -0,0 +1,8 @@
+/* @flow */
+
+let tests = [
+  function() {
+    let x = {};
+    Object.defineProperty(x, 'foo', { value: '' });
+  },
+];
diff --git a/tests/type-at-pos/optional.js b/tests/type-at-pos/optional.js
new file mode 100644
index 000000000000..1ed4c4b71c02
--- /dev/null
+++ b/tests/type-at-pos/optional.js
@@ -0,0 +1,15 @@
+// @flow
+
+function foo(x?: string) {
+  return x;
+}
+
+foo();
+
+function bar(obj: { x?: string }) {
+  return obj.x;
+}
+
+function qux(x?) {
+  return x;
+}
diff --git a/tests/type-at-pos/predicates.js b/tests/type-at-pos/predicates.js
new file mode 100644
index 000000000000..0c68d6da5a4e
--- /dev/null
+++ b/tests/type-at-pos/predicates.js
@@ -0,0 +1,6 @@
+/* @flow */
+
+let x = 0;
+if (x == null) {}
+if (x == undefined) {}
+if (Array.isArray(x)) {}
diff --git a/tests/type-at-pos/react.js b/tests/type-at-pos/react.js
new file mode 100644
index 000000000000..0921cb496171
--- /dev/null
+++ b/tests/type-at-pos/react.js
@@ -0,0 +1,2 @@
+import React from "react";
+React.createElement;
diff --git a/tests/type-at-pos/templates.js b/tests/type-at-pos/templates.js
new file mode 100644
index 000000000000..2ce2ae0fba5f
--- /dev/null
+++ b/tests/type-at-pos/templates.js
@@ -0,0 +1,2 @@
+/* @flow */
+`foo bar`;
diff --git a/tests/type-at-pos/test.js b/tests/type-at-pos/test.js
new file mode 100644
index 000000000000..66d5c396be70
--- /dev/null
+++ b/tests/type-at-pos/test.js
@@ -0,0 +1,14 @@
+// @flow
+var str = require('./import');
+function foo() { }
+foo();
+str
+
+type Point = [number, string];
+const x:Point = [1, "foo"];
+type MyStr = "cool";
+const y:MyStr = "cool";
+type MyBool = true;
+const z:MyBool = true;
+type MyNum = 42;
+const w:MyNum = 42;
diff --git a/tests/type-at-pos/trycatch.js b/tests/type-at-pos/trycatch.js
new file mode 100644
index 000000000000..35196da89c67
--- /dev/null
+++ b/tests/type-at-pos/trycatch.js
@@ -0,0 +1,5 @@
+// @flow
+
+try {
+  throw "foo";
+} catch (e) {}
diff --git a/tests/type-destructors/__snapshots__/jsfmt.spec.js.snap b/tests/type-destructors/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..98f9765766b6
--- /dev/null
+++ b/tests/type-destructors/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,86 @@
+exports[`test non_maybe_type.js 1`] = `
+"// @flow
+
+function foo(x: ?string): $NonMaybeType<?string> {
+  if (x != null) { return x; }
+  else return 0; // this should be an error
+}
+
+//(foo(): string); // should not be necessary to expose the error above
+
+(0: $NonMaybeType<null>); // error
+(0: $NonMaybeType<?number>); // ok
+(0: $NonMaybeType<number | null>); // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test property_type.js 1`] = `
+"type Malformed = $PropertyType<any, number>;
+
+type Obj = { x: string };
+type Obj_Prop_x = $PropertyType<Obj, \'x\'>;
+
+(42: Obj_Prop_x);
+
+function foo(o: Obj): $PropertyType<Obj, \'x\'> {
+  if (false) return o.x;
+  else return 0;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test union.js 1`] = `
+"var x0: $NonMaybeType<number|string> = 0; // ok, number ~> number|string
+var x1: $NonMaybeType<number|string> = true; // err, boolean ~> number|string
+var x2: $PropertyType<{p:number}|{p:string},\'p\'> = 0; // ok, number ~> number|string
+var x3: $PropertyType<{p:number}|{p:string},\'p\'> = true; // err, boolean ~> number|string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type-destructors/jsfmt.spec.js b/tests/type-destructors/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type-destructors/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type-destructors/non_maybe_type.js b/tests/type-destructors/non_maybe_type.js
new file mode 100644
index 000000000000..f3240e822337
--- /dev/null
+++ b/tests/type-destructors/non_maybe_type.js
@@ -0,0 +1,12 @@
+// @flow
+
+function foo(x: ?string): $NonMaybeType<?string> {
+  if (x != null) { return x; }
+  else return 0; // this should be an error
+}
+
+//(foo(): string); // should not be necessary to expose the error above
+
+(0: $NonMaybeType<null>); // error
+(0: $NonMaybeType<?number>); // ok
+(0: $NonMaybeType<number | null>); // ok
diff --git a/tests/type-destructors/property_type.js b/tests/type-destructors/property_type.js
new file mode 100644
index 000000000000..c7bb9752eac2
--- /dev/null
+++ b/tests/type-destructors/property_type.js
@@ -0,0 +1,11 @@
+type Malformed = $PropertyType<any, number>;
+
+type Obj = { x: string };
+type Obj_Prop_x = $PropertyType<Obj, 'x'>;
+
+(42: Obj_Prop_x);
+
+function foo(o: Obj): $PropertyType<Obj, 'x'> {
+  if (false) return o.x;
+  else return 0;
+}
diff --git a/tests/type-destructors/union.js b/tests/type-destructors/union.js
new file mode 100644
index 000000000000..bc8b0abc9f40
--- /dev/null
+++ b/tests/type-destructors/union.js
@@ -0,0 +1,4 @@
+var x0: $NonMaybeType<number|string> = 0; // ok, number ~> number|string
+var x1: $NonMaybeType<number|string> = true; // err, boolean ~> number|string
+var x2: $PropertyType<{p:number}|{p:string},'p'> = 0; // ok, number ~> number|string
+var x3: $PropertyType<{p:number}|{p:string},'p'> = true; // err, boolean ~> number|string
diff --git a/tests/type-printer/__snapshots__/jsfmt.spec.js.snap b/tests/type-printer/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..001e98bea762
--- /dev/null
+++ b/tests/type-printer/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,5104 @@
+exports[`test printBinaryExpression.js 1`] = `
+"\'use babel\';
+/* @flow */
+
+/*
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the license found in the LICENSE file in
+ * the root directory of this source tree.
+ */
+
+import type {BinaryExpression} from \'./types\';
+
+function printBinaryExpression(
+  node: BinaryExpression,
+) {
+  console.log(node);
+}
+
+module.exports = printBinaryExpression;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\"use babel\";
+/* @flow */
+/*
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the license found in the LICENSE file in
+ * the root directory of this source tree.
+ */
+import type { BinaryExpression } from \"./types\";
+function printBinaryExpression(node: BinaryExpression) {
+  console.log(node);
+}
+module.exports = printBinaryExpression;
+
+"
+`;
+
+exports[`test types.js 1`] = `
+"/**
+ * @flow
+ */
+
+\'use strict\';
+
+/*
+ * Flow types for the Babylon AST.
+ */
+
+// Abstract types. Something must extend these.
+
+export type Comment = {
+  type: \'CommentLine\';
+  _CommentLine: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+} | {
+  type: \'CommentBlock\';
+  _CommentBlock: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+};
+
+export type Declaration = {
+  type: \'ClassBody\';
+  _ClassBody: void;
+  body: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassDeclaration\';
+  _ClassDeclaration: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'FunctionDeclaration\';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'MethodDefinition\';
+  _MethodDefinition: void;
+  computed: boolean;
+  key: Node;
+  kind: \'constructor\' | \'method\' | \'get\' | \'set\';
+  static: boolean;
+  value: FunctionExpression;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'VariableDeclaration\';
+  _VariableDeclaration: void;
+  declarations: Array<VariableDeclarator>;
+  kind: \'var\' | \'let\' | \'const\';
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassProperty\';
+  _ClassProperty: void;
+  computed: boolean;
+  key: Node;
+  static: boolean;
+  typeAnnotation: ?TypeAnnotation;
+  value: ?Expression;
+  decorators: Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Expression = {
+  type: \'ArrayExpression\';
+  _ArrayExpression: void;
+  elements: Array<?Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'AssignmentExpression\';
+  _AssignmentExpression: void;
+  left: Pattern;
+  operator: AssignmentOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'AwaitExpression\';
+  _AwaitExpression: void;
+  all: boolean;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BinaryExpression\';
+  _BinaryExpression: void;
+  left: Expression;
+  operator: BinaryOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BindExpression\';
+  _BindExpression: void;
+  callee: Node;
+  object: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'CallExpression\';
+  _CallExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassExpression\';
+  _ClassExpression: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ComprehensionExpression\';
+  _ComprehensionExpression: void;
+  body: Expression;
+  blocks: Array<ComprehensionBlock>;
+  filter: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ConditionalExpression\';
+  _ConditionalExpression: void;
+  alternate: Expression;
+  consequent: Expression;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DoExpression\';
+  _DoExpression: void;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'FunctionExpression\';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'Identifier\';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Literal\';
+  _Literal: void;
+  raw: string;
+  regex: ?{pattern: string, flags: string};
+  value: ?(string | boolean | number | RegExp);
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'LogicalExpression\';
+  _LogicalExpression: void;
+  left: Expression;
+  operator: LogicalOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'MemberExpression\';
+  _MemberExpression: void;
+  computed: boolean;
+  object: Expression;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NewExpression\';
+  _NewExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectExpression\';
+  _ObjectExpression: void;
+  properties: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SequenceExpression\';
+  _SequenceExpression: void;
+  expression: Array<Expression>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TaggedTemplateExpression\';
+  _TaggedTemplateExpression: void;
+  quasi: TemplateLiteral;
+  tag: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TemplateLiteral\';
+  _TemplateLiteral: void;
+  expressions: Array<Expression>;
+  quasis: Array<TemplateElement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ThisExpression\';
+  _ThisExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'UnaryExpression\';
+  _UnaryExpression: void;
+  argument: Expression;
+  operator: UnaryOperator;
+  prefix: true;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'UpdateExpression\';
+  _UpdateExpression: void;
+  argument: Expression;
+  operator: UpdateOperator;
+  prefix: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'YieldExpression\';
+  _YieldExpression: void;
+  argument: ?Expression;
+  delegate: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeCastExpression\';
+  _TypeCastExpression: void;
+  expression: Expression;
+  typeAnnotation: TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXElement\';
+  _JSXElement: void;
+  children: Array<Node>;
+  closingElement: ?JSXClosingElement;
+  openingElement: JSXOpeningElement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXEmptyExpression\';
+  _JSXEmptyExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXExpressionContainer\';
+  _JSXExpressionContainer: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXMemberExpression\';
+  _JSXMemberExpression: void;
+  computed: boolean;
+  object: Node;
+  property: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Function = {
+  type: \'ArrowFunctionExpression\';
+  _ArrowFunctionExpression: void;
+  body: Node;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'FunctionDeclaration\';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'FunctionExpression\';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+export type Node = {
+  type: \'ArrayExpression\';
+  _ArrayExpression: void;
+  elements: Array<?Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ArrayPattern\';
+  _ArrayPattern: void;
+  elements: Array<?Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ArrowFunctionExpression\';
+  _ArrowFunctionExpression: void;
+  body: Node;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'AssignmentExpression\';
+  _AssignmentExpression: void;
+  left: Pattern;
+  operator: AssignmentOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'AssignmentPattern\';
+  _AssignmentPattern: void;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'AwaitExpression\';
+  _AwaitExpression: void;
+  all: boolean;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BinaryExpression\';
+  _BinaryExpression: void;
+  left: Expression;
+  operator: BinaryOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BindExpression\';
+  _BindExpression: void;
+  callee: Node;
+  object: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BlockStatement\';
+  _BlockStatement: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BreakStatement\';
+  _BreakStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'CallExpression\';
+  _CallExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'CatchClause\';
+  _CatchClause: void;
+  body: BlockStatement;
+  param: Pattern;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassBody\';
+  _ClassBody: void;
+  body: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassDeclaration\';
+  _ClassDeclaration: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassExpression\';
+  _ClassExpression: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ComprehensionBlock\';
+  _ComprehensionBlock: void;
+  each: boolean;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ComprehensionExpression\';
+  _ComprehensionExpression: void;
+  body: Expression;
+  blocks: Array<ComprehensionBlock>;
+  filter: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ConditionalExpression\';
+  _ConditionalExpression: void;
+  alternate: Expression;
+  consequent: Expression;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ContinueStatement\';
+  _ContinueStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Decorator\';
+  _Decorator: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DebuggerStatement\';
+  _DebuggerStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DoWhileStatement\';
+  _DoWhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DoExpression\';
+  _DoExpression: void;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'EmptyStatement\';
+  _EmptyStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExpressionStatement\';
+  _ExpressionStatement: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'File\';
+  _File: void;
+  program: Program;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ForInStatement\';
+  _ForInStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ForOfStatement\';
+  _ForOfStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ForStatement\';
+  _ForStatement: void;
+  init: ?Node;
+  test: ?Expression;
+  update: ?Expression;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'FunctionDeclaration\';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'FunctionExpression\';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: \'Identifier\';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'IfStatement\';
+  _IfStatement: void;
+  alternate: ?Statement;
+  consequent: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ImportDefaultSpecifier\';
+  _ImportDefaultSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ImportNamespaceSpecifier\';
+  _ImportNamespaceSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ImportDeclaration\';
+  _ImportDeclaration: void;
+  specifiers: Array<Node>;
+  source: Literal;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ImportSpecifier\';
+  _ImportSpecifier: void;
+  imported: Node;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'LabeledStatement\';
+  _LabeledStatement: void;
+  body: Statement;
+  label: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Literal\';
+  _Literal: void;
+  raw: string;
+  regex: ?{pattern: string, flags: string};
+  value: ?(string | boolean | number | RegExp);
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'LogicalExpression\';
+  _LogicalExpression: void;
+  left: Expression;
+  operator: LogicalOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'MemberExpression\';
+  _MemberExpression: void;
+  computed: boolean;
+  object: Expression;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'MetaProperty\';
+  _MetaProperty: void;
+  meta: Node;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'MethodDefinition\';
+  _MethodDefinition: void;
+  computed: boolean;
+  key: Node;
+  kind: \'constructor\' | \'method\' | \'get\' | \'set\';
+  static: boolean;
+  value: FunctionExpression;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NewExpression\';
+  _NewExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Noop\';
+  _Noop: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectExpression\';
+  _ObjectExpression: void;
+  properties: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectPattern\';
+  _ObjectPattern: void;
+  properties: Array<Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Program\';
+  _Program: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Property\';
+  _Property: void;
+  computed: boolean;
+  key: Node;
+  kind: \'init\' | \'get\' | \'set\';
+  method: boolean;
+  shorthand: boolean;
+  value: Node;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'RestElement\';
+  _RestElement: void;
+  argument: Pattern;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ReturnStatement\';
+  _ReturnStatement: void;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SequenceExpression\';
+  _SequenceExpression: void;
+  expression: Array<Expression>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SpreadElement\';
+  _SpreadElement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SpreadProperty\';
+  _SpreadProperty: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Super\';
+  _Super: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SwitchCase\';
+  _SwitchCase: void;
+  consequent: Array<Statement>;
+  test: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SwitchStatement\';
+  _SwitchStatement: void;
+  cases: Array<SwitchCase>;
+  discriminant: Expression;
+  lexical: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TaggedTemplateExpression\';
+  _TaggedTemplateExpression: void;
+  quasi: TemplateLiteral;
+  tag: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TemplateElement\';
+  _TemplateElement: void;
+  tail: boolean;
+  value: {cooked: string, raw: string};
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TemplateLiteral\';
+  _TemplateLiteral: void;
+  expressions: Array<Expression>;
+  quasis: Array<TemplateElement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ThisExpression\';
+  _ThisExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ThrowStatement\';
+  _ThrowStatement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TryStatement\';
+  _TryStatement: void;
+  block: BlockStatement;
+  finalizer: ?BlockStatement;
+  guardedHandlers: Array<CatchClause>;
+  handler: ?CatchClause;
+  handlers: ?Array<CatchClause>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'UnaryExpression\';
+  _UnaryExpression: void;
+  argument: Expression;
+  operator: UnaryOperator;
+  prefix: true;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'UpdateExpression\';
+  _UpdateExpression: void;
+  argument: Expression;
+  operator: UpdateOperator;
+  prefix: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'VariableDeclaration\';
+  _VariableDeclaration: void;
+  declarations: Array<VariableDeclarator>;
+  kind: \'var\' | \'let\' | \'const\';
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'VariableDeclarator\';
+  _VariableDeclarator: void;
+  id: Pattern;
+  init: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'WhileStatement\';
+  _WhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'WithStatement\';
+  _WithStatement: void;
+  body: Statement;
+  object: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'YieldExpression\';
+  _YieldExpression: void;
+  argument: ?Expression;
+  delegate: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExportAllDeclaration\';
+  _ExportAllDeclaration: void;
+  exported: Node;
+  source: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExportDefaultDeclaration\';
+  _ExportDefaultDeclaration: void;
+  declaration: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExportNamedDeclaration\';
+  _ExportNamedDeclaration: void;
+  declaration: Node;
+  source: Literal;
+  specifiers: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExportDefaultSpecifier\';
+  _ExportDefaultSpecifier: void;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExportNamespaceSpecifier\';
+  _ExportNamespaceSpecifier: void;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExportSpecifier\';
+  _ExportSpecifier: void;
+  local: Node;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'AnyTypeAnnotation\';
+  _AnyTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ArrayTypeAnnotation\';
+  _ArrayTypeAnnotation: void;
+  elementType: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BooleanLiteralTypeAnnotation\';
+  _BooleanLiteralTypeAnnotation: void;
+  raw: string;
+  value: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BooleanTypeAnnotation\';
+  _BooleanTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassImplements\';
+  _ClassImplements: void;
+  id: Identifier;
+  typeParameters: ?TypeParameterInstantiation;
+  superClass: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ClassProperty\';
+  _ClassProperty: void;
+  computed: boolean;
+  key: Node;
+  static: boolean;
+  typeAnnotation: ?TypeAnnotation;
+  value: ?Expression;
+  decorators: Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareClass\';
+  _DeclareClass: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareFunction\';
+  _DeclareFunction: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareModule\';
+  _DeclareModule: void;
+  body: BlockStatement;
+  id: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareVariable\';
+  _DeclareVariable: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'FunctionTypeAnnotation\';
+  _FunctionTypeAnnotation: void;
+  params: Array<FunctionTypeParam>;
+  rest: ?FunctionTypeParam;
+  returnType: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'FunctionTypeParam\';
+  _FunctionTypeParam: void;
+  name: Identifier;
+  optional: boolean;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'GenericTypeAnnotation\';
+  _GenericTypeAnnotation: void;
+  id: Node;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'InterfaceExtends\';
+  _InterfaceExtends: void;
+  id: Identifier;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'InterfaceDeclaration\';
+  _InterfaceDeclaration: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'IntersectionTypeAnnotation\';
+  _IntersectionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'MixedTypeAnnotation\';
+  _MixedTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NullableTypeAnnotation\';
+  _NullableTypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NumberLiteralTypeAnnotation\';
+  _NumberLiteralTypeAnnotation: void;
+  raw: string;
+  value: number;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NumberTypeAnnotation\';
+  _NumberTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'StringLiteralTypeAnnotation\';
+  _StringLiteralTypeAnnotation: void;
+  raw: string;
+  value: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'StringTypeAnnotation\';
+  _StringTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TupleTypeAnnotation\';
+  _TupleTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeofTypeAnnotation\';
+  _TypeofTypeAnnotation: void;
+  argument: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeAlias\';
+  _TypeAlias: void;
+  id: Identifier;
+  right: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeAnnotation\';
+  _TypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeCastExpression\';
+  _TypeCastExpression: void;
+  expression: Expression;
+  typeAnnotation: TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeParameterDeclaration\';
+  _TypeParameterDeclaration: void;
+  params: Array<Identifier>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeParameterInstantiation\';
+  _TypeParameterInstantiation: void;
+  params: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectTypeAnnotation\';
+  _ObjectTypeAnnotation: void;
+  callProperties: Array<ObjectTypeCallProperty>;
+  indexers: Array<ObjectTypeIndexer>;
+  properties: Array<ObjectTypeProperty>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectTypeCallProperty\';
+  _ObjectTypeCallProperty: void;
+  static: boolean;
+  value: FunctionTypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectTypeIndexer\';
+  _ObjectTypeIndexer: void;
+  id: Identifier;
+  key: Type;
+  value: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectTypeProperty\';
+  _ObjectTypeProperty: void;
+  key: Node;
+  optional: boolean;
+  value: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'QualifiedTypeIdentifier\';
+  _QualifiedTypeIdentifier: void;
+  id: Identifier;
+  qualification: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'UnionTypeAnnotation\';
+  _UnionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'VoidTypeAnnotation\';
+  _VoidTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXAttribute\';
+  _JSXAttribute: void;
+  name: Node;
+  value: ?Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXClosingElement\';
+  _JSXClosingElement: void;
+  name: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXElement\';
+  _JSXElement: void;
+  children: Array<Node>;
+  closingElement: ?JSXClosingElement;
+  openingElement: JSXOpeningElement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXEmptyExpression\';
+  _JSXEmptyExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXExpressionContainer\';
+  _JSXExpressionContainer: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXIdentifier\';
+  _JSXIdentifier: void;
+  name: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXMemberExpression\';
+  _JSXMemberExpression: void;
+  computed: boolean;
+  object: Node;
+  property: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXNamespacedName\';
+  _JSXNamespacedName: void;
+  name: JSXIdentifier;
+  namespace: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXOpeningElement\';
+  _JSXOpeningElement: void;
+  attributes: Array<Node>;
+  name: Array<Node>;
+  selfClosing: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'JSXSpreadAttribute\';
+  _JSXSpreadAttribute: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Pattern = {
+  type: \'ArrayPattern\';
+  _ArrayPattern: void;
+  elements: Array<?Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'AssignmentPattern\';
+  _AssignmentPattern: void;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'Identifier\';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectPattern\';
+  _ObjectPattern: void;
+  properties: Array<Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'RestElement\';
+  _RestElement: void;
+  argument: Pattern;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Statement = {
+  type: \'BlockStatement\';
+  _BlockStatement: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BreakStatement\';
+  _BreakStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ContinueStatement\';
+  _ContinueStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DoWhileStatement\';
+  _DoWhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'EmptyStatement\';
+  _EmptyStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ExpressionStatement\';
+  _ExpressionStatement: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ForInStatement\';
+  _ForInStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ForOfStatement\';
+  _ForOfStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ForStatement\';
+  _ForStatement: void;
+  init: ?Node;
+  test: ?Expression;
+  update: ?Expression;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'IfStatement\';
+  _IfStatement: void;
+  alternate: ?Statement;
+  consequent: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'LabeledStatement\';
+  _LabeledStatement: void;
+  body: Statement;
+  label: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ReturnStatement\';
+  _ReturnStatement: void;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'SwitchStatement\';
+  _SwitchStatement: void;
+  cases: Array<SwitchCase>;
+  discriminant: Expression;
+  lexical: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ThrowStatement\';
+  _ThrowStatement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TryStatement\';
+  _TryStatement: void;
+  block: BlockStatement;
+  finalizer: ?BlockStatement;
+  guardedHandlers: Array<CatchClause>;
+  handler: ?CatchClause;
+  handlers: ?Array<CatchClause>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'WhileStatement\';
+  _WhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'WithStatement\';
+  _WithStatement: void;
+  body: Statement;
+  object: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareClass\';
+  _DeclareClass: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareFunction\';
+  _DeclareFunction: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareModule\';
+  _DeclareModule: void;
+  body: BlockStatement;
+  id: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'DeclareVariable\';
+  _DeclareVariable: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'InterfaceDeclaration\';
+  _InterfaceDeclaration: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TypeAlias\';
+  _TypeAlias: void;
+  id: Identifier;
+  right: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Type = {
+  type: \'AnyTypeAnnotation\';
+  _AnyTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ArrayTypeAnnotation\';
+  _ArrayTypeAnnotation: void;
+  elementType: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BooleanLiteralTypeAnnotation\';
+  _BooleanLiteralTypeAnnotation: void;
+  raw: string;
+  value: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'BooleanTypeAnnotation\';
+  _BooleanTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'FunctionTypeAnnotation\';
+  _FunctionTypeAnnotation: void;
+  params: Array<FunctionTypeParam>;
+  rest: ?FunctionTypeParam;
+  returnType: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'GenericTypeAnnotation\';
+  _GenericTypeAnnotation: void;
+  id: Node;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'IntersectionTypeAnnotation\';
+  _IntersectionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'MixedTypeAnnotation\';
+  _MixedTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NullableTypeAnnotation\';
+  _NullableTypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NumberLiteralTypeAnnotation\';
+  _NumberLiteralTypeAnnotation: void;
+  raw: string;
+  value: number;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'NumberTypeAnnotation\';
+  _NumberTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'StringLiteralTypeAnnotation\';
+  _StringLiteralTypeAnnotation: void;
+  raw: string;
+  value: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'StringTypeAnnotation\';
+  _StringTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'TupleTypeAnnotation\';
+  _TupleTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'ObjectTypeAnnotation\';
+  _ObjectTypeAnnotation: void;
+  callProperties: Array<ObjectTypeCallProperty>;
+  indexers: Array<ObjectTypeIndexer>;
+  properties: Array<ObjectTypeProperty>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'UnionTypeAnnotation\';
+  _UnionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: \'VoidTypeAnnotation\';
+  _VoidTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// Concrete Types. Nothing can extend these.
+
+export type CommentLine = {
+  type: \'CommentLine\';
+  _CommentLine: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+};
+
+export type CommentBlock = {
+  type: \'CommentBlock\';
+  _CommentBlock: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+};
+
+// Babel concrete types.
+
+export type ArrayExpression = {
+  type: \'ArrayExpression\';
+  _ArrayExpression: void;
+  elements: Array<?Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ArrayPattern = {
+  type: \'ArrayPattern\';
+  _ArrayPattern: void;
+  elements: Array<?Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ArrowFunctionExpression = {
+  type: \'ArrowFunctionExpression\';
+  _ArrowFunctionExpression: void;
+  body: Node;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+type AssignmentOperator =
+  \'=\' |
+  \'+=\' |
+  \'-=\' |
+  \'*=\' |
+  \'/=\' |
+  \'%=\' |
+  \'<<=\' |
+  \'>>=\' |
+  \'>>>=\' |
+  \'|=\' |
+  \'^=\' |
+  \'&=\';
+
+export type AssignmentExpression = {
+  type: \'AssignmentExpression\';
+  _AssignmentExpression: void;
+  left: Pattern;
+  operator: AssignmentOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type AssignmentPattern = {
+  type: \'AssignmentPattern\';
+  _AssignmentPattern: void;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type AwaitExpression = {
+  type: \'AwaitExpression\';
+  _AwaitExpression: void;
+  all: boolean;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type BinaryOperator =
+  \'==\' |
+  \'!=\' |
+  \'===\' |
+  \'!==\' |
+  \'<\' |
+  \'<=\' |
+  \'>\' |
+  \'>=\' |
+  \'<<\' |
+  \'>>\' |
+  \'>>>\' |
+  \'+\' |
+  \'-\' |
+  \'*\' |
+  \'/\' |
+  \'%\' |
+  \'&\' |
+  \'|\' |
+  \'^\' |
+  \'in\' |
+  \'instanceof\' |
+  \'..\';
+
+export type BinaryExpression = {
+  type: \'BinaryExpression\';
+  _BinaryExpression: void;
+  left: Expression;
+  operator: BinaryOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: What is this?
+export type BindExpression = {
+  type: \'BindExpression\';
+  _BindExpression: void;
+  callee: Node;
+  object: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BlockStatement = {
+  type: \'BlockStatement\';
+  _BlockStatement: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BreakStatement = {
+  type: \'BreakStatement\';
+  _BreakStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type CallExpression = {
+  type: \'CallExpression\';
+  _CallExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type CatchClause = {
+  type: \'CatchClause\';
+  _CatchClause: void;
+  body: BlockStatement;
+  param: Pattern;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassBody = {
+  type: \'ClassBody\';
+  _ClassBody: void;
+  body: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassDeclaration = {
+  type: \'ClassDeclaration\';
+  _ClassDeclaration: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassExpression = {
+  type: \'ClassExpression\';
+  _ClassExpression: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ComprehensionBlock = {
+  type: \'ComprehensionBlock\';
+  _ComprehensionBlock: void;
+  each: boolean;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ComprehensionExpression = {
+  type: \'ComprehensionExpression\';
+  _ComprehensionExpression: void;
+  body: Expression;
+  blocks: Array<ComprehensionBlock>;
+  filter: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ConditionalExpression = {
+  type: \'ConditionalExpression\';
+  _ConditionalExpression: void;
+  alternate: Expression;
+  consequent: Expression;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ContinueStatement = {
+  type: \'ContinueStatement\';
+  _ContinueStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type Decorator = {
+  type: \'Decorator\';
+  _Decorator: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DebuggerStatement = {
+  type: \'DebuggerStatement\';
+  _DebuggerStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DoWhileStatement = {
+  type: \'DoWhileStatement\';
+  _DoWhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type DoExpression = {
+  type: \'DoExpression\';
+  _DoExpression: void;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type EmptyStatement = {
+  type: \'EmptyStatement\';
+  _EmptyStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ExpressionStatement = {
+  type: \'ExpressionStatement\';
+  _ExpressionStatement: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type File = {
+  type: \'File\';
+  _File: void;
+  program: Program;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ForInStatement = {
+  type: \'ForInStatement\';
+  _ForInStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ForOfStatement = {
+  type: \'ForOfStatement\';
+  _ForOfStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ForStatement = {
+  type: \'ForStatement\';
+  _ForStatement: void;
+  init: ?Node;
+  test: ?Expression;
+  update: ?Expression;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type FunctionDeclaration = {
+  type: \'FunctionDeclaration\';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+export type FunctionExpression = {
+  type: \'FunctionExpression\';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+export type Identifier = {
+  type: \'Identifier\';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type IfStatement = {
+  type: \'IfStatement\';
+  _IfStatement: void;
+  alternate: ?Statement;
+  consequent: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportDefaultSpecifier = {
+  type: \'ImportDefaultSpecifier\';
+  _ImportDefaultSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportNamespaceSpecifier = {
+  type: \'ImportNamespaceSpecifier\';
+  _ImportNamespaceSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportDeclaration = {
+  type: \'ImportDeclaration\';
+  _ImportDeclaration: void;
+  specifiers: Array<Node>;
+  source: Literal;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportSpecifier = {
+  type: \'ImportSpecifier\';
+  _ImportSpecifier: void;
+  imported: Node;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type LabeledStatement = {
+  type: \'LabeledStatement\';
+  _LabeledStatement: void;
+  body: Statement;
+  label: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Literal = {
+  type: \'Literal\';
+  _Literal: void;
+  raw: string;
+  regex: ?{pattern: string, flags: string};
+  value: ?(string | boolean | number | RegExp);
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type LogicalOperator = \'||\' | \'&&\';
+
+export type LogicalExpression = {
+  type: \'LogicalExpression\';
+  _LogicalExpression: void;
+  left: Expression;
+  operator: LogicalOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type MemberExpression = {
+  type: \'MemberExpression\';
+  _MemberExpression: void;
+  computed: boolean;
+  object: Expression;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type MetaProperty = {
+  type: \'MetaProperty\';
+  _MetaProperty: void;
+  meta: Node;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type MethodDefinition = {
+  type: \'MethodDefinition\';
+  _MethodDefinition: void;
+  computed: boolean;
+  key: Node;
+  kind: \'constructor\' | \'method\' | \'get\' | \'set\';
+  static: boolean;
+  value: FunctionExpression;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NewExpression = {
+  type: \'NewExpression\';
+  _NewExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Noop = {
+  type: \'Noop\';
+  _Noop: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectExpression = {
+  type: \'ObjectExpression\';
+  _ObjectExpression: void;
+  properties: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectPattern = {
+  type: \'ObjectPattern\';
+  _ObjectPattern: void;
+  properties: Array<Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Program = {
+  type: \'Program\';
+  _Program: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Property = {
+  type: \'Property\';
+  _Property: void;
+  computed: boolean;
+  key: Node;
+  kind: \'init\' | \'get\' | \'set\';
+  method: boolean;
+  shorthand: boolean;
+  value: Node;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type RestElement = {
+  type: \'RestElement\';
+  _RestElement: void;
+  argument: Pattern;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ReturnStatement = {
+  type: \'ReturnStatement\';
+  _ReturnStatement: void;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SequenceExpression = {
+  type: \'SequenceExpression\';
+  _SequenceExpression: void;
+  expression: Array<Expression>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SpreadElement = {
+  type: \'SpreadElement\';
+  _SpreadElement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SpreadProperty = {
+  type: \'SpreadProperty\';
+  _SpreadProperty: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Super = {
+  type: \'Super\';
+  _Super: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SwitchCase = {
+  type: \'SwitchCase\';
+  _SwitchCase: void;
+  consequent: Array<Statement>;
+  test: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SwitchStatement = {
+  type: \'SwitchStatement\';
+  _SwitchStatement: void;
+  cases: Array<SwitchCase>;
+  discriminant: Expression;
+  lexical: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TaggedTemplateExpression = {
+  type: \'TaggedTemplateExpression\';
+  _TaggedTemplateExpression: void;
+  quasi: TemplateLiteral;
+  tag: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TemplateElement = {
+  type: \'TemplateElement\';
+  _TemplateElement: void;
+  tail: boolean;
+  value: {cooked: string, raw: string};
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TemplateLiteral = {
+  type: \'TemplateLiteral\';
+  _TemplateLiteral: void;
+  expressions: Array<Expression>;
+  quasis: Array<TemplateElement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ThisExpression = {
+  type: \'ThisExpression\';
+  _ThisExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ThrowStatement = {
+  type: \'ThrowStatement\';
+  _ThrowStatement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TryStatement = {
+  type: \'TryStatement\';
+  _TryStatement: void;
+  block: BlockStatement;
+  finalizer: ?BlockStatement;
+  guardedHandlers: Array<CatchClause>;
+  handler: ?CatchClause;
+  handlers: ?Array<CatchClause>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type UnaryOperator = \'-\' | \'+\' | \'!\' | \'~\' | \'typeof\' | \'void\' | \'delete\';
+
+export type UnaryExpression = {
+  type: \'UnaryExpression\';
+  _UnaryExpression: void;
+  argument: Expression;
+  operator: UnaryOperator;
+  prefix: true;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type UpdateOperator = \'++\' | \'--\';
+
+export type UpdateExpression = {
+  type: \'UpdateExpression\';
+  _UpdateExpression: void;
+  argument: Expression;
+  operator: UpdateOperator;
+  prefix: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type VariableDeclaration = {
+  type: \'VariableDeclaration\';
+  _VariableDeclaration: void;
+  declarations: Array<VariableDeclarator>;
+  kind: \'var\' | \'let\' | \'const\';
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type VariableDeclarator = {
+  type: \'VariableDeclarator\';
+  _VariableDeclarator: void;
+  id: Pattern;
+  init: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type WhileStatement = {
+  type: \'WhileStatement\';
+  _WhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type WithStatement = {
+  type: \'WithStatement\';
+  _WithStatement: void;
+  body: Statement;
+  object: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type YieldExpression = {
+  type: \'YieldExpression\';
+  _YieldExpression: void;
+  argument: ?Expression;
+  delegate: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportAllDeclaration = {
+  type: \'ExportAllDeclaration\';
+  _ExportAllDeclaration: void;
+  exported: Node;
+  source: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportDefaultDeclaration = {
+  type: \'ExportDefaultDeclaration\';
+  _ExportDefaultDeclaration: void;
+  declaration: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportNamedDeclaration = {
+  type: \'ExportNamedDeclaration\';
+  _ExportNamedDeclaration: void;
+  declaration: Node;
+  source: Literal;
+  specifiers: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportDefaultSpecifier = {
+  type: \'ExportDefaultSpecifier\';
+  _ExportDefaultSpecifier: void;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportNamespaceSpecifier = {
+  type: \'ExportNamespaceSpecifier\';
+  _ExportNamespaceSpecifier: void;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportSpecifier = {
+  type: \'ExportSpecifier\';
+  _ExportSpecifier: void;
+  local: Node;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type AnyTypeAnnotation = {
+  type: \'AnyTypeAnnotation\';
+  _AnyTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ArrayTypeAnnotation = {
+  type: \'ArrayTypeAnnotation\';
+  _ArrayTypeAnnotation: void;
+  elementType: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BooleanLiteralTypeAnnotation = {
+  type: \'BooleanLiteralTypeAnnotation\';
+  _BooleanLiteralTypeAnnotation: void;
+  raw: string;
+  value: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BooleanTypeAnnotation = {
+  type: \'BooleanTypeAnnotation\';
+  _BooleanTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassImplements = {
+  type: \'ClassImplements\';
+  _ClassImplements: void;
+  id: Identifier;
+  typeParameters: ?TypeParameterInstantiation;
+  superClass: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassProperty = {
+  type: \'ClassProperty\';
+  _ClassProperty: void;
+  computed: boolean;
+  key: Node;
+  static: boolean;
+  typeAnnotation: ?TypeAnnotation;
+  value: ?Expression;
+  decorators: Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DeclareClass = {
+  type: \'DeclareClass\';
+  _DeclareClass: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type DeclareFunction = {
+  type: \'DeclareFunction\';
+  _DeclareFunction: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DeclareModule = {
+  type: \'DeclareModule\';
+  _DeclareModule: void;
+  body: BlockStatement;
+  id: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type DeclareVariable = {
+  type: \'DeclareVariable\';
+  _DeclareVariable: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type FunctionTypeAnnotation = {
+  type: \'FunctionTypeAnnotation\';
+  _FunctionTypeAnnotation: void;
+  params: Array<FunctionTypeParam>;
+  rest: ?FunctionTypeParam;
+  returnType: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type FunctionTypeParam = {
+  type: \'FunctionTypeParam\';
+  _FunctionTypeParam: void;
+  name: Identifier;
+  optional: boolean;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type GenericTypeAnnotation = {
+  type: \'GenericTypeAnnotation\';
+  _GenericTypeAnnotation: void;
+  id: Node;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type InterfaceExtends = {
+  type: \'InterfaceExtends\';
+  _InterfaceExtends: void;
+  id: Identifier;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type InterfaceDeclaration = {
+  type: \'InterfaceDeclaration\';
+  _InterfaceDeclaration: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type IntersectionTypeAnnotation = {
+  type: \'IntersectionTypeAnnotation\';
+  _IntersectionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type MixedTypeAnnotation = {
+  type: \'MixedTypeAnnotation\';
+  _MixedTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NullableTypeAnnotation = {
+  type: \'NullableTypeAnnotation\';
+  _NullableTypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NumberLiteralTypeAnnotation = {
+  type: \'NumberLiteralTypeAnnotation\';
+  _NumberLiteralTypeAnnotation: void;
+  raw: string;
+  value: number;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NumberTypeAnnotation = {
+  type: \'NumberTypeAnnotation\';
+  _NumberTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type StringLiteralTypeAnnotation = {
+  type: \'StringLiteralTypeAnnotation\';
+  _StringLiteralTypeAnnotation: void;
+  raw: string;
+  value: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type StringTypeAnnotation = {
+  type: \'StringTypeAnnotation\';
+  _StringTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TupleTypeAnnotation = {
+  type: \'TupleTypeAnnotation\';
+  _TupleTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeofTypeAnnotation = {
+  type: \'TypeofTypeAnnotation\';
+  _TypeofTypeAnnotation: void;
+  argument: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeAlias = {
+  type: \'TypeAlias\';
+  _TypeAlias: void;
+  id: Identifier;
+  right: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeAnnotation = {
+  type: \'TypeAnnotation\';
+  _TypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeCastExpression = {
+  type: \'TypeCastExpression\';
+  _TypeCastExpression: void;
+  expression: Expression;
+  typeAnnotation: TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeParameterDeclaration = {
+  type: \'TypeParameterDeclaration\';
+  _TypeParameterDeclaration: void;
+  params: Array<Identifier>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeParameterInstantiation = {
+  type: \'TypeParameterInstantiation\';
+  _TypeParameterInstantiation: void;
+  params: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeAnnotation = {
+  type: \'ObjectTypeAnnotation\';
+  _ObjectTypeAnnotation: void;
+  callProperties: Array<ObjectTypeCallProperty>;
+  indexers: Array<ObjectTypeIndexer>;
+  properties: Array<ObjectTypeProperty>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeCallProperty = {
+  type: \'ObjectTypeCallProperty\';
+  _ObjectTypeCallProperty: void;
+  static: boolean;
+  value: FunctionTypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeIndexer = {
+  type: \'ObjectTypeIndexer\';
+  _ObjectTypeIndexer: void;
+  id: Identifier;
+  key: Type;
+  value: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeProperty = {
+  type: \'ObjectTypeProperty\';
+  _ObjectTypeProperty: void;
+  key: Node;
+  optional: boolean;
+  value: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type QualifiedTypeIdentifier = {
+  type: \'QualifiedTypeIdentifier\';
+  _QualifiedTypeIdentifier: void;
+  id: Identifier;
+  qualification: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type UnionTypeAnnotation = {
+  type: \'UnionTypeAnnotation\';
+  _UnionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type VoidTypeAnnotation = {
+  type: \'VoidTypeAnnotation\';
+  _VoidTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXAttribute = {
+  type: \'JSXAttribute\';
+  _JSXAttribute: void;
+  name: Node;
+  value: ?Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXClosingElement = {
+  type: \'JSXClosingElement\';
+  _JSXClosingElement: void;
+  name: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXElement = {
+  type: \'JSXElement\';
+  _JSXElement: void;
+  children: Array<Node>;
+  closingElement: ?JSXClosingElement;
+  openingElement: JSXOpeningElement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXEmptyExpression = {
+  type: \'JSXEmptyExpression\';
+  _JSXEmptyExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXExpressionContainer = {
+  type: \'JSXExpressionContainer\';
+  _JSXExpressionContainer: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXIdentifier = {
+  type: \'JSXIdentifier\';
+  _JSXIdentifier: void;
+  name: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXMemberExpression = {
+  type: \'JSXMemberExpression\';
+  _JSXMemberExpression: void;
+  computed: boolean;
+  object: Node;
+  property: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXNamespacedName = {
+  type: \'JSXNamespacedName\';
+  _JSXNamespacedName: void;
+  name: JSXIdentifier;
+  namespace: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXOpeningElement = {
+  type: \'JSXOpeningElement\';
+  _JSXOpeningElement: void;
+  attributes: Array<Node>;
+  name: Array<Node>;
+  selfClosing: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXSpreadAttribute = {
+  type: \'JSXSpreadAttribute\';
+  _JSXSpreadAttribute: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type-printer/jsfmt.spec.js b/tests/type-printer/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type-printer/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type-printer/printBinaryExpression.js b/tests/type-printer/printBinaryExpression.js
new file mode 100644
index 000000000000..4b3241fd1bd2
--- /dev/null
+++ b/tests/type-printer/printBinaryExpression.js
@@ -0,0 +1,20 @@
+'use babel';
+/* @flow */
+
+/*
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the license found in the LICENSE file in
+ * the root directory of this source tree.
+ */
+
+import type {BinaryExpression} from './types';
+
+function printBinaryExpression(
+  node: BinaryExpression,
+) {
+  console.log(node);
+}
+
+module.exports = printBinaryExpression;
diff --git a/tests/type-printer/types.js b/tests/type-printer/types.js
new file mode 100644
index 000000000000..4f7e499e4def
--- /dev/null
+++ b/tests/type-printer/types.js
@@ -0,0 +1,5045 @@
+/**
+ * @flow
+ */
+
+'use strict';
+
+/*
+ * Flow types for the Babylon AST.
+ */
+
+// Abstract types. Something must extend these.
+
+export type Comment = {
+  type: 'CommentLine';
+  _CommentLine: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+} | {
+  type: 'CommentBlock';
+  _CommentBlock: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+};
+
+export type Declaration = {
+  type: 'ClassBody';
+  _ClassBody: void;
+  body: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ClassDeclaration';
+  _ClassDeclaration: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'FunctionDeclaration';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'MethodDefinition';
+  _MethodDefinition: void;
+  computed: boolean;
+  key: Node;
+  kind: 'constructor' | 'method' | 'get' | 'set';
+  static: boolean;
+  value: FunctionExpression;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'VariableDeclaration';
+  _VariableDeclaration: void;
+  declarations: Array<VariableDeclarator>;
+  kind: 'var' | 'let' | 'const';
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ClassProperty';
+  _ClassProperty: void;
+  computed: boolean;
+  key: Node;
+  static: boolean;
+  typeAnnotation: ?TypeAnnotation;
+  value: ?Expression;
+  decorators: Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Expression = {
+  type: 'ArrayExpression';
+  _ArrayExpression: void;
+  elements: Array<?Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'AssignmentExpression';
+  _AssignmentExpression: void;
+  left: Pattern;
+  operator: AssignmentOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'AwaitExpression';
+  _AwaitExpression: void;
+  all: boolean;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BinaryExpression';
+  _BinaryExpression: void;
+  left: Expression;
+  operator: BinaryOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BindExpression';
+  _BindExpression: void;
+  callee: Node;
+  object: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'CallExpression';
+  _CallExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ClassExpression';
+  _ClassExpression: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ComprehensionExpression';
+  _ComprehensionExpression: void;
+  body: Expression;
+  blocks: Array<ComprehensionBlock>;
+  filter: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ConditionalExpression';
+  _ConditionalExpression: void;
+  alternate: Expression;
+  consequent: Expression;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DoExpression';
+  _DoExpression: void;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'FunctionExpression';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'Identifier';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Literal';
+  _Literal: void;
+  raw: string;
+  regex: ?{pattern: string, flags: string};
+  value: ?(string | boolean | number | RegExp);
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'LogicalExpression';
+  _LogicalExpression: void;
+  left: Expression;
+  operator: LogicalOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'MemberExpression';
+  _MemberExpression: void;
+  computed: boolean;
+  object: Expression;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'NewExpression';
+  _NewExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ObjectExpression';
+  _ObjectExpression: void;
+  properties: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SequenceExpression';
+  _SequenceExpression: void;
+  expression: Array<Expression>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TaggedTemplateExpression';
+  _TaggedTemplateExpression: void;
+  quasi: TemplateLiteral;
+  tag: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TemplateLiteral';
+  _TemplateLiteral: void;
+  expressions: Array<Expression>;
+  quasis: Array<TemplateElement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ThisExpression';
+  _ThisExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'UnaryExpression';
+  _UnaryExpression: void;
+  argument: Expression;
+  operator: UnaryOperator;
+  prefix: true;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'UpdateExpression';
+  _UpdateExpression: void;
+  argument: Expression;
+  operator: UpdateOperator;
+  prefix: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'YieldExpression';
+  _YieldExpression: void;
+  argument: ?Expression;
+  delegate: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TypeCastExpression';
+  _TypeCastExpression: void;
+  expression: Expression;
+  typeAnnotation: TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXElement';
+  _JSXElement: void;
+  children: Array<Node>;
+  closingElement: ?JSXClosingElement;
+  openingElement: JSXOpeningElement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXEmptyExpression';
+  _JSXEmptyExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXExpressionContainer';
+  _JSXExpressionContainer: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXMemberExpression';
+  _JSXMemberExpression: void;
+  computed: boolean;
+  object: Node;
+  property: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Function = {
+  type: 'ArrowFunctionExpression';
+  _ArrowFunctionExpression: void;
+  body: Node;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'FunctionDeclaration';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'FunctionExpression';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+export type Node = {
+  type: 'ArrayExpression';
+  _ArrayExpression: void;
+  elements: Array<?Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ArrayPattern';
+  _ArrayPattern: void;
+  elements: Array<?Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ArrowFunctionExpression';
+  _ArrowFunctionExpression: void;
+  body: Node;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'AssignmentExpression';
+  _AssignmentExpression: void;
+  left: Pattern;
+  operator: AssignmentOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'AssignmentPattern';
+  _AssignmentPattern: void;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'AwaitExpression';
+  _AwaitExpression: void;
+  all: boolean;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BinaryExpression';
+  _BinaryExpression: void;
+  left: Expression;
+  operator: BinaryOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BindExpression';
+  _BindExpression: void;
+  callee: Node;
+  object: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BlockStatement';
+  _BlockStatement: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BreakStatement';
+  _BreakStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'CallExpression';
+  _CallExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'CatchClause';
+  _CatchClause: void;
+  body: BlockStatement;
+  param: Pattern;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ClassBody';
+  _ClassBody: void;
+  body: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ClassDeclaration';
+  _ClassDeclaration: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ClassExpression';
+  _ClassExpression: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ComprehensionBlock';
+  _ComprehensionBlock: void;
+  each: boolean;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ComprehensionExpression';
+  _ComprehensionExpression: void;
+  body: Expression;
+  blocks: Array<ComprehensionBlock>;
+  filter: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ConditionalExpression';
+  _ConditionalExpression: void;
+  alternate: Expression;
+  consequent: Expression;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ContinueStatement';
+  _ContinueStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Decorator';
+  _Decorator: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DebuggerStatement';
+  _DebuggerStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DoWhileStatement';
+  _DoWhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DoExpression';
+  _DoExpression: void;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'EmptyStatement';
+  _EmptyStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ExpressionStatement';
+  _ExpressionStatement: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'File';
+  _File: void;
+  program: Program;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ForInStatement';
+  _ForInStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ForOfStatement';
+  _ForOfStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ForStatement';
+  _ForStatement: void;
+  init: ?Node;
+  test: ?Expression;
+  update: ?Expression;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'FunctionDeclaration';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'FunctionExpression';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+} | {
+  type: 'Identifier';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'IfStatement';
+  _IfStatement: void;
+  alternate: ?Statement;
+  consequent: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ImportDefaultSpecifier';
+  _ImportDefaultSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ImportNamespaceSpecifier';
+  _ImportNamespaceSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ImportDeclaration';
+  _ImportDeclaration: void;
+  specifiers: Array<Node>;
+  source: Literal;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ImportSpecifier';
+  _ImportSpecifier: void;
+  imported: Node;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'LabeledStatement';
+  _LabeledStatement: void;
+  body: Statement;
+  label: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Literal';
+  _Literal: void;
+  raw: string;
+  regex: ?{pattern: string, flags: string};
+  value: ?(string | boolean | number | RegExp);
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'LogicalExpression';
+  _LogicalExpression: void;
+  left: Expression;
+  operator: LogicalOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'MemberExpression';
+  _MemberExpression: void;
+  computed: boolean;
+  object: Expression;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'MetaProperty';
+  _MetaProperty: void;
+  meta: Node;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'MethodDefinition';
+  _MethodDefinition: void;
+  computed: boolean;
+  key: Node;
+  kind: 'constructor' | 'method' | 'get' | 'set';
+  static: boolean;
+  value: FunctionExpression;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'NewExpression';
+  _NewExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Noop';
+  _Noop: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ObjectExpression';
+  _ObjectExpression: void;
+  properties: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ObjectPattern';
+  _ObjectPattern: void;
+  properties: Array<Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Program';
+  _Program: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Property';
+  _Property: void;
+  computed: boolean;
+  key: Node;
+  kind: 'init' | 'get' | 'set';
+  method: boolean;
+  shorthand: boolean;
+  value: Node;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'RestElement';
+  _RestElement: void;
+  argument: Pattern;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ReturnStatement';
+  _ReturnStatement: void;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SequenceExpression';
+  _SequenceExpression: void;
+  expression: Array<Expression>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SpreadElement';
+  _SpreadElement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SpreadProperty';
+  _SpreadProperty: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Super';
+  _Super: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SwitchCase';
+  _SwitchCase: void;
+  consequent: Array<Statement>;
+  test: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SwitchStatement';
+  _SwitchStatement: void;
+  cases: Array<SwitchCase>;
+  discriminant: Expression;
+  lexical: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TaggedTemplateExpression';
+  _TaggedTemplateExpression: void;
+  quasi: TemplateLiteral;
+  tag: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TemplateElement';
+  _TemplateElement: void;
+  tail: boolean;
+  value: {cooked: string, raw: string};
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TemplateLiteral';
+  _TemplateLiteral: void;
+  expressions: Array<Expression>;
+  quasis: Array<TemplateElement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ThisExpression';
+  _ThisExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ThrowStatement';
+  _ThrowStatement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TryStatement';
+  _TryStatement: void;
+  block: BlockStatement;
+  finalizer: ?BlockStatement;
+  guardedHandlers: Array<CatchClause>;
+  handler: ?CatchClause;
+  handlers: ?Array<CatchClause>;
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+  leadingComments: ?Array<Comment>;
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+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'UnaryExpression';
+  _UnaryExpression: void;
+  argument: Expression;
+  operator: UnaryOperator;
+  prefix: true;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'UpdateExpression';
+  _UpdateExpression: void;
+  argument: Expression;
+  operator: UpdateOperator;
+  prefix: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'VariableDeclaration';
+  _VariableDeclaration: void;
+  declarations: Array<VariableDeclarator>;
+  kind: 'var' | 'let' | 'const';
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'VariableDeclarator';
+  _VariableDeclarator: void;
+  id: Pattern;
+  init: ?Expression;
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
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+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'WhileStatement';
+  _WhileStatement: void;
+  body: Statement;
+  test: Expression;
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+} | {
+  type: 'WithStatement';
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'YieldExpression';
+  _YieldExpression: void;
+  argument: ?Expression;
+  delegate: boolean;
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+  start: number;
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+} | {
+  type: 'ExportAllDeclaration';
+  _ExportAllDeclaration: void;
+  exported: Node;
+  source: Node;
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+} | {
+  type: 'ExportDefaultDeclaration';
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+    start: {column: number, line: number},
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+} | {
+  type: 'ExportNamedDeclaration';
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+  source: Literal;
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+  innerComments: ?Array<Comment>;
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+} | {
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+} | {
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+  exported: Node;
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+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
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+} | {
+  type: 'ExportSpecifier';
+  _ExportSpecifier: void;
+  local: Node;
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+  leadingComments: ?Array<Comment>;
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+} | {
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+  loc: {
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+} | {
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+  leadingComments: ?Array<Comment>;
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+} | {
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+  leadingComments: ?Array<Comment>;
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+    start: {column: number, line: number},
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+  id: Identifier;
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+  loc: {
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+} | {
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+} | {
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+  optional: boolean;
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
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+    start: {column: number, line: number},
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+} | {
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+    start: {column: number, line: number},
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+} | {
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+  id: Identifier;
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+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+} | {
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+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXEmptyExpression';
+  _JSXEmptyExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXExpressionContainer';
+  _JSXExpressionContainer: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXIdentifier';
+  _JSXIdentifier: void;
+  name: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXMemberExpression';
+  _JSXMemberExpression: void;
+  computed: boolean;
+  object: Node;
+  property: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXNamespacedName';
+  _JSXNamespacedName: void;
+  name: JSXIdentifier;
+  namespace: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXOpeningElement';
+  _JSXOpeningElement: void;
+  attributes: Array<Node>;
+  name: Array<Node>;
+  selfClosing: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'JSXSpreadAttribute';
+  _JSXSpreadAttribute: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Pattern = {
+  type: 'ArrayPattern';
+  _ArrayPattern: void;
+  elements: Array<?Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'AssignmentPattern';
+  _AssignmentPattern: void;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'Identifier';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ObjectPattern';
+  _ObjectPattern: void;
+  properties: Array<Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'RestElement';
+  _RestElement: void;
+  argument: Pattern;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Statement = {
+  type: 'BlockStatement';
+  _BlockStatement: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BreakStatement';
+  _BreakStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ContinueStatement';
+  _ContinueStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DoWhileStatement';
+  _DoWhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'EmptyStatement';
+  _EmptyStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ExpressionStatement';
+  _ExpressionStatement: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ForInStatement';
+  _ForInStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ForOfStatement';
+  _ForOfStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ForStatement';
+  _ForStatement: void;
+  init: ?Node;
+  test: ?Expression;
+  update: ?Expression;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'IfStatement';
+  _IfStatement: void;
+  alternate: ?Statement;
+  consequent: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'LabeledStatement';
+  _LabeledStatement: void;
+  body: Statement;
+  label: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ReturnStatement';
+  _ReturnStatement: void;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'SwitchStatement';
+  _SwitchStatement: void;
+  cases: Array<SwitchCase>;
+  discriminant: Expression;
+  lexical: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ThrowStatement';
+  _ThrowStatement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TryStatement';
+  _TryStatement: void;
+  block: BlockStatement;
+  finalizer: ?BlockStatement;
+  guardedHandlers: Array<CatchClause>;
+  handler: ?CatchClause;
+  handlers: ?Array<CatchClause>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'WhileStatement';
+  _WhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'WithStatement';
+  _WithStatement: void;
+  body: Statement;
+  object: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DeclareClass';
+  _DeclareClass: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DeclareFunction';
+  _DeclareFunction: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DeclareModule';
+  _DeclareModule: void;
+  body: BlockStatement;
+  id: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'DeclareVariable';
+  _DeclareVariable: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'InterfaceDeclaration';
+  _InterfaceDeclaration: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TypeAlias';
+  _TypeAlias: void;
+  id: Identifier;
+  right: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Type = {
+  type: 'AnyTypeAnnotation';
+  _AnyTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ArrayTypeAnnotation';
+  _ArrayTypeAnnotation: void;
+  elementType: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BooleanLiteralTypeAnnotation';
+  _BooleanLiteralTypeAnnotation: void;
+  raw: string;
+  value: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'BooleanTypeAnnotation';
+  _BooleanTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'FunctionTypeAnnotation';
+  _FunctionTypeAnnotation: void;
+  params: Array<FunctionTypeParam>;
+  rest: ?FunctionTypeParam;
+  returnType: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'GenericTypeAnnotation';
+  _GenericTypeAnnotation: void;
+  id: Node;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'IntersectionTypeAnnotation';
+  _IntersectionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'MixedTypeAnnotation';
+  _MixedTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'NullableTypeAnnotation';
+  _NullableTypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'NumberLiteralTypeAnnotation';
+  _NumberLiteralTypeAnnotation: void;
+  raw: string;
+  value: number;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'NumberTypeAnnotation';
+  _NumberTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'StringLiteralTypeAnnotation';
+  _StringLiteralTypeAnnotation: void;
+  raw: string;
+  value: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'StringTypeAnnotation';
+  _StringTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'TupleTypeAnnotation';
+  _TupleTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'ObjectTypeAnnotation';
+  _ObjectTypeAnnotation: void;
+  callProperties: Array<ObjectTypeCallProperty>;
+  indexers: Array<ObjectTypeIndexer>;
+  properties: Array<ObjectTypeProperty>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'UnionTypeAnnotation';
+  _UnionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+} | {
+  type: 'VoidTypeAnnotation';
+  _VoidTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// Concrete Types. Nothing can extend these.
+
+export type CommentLine = {
+  type: 'CommentLine';
+  _CommentLine: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+};
+
+export type CommentBlock = {
+  type: 'CommentBlock';
+  _CommentBlock: void;
+  value: string;
+  end: number;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+};
+
+// Babel concrete types.
+
+export type ArrayExpression = {
+  type: 'ArrayExpression';
+  _ArrayExpression: void;
+  elements: Array<?Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ArrayPattern = {
+  type: 'ArrayPattern';
+  _ArrayPattern: void;
+  elements: Array<?Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ArrowFunctionExpression = {
+  type: 'ArrowFunctionExpression';
+  _ArrowFunctionExpression: void;
+  body: Node;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+type AssignmentOperator =
+  '=' |
+  '+=' |
+  '-=' |
+  '*=' |
+  '/=' |
+  '%=' |
+  '<<=' |
+  '>>=' |
+  '>>>=' |
+  '|=' |
+  '^=' |
+  '&=';
+
+export type AssignmentExpression = {
+  type: 'AssignmentExpression';
+  _AssignmentExpression: void;
+  left: Pattern;
+  operator: AssignmentOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type AssignmentPattern = {
+  type: 'AssignmentPattern';
+  _AssignmentPattern: void;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type AwaitExpression = {
+  type: 'AwaitExpression';
+  _AwaitExpression: void;
+  all: boolean;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type BinaryOperator =
+  '==' |
+  '!=' |
+  '===' |
+  '!==' |
+  '<' |
+  '<=' |
+  '>' |
+  '>=' |
+  '<<' |
+  '>>' |
+  '>>>' |
+  '+' |
+  '-' |
+  '*' |
+  '/' |
+  '%' |
+  '&' |
+  '|' |
+  '^' |
+  'in' |
+  'instanceof' |
+  '..';
+
+export type BinaryExpression = {
+  type: 'BinaryExpression';
+  _BinaryExpression: void;
+  left: Expression;
+  operator: BinaryOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: What is this?
+export type BindExpression = {
+  type: 'BindExpression';
+  _BindExpression: void;
+  callee: Node;
+  object: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BlockStatement = {
+  type: 'BlockStatement';
+  _BlockStatement: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BreakStatement = {
+  type: 'BreakStatement';
+  _BreakStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type CallExpression = {
+  type: 'CallExpression';
+  _CallExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type CatchClause = {
+  type: 'CatchClause';
+  _CatchClause: void;
+  body: BlockStatement;
+  param: Pattern;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassBody = {
+  type: 'ClassBody';
+  _ClassBody: void;
+  body: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassDeclaration = {
+  type: 'ClassDeclaration';
+  _ClassDeclaration: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassExpression = {
+  type: 'ClassExpression';
+  _ClassExpression: void;
+  body: ClassBody;
+  id: ?Identifier;
+  superClass: ?Expression;
+  decorators: any;
+  superTypeParameters: any;
+  typeParameters: any;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ComprehensionBlock = {
+  type: 'ComprehensionBlock';
+  _ComprehensionBlock: void;
+  each: boolean;
+  left: Pattern;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ComprehensionExpression = {
+  type: 'ComprehensionExpression';
+  _ComprehensionExpression: void;
+  body: Expression;
+  blocks: Array<ComprehensionBlock>;
+  filter: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ConditionalExpression = {
+  type: 'ConditionalExpression';
+  _ConditionalExpression: void;
+  alternate: Expression;
+  consequent: Expression;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ContinueStatement = {
+  type: 'ContinueStatement';
+  _ContinueStatement: void;
+  label: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type Decorator = {
+  type: 'Decorator';
+  _Decorator: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DebuggerStatement = {
+  type: 'DebuggerStatement';
+  _DebuggerStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DoWhileStatement = {
+  type: 'DoWhileStatement';
+  _DoWhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type DoExpression = {
+  type: 'DoExpression';
+  _DoExpression: void;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type EmptyStatement = {
+  type: 'EmptyStatement';
+  _EmptyStatement: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ExpressionStatement = {
+  type: 'ExpressionStatement';
+  _ExpressionStatement: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type File = {
+  type: 'File';
+  _File: void;
+  program: Program;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ForInStatement = {
+  type: 'ForInStatement';
+  _ForInStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ForOfStatement = {
+  type: 'ForOfStatement';
+  _ForOfStatement: void;
+  body: Statement;
+  left: Node;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ForStatement = {
+  type: 'ForStatement';
+  _ForStatement: void;
+  init: ?Node;
+  test: ?Expression;
+  update: ?Expression;
+  body: Statement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type FunctionDeclaration = {
+  type: 'FunctionDeclaration';
+  _FunctionDeclaration: void;
+  body: BlockStatement;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+export type FunctionExpression = {
+  type: 'FunctionExpression';
+  _FunctionExpression: void;
+  body: BlockStatement;
+  id: ?Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+  async: boolean;
+  defaults: Array<?Expression>;
+  expression: boolean;
+  generator: boolean;
+  params: Array<Pattern>;
+  rest: ?Identifier;
+  returnType: ?TypeAnnotation;
+  typeParameters: ?TypeParameterDeclaration;
+};
+
+export type Identifier = {
+  type: 'Identifier';
+  _Identifier: void;
+  name: string;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type IfStatement = {
+  type: 'IfStatement';
+  _IfStatement: void;
+  alternate: ?Statement;
+  consequent: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportDefaultSpecifier = {
+  type: 'ImportDefaultSpecifier';
+  _ImportDefaultSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportNamespaceSpecifier = {
+  type: 'ImportNamespaceSpecifier';
+  _ImportNamespaceSpecifier: void;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportDeclaration = {
+  type: 'ImportDeclaration';
+  _ImportDeclaration: void;
+  specifiers: Array<Node>;
+  source: Literal;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ImportSpecifier = {
+  type: 'ImportSpecifier';
+  _ImportSpecifier: void;
+  imported: Node;
+  local: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type LabeledStatement = {
+  type: 'LabeledStatement';
+  _LabeledStatement: void;
+  body: Statement;
+  label: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Literal = {
+  type: 'Literal';
+  _Literal: void;
+  raw: string;
+  regex: ?{pattern: string, flags: string};
+  value: ?(string | boolean | number | RegExp);
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type LogicalOperator = '||' | '&&';
+
+export type LogicalExpression = {
+  type: 'LogicalExpression';
+  _LogicalExpression: void;
+  left: Expression;
+  operator: LogicalOperator;
+  right: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type MemberExpression = {
+  type: 'MemberExpression';
+  _MemberExpression: void;
+  computed: boolean;
+  object: Expression;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type MetaProperty = {
+  type: 'MetaProperty';
+  _MetaProperty: void;
+  meta: Node;
+  property: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type MethodDefinition = {
+  type: 'MethodDefinition';
+  _MethodDefinition: void;
+  computed: boolean;
+  key: Node;
+  kind: 'constructor' | 'method' | 'get' | 'set';
+  static: boolean;
+  value: FunctionExpression;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NewExpression = {
+  type: 'NewExpression';
+  _NewExpression: void;
+  arguments: Array<Node>;
+  callee: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Noop = {
+  type: 'Noop';
+  _Noop: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectExpression = {
+  type: 'ObjectExpression';
+  _ObjectExpression: void;
+  properties: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectPattern = {
+  type: 'ObjectPattern';
+  _ObjectPattern: void;
+  properties: Array<Node>;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Program = {
+  type: 'Program';
+  _Program: void;
+  body: Array<Statement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Property = {
+  type: 'Property';
+  _Property: void;
+  computed: boolean;
+  key: Node;
+  kind: 'init' | 'get' | 'set';
+  method: boolean;
+  shorthand: boolean;
+  value: Node;
+  decorators: ?Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type RestElement = {
+  type: 'RestElement';
+  _RestElement: void;
+  argument: Pattern;
+  typeAnnotation: ?TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ReturnStatement = {
+  type: 'ReturnStatement';
+  _ReturnStatement: void;
+  argument: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SequenceExpression = {
+  type: 'SequenceExpression';
+  _SequenceExpression: void;
+  expression: Array<Expression>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SpreadElement = {
+  type: 'SpreadElement';
+  _SpreadElement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SpreadProperty = {
+  type: 'SpreadProperty';
+  _SpreadProperty: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type Super = {
+  type: 'Super';
+  _Super: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SwitchCase = {
+  type: 'SwitchCase';
+  _SwitchCase: void;
+  consequent: Array<Statement>;
+  test: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type SwitchStatement = {
+  type: 'SwitchStatement';
+  _SwitchStatement: void;
+  cases: Array<SwitchCase>;
+  discriminant: Expression;
+  lexical: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TaggedTemplateExpression = {
+  type: 'TaggedTemplateExpression';
+  _TaggedTemplateExpression: void;
+  quasi: TemplateLiteral;
+  tag: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TemplateElement = {
+  type: 'TemplateElement';
+  _TemplateElement: void;
+  tail: boolean;
+  value: {cooked: string, raw: string};
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TemplateLiteral = {
+  type: 'TemplateLiteral';
+  _TemplateLiteral: void;
+  expressions: Array<Expression>;
+  quasis: Array<TemplateElement>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ThisExpression = {
+  type: 'ThisExpression';
+  _ThisExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ThrowStatement = {
+  type: 'ThrowStatement';
+  _ThrowStatement: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TryStatement = {
+  type: 'TryStatement';
+  _TryStatement: void;
+  block: BlockStatement;
+  finalizer: ?BlockStatement;
+  guardedHandlers: Array<CatchClause>;
+  handler: ?CatchClause;
+  handlers: ?Array<CatchClause>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type UnaryOperator = '-' | '+' | '!' | '~' | 'typeof' | 'void' | 'delete';
+
+export type UnaryExpression = {
+  type: 'UnaryExpression';
+  _UnaryExpression: void;
+  argument: Expression;
+  operator: UnaryOperator;
+  prefix: true;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+type UpdateOperator = '++' | '--';
+
+export type UpdateExpression = {
+  type: 'UpdateExpression';
+  _UpdateExpression: void;
+  argument: Expression;
+  operator: UpdateOperator;
+  prefix: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type VariableDeclaration = {
+  type: 'VariableDeclaration';
+  _VariableDeclaration: void;
+  declarations: Array<VariableDeclarator>;
+  kind: 'var' | 'let' | 'const';
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type VariableDeclarator = {
+  type: 'VariableDeclarator';
+  _VariableDeclarator: void;
+  id: Pattern;
+  init: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type WhileStatement = {
+  type: 'WhileStatement';
+  _WhileStatement: void;
+  body: Statement;
+  test: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type WithStatement = {
+  type: 'WithStatement';
+  _WithStatement: void;
+  body: Statement;
+  object: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type YieldExpression = {
+  type: 'YieldExpression';
+  _YieldExpression: void;
+  argument: ?Expression;
+  delegate: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportAllDeclaration = {
+  type: 'ExportAllDeclaration';
+  _ExportAllDeclaration: void;
+  exported: Node;
+  source: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportDefaultDeclaration = {
+  type: 'ExportDefaultDeclaration';
+  _ExportDefaultDeclaration: void;
+  declaration: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportNamedDeclaration = {
+  type: 'ExportNamedDeclaration';
+  _ExportNamedDeclaration: void;
+  declaration: Node;
+  source: Literal;
+  specifiers: Array<Node>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportDefaultSpecifier = {
+  type: 'ExportDefaultSpecifier';
+  _ExportDefaultSpecifier: void;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportNamespaceSpecifier = {
+  type: 'ExportNamespaceSpecifier';
+  _ExportNamespaceSpecifier: void;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type ExportSpecifier = {
+  type: 'ExportSpecifier';
+  _ExportSpecifier: void;
+  local: Node;
+  exported: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type AnyTypeAnnotation = {
+  type: 'AnyTypeAnnotation';
+  _AnyTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ArrayTypeAnnotation = {
+  type: 'ArrayTypeAnnotation';
+  _ArrayTypeAnnotation: void;
+  elementType: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BooleanLiteralTypeAnnotation = {
+  type: 'BooleanLiteralTypeAnnotation';
+  _BooleanLiteralTypeAnnotation: void;
+  raw: string;
+  value: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type BooleanTypeAnnotation = {
+  type: 'BooleanTypeAnnotation';
+  _BooleanTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassImplements = {
+  type: 'ClassImplements';
+  _ClassImplements: void;
+  id: Identifier;
+  typeParameters: ?TypeParameterInstantiation;
+  superClass: ?Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ClassProperty = {
+  type: 'ClassProperty';
+  _ClassProperty: void;
+  computed: boolean;
+  key: Node;
+  static: boolean;
+  typeAnnotation: ?TypeAnnotation;
+  value: ?Expression;
+  decorators: Array<Decorator>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DeclareClass = {
+  type: 'DeclareClass';
+  _DeclareClass: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type DeclareFunction = {
+  type: 'DeclareFunction';
+  _DeclareFunction: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type DeclareModule = {
+  type: 'DeclareModule';
+  _DeclareModule: void;
+  body: BlockStatement;
+  id: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+// TODO: Make this correct.
+export type DeclareVariable = {
+  type: 'DeclareVariable';
+  _DeclareVariable: void;
+  id: Identifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type FunctionTypeAnnotation = {
+  type: 'FunctionTypeAnnotation';
+  _FunctionTypeAnnotation: void;
+  params: Array<FunctionTypeParam>;
+  rest: ?FunctionTypeParam;
+  returnType: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type FunctionTypeParam = {
+  type: 'FunctionTypeParam';
+  _FunctionTypeParam: void;
+  name: Identifier;
+  optional: boolean;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type GenericTypeAnnotation = {
+  type: 'GenericTypeAnnotation';
+  _GenericTypeAnnotation: void;
+  id: Node;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type InterfaceExtends = {
+  type: 'InterfaceExtends';
+  _InterfaceExtends: void;
+  id: Identifier;
+  typeParameters: ?TypeParameterInstantiation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type InterfaceDeclaration = {
+  type: 'InterfaceDeclaration';
+  _InterfaceDeclaration: void;
+  body: ObjectTypeAnnotation;
+  extends: Array<InterfaceExtends>;
+  id: Identifier;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type IntersectionTypeAnnotation = {
+  type: 'IntersectionTypeAnnotation';
+  _IntersectionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type MixedTypeAnnotation = {
+  type: 'MixedTypeAnnotation';
+  _MixedTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NullableTypeAnnotation = {
+  type: 'NullableTypeAnnotation';
+  _NullableTypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NumberLiteralTypeAnnotation = {
+  type: 'NumberLiteralTypeAnnotation';
+  _NumberLiteralTypeAnnotation: void;
+  raw: string;
+  value: number;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type NumberTypeAnnotation = {
+  type: 'NumberTypeAnnotation';
+  _NumberTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type StringLiteralTypeAnnotation = {
+  type: 'StringLiteralTypeAnnotation';
+  _StringLiteralTypeAnnotation: void;
+  raw: string;
+  value: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type StringTypeAnnotation = {
+  type: 'StringTypeAnnotation';
+  _StringTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TupleTypeAnnotation = {
+  type: 'TupleTypeAnnotation';
+  _TupleTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeofTypeAnnotation = {
+  type: 'TypeofTypeAnnotation';
+  _TypeofTypeAnnotation: void;
+  argument: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeAlias = {
+  type: 'TypeAlias';
+  _TypeAlias: void;
+  id: Identifier;
+  right: Type;
+  typeParameters: ?TypeParameterDeclaration;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeAnnotation = {
+  type: 'TypeAnnotation';
+  _TypeAnnotation: void;
+  typeAnnotation: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeCastExpression = {
+  type: 'TypeCastExpression';
+  _TypeCastExpression: void;
+  expression: Expression;
+  typeAnnotation: TypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeParameterDeclaration = {
+  type: 'TypeParameterDeclaration';
+  _TypeParameterDeclaration: void;
+  params: Array<Identifier>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type TypeParameterInstantiation = {
+  type: 'TypeParameterInstantiation';
+  _TypeParameterInstantiation: void;
+  params: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeAnnotation = {
+  type: 'ObjectTypeAnnotation';
+  _ObjectTypeAnnotation: void;
+  callProperties: Array<ObjectTypeCallProperty>;
+  indexers: Array<ObjectTypeIndexer>;
+  properties: Array<ObjectTypeProperty>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeCallProperty = {
+  type: 'ObjectTypeCallProperty';
+  _ObjectTypeCallProperty: void;
+  static: boolean;
+  value: FunctionTypeAnnotation;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeIndexer = {
+  type: 'ObjectTypeIndexer';
+  _ObjectTypeIndexer: void;
+  id: Identifier;
+  key: Type;
+  value: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type ObjectTypeProperty = {
+  type: 'ObjectTypeProperty';
+  _ObjectTypeProperty: void;
+  key: Node;
+  optional: boolean;
+  value: Type;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type QualifiedTypeIdentifier = {
+  type: 'QualifiedTypeIdentifier';
+  _QualifiedTypeIdentifier: void;
+  id: Identifier;
+  qualification: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type UnionTypeAnnotation = {
+  type: 'UnionTypeAnnotation';
+  _UnionTypeAnnotation: void;
+  types: Array<Type>;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type VoidTypeAnnotation = {
+  type: 'VoidTypeAnnotation';
+  _VoidTypeAnnotation: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXAttribute = {
+  type: 'JSXAttribute';
+  _JSXAttribute: void;
+  name: Node;
+  value: ?Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXClosingElement = {
+  type: 'JSXClosingElement';
+  _JSXClosingElement: void;
+  name: Node;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXElement = {
+  type: 'JSXElement';
+  _JSXElement: void;
+  children: Array<Node>;
+  closingElement: ?JSXClosingElement;
+  openingElement: JSXOpeningElement;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXEmptyExpression = {
+  type: 'JSXEmptyExpression';
+  _JSXEmptyExpression: void;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXExpressionContainer = {
+  type: 'JSXExpressionContainer';
+  _JSXExpressionContainer: void;
+  expression: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXIdentifier = {
+  type: 'JSXIdentifier';
+  _JSXIdentifier: void;
+  name: string;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXMemberExpression = {
+  type: 'JSXMemberExpression';
+  _JSXMemberExpression: void;
+  computed: boolean;
+  object: Node;
+  property: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXNamespacedName = {
+  type: 'JSXNamespacedName';
+  _JSXNamespacedName: void;
+  name: JSXIdentifier;
+  namespace: JSXIdentifier;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXOpeningElement = {
+  type: 'JSXOpeningElement';
+  _JSXOpeningElement: void;
+  attributes: Array<Node>;
+  name: Array<Node>;
+  selfClosing: boolean;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
+
+export type JSXSpreadAttribute = {
+  type: 'JSXSpreadAttribute';
+  _JSXSpreadAttribute: void;
+  argument: Expression;
+  end: number;
+  innerComments: ?Array<Comment>;
+  leadingComments: ?Array<Comment>;
+  loc: {
+    end: {column: number, line: number},
+    start: {column: number, line: number},
+  };
+  start: number;
+  trailingComments: ?Array<Comment>;
+};
diff --git a/tests/type_args_nonstrict/__snapshots__/jsfmt.spec.js.snap b/tests/type_args_nonstrict/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a7603c13b402
--- /dev/null
+++ b/tests/type_args_nonstrict/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,91 @@
+exports[`test test.js 1`] = `
+"/**
+ * Test nonstrict type param arity checking,
+ * as enabled by
+ *
+ * [options]
+ * experimental.strict_type_args=false
+ *
+ * in .flowconfig.
+ *
+ * @flow
+ */
+
+// no arity error in type annotation using polymorphic class
+
+class MyClass<T> {
+  x: T;
+  constructor(x: T) {
+    this.x = x;
+  }
+}
+
+var c: MyClass = new MyClass(0); // no error
+
+// no arity error in type annotation using polymorphic class with defaulting
+
+class MyClass2<T, U = string> {
+  x: T;
+  y: U;
+  constructor(x: T, y: U) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
+var c2: MyClass2 = new MyClass2(0, \"\"); // no error
+
+// no arity error in type annotation using polymorphic type alias
+
+type MyObject<T> = {
+  x: T;
+}
+
+var o: MyObject = { x: 0 }; // no error
+
+// arity error in type alias rhs
+
+type MySubobject = { y: number } & MyObject; // no error
+
+// arity error in interface extends
+
+interface MyInterface<T> {
+  x: T;
+}
+
+interface MySubinterface extends MyInterface { // no error
+  y: number;
+}
+
+// no arity error in extends of polymorphic class
+
+class MySubclass extends MyClass { // ok, type arg inferred
+  y: number;
+  constructor(y: number) {
+    super(y);
+  }
+}
+
+// no arity error in call of polymorphic function
+
+function singleton<T>(x: T):Array<T> { return [x]; }
+
+var num_array:Array<number> = singleton(0); // ok, type arg inferred
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_args_nonstrict/jsfmt.spec.js b/tests/type_args_nonstrict/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_args_nonstrict/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_args_nonstrict/test.js b/tests/type_args_nonstrict/test.js
new file mode 100644
index 000000000000..79ad1329f72b
--- /dev/null
+++ b/tests/type_args_nonstrict/test.js
@@ -0,0 +1,72 @@
+/**
+ * Test nonstrict type param arity checking,
+ * as enabled by
+ *
+ * [options]
+ * experimental.strict_type_args=false
+ *
+ * in .flowconfig.
+ *
+ * @flow
+ */
+
+// no arity error in type annotation using polymorphic class
+
+class MyClass<T> {
+  x: T;
+  constructor(x: T) {
+    this.x = x;
+  }
+}
+
+var c: MyClass = new MyClass(0); // no error
+
+// no arity error in type annotation using polymorphic class with defaulting
+
+class MyClass2<T, U = string> {
+  x: T;
+  y: U;
+  constructor(x: T, y: U) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
+var c2: MyClass2 = new MyClass2(0, ""); // no error
+
+// no arity error in type annotation using polymorphic type alias
+
+type MyObject<T> = {
+  x: T;
+}
+
+var o: MyObject = { x: 0 }; // no error
+
+// arity error in type alias rhs
+
+type MySubobject = { y: number } & MyObject; // no error
+
+// arity error in interface extends
+
+interface MyInterface<T> {
+  x: T;
+}
+
+interface MySubinterface extends MyInterface { // no error
+  y: number;
+}
+
+// no arity error in extends of polymorphic class
+
+class MySubclass extends MyClass { // ok, type arg inferred
+  y: number;
+  constructor(y: number) {
+    super(y);
+  }
+}
+
+// no arity error in call of polymorphic function
+
+function singleton<T>(x: T):Array<T> { return [x]; }
+
+var num_array:Array<number> = singleton(0); // ok, type arg inferred
diff --git a/tests/type_args_strict/__snapshots__/jsfmt.spec.js.snap b/tests/type_args_strict/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..07374c543490
--- /dev/null
+++ b/tests/type_args_strict/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,90 @@
+exports[`test test.js 1`] = `
+"/**
+ * Test strict type param arity checking.
+ *
+ * Full type argument lists are required in type expressions,
+ * such as type annotations and interface extends clauses.
+ * Type arguments are optional in value expressions, such as
+ * class extends clauses and calls of polymorphic functions.
+ *
+ * @flow
+ */
+
+// arity error in type annotation using polymorphic class
+
+class MyClass<T> {
+  x: T;
+  constructor(x: T) {
+    this.x = x;
+  }
+}
+
+var c: MyClass = new MyClass(0); // error, missing argument list (1)
+
+// arity error in type annotation using polymorphic class with defaulting
+
+class MyClass2<T, U = string> {
+  x: T;
+  y: U;
+  constructor(x: T, y: U) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
+var c2: MyClass2 = new MyClass2(0, \"\"); // error, missing argument list (1-2)
+
+// arity error in type annotation using polymorphic type alias
+
+type MyObject<T> = {
+  x: T;
+}
+
+var o: MyObject = { x: 0 }; // error, missing argument list
+
+// arity error in type alias rhs
+
+type MySubobject = { y: number } & MyObject; // error, missing argument list
+
+// arity error in interface extends
+
+interface MyInterface<T> {
+  x: T;
+}
+
+interface MySubinterface extends MyInterface { // error, missing argument list
+  y: number;
+}
+
+// *no* arity error in extends of polymorphic class
+
+class MySubclass extends MyClass { // ok, type arg inferred
+  y: number;
+  constructor(y: number) {
+    super(y);
+  }
+}
+
+// *no* arity error in call of polymorphic function
+
+function singleton<T>(x: T):Array<T> { return [x]; }
+
+var num_array:Array<number> = singleton(0); // ok, type arg inferred
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_args_strict/jsfmt.spec.js b/tests/type_args_strict/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_args_strict/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_args_strict/test.js b/tests/type_args_strict/test.js
new file mode 100644
index 000000000000..785285f5e63c
--- /dev/null
+++ b/tests/type_args_strict/test.js
@@ -0,0 +1,71 @@
+/**
+ * Test strict type param arity checking.
+ *
+ * Full type argument lists are required in type expressions,
+ * such as type annotations and interface extends clauses.
+ * Type arguments are optional in value expressions, such as
+ * class extends clauses and calls of polymorphic functions.
+ *
+ * @flow
+ */
+
+// arity error in type annotation using polymorphic class
+
+class MyClass<T> {
+  x: T;
+  constructor(x: T) {
+    this.x = x;
+  }
+}
+
+var c: MyClass = new MyClass(0); // error, missing argument list (1)
+
+// arity error in type annotation using polymorphic class with defaulting
+
+class MyClass2<T, U = string> {
+  x: T;
+  y: U;
+  constructor(x: T, y: U) {
+    this.x = x;
+    this.y = y;
+  }
+}
+
+var c2: MyClass2 = new MyClass2(0, ""); // error, missing argument list (1-2)
+
+// arity error in type annotation using polymorphic type alias
+
+type MyObject<T> = {
+  x: T;
+}
+
+var o: MyObject = { x: 0 }; // error, missing argument list
+
+// arity error in type alias rhs
+
+type MySubobject = { y: number } & MyObject; // error, missing argument list
+
+// arity error in interface extends
+
+interface MyInterface<T> {
+  x: T;
+}
+
+interface MySubinterface extends MyInterface { // error, missing argument list
+  y: number;
+}
+
+// *no* arity error in extends of polymorphic class
+
+class MySubclass extends MyClass { // ok, type arg inferred
+  y: number;
+  constructor(y: number) {
+    super(y);
+  }
+}
+
+// *no* arity error in call of polymorphic function
+
+function singleton<T>(x: T):Array<T> { return [x]; }
+
+var num_array:Array<number> = singleton(0); // ok, type arg inferred
diff --git a/tests/type_only_vars/A.js b/tests/type_only_vars/A.js
new file mode 100644
index 000000000000..9473797985ff
--- /dev/null
+++ b/tests/type_only_vars/A.js
@@ -0,0 +1,14 @@
+/**
+ * @flow
+ */
+
+class Foo {
+}
+
+class Bar {
+}
+
+module.exports = {
+  Foo: Foo,
+  Bar: Bar
+};
diff --git a/tests/type_only_vars/__snapshots__/jsfmt.spec.js.snap b/tests/type_only_vars/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..7ddfb0e9f771
--- /dev/null
+++ b/tests/type_only_vars/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,174 @@
+exports[`test A.js 1`] = `
+"/**
+ * @flow
+ */
+
+class Foo {
+}
+
+class Bar {
+}
+
+module.exports = {
+  Foo: Foo,
+  Bar: Bar
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+class Foo {}
+class Bar {}
+module.exports = { Foo: Foo, Bar: Bar };
+
+"
+`;
+
+exports[`test bad_shadowing.js 1`] = `
+"/**
+ * @flow
+ */
+
+import typeof A from \"./A.js\";
+import type {Foo, Bar as Baz} from \"./A.js\";
+
+type duck = {
+  quack: () => string;
+}
+
+// These string types should confict with the imported types
+var A: string = \"Hello\";
+var Foo: string = \"Goodbye\";
+var Baz: string = \"Go away please\";
+
+// This string type should conflict with the typedef
+var duck: string = \"quack\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test good_shadowing.js 1`] = `
+"/**
+ * @flow
+ */
+
+import typeof A from \"./A.js\";
+import type {Foo, Bar as Baz} from \"./A.js\";
+
+var A = require(\'./A.js\');
+var Foo = A.Foo;
+var Baz = A.Bar;
+
+// errors in prev block leave type bindings in place, so these are errors
+var m = A;
+var n = Foo;
+var o = Baz;
+
+// errors from value positions only
+var a: Foo = new Foo();
+var b: Foo = new A.Foo();
+(new A.Bar(): Baz);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+import typeof A from \"./A.js\";
+import type { Foo, Bar as Baz } from \"./A.js\";
+var A = require(\"./A.js\");
+var Foo = A.Foo;
+var Baz = A.Bar;
+// errors in prev block leave type bindings in place, so these are errors
+var m = A;
+var n = Foo;
+var o = Baz;
+// errors from value positions only
+var a: Foo = new Foo();
+var b: Foo = new A.Foo();
+(new A.Bar(): Baz);
+
+"
+`;
+
+exports[`test import_type.js 1`] = `
+"/**
+ * @flow
+ */
+
+import typeof A from \"./A.js\";
+import type {Foo, Bar as Baz} from \"./A.js\";
+
+var actualA = require(\'./A.js\');
+
+// You can\'t use it as an identifier
+var m = A;
+var n = Foo;
+var o = Baz;
+
+// But using it in a type should still work
+var a: Foo = new actualA.Foo();
+(new actualA.Bar(): Baz);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+import typeof A from \"./A.js\";
+import type { Foo, Bar as Baz } from \"./A.js\";
+var actualA = require(\"./A.js\");
+// You can\'t use it as an identifier
+var m = A;
+var n = Foo;
+var o = Baz;
+// But using it in a type should still work
+var a: Foo = new actualA.Foo();
+(new actualA.Bar(): Baz);
+
+"
+`;
+
+exports[`test type_alias.js 1`] = `
+"/**
+ * @flow
+ */
+
+type Foo = number;
+
+// You can\'t use it as an identifier
+var x = Foo;
+
+// But using it in a type should still work
+var a: Foo = 123;
+var b: Array<Foo> = [123];
+type c = Foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_only_vars/bad_shadowing.js b/tests/type_only_vars/bad_shadowing.js
new file mode 100644
index 000000000000..44fda51444e7
--- /dev/null
+++ b/tests/type_only_vars/bad_shadowing.js
@@ -0,0 +1,18 @@
+/**
+ * @flow
+ */
+
+import typeof A from "./A.js";
+import type {Foo, Bar as Baz} from "./A.js";
+
+type duck = {
+  quack: () => string;
+}
+
+// These string types should confict with the imported types
+var A: string = "Hello";
+var Foo: string = "Goodbye";
+var Baz: string = "Go away please";
+
+// This string type should conflict with the typedef
+var duck: string = "quack";
diff --git a/tests/type_only_vars/good_shadowing.js b/tests/type_only_vars/good_shadowing.js
new file mode 100644
index 000000000000..010dbabfebbb
--- /dev/null
+++ b/tests/type_only_vars/good_shadowing.js
@@ -0,0 +1,20 @@
+/**
+ * @flow
+ */
+
+import typeof A from "./A.js";
+import type {Foo, Bar as Baz} from "./A.js";
+
+var A = require('./A.js');
+var Foo = A.Foo;
+var Baz = A.Bar;
+
+// errors in prev block leave type bindings in place, so these are errors
+var m = A;
+var n = Foo;
+var o = Baz;
+
+// errors from value positions only
+var a: Foo = new Foo();
+var b: Foo = new A.Foo();
+(new A.Bar(): Baz);
diff --git a/tests/type_only_vars/import_type.js b/tests/type_only_vars/import_type.js
new file mode 100644
index 000000000000..b8250c2eff86
--- /dev/null
+++ b/tests/type_only_vars/import_type.js
@@ -0,0 +1,17 @@
+/**
+ * @flow
+ */
+
+import typeof A from "./A.js";
+import type {Foo, Bar as Baz} from "./A.js";
+
+var actualA = require('./A.js');
+
+// You can't use it as an identifier
+var m = A;
+var n = Foo;
+var o = Baz;
+
+// But using it in a type should still work
+var a: Foo = new actualA.Foo();
+(new actualA.Bar(): Baz);
diff --git a/tests/type_only_vars/jsfmt.spec.js b/tests/type_only_vars/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_only_vars/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_only_vars/type_alias.js b/tests/type_only_vars/type_alias.js
new file mode 100644
index 000000000000..1633b664d2a7
--- /dev/null
+++ b/tests/type_only_vars/type_alias.js
@@ -0,0 +1,13 @@
+/**
+ * @flow
+ */
+
+type Foo = number;
+
+// You can't use it as an identifier
+var x = Foo;
+
+// But using it in a type should still work
+var a: Foo = 123;
+var b: Array<Foo> = [123];
+type c = Foo;
diff --git a/tests/type_param_defaults/__snapshots__/jsfmt.spec.js.snap b/tests/type_param_defaults/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3e30daf61552
--- /dev/null
+++ b/tests/type_param_defaults/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,84 @@
+exports[`test classes.js 1`] = `
+"/* @flow */
+
+class A<T> {
+  p: T;
+  constructor(p: T) {
+    this.p = p;
+  }
+}
+
+// Test out simple defaults
+class B<T = string> extends A<T> {}
+
+var b_number: B<number> = new B(123);
+var b_void: B<void> = new B();
+var b_default: B<> = new B(\'hello\');
+
+var b_star: B<*> = new B(123);
+
+(b_number.p: boolean); // Error number ~> boolean
+(b_void.p: boolean); // Error void ~> boolean
+(b_default.p: boolean); // Error string ~> boolean
+
+(b_star.p: boolean); // Error number ~> boolean
+
+class C<T: ?string = string> extends A<T> {}
+
+var c_number: C<number> = new C(123); // Error number ~> ?string
+var c_void: C<void> = new C();
+var c_default: C<> = new C(\'hello\');
+var c_star: C<*> = new C(\'hello\');
+
+(c_void.p: boolean); // Error void ~> boolean
+(c_default.p: boolean); // Error string ~> boolean
+(c_star.p: boolean); // Error string ~> boolean
+
+class D<S, T = string> extends A<T> {}
+var d_number: D<mixed, number> = new D(123);
+var d_void: D<mixed, void> = new D();
+var d_default: D<mixed> = new D(\'hello\');
+var d_too_few_args: D<> = new D(\'hello\'); // Error too few tparams
+var d_too_many: D<mixed, string, string> = new D(\'hello\'); // Error too many tparams
+var d_star: D<*> = new D(10); // error, number ~> string
+
+(d_number.p: boolean); // Error number ~> boolean
+(d_void.p: boolean); // Error void ~> boolean
+(d_default.p: boolean); // Error string ~> boolean
+(d_star.p: boolean); // Error number ~> boolean
+
+class E<S: string, T: number = S> {} // Error: string ~> number
+class F<S: string, T: S = number> {} // Error: number ~> string
+
+class G<S: string, T = S> extends A<T> {}
+
+var g_default: G<string> = new G(\'hello\');
+
+(g_default.p: boolean); // Error string ~> boolean
+
+class H<S = T, T = string> {} // Error - can\'t refer to T before it\'s defined
+
+class I<T: ?string = *> extends A<T> {}
+
+var i_number: I<number> = new I(123); // Error number ~> ?string
+var i_void: I<void> = new I();
+var i_default: I<> = new I(\'hello\');
+var i_star: I<*> = new I(\'hello\');
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_param_defaults/classes.js b/tests/type_param_defaults/classes.js
new file mode 100644
index 000000000000..3c6797bc00c9
--- /dev/null
+++ b/tests/type_param_defaults/classes.js
@@ -0,0 +1,65 @@
+/* @flow */
+
+class A<T> {
+  p: T;
+  constructor(p: T) {
+    this.p = p;
+  }
+}
+
+// Test out simple defaults
+class B<T = string> extends A<T> {}
+
+var b_number: B<number> = new B(123);
+var b_void: B<void> = new B();
+var b_default: B<> = new B('hello');
+
+var b_star: B<*> = new B(123);
+
+(b_number.p: boolean); // Error number ~> boolean
+(b_void.p: boolean); // Error void ~> boolean
+(b_default.p: boolean); // Error string ~> boolean
+
+(b_star.p: boolean); // Error number ~> boolean
+
+class C<T: ?string = string> extends A<T> {}
+
+var c_number: C<number> = new C(123); // Error number ~> ?string
+var c_void: C<void> = new C();
+var c_default: C<> = new C('hello');
+var c_star: C<*> = new C('hello');
+
+(c_void.p: boolean); // Error void ~> boolean
+(c_default.p: boolean); // Error string ~> boolean
+(c_star.p: boolean); // Error string ~> boolean
+
+class D<S, T = string> extends A<T> {}
+var d_number: D<mixed, number> = new D(123);
+var d_void: D<mixed, void> = new D();
+var d_default: D<mixed> = new D('hello');
+var d_too_few_args: D<> = new D('hello'); // Error too few tparams
+var d_too_many: D<mixed, string, string> = new D('hello'); // Error too many tparams
+var d_star: D<*> = new D(10); // error, number ~> string
+
+(d_number.p: boolean); // Error number ~> boolean
+(d_void.p: boolean); // Error void ~> boolean
+(d_default.p: boolean); // Error string ~> boolean
+(d_star.p: boolean); // Error number ~> boolean
+
+class E<S: string, T: number = S> {} // Error: string ~> number
+class F<S: string, T: S = number> {} // Error: number ~> string
+
+class G<S: string, T = S> extends A<T> {}
+
+var g_default: G<string> = new G('hello');
+
+(g_default.p: boolean); // Error string ~> boolean
+
+class H<S = T, T = string> {} // Error - can't refer to T before it's defined
+
+class I<T: ?string = *> extends A<T> {}
+
+var i_number: I<number> = new I(123); // Error number ~> ?string
+var i_void: I<void> = new I();
+var i_default: I<> = new I('hello');
+var i_star: I<*> = new I('hello');
diff --git a/tests/type_param_defaults/jsfmt.spec.js b/tests/type_param_defaults/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_param_defaults/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_param_scope/__snapshots__/jsfmt.spec.js.snap b/tests/type_param_scope/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..355cffb598e1
--- /dev/null
+++ b/tests/type_param_scope/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,132 @@
+exports[`test class.js 1`] = `
+"class C<T> {
+  a<A>(x:T, a:A) {
+    this.b(x); // ok
+    this.b(a); // error: A ~> incompatible instance of T
+  }
+
+  b(x:T) {}
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test default_params.js 1`] = `
+"function f<T>(a:T) {
+  function g<U>(b:U, c:T = a) {
+    function h(d:U = b) {}
+    h(); // ok
+    h(b); // ok
+    h(c); // err, T ~> U
+  }
+  g(0); // ok
+  g(0,a); // ok
+  g(0,0); // error: number ~> T
+}
+f(0); // ok
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test method_shadow.js 1`] = `
+"// Ensure method type params properly shadow outer type params. Subclass ensures
+// the generated insttype has the correct tvars. Should behave the same for
+// classes, interfaces, and declared classes.
+
+class A<T> {
+  x:T;
+  constructor(x:T) { this.x = x }
+  m<T>(x:T):A<T> { return new A(x) }
+}
+
+class B<T> extends A<T> {
+  m<T>(x:T):B<T> { return new B(x) }
+}
+
+interface C<T> {
+  m<T>(x:T):C<T>;
+}
+
+interface D<T> extends C<T> {
+  m<T>(x:T):D<T>;
+}
+
+declare class E<T> {
+  m<T>(x:T):E<T>;
+}
+
+declare class F<T> extends E<T> {
+  m<T>(x:T):F<T>;
+}
+
+
+// Bounds can refer to parent type params (until they are shadowed).
+
+class G<T> {
+  x:T;
+  constructor(x:T) { this.x = x }
+  m<T:T>(x:T):G<T> { return new G(x) } // T-as-bound is G\'s T
+}
+
+declare var g: G<number|string>;
+g.m(0); // ok
+g.m(true); // err, bool ~> number|string
+(g.m(\"\"): G<number>); // err, string ~> number
+
+
+// Shadow bounds incompatible with parent
+
+class H<T> {
+    x:T;
+    m<T>(x:T) {
+        this.x = x; // err, m\'s T != H\'s T
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_param_scope/class.js b/tests/type_param_scope/class.js
new file mode 100644
index 000000000000..ef25adc20642
--- /dev/null
+++ b/tests/type_param_scope/class.js
@@ -0,0 +1,8 @@
+class C<T> {
+  a<A>(x:T, a:A) {
+    this.b(x); // ok
+    this.b(a); // error: A ~> incompatible instance of T
+  }
+
+  b(x:T) {}
+}
diff --git a/tests/type_param_scope/default_params.js b/tests/type_param_scope/default_params.js
new file mode 100644
index 000000000000..1c48b67b206c
--- /dev/null
+++ b/tests/type_param_scope/default_params.js
@@ -0,0 +1,12 @@
+function f<T>(a:T) {
+  function g<U>(b:U, c:T = a) {
+    function h(d:U = b) {}
+    h(); // ok
+    h(b); // ok
+    h(c); // err, T ~> U
+  }
+  g(0); // ok
+  g(0,a); // ok
+  g(0,0); // error: number ~> T
+}
+f(0); // ok
diff --git a/tests/type_param_scope/jsfmt.spec.js b/tests/type_param_scope/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_param_scope/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_param_scope/method_shadow.js b/tests/type_param_scope/method_shadow.js
new file mode 100644
index 000000000000..93b1223c6f37
--- /dev/null
+++ b/tests/type_param_scope/method_shadow.js
@@ -0,0 +1,53 @@
+// Ensure method type params properly shadow outer type params. Subclass ensures
+// the generated insttype has the correct tvars. Should behave the same for
+// classes, interfaces, and declared classes.
+
+class A<T> {
+  x:T;
+  constructor(x:T) { this.x = x }
+  m<T>(x:T):A<T> { return new A(x) }
+}
+
+class B<T> extends A<T> {
+  m<T>(x:T):B<T> { return new B(x) }
+}
+
+interface C<T> {
+  m<T>(x:T):C<T>;
+}
+
+interface D<T> extends C<T> {
+  m<T>(x:T):D<T>;
+}
+
+declare class E<T> {
+  m<T>(x:T):E<T>;
+}
+
+declare class F<T> extends E<T> {
+  m<T>(x:T):F<T>;
+}
+
+
+// Bounds can refer to parent type params (until they are shadowed).
+
+class G<T> {
+  x:T;
+  constructor(x:T) { this.x = x }
+  m<T:T>(x:T):G<T> { return new G(x) } // T-as-bound is G's T
+}
+
+declare var g: G<number|string>;
+g.m(0); // ok
+g.m(true); // err, bool ~> number|string
+(g.m(""): G<number>); // err, string ~> number
+
+
+// Shadow bounds incompatible with parent
+
+class H<T> {
+    x:T;
+    m<T>(x:T) {
+        this.x = x; // err, m's T != H's T
+    }
+}
diff --git a/tests/type_param_variance/__snapshots__/jsfmt.spec.js.snap b/tests/type_param_variance/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..a5ec84a76359
--- /dev/null
+++ b/tests/type_param_variance/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,46 @@
+exports[`test promise.js 1`] = `
+"/**
+ * At the moment, all type params are invariant with
+ * the exception of the single param to the Promise class,
+ * which is covariant.
+ *
+ * Explicit variance control via annotation is coming,
+ * but not immediately. In the meantime, Promise\'s
+ * participation in async/await makes certain kinds of
+ * errors onerous (and nonobvious) without covariance.
+ *
+ * @flow
+ */
+
+async function foo(x: boolean): Promise<?{bar: string}> {
+  if (x) {
+    return {bar: \'baz\'};  // OK, because of covariant type param
+  } else {
+    return null;
+  }
+}
+
+async function run() {
+  console.log(await foo(true));
+  console.log(await foo(false));
+}
+
+run()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_param_variance/jsfmt.spec.js b/tests/type_param_variance/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_param_variance/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_param_variance/promise.js b/tests/type_param_variance/promise.js
new file mode 100644
index 000000000000..221bc1e52dbc
--- /dev/null
+++ b/tests/type_param_variance/promise.js
@@ -0,0 +1,27 @@
+/**
+ * At the moment, all type params are invariant with
+ * the exception of the single param to the Promise class,
+ * which is covariant.
+ *
+ * Explicit variance control via annotation is coming,
+ * but not immediately. In the meantime, Promise's
+ * participation in async/await makes certain kinds of
+ * errors onerous (and nonobvious) without covariance.
+ *
+ * @flow
+ */
+
+async function foo(x: boolean): Promise<?{bar: string}> {
+  if (x) {
+    return {bar: 'baz'};  // OK, because of covariant type param
+  } else {
+    return null;
+  }
+}
+
+async function run() {
+  console.log(await foo(true));
+  console.log(await foo(false));
+}
+
+run()
diff --git a/tests/type_param_variance2/__snapshots__/jsfmt.spec.js.snap b/tests/type_param_variance2/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3d2b133ccb94
--- /dev/null
+++ b/tests/type_param_variance2/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,43 @@
+exports[`test promise.js 1`] = `
+"/**
+ * Here the definition of Promise<T> is routed to the class Promise
+ * in the user-specified library libs/Promise.js
+ *
+ * In such situations we must desugar async/await primitives
+ * to the shadowed library definition.
+ *
+ * @flow
+ */
+
+async function foo(x: boolean): Promise<?{bar: string}> {
+  if (x) {
+    return {bar: \'baz\'};  // OK, because of covariant type param
+  } else {
+    return null;
+  }
+}
+
+async function run() {
+  console.log(await foo(true));
+  console.log(await foo(false));
+}
+
+run()
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_param_variance2/jsfmt.spec.js b/tests/type_param_variance2/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_param_variance2/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_param_variance2/libs/Promise.js b/tests/type_param_variance2/libs/Promise.js
new file mode 100644
index 000000000000..a0b2a5ce810e
--- /dev/null
+++ b/tests/type_param_variance2/libs/Promise.js
@@ -0,0 +1,47 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+// These annotations are copy/pasted from the built-in Flow definitions for
+// Native Promises (https://phabricator.fb.com/P19792689),
+// with www-specific additions added in.
+
+// Any definitions here will override similarly-named ones in
+// library files declared earlier, including default flow libs.
+
+declare class Promise<R> {
+  constructor(callback: (
+    resolve: (result?: Promise<R> | R) => void,
+    reject: (error?: any) => void
+  ) => void): void;
+
+  then<U>(
+    onFulfill?: ?(value: R) => Promise<U> | ?U,
+    onReject?: ?(error: any) => Promise<U> | ?U
+  ): Promise<U>;
+
+  done<U>(
+    onFulfill?: ?(value: R) => void,
+    onReject?: ?(error: any) => void
+  ): void;
+
+  catch<U>(
+    onReject?: (error: any) => ?Promise<U> | U
+  ): Promise<U>;
+
+  static resolve<T>(object?: Promise<T> | T): Promise<T>;
+  static reject<T>(error?: any): Promise<T>;
+
+  // Non-standard APIs
+  finally<U>(
+    onSettled?: ?(value: any) => Promise<U> | U
+  ): Promise<U>;
+
+  static cast<T>(object?: T): Promise<T>;
+  static all<T>(
+    promises: Array<?Promise<T> | T>,
+  ): Promise<Array<T>>;
+  static race<T>(promises: Array<Promise<T>>): Promise<T>;
+
+  static allObject<T: Object>(
+    promisesByKey: T
+  ): Promise<{[key: $Keys<T>]: any}>;
+}
diff --git a/tests/type_param_variance2/libs/__snapshots__/jsfmt.spec.js.snap b/tests/type_param_variance2/libs/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..acce7f354305
--- /dev/null
+++ b/tests/type_param_variance2/libs/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,66 @@
+exports[`test Promise.js 1`] = `
+"// Copyright 2004-present Facebook. All Rights Reserved.
+
+// These annotations are copy/pasted from the built-in Flow definitions for
+// Native Promises (https://phabricator.fb.com/P19792689),
+// with www-specific additions added in.
+
+// Any definitions here will override similarly-named ones in
+// library files declared earlier, including default flow libs.
+
+declare class Promise<R> {
+  constructor(callback: (
+    resolve: (result?: Promise<R> | R) => void,
+    reject: (error?: any) => void
+  ) => void): void;
+
+  then<U>(
+    onFulfill?: ?(value: R) => Promise<U> | ?U,
+    onReject?: ?(error: any) => Promise<U> | ?U
+  ): Promise<U>;
+
+  done<U>(
+    onFulfill?: ?(value: R) => void,
+    onReject?: ?(error: any) => void
+  ): void;
+
+  catch<U>(
+    onReject?: (error: any) => ?Promise<U> | U
+  ): Promise<U>;
+
+  static resolve<T>(object?: Promise<T> | T): Promise<T>;
+  static reject<T>(error?: any): Promise<T>;
+
+  // Non-standard APIs
+  finally<U>(
+    onSettled?: ?(value: any) => Promise<U> | U
+  ): Promise<U>;
+
+  static cast<T>(object?: T): Promise<T>;
+  static all<T>(
+    promises: Array<?Promise<T> | T>,
+  ): Promise<Array<T>>;
+  static race<T>(promises: Array<Promise<T>>): Promise<T>;
+
+  static allObject<T: Object>(
+    promisesByKey: T
+  ): Promise<{[key: $Keys<T>]: any}>;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/type_param_variance2/libs/jsfmt.spec.js b/tests/type_param_variance2/libs/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/type_param_variance2/libs/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/type_param_variance2/promise.js b/tests/type_param_variance2/promise.js
new file mode 100644
index 000000000000..1d09fca1ebe4
--- /dev/null
+++ b/tests/type_param_variance2/promise.js
@@ -0,0 +1,24 @@
+/**
+ * Here the definition of Promise<T> is routed to the class Promise
+ * in the user-specified library libs/Promise.js
+ *
+ * In such situations we must desugar async/await primitives
+ * to the shadowed library definition.
+ *
+ * @flow
+ */
+
+async function foo(x: boolean): Promise<?{bar: string}> {
+  if (x) {
+    return {bar: 'baz'};  // OK, because of covariant type param
+  } else {
+    return null;
+  }
+}
+
+async function run() {
+  console.log(await foo(true));
+  console.log(await foo(false));
+}
+
+run()
diff --git a/tests/typeapp_perf/__snapshots__/jsfmt.spec.js.snap b/tests/typeapp_perf/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..11abc849d200
--- /dev/null
+++ b/tests/typeapp_perf/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,79 @@
+exports[`test test1.js 1`] = `
+"/* This test ensures that the code below does not take a long time to check. If
+ * this test is taking a very long time to complete, there is a bug. */
+
+class A {}
+
+type B<T> = A & {
+  +a: () => B<T>;
+  +b: () => B<T>;
+  +c: () => B<T>;
+  +d: () => B<T>;
+  +e: () => B<T>;
+  +f: () => B<T>;
+  +g: () => B<T>;
+  +h: () => B<T>;
+  +i: () => B<T>;
+};
+
+declare var b: B<any>;
+
+(b: B<any>);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"/* This test ensures that the code below does not take a long time to check. If
+ * this test is taking a very long time to complete, there is a bug. */
+
+class A {}
+
+type B<T> = A & {
+  +a: (x: B<T>) => void;
+  +b: (x: B<T>) => void;
+  +c: (x: B<T>) => void;
+  +d: (x: B<T>) => void;
+  +e: (x: B<T>) => void;
+  +f: (x: B<T>) => void;
+  +g: (x: B<T>) => void;
+  +h: (x: B<T>) => void;
+  +i: (x: B<T>) => void;
+};
+
+declare var b: B<any>;
+
+(b: B<any>);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/typeapp_perf/jsfmt.spec.js b/tests/typeapp_perf/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/typeapp_perf/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/typeapp_perf/test1.js b/tests/typeapp_perf/test1.js
new file mode 100644
index 000000000000..485e397ce548
--- /dev/null
+++ b/tests/typeapp_perf/test1.js
@@ -0,0 +1,20 @@
+/* This test ensures that the code below does not take a long time to check. If
+ * this test is taking a very long time to complete, there is a bug. */
+
+class A {}
+
+type B<T> = A & {
+  +a: () => B<T>;
+  +b: () => B<T>;
+  +c: () => B<T>;
+  +d: () => B<T>;
+  +e: () => B<T>;
+  +f: () => B<T>;
+  +g: () => B<T>;
+  +h: () => B<T>;
+  +i: () => B<T>;
+};
+
+declare var b: B<any>;
+
+(b: B<any>);
diff --git a/tests/typeapp_perf/test2.js b/tests/typeapp_perf/test2.js
new file mode 100644
index 000000000000..ee8c145c9a7f
--- /dev/null
+++ b/tests/typeapp_perf/test2.js
@@ -0,0 +1,20 @@
+/* This test ensures that the code below does not take a long time to check. If
+ * this test is taking a very long time to complete, there is a bug. */
+
+class A {}
+
+type B<T> = A & {
+  +a: (x: B<T>) => void;
+  +b: (x: B<T>) => void;
+  +c: (x: B<T>) => void;
+  +d: (x: B<T>) => void;
+  +e: (x: B<T>) => void;
+  +f: (x: B<T>) => void;
+  +g: (x: B<T>) => void;
+  +h: (x: B<T>) => void;
+  +i: (x: B<T>) => void;
+};
+
+declare var b: B<any>;
+
+(b: B<any>);
diff --git a/tests/typecast/__snapshots__/jsfmt.spec.js.snap b/tests/typecast/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..98b7ec6dc2c4
--- /dev/null
+++ b/tests/typecast/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,45 @@
+exports[`test typecast.js 1`] = `
+"/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ */
+var tests = [
+  () => {
+    // erroneous typcasts raise errors...
+    var n = (\"hey\" : number);
+    // ...but \'any\' does dynamic downcasts, if you must
+    var x: number = (\"hey\": any);
+    var y = ((\"hey\": any): number);
+  },
+
+  () => {
+    // typecasts in sequences
+    // (parens always required around typecasts)
+    var s: string = ((0: number), (\"hey\": string));
+  },
+
+  () => {
+    // TODO pending array element inference issues
+    // control case:
+    // var a : Array<?number> = [0, 1, 2, 3, 4, 5, 6, 7, null];
+    // typecast case:
+    // var b = [(0 : ?number), 1, 2, 3, 4, 5, 6, 7, null];
+  }
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:706
+      return fromString(\", \").join(path.map(print, \"expressions\"));
+                              ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:706:31)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:812:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/typecast/jsfmt.spec.js b/tests/typecast/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/typecast/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/typecast/typecast.js b/tests/typecast/typecast.js
new file mode 100644
index 000000000000..c3d4d9990534
--- /dev/null
+++ b/tests/typecast/typecast.js
@@ -0,0 +1,26 @@
+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ */
+var tests = [
+  () => {
+    // erroneous typcasts raise errors...
+    var n = ("hey" : number);
+    // ...but 'any' does dynamic downcasts, if you must
+    var x: number = ("hey": any);
+    var y = (("hey": any): number);
+  },
+
+  () => {
+    // typecasts in sequences
+    // (parens always required around typecasts)
+    var s: string = ((0: number), ("hey": string));
+  },
+
+  () => {
+    // TODO pending array element inference issues
+    // control case:
+    // var a : Array<?number> = [0, 1, 2, 3, 4, 5, 6, 7, null];
+    // typecast case:
+    // var b = [(0 : ?number), 1, 2, 3, 4, 5, 6, 7, null];
+  }
+];
diff --git a/tests/typeof/__snapshots__/jsfmt.spec.js.snap b/tests/typeof/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..935fbee15539
--- /dev/null
+++ b/tests/typeof/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,101 @@
+exports[`test typeof.js 1`] = `
+"/**
+ * @flow
+ */
+
+//////////////////////////////////
+// == typeof <<class value>> == //
+//////////////////////////////////
+
+// MyClass1 is a runtime value, a constructor function
+//
+class MyClass1 {
+  getNumber(): number { return 42; }
+}
+
+// a is an instance of MyClass1 - in runtime terms,
+// an object produced by the MyClass1 constructor
+// function.
+//
+var a: MyClass1 = new MyClass1();
+
+// Following tests are errors which conflate the type
+// of the class value itself with the type of its
+// instances.
+
+// Aside: it\'s worth staring at the following (correct)
+// type annotations until they make sense:
+//
+//    MyClass1 : Class<MyClass1>
+//    (new MyClass1()) : MyClass1
+//
+// The first says that the MyClass1 value (constructor
+// function) has type Class<MyClass1> - the type of
+// functions which produce instances of MyClass1 when
+// called as a constructor.
+//
+// The second says that objects produced by the MyClass1
+// constructor function have type MyClass1 - the type of
+// instances of MyClass1.
+
+// Error: assign the actual MyClass1 value to a  variable
+// whose annotated type is of instances of MyClass1.
+//
+var b: MyClass1 = MyClass1;
+
+class MyClass2 {
+  getNumber1(): number { return 42; }
+}
+
+// The opposite error: assign an *instance* of MyClass2
+// to a variable whose annotated type is the type of
+// the class value (constructor function) MyClass2 itself.
+//
+var c: typeof MyClass2 = new MyClass2();
+
+//////////////////////////////////////
+// == typeof <<non-class value>> == //
+//////////////////////////////////////
+
+var numValue:number = 42;
+var d: typeof numValue = 100;
+var e: typeof numValue = \'asdf\'; // Error: string ~> number
+
+/////////////////////////////////
+// == typeof <<type-alias>> == //
+/////////////////////////////////
+
+type numberAlias = number;
+
+// This is an error because typeof takes a value, not
+// a type, as an argument. However, the current error
+// is suboptimal - just \'cannot resolve name\'. TODO.
+//
+var f: typeof numberAlias = 42; // Error: \'typeof <<type-alias>>\' makes no sense...
+
+/**
+ * Use of a non-class/non-function value in type annotation.
+ * These provoke a specific error, not just the generic
+ * \"type is incompatible\"
+ */
+
+ var Map = { \"A\": \"this is A\", \"B\": \"this is B\", \"C\": \"this is C\" };
+ var keys: $Keys<Map> = \"A\";  // Error: ineligible value used in type anno
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/typeof/jsfmt.spec.js b/tests/typeof/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/typeof/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/typeof/typeof.js b/tests/typeof/typeof.js
new file mode 100644
index 000000000000..f974bb4d58f5
--- /dev/null
+++ b/tests/typeof/typeof.js
@@ -0,0 +1,82 @@
+/**
+ * @flow
+ */
+
+//////////////////////////////////
+// == typeof <<class value>> == //
+//////////////////////////////////
+
+// MyClass1 is a runtime value, a constructor function
+//
+class MyClass1 {
+  getNumber(): number { return 42; }
+}
+
+// a is an instance of MyClass1 - in runtime terms,
+// an object produced by the MyClass1 constructor
+// function.
+//
+var a: MyClass1 = new MyClass1();
+
+// Following tests are errors which conflate the type
+// of the class value itself with the type of its
+// instances.
+
+// Aside: it's worth staring at the following (correct)
+// type annotations until they make sense:
+//
+//    MyClass1 : Class<MyClass1>
+//    (new MyClass1()) : MyClass1
+//
+// The first says that the MyClass1 value (constructor
+// function) has type Class<MyClass1> - the type of
+// functions which produce instances of MyClass1 when
+// called as a constructor.
+//
+// The second says that objects produced by the MyClass1
+// constructor function have type MyClass1 - the type of
+// instances of MyClass1.
+
+// Error: assign the actual MyClass1 value to a  variable
+// whose annotated type is of instances of MyClass1.
+//
+var b: MyClass1 = MyClass1;
+
+class MyClass2 {
+  getNumber1(): number { return 42; }
+}
+
+// The opposite error: assign an *instance* of MyClass2
+// to a variable whose annotated type is the type of
+// the class value (constructor function) MyClass2 itself.
+//
+var c: typeof MyClass2 = new MyClass2();
+
+//////////////////////////////////////
+// == typeof <<non-class value>> == //
+//////////////////////////////////////
+
+var numValue:number = 42;
+var d: typeof numValue = 100;
+var e: typeof numValue = 'asdf'; // Error: string ~> number
+
+/////////////////////////////////
+// == typeof <<type-alias>> == //
+/////////////////////////////////
+
+type numberAlias = number;
+
+// This is an error because typeof takes a value, not
+// a type, as an argument. However, the current error
+// is suboptimal - just 'cannot resolve name'. TODO.
+//
+var f: typeof numberAlias = 42; // Error: 'typeof <<type-alias>>' makes no sense...
+
+/**
+ * Use of a non-class/non-function value in type annotation.
+ * These provoke a specific error, not just the generic
+ * "type is incompatible"
+ */
+
+ var Map = { "A": "this is A", "B": "this is B", "C": "this is C" };
+ var keys: $Keys<Map> = "A";  // Error: ineligible value used in type anno
diff --git a/tests/unary/__snapshots__/jsfmt.spec.js.snap b/tests/unary/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..b8235d8dedbe
--- /dev/null
+++ b/tests/unary/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,113 @@
+exports[`test unary.js 1`] = `
+"/* @flow */
+
+function x0(y: string): number {
+  return +y; // ok, + exists solely for coercion
+}
+
+function x1(y: string): number {
+  return -y; // error, we don't allow coercion here
+}
+
+function x3(y: string) {
+  return ~y;  // error, we don't allow coercion here
+}
+
+function x4(y: string): boolean {
+  return !y; // ok, coercion is allowed
+}
+
+(-1: void); // error, number ~> void
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function x0(y: string): number {
+  return +y;// ok, + exists solely for coercion
+}
+function x1(y: string): number {
+  return -y;// error, we don't allow coercion here
+}
+function x3(y: string) {
+  return ~y;// error, we don't allow coercion here
+}
+function x4(y: string): boolean {
+  return !y;// ok, coercion is allowed
+}
+(-1: void);// error, number ~> void
+
+"
+`;
+
+exports[`test update.js 1`] = `
+"// @flow
+
+let tests = [
+  function(y: number) {
+    y++;
+    y--;
+    ++y;
+    --y;
+  },
+
+  function(y: string) {
+    y++; // error, we don't allow coercion here
+    (y: number); // ok, y is a number now
+    y++; // error, but you still can't write a number to a string
+  },
+
+  function(y: string) {
+    y--; // error, we don't allow coercion here
+  },
+
+  function(y: string) {
+    ++y; // error, we don't allow coercion here
+  },
+
+  function(y: string) {
+    --y; // error, we don't allow coercion here
+  },
+
+  function() {
+    const y = 123;
+    y++; // error, can't update const
+    y--; // error, can't update const
+  },
+
+  function(y: any) {
+    y++; // ok
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  function(y: number) {
+    y++;
+    y--;
+    ++y;
+    --y;
+  },
+  function(y: string) {
+    y++;// error, we don't allow coercion here
+    (y: number);// ok, y is a number now
+    y++;// error, but you still can't write a number to a string
+  },
+  function(y: string) {
+    y--;// error, we don't allow coercion here
+  },
+  function(y: string) {
+    ++y;// error, we don't allow coercion here
+  },
+  function(y: string) {
+    --y;// error, we don't allow coercion here
+  },
+  function() {
+    const y = 123;
+    y++;// error, can't update const
+    y--;// error, can't update const
+  },
+  function(y: any) {
+    y++;// ok
+  }
+];
+
+"
+`;
diff --git a/tests/unary/jsfmt.spec.js b/tests/unary/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/unary/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/unary/unary.js b/tests/unary/unary.js
new file mode 100644
index 000000000000..6588336aaa87
--- /dev/null
+++ b/tests/unary/unary.js
@@ -0,0 +1,19 @@
+/* @flow */
+
+function x0(y: string): number {
+  return +y; // ok, + exists solely for coercion
+}
+
+function x1(y: string): number {
+  return -y; // error, we don't allow coercion here
+}
+
+function x3(y: string) {
+  return ~y;  // error, we don't allow coercion here
+}
+
+function x4(y: string): boolean {
+  return !y; // ok, coercion is allowed
+}
+
+(-1: void); // error, number ~> void
diff --git a/tests/unary/update.js b/tests/unary/update.js
new file mode 100644
index 000000000000..690a62243627
--- /dev/null
+++ b/tests/unary/update.js
@@ -0,0 +1,38 @@
+// @flow
+
+let tests = [
+  function(y: number) {
+    y++;
+    y--;
+    ++y;
+    --y;
+  },
+
+  function(y: string) {
+    y++; // error, we don't allow coercion here
+    (y: number); // ok, y is a number now
+    y++; // error, but you still can't write a number to a string
+  },
+
+  function(y: string) {
+    y--; // error, we don't allow coercion here
+  },
+
+  function(y: string) {
+    ++y; // error, we don't allow coercion here
+  },
+
+  function(y: string) {
+    --y; // error, we don't allow coercion here
+  },
+
+  function() {
+    const y = 123;
+    y++; // error, can't update const
+    y--; // error, can't update const
+  },
+
+  function(y: any) {
+    y++; // ok
+  },
+];
diff --git a/tests/unchecked_haste_module_vs_lib/__snapshots__/jsfmt.spec.js.snap b/tests/unchecked_haste_module_vs_lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fd33665c37b8
--- /dev/null
+++ b/tests/unchecked_haste_module_vs_lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,59 @@
+exports[`test buffer.js 1`] = `
+"/**
+ * @providesModule buffer
+ *
+ * Not in flow.
+ * If this module is successfully imported/required, its
+ * type will be Any, so arbitraty uses won't cause errors.
+ * However, if a library module declaration is bound to
+ * the same name as an unchecked module, it will be used
+ * to satisfy imports/requires instead.
+ */
+
+export var INSPECT_MAX_BYTES = 0;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @providesModule buffer
+ *
+ * Not in flow.
+ * If this module is successfully imported/required, its
+ * type will be Any, so arbitraty uses won't cause errors.
+ * However, if a library module declaration is bound to
+ * the same name as an unchecked module, it will be used
+ * to satisfy imports/requires instead.
+ */
+export var INSPECT_MAX_BYTES = 0;
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
+ */
+
+/* 'buffer' is the name of both an unchecked module in this directory,
+ * and a module declared in library file node.js.
+ * If the require below resolves to the unchecked module, the mistyping
+ * that follows will cause no errors, but if we resolve to the library
+ * instead, we'll get the desired error.
+ */
+var buffer = require("buffer");
+var x: string = buffer.INSPECT_MAX_BYTES; // error, number ~/> string
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
+ */
+/* 'buffer' is the name of both an unchecked module in this directory,
+ * and a module declared in library file node.js.
+ * If the require below resolves to the unchecked module, the mistyping
+ * that follows will cause no errors, but if we resolve to the library
+ * instead, we'll get the desired error.
+ */
+var buffer = require("buffer");
+var x: string = buffer.INSPECT_MAX_BYTES;// error, number ~/> string
+
+"
+`;
diff --git a/tests/unchecked_haste_module_vs_lib/buffer.js b/tests/unchecked_haste_module_vs_lib/buffer.js
new file mode 100644
index 000000000000..223b08155060
--- /dev/null
+++ b/tests/unchecked_haste_module_vs_lib/buffer.js
@@ -0,0 +1,12 @@
+/**
+ * @providesModule buffer
+ *
+ * Not in flow.
+ * If this module is successfully imported/required, its
+ * type will be Any, so arbitraty uses won't cause errors.
+ * However, if a library module declaration is bound to
+ * the same name as an unchecked module, it will be used
+ * to satisfy imports/requires instead.
+ */
+
+export var INSPECT_MAX_BYTES = 0;
diff --git a/tests/unchecked_haste_module_vs_lib/jsfmt.spec.js b/tests/unchecked_haste_module_vs_lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/unchecked_haste_module_vs_lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/unchecked_haste_module_vs_lib/test.js b/tests/unchecked_haste_module_vs_lib/test.js
new file mode 100644
index 000000000000..9cb508a5e998
--- /dev/null
+++ b/tests/unchecked_haste_module_vs_lib/test.js
@@ -0,0 +1,13 @@
+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ * @flow
+ */
+
+/* 'buffer' is the name of both an unchecked module in this directory,
+ * and a module declared in library file node.js.
+ * If the require below resolves to the unchecked module, the mistyping
+ * that follows will cause no errors, but if we resolve to the library
+ * instead, we'll get the desired error.
+ */
+var buffer = require("buffer");
+var x: string = buffer.INSPECT_MAX_BYTES; // error, number ~/> string
diff --git a/tests/unchecked_node_module_vs_lib/__snapshots__/jsfmt.spec.js.snap b/tests/unchecked_node_module_vs_lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..3831c78c27d0
--- /dev/null
+++ b/tests/unchecked_node_module_vs_lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,53 @@
+exports[`test test.js 1`] = `
+"/**
+ * Test resolution precedence in node:
+ * checked module > lib def > unchecked module
+ *
+ * @flow
+ */
+
+// node_modules/buffer/index.js is unchecked,
+// so we shouldn't pick up its boolean redefinition of INSPECT_MAX_BYTES
+//
+var buffer = require("buffer");
+var b: boolean = buffer.INSPECT_MAX_BYTES; // error, number ~/> boolean
+
+// node_modules/crypto/index.js is checked,
+// so we should pick up its boolean redefinition of DEFAULT_ENCODING
+//
+var crypto = require("crypto");
+var b: boolean = crypto.DEFAULT_ENCODING; // no error, we've overridden
+
+// names that are explicit paths shouldn't fall back to lib defs
+//
+var buffer2 = require("./buffer");
+var x2: string = buffer2.INSPECT_MAX_BYTES; // error, module not found
+
+var buffer3 = require("./buffer.js");
+var x3: string = buffer3.INSPECT_MAX_BYTES; // error, module not found
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * Test resolution precedence in node:
+ * checked module > lib def > unchecked module
+ *
+ * @flow
+ */
+// node_modules/buffer/index.js is unchecked,
+// so we shouldn't pick up its boolean redefinition of INSPECT_MAX_BYTES
+//
+var buffer = require("buffer");
+var b: boolean = buffer.INSPECT_MAX_BYTES;// error, number ~/> boolean
+// node_modules/crypto/index.js is checked,
+// so we should pick up its boolean redefinition of DEFAULT_ENCODING
+//
+var crypto = require("crypto");
+var b: boolean = crypto.DEFAULT_ENCODING;// no error, we've overridden
+// names that are explicit paths shouldn't fall back to lib defs
+//
+var buffer2 = require("./buffer");
+var x2: string = buffer2.INSPECT_MAX_BYTES;// error, module not found
+var buffer3 = require("./buffer.js");
+var x3: string = buffer3.INSPECT_MAX_BYTES;// error, module not found
+
+"
+`;
diff --git a/tests/unchecked_node_module_vs_lib/jsfmt.spec.js b/tests/unchecked_node_module_vs_lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/unchecked_node_module_vs_lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/unchecked_node_module_vs_lib/test.js b/tests/unchecked_node_module_vs_lib/test.js
new file mode 100644
index 000000000000..06b24ab57875
--- /dev/null
+++ b/tests/unchecked_node_module_vs_lib/test.js
@@ -0,0 +1,26 @@
+/**
+ * Test resolution precedence in node:
+ * checked module > lib def > unchecked module
+ *
+ * @flow
+ */
+
+// node_modules/buffer/index.js is unchecked,
+// so we shouldn't pick up its boolean redefinition of INSPECT_MAX_BYTES
+//
+var buffer = require("buffer");
+var b: boolean = buffer.INSPECT_MAX_BYTES; // error, number ~/> boolean
+
+// node_modules/crypto/index.js is checked,
+// so we should pick up its boolean redefinition of DEFAULT_ENCODING
+//
+var crypto = require("crypto");
+var b: boolean = crypto.DEFAULT_ENCODING; // no error, we've overridden
+
+// names that are explicit paths shouldn't fall back to lib defs
+//
+var buffer2 = require("./buffer");
+var x2: string = buffer2.INSPECT_MAX_BYTES; // error, module not found
+
+var buffer3 = require("./buffer.js");
+var x3: string = buffer3.INSPECT_MAX_BYTES; // error, module not found
diff --git a/tests/undefined/__snapshots__/jsfmt.spec.js.snap b/tests/undefined/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..543dc8f9448e
--- /dev/null
+++ b/tests/undefined/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,119 @@
+exports[`test issue-518.js 1`] = `
+"function doSomethingAsync(): Promise<void> {
+  return new Promise((resolve, reject) => {
+    resolve(); // OK to leave out arg, same as resolve(undefined)
+
+    var anotherVoidPromise: Promise<void> = Promise.resolve();
+    resolve(anotherVoidPromise);
+  });
+}
+
+// simpler repro to show that too few args are fine when expecting void
+function foo(x: void) { }
+foo();
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test undefined.js 1`] = `
+"function foo() {
+    var x;
+    x.foo();
+}
+
+function bar() {
+    var x:?{ bar():void; };
+    if (x) x.bar();
+}
+
+function qux(x?: number, y:string = \"\", z) { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test undefined2.js 1`] = `
+"// @flow
+
+let tests = [
+  function(x: number) {
+    var id;
+    var name = id ? \'John\' : undefined;
+    (name: boolean); // error, string or void
+
+    const bar = [
+      undefined,
+      \'bar\',
+    ];
+    (bar[x]: boolean); // error, string or void
+  },
+
+  function(x: number) {
+    var undefined = \'foo\';
+    (undefined: string); // ok
+
+    var x;
+    if (x !== undefined) {
+      x[0]; // should error, could be void
+    }
+
+    const bar = [
+      undefined,
+      \'bar\',
+    ];
+    (bar[x]: boolean); // error, string only
+  },
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+let tests = [
+  function(x: number) {
+    var id;
+    var name = (id ? \"John\" : undefined);
+    (name: boolean);// error, string or void
+    const bar = [ undefined, \"bar\" ];
+    (bar[x]: boolean);// error, string or void
+  },
+  function(x: number) {
+    var undefined = \"foo\";
+    (undefined: string);// ok
+    var x;
+    if (x !== undefined) {
+      x[0];// should error, could be void
+    }
+    const bar = [ undefined, \"bar\" ];
+    (bar[x]: boolean);// error, string only
+  }
+];
+
+"
+`;
diff --git a/tests/undefined/issue-518.js b/tests/undefined/issue-518.js
new file mode 100644
index 000000000000..e73c51091cb1
--- /dev/null
+++ b/tests/undefined/issue-518.js
@@ -0,0 +1,12 @@
+function doSomethingAsync(): Promise<void> {
+  return new Promise((resolve, reject) => {
+    resolve(); // OK to leave out arg, same as resolve(undefined)
+
+    var anotherVoidPromise: Promise<void> = Promise.resolve();
+    resolve(anotherVoidPromise);
+  });
+}
+
+// simpler repro to show that too few args are fine when expecting void
+function foo(x: void) { }
+foo();
diff --git a/tests/undefined/jsfmt.spec.js b/tests/undefined/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/undefined/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/undefined/undefined.js b/tests/undefined/undefined.js
new file mode 100644
index 000000000000..347d6206cfc3
--- /dev/null
+++ b/tests/undefined/undefined.js
@@ -0,0 +1,11 @@
+function foo() {
+    var x;
+    x.foo();
+}
+
+function bar() {
+    var x:?{ bar():void; };
+    if (x) x.bar();
+}
+
+function qux(x?: number, y:string = "", z) { }
diff --git a/tests/undefined/undefined2.js b/tests/undefined/undefined2.js
new file mode 100644
index 000000000000..bf7f503f38b5
--- /dev/null
+++ b/tests/undefined/undefined2.js
@@ -0,0 +1,31 @@
+// @flow
+
+let tests = [
+  function(x: number) {
+    var id;
+    var name = id ? 'John' : undefined;
+    (name: boolean); // error, string or void
+
+    const bar = [
+      undefined,
+      'bar',
+    ];
+    (bar[x]: boolean); // error, string or void
+  },
+
+  function(x: number) {
+    var undefined = 'foo';
+    (undefined: string); // ok
+
+    var x;
+    if (x !== undefined) {
+      x[0]; // should error, could be void
+    }
+
+    const bar = [
+      undefined,
+      'bar',
+    ];
+    (bar[x]: boolean); // error, string only
+  },
+];
diff --git a/tests/unicode/UnicodeUtils.js b/tests/unicode/UnicodeUtils.js
new file mode 100644
index 000000000000..3a06fc53b987
--- /dev/null
+++ b/tests/unicode/UnicodeUtils.js
@@ -0,0 +1,34 @@
+/**
+ * @flow
+ */
+
+/**
+ * @param {number} codeUnit   A Unicode code-unit, in range [0, 0x10FFFF]
+ * @return {boolean}      Whether code-unit is in a surrogate (hi/low) range
+ */
+function inSurrogateRange(codeUnit) {
+  return 0xD800 <= codeUnit && codeUnit <= 0xDFFF;
+}
+
+
+/**
+ * Return the length of the original Unicode character at given position in the
+ * String by looking into the UTF-16 code unit; that is equal to 1 for any
+ * non-surrogate characters in BMP ([U+0000..U+D7FF] and [U+E000, U+FFFF]); and
+ * returns 2 for the hi/low surrogates ([U+D800..U+DFFF]), which are in fact
+ * representing non-BMP characters ([U+10000..U+10FFFF]).
+ *
+ * Examples:
+ * - '\u0020' => 1
+ * - '\u3020' => 1
+ * - '\uD835' => 2
+ * - '\uD835\uDDEF' => 2
+ * - '\uDDEF' => 2
+ *
+ * @param {string} str  Non-empty string
+ * @param {number} pos  Position in the string to look for one code unit
+ * @return {number}      Number 1 or 2
+ */
+function utf16Length(str, pos) {
+  return 1 + inSurrogateRange(str.charCodeAt(pos));
+}
diff --git a/tests/unicode/__snapshots__/jsfmt.spec.js.snap b/tests/unicode/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2ede222aa532
--- /dev/null
+++ b/tests/unicode/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,70 @@
+exports[`test UnicodeUtils.js 1`] = `
+"/**
+ * @flow
+ */
+
+/**
+ * @param {number} codeUnit   A Unicode code-unit, in range [0, 0x10FFFF]
+ * @return {boolean}      Whether code-unit is in a surrogate (hi/low) range
+ */
+function inSurrogateRange(codeUnit) {
+  return 0xD800 <= codeUnit && codeUnit <= 0xDFFF;
+}
+
+
+/**
+ * Return the length of the original Unicode character at given position in the
+ * String by looking into the UTF-16 code unit; that is equal to 1 for any
+ * non-surrogate characters in BMP ([U+0000..U+D7FF] and [U+E000, U+FFFF]); and
+ * returns 2 for the hi/low surrogates ([U+D800..U+DFFF]), which are in fact
+ * representing non-BMP characters ([U+10000..U+10FFFF]).
+ *
+ * Examples:
+ * - \'\\u0020\' => 1
+ * - \'\\u3020\' => 1
+ * - \'\\uD835\' => 2
+ * - \'\\uD835\\uDDEF\' => 2
+ * - \'\\uDDEF\' => 2
+ *
+ * @param {string} str  Non-empty string
+ * @param {number} pos  Position in the string to look for one code unit
+ * @return {number}      Number 1 or 2
+ */
+function utf16Length(str, pos) {
+  return 1 + inSurrogateRange(str.charCodeAt(pos));
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @flow
+ */
+/**
+ * @param {number} codeUnit   A Unicode code-unit, in range [0, 0x10FFFF]
+ * @return {boolean}      Whether code-unit is in a surrogate (hi/low) range
+ */
+function inSurrogateRange(codeUnit) {
+  return 55296 <= codeUnit && codeUnit <= 57343;
+}
+/**
+ * Return the length of the original Unicode character at given position in the
+ * String by looking into the UTF-16 code unit; that is equal to 1 for any
+ * non-surrogate characters in BMP ([U+0000..U+D7FF] and [U+E000, U+FFFF]); and
+ * returns 2 for the hi/low surrogates ([U+D800..U+DFFF]), which are in fact
+ * representing non-BMP characters ([U+10000..U+10FFFF]).
+ *
+ * Examples:
+ * - \'\\u0020\' => 1
+ * - \'\\u3020\' => 1
+ * - \'\\uD835\' => 2
+ * - \'\\uD835\\uDDEF\' => 2
+ * - \'\\uDDEF\' => 2
+ *
+ * @param {string} str  Non-empty string
+ * @param {number} pos  Position in the string to look for one code unit
+ * @return {number}      Number 1 or 2
+ */
+function utf16Length(str, pos) {
+  return 1 + inSurrogateRange(str.charCodeAt(pos));
+}
+
+"
+`;
diff --git a/tests/unicode/jsfmt.spec.js b/tests/unicode/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/unicode/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/union-intersection/__snapshots__/jsfmt.spec.js.snap b/tests/union-intersection/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..9ae9ba5a1427
--- /dev/null
+++ b/tests/union-intersection/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,4057 @@
+exports[`test gen_big_disjoint_union.js 1`] = `
+"// perf test for big disjoint union with 1000 cases
+type TAction =
+{
+  type: \'a1\',
+  a1: number,
+} |
+{
+  type: \'a2\',
+  a1: number,
+} |
+{
+  type: \'a3\',
+  a1: number,
+} |
+{
+  type: \'a4\',
+  a1: number,
+} |
+{
+  type: \'a5\',
+  a1: number,
+} |
+{
+  type: \'a6\',
+  a1: number,
+} |
+{
+  type: \'a7\',
+  a1: number,
+} |
+{
+  type: \'a8\',
+  a1: number,
+} |
+{
+  type: \'a9\',
+  a1: number,
+} |
+{
+  type: \'a10\',
+  a1: number,
+} |
+{
+  type: \'a11\',
+  a2: number,
+} |
+{
+  type: \'a12\',
+  a2: number,
+} |
+{
+  type: \'a13\',
+  a2: number,
+} |
+{
+  type: \'a14\',
+  a2: number,
+} |
+{
+  type: \'a15\',
+  a2: number,
+} |
+{
+  type: \'a16\',
+  a2: number,
+} |
+{
+  type: \'a17\',
+  a2: number,
+} |
+{
+  type: \'a18\',
+  a2: number,
+} |
+{
+  type: \'a19\',
+  a2: number,
+} |
+{
+  type: \'a20\',
+  a2: number,
+} |
+{
+  type: \'a21\',
+  a3: number,
+} |
+{
+  type: \'a22\',
+  a3: number,
+} |
+{
+  type: \'a23\',
+  a3: number,
+} |
+{
+  type: \'a24\',
+  a3: number,
+} |
+{
+  type: \'a25\',
+  a3: number,
+} |
+{
+  type: \'a26\',
+  a3: number,
+} |
+{
+  type: \'a27\',
+  a3: number,
+} |
+{
+  type: \'a28\',
+  a3: number,
+} |
+{
+  type: \'a29\',
+  a3: number,
+} |
+{
+  type: \'a30\',
+  a3: number,
+} |
+{
+  type: \'a31\',
+  a4: number,
+} |
+{
+  type: \'a32\',
+  a4: number,
+} |
+{
+  type: \'a33\',
+  a4: number,
+} |
+{
+  type: \'a34\',
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+{
+  type: \'a907\',
+  a91: number,
+} |
+{
+  type: \'a908\',
+  a91: number,
+} |
+{
+  type: \'a909\',
+  a91: number,
+} |
+{
+  type: \'a910\',
+  a91: number,
+} |
+{
+  type: \'a911\',
+  a92: number,
+} |
+{
+  type: \'a912\',
+  a92: number,
+} |
+{
+  type: \'a913\',
+  a92: number,
+} |
+{
+  type: \'a914\',
+  a92: number,
+} |
+{
+  type: \'a915\',
+  a92: number,
+} |
+{
+  type: \'a916\',
+  a92: number,
+} |
+{
+  type: \'a917\',
+  a92: number,
+} |
+{
+  type: \'a918\',
+  a92: number,
+} |
+{
+  type: \'a919\',
+  a92: number,
+} |
+{
+  type: \'a920\',
+  a92: number,
+} |
+{
+  type: \'a921\',
+  a93: number,
+} |
+{
+  type: \'a922\',
+  a93: number,
+} |
+{
+  type: \'a923\',
+  a93: number,
+} |
+{
+  type: \'a924\',
+  a93: number,
+} |
+{
+  type: \'a925\',
+  a93: number,
+} |
+{
+  type: \'a926\',
+  a93: number,
+} |
+{
+  type: \'a927\',
+  a93: number,
+} |
+{
+  type: \'a928\',
+  a93: number,
+} |
+{
+  type: \'a929\',
+  a93: number,
+} |
+{
+  type: \'a930\',
+  a93: number,
+} |
+{
+  type: \'a931\',
+  a94: number,
+} |
+{
+  type: \'a932\',
+  a94: number,
+} |
+{
+  type: \'a933\',
+  a94: number,
+} |
+{
+  type: \'a934\',
+  a94: number,
+} |
+{
+  type: \'a935\',
+  a94: number,
+} |
+{
+  type: \'a936\',
+  a94: number,
+} |
+{
+  type: \'a937\',
+  a94: number,
+} |
+{
+  type: \'a938\',
+  a94: number,
+} |
+{
+  type: \'a939\',
+  a94: number,
+} |
+{
+  type: \'a940\',
+  a94: number,
+} |
+{
+  type: \'a941\',
+  a95: number,
+} |
+{
+  type: \'a942\',
+  a95: number,
+} |
+{
+  type: \'a943\',
+  a95: number,
+} |
+{
+  type: \'a944\',
+  a95: number,
+} |
+{
+  type: \'a945\',
+  a95: number,
+} |
+{
+  type: \'a946\',
+  a95: number,
+} |
+{
+  type: \'a947\',
+  a95: number,
+} |
+{
+  type: \'a948\',
+  a95: number,
+} |
+{
+  type: \'a949\',
+  a95: number,
+} |
+{
+  type: \'a950\',
+  a95: number,
+} |
+{
+  type: \'a951\',
+  a96: number,
+} |
+{
+  type: \'a952\',
+  a96: number,
+} |
+{
+  type: \'a953\',
+  a96: number,
+} |
+{
+  type: \'a954\',
+  a96: number,
+} |
+{
+  type: \'a955\',
+  a96: number,
+} |
+{
+  type: \'a956\',
+  a96: number,
+} |
+{
+  type: \'a957\',
+  a96: number,
+} |
+{
+  type: \'a958\',
+  a96: number,
+} |
+{
+  type: \'a959\',
+  a96: number,
+} |
+{
+  type: \'a960\',
+  a96: number,
+} |
+{
+  type: \'a961\',
+  a97: number,
+} |
+{
+  type: \'a962\',
+  a97: number,
+} |
+{
+  type: \'a963\',
+  a97: number,
+} |
+{
+  type: \'a964\',
+  a97: number,
+} |
+{
+  type: \'a965\',
+  a97: number,
+} |
+{
+  type: \'a966\',
+  a97: number,
+} |
+{
+  type: \'a967\',
+  a97: number,
+} |
+{
+  type: \'a968\',
+  a97: number,
+} |
+{
+  type: \'a969\',
+  a97: number,
+} |
+{
+  type: \'a970\',
+  a97: number,
+} |
+{
+  type: \'a971\',
+  a98: number,
+} |
+{
+  type: \'a972\',
+  a98: number,
+} |
+{
+  type: \'a973\',
+  a98: number,
+} |
+{
+  type: \'a974\',
+  a98: number,
+} |
+{
+  type: \'a975\',
+  a98: number,
+} |
+{
+  type: \'a976\',
+  a98: number,
+} |
+{
+  type: \'a977\',
+  a98: number,
+} |
+{
+  type: \'a978\',
+  a98: number,
+} |
+{
+  type: \'a979\',
+  a98: number,
+} |
+{
+  type: \'a980\',
+  a98: number,
+} |
+{
+  type: \'a981\',
+  a99: number,
+} |
+{
+  type: \'a982\',
+  a99: number,
+} |
+{
+  type: \'a983\',
+  a99: number,
+} |
+{
+  type: \'a984\',
+  a99: number,
+} |
+{
+  type: \'a985\',
+  a99: number,
+} |
+{
+  type: \'a986\',
+  a99: number,
+} |
+{
+  type: \'a987\',
+  a99: number,
+} |
+{
+  type: \'a988\',
+  a99: number,
+} |
+{
+  type: \'a989\',
+  a99: number,
+} |
+{
+  type: \'a990\',
+  a99: number,
+} |
+{
+  type: \'a991\',
+  a100: number,
+} |
+{
+  type: \'a992\',
+  a100: number,
+} |
+{
+  type: \'a993\',
+  a100: number,
+} |
+{
+  type: \'a994\',
+  a100: number,
+} |
+{
+  type: \'a995\',
+  a100: number,
+} |
+{
+  type: \'a996\',
+  a100: number,
+} |
+{
+  type: \'a997\',
+  a100: number,
+} |
+{
+  type: \'a998\',
+  a100: number,
+} |
+{
+  type: \'a999\',
+  a100: number,
+} |
+{
+  type: \'a1000\',
+  a100: number,
+};
+function foo(x: TAction): TAction { return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"type A = {a: number};
+type B = {b: number};
+type C = {c: number};
+
+type T1 = (A | B) & C;
+function f1(x: T1): T1 { return x; }
+
+type T2 = (A & B) | C;
+function f2(x: T2): T2 { return x; }
+
+type T3 = (A & C) | (B & C);
+function f3(x: T3): T3 { return x; }
+
+type T4 = (A | C) & (B | C);
+function f4(x: T4): T4 { return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1407:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/union-intersection/gen_big_disjoint_union.js b/tests/union-intersection/gen_big_disjoint_union.js
new file mode 100644
index 000000000000..7dcc0b8126ad
--- /dev/null
+++ b/tests/union-intersection/gen_big_disjoint_union.js
@@ -0,0 +1,4003 @@
+// perf test for big disjoint union with 1000 cases
+type TAction =
+{
+  type: 'a1',
+  a1: number,
+} |
+{
+  type: 'a2',
+  a1: number,
+} |
+{
+  type: 'a3',
+  a1: number,
+} |
+{
+  type: 'a4',
+  a1: number,
+} |
+{
+  type: 'a5',
+  a1: number,
+} |
+{
+  type: 'a6',
+  a1: number,
+} |
+{
+  type: 'a7',
+  a1: number,
+} |
+{
+  type: 'a8',
+  a1: number,
+} |
+{
+  type: 'a9',
+  a1: number,
+} |
+{
+  type: 'a10',
+  a1: number,
+} |
+{
+  type: 'a11',
+  a2: number,
+} |
+{
+  type: 'a12',
+  a2: number,
+} |
+{
+  type: 'a13',
+  a2: number,
+} |
+{
+  type: 'a14',
+  a2: number,
+} |
+{
+  type: 'a15',
+  a2: number,
+} |
+{
+  type: 'a16',
+  a2: number,
+} |
+{
+  type: 'a17',
+  a2: number,
+} |
+{
+  type: 'a18',
+  a2: number,
+} |
+{
+  type: 'a19',
+  a2: number,
+} |
+{
+  type: 'a20',
+  a2: number,
+} |
+{
+  type: 'a21',
+  a3: number,
+} |
+{
+  type: 'a22',
+  a3: number,
+} |
+{
+  type: 'a23',
+  a3: number,
+} |
+{
+  type: 'a24',
+  a3: number,
+} |
+{
+  type: 'a25',
+  a3: number,
+} |
+{
+  type: 'a26',
+  a3: number,
+} |
+{
+  type: 'a27',
+  a3: number,
+} |
+{
+  type: 'a28',
+  a3: number,
+} |
+{
+  type: 'a29',
+  a3: number,
+} |
+{
+  type: 'a30',
+  a3: number,
+} |
+{
+  type: 'a31',
+  a4: number,
+} |
+{
+  type: 'a32',
+  a4: number,
+} |
+{
+  type: 'a33',
+  a4: number,
+} |
+{
+  type: 'a34',
+  a4: number,
+} |
+{
+  type: 'a35',
+  a4: number,
+} |
+{
+  type: 'a36',
+  a4: number,
+} |
+{
+  type: 'a37',
+  a4: number,
+} |
+{
+  type: 'a38',
+  a4: number,
+} |
+{
+  type: 'a39',
+  a4: number,
+} |
+{
+  type: 'a40',
+  a4: number,
+} |
+{
+  type: 'a41',
+  a5: number,
+} |
+{
+  type: 'a42',
+  a5: number,
+} |
+{
+  type: 'a43',
+  a5: number,
+} |
+{
+  type: 'a44',
+  a5: number,
+} |
+{
+  type: 'a45',
+  a5: number,
+} |
+{
+  type: 'a46',
+  a5: number,
+} |
+{
+  type: 'a47',
+  a5: number,
+} |
+{
+  type: 'a48',
+  a5: number,
+} |
+{
+  type: 'a49',
+  a5: number,
+} |
+{
+  type: 'a50',
+  a5: number,
+} |
+{
+  type: 'a51',
+  a6: number,
+} |
+{
+  type: 'a52',
+  a6: number,
+} |
+{
+  type: 'a53',
+  a6: number,
+} |
+{
+  type: 'a54',
+  a6: number,
+} |
+{
+  type: 'a55',
+  a6: number,
+} |
+{
+  type: 'a56',
+  a6: number,
+} |
+{
+  type: 'a57',
+  a6: number,
+} |
+{
+  type: 'a58',
+  a6: number,
+} |
+{
+  type: 'a59',
+  a6: number,
+} |
+{
+  type: 'a60',
+  a6: number,
+} |
+{
+  type: 'a61',
+  a7: number,
+} |
+{
+  type: 'a62',
+  a7: number,
+} |
+{
+  type: 'a63',
+  a7: number,
+} |
+{
+  type: 'a64',
+  a7: number,
+} |
+{
+  type: 'a65',
+  a7: number,
+} |
+{
+  type: 'a66',
+  a7: number,
+} |
+{
+  type: 'a67',
+  a7: number,
+} |
+{
+  type: 'a68',
+  a7: number,
+} |
+{
+  type: 'a69',
+  a7: number,
+} |
+{
+  type: 'a70',
+  a7: number,
+} |
+{
+  type: 'a71',
+  a8: number,
+} |
+{
+  type: 'a72',
+  a8: number,
+} |
+{
+  type: 'a73',
+  a8: number,
+} |
+{
+  type: 'a74',
+  a8: number,
+} |
+{
+  type: 'a75',
+  a8: number,
+} |
+{
+  type: 'a76',
+  a8: number,
+} |
+{
+  type: 'a77',
+  a8: number,
+} |
+{
+  type: 'a78',
+  a8: number,
+} |
+{
+  type: 'a79',
+  a8: number,
+} |
+{
+  type: 'a80',
+  a8: number,
+} |
+{
+  type: 'a81',
+  a9: number,
+} |
+{
+  type: 'a82',
+  a9: number,
+} |
+{
+  type: 'a83',
+  a9: number,
+} |
+{
+  type: 'a84',
+  a9: number,
+} |
+{
+  type: 'a85',
+  a9: number,
+} |
+{
+  type: 'a86',
+  a9: number,
+} |
+{
+  type: 'a87',
+  a9: number,
+} |
+{
+  type: 'a88',
+  a9: number,
+} |
+{
+  type: 'a89',
+  a9: number,
+} |
+{
+  type: 'a90',
+  a9: number,
+} |
+{
+  type: 'a91',
+  a10: number,
+} |
+{
+  type: 'a92',
+  a10: number,
+} |
+{
+  type: 'a93',
+  a10: number,
+} |
+{
+  type: 'a94',
+  a10: number,
+} |
+{
+  type: 'a95',
+  a10: number,
+} |
+{
+  type: 'a96',
+  a10: number,
+} |
+{
+  type: 'a97',
+  a10: number,
+} |
+{
+  type: 'a98',
+  a10: number,
+} |
+{
+  type: 'a99',
+  a10: number,
+} |
+{
+  type: 'a100',
+  a10: number,
+} |
+{
+  type: 'a101',
+  a11: number,
+} |
+{
+  type: 'a102',
+  a11: number,
+} |
+{
+  type: 'a103',
+  a11: number,
+} |
+{
+  type: 'a104',
+  a11: number,
+} |
+{
+  type: 'a105',
+  a11: number,
+} |
+{
+  type: 'a106',
+  a11: number,
+} |
+{
+  type: 'a107',
+  a11: number,
+} |
+{
+  type: 'a108',
+  a11: number,
+} |
+{
+  type: 'a109',
+  a11: number,
+} |
+{
+  type: 'a110',
+  a11: number,
+} |
+{
+  type: 'a111',
+  a12: number,
+} |
+{
+  type: 'a112',
+  a12: number,
+} |
+{
+  type: 'a113',
+  a12: number,
+} |
+{
+  type: 'a114',
+  a12: number,
+} |
+{
+  type: 'a115',
+  a12: number,
+} |
+{
+  type: 'a116',
+  a12: number,
+} |
+{
+  type: 'a117',
+  a12: number,
+} |
+{
+  type: 'a118',
+  a12: number,
+} |
+{
+  type: 'a119',
+  a12: number,
+} |
+{
+  type: 'a120',
+  a12: number,
+} |
+{
+  type: 'a121',
+  a13: number,
+} |
+{
+  type: 'a122',
+  a13: number,
+} |
+{
+  type: 'a123',
+  a13: number,
+} |
+{
+  type: 'a124',
+  a13: number,
+} |
+{
+  type: 'a125',
+  a13: number,
+} |
+{
+  type: 'a126',
+  a13: number,
+} |
+{
+  type: 'a127',
+  a13: number,
+} |
+{
+  type: 'a128',
+  a13: number,
+} |
+{
+  type: 'a129',
+  a13: number,
+} |
+{
+  type: 'a130',
+  a13: number,
+} |
+{
+  type: 'a131',
+  a14: number,
+} |
+{
+  type: 'a132',
+  a14: number,
+} |
+{
+  type: 'a133',
+  a14: number,
+} |
+{
+  type: 'a134',
+  a14: number,
+} |
+{
+  type: 'a135',
+  a14: number,
+} |
+{
+  type: 'a136',
+  a14: number,
+} |
+{
+  type: 'a137',
+  a14: number,
+} |
+{
+  type: 'a138',
+  a14: number,
+} |
+{
+  type: 'a139',
+  a14: number,
+} |
+{
+  type: 'a140',
+  a14: number,
+} |
+{
+  type: 'a141',
+  a15: number,
+} |
+{
+  type: 'a142',
+  a15: number,
+} |
+{
+  type: 'a143',
+  a15: number,
+} |
+{
+  type: 'a144',
+  a15: number,
+} |
+{
+  type: 'a145',
+  a15: number,
+} |
+{
+  type: 'a146',
+  a15: number,
+} |
+{
+  type: 'a147',
+  a15: number,
+} |
+{
+  type: 'a148',
+  a15: number,
+} |
+{
+  type: 'a149',
+  a15: number,
+} |
+{
+  type: 'a150',
+  a15: number,
+} |
+{
+  type: 'a151',
+  a16: number,
+} |
+{
+  type: 'a152',
+  a16: number,
+} |
+{
+  type: 'a153',
+  a16: number,
+} |
+{
+  type: 'a154',
+  a16: number,
+} |
+{
+  type: 'a155',
+  a16: number,
+} |
+{
+  type: 'a156',
+  a16: number,
+} |
+{
+  type: 'a157',
+  a16: number,
+} |
+{
+  type: 'a158',
+  a16: number,
+} |
+{
+  type: 'a159',
+  a16: number,
+} |
+{
+  type: 'a160',
+  a16: number,
+} |
+{
+  type: 'a161',
+  a17: number,
+} |
+{
+  type: 'a162',
+  a17: number,
+} |
+{
+  type: 'a163',
+  a17: number,
+} |
+{
+  type: 'a164',
+  a17: number,
+} |
+{
+  type: 'a165',
+  a17: number,
+} |
+{
+  type: 'a166',
+  a17: number,
+} |
+{
+  type: 'a167',
+  a17: number,
+} |
+{
+  type: 'a168',
+  a17: number,
+} |
+{
+  type: 'a169',
+  a17: number,
+} |
+{
+  type: 'a170',
+  a17: number,
+} |
+{
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+} |
+{
+  type: 'a776',
+  a78: number,
+} |
+{
+  type: 'a777',
+  a78: number,
+} |
+{
+  type: 'a778',
+  a78: number,
+} |
+{
+  type: 'a779',
+  a78: number,
+} |
+{
+  type: 'a780',
+  a78: number,
+} |
+{
+  type: 'a781',
+  a79: number,
+} |
+{
+  type: 'a782',
+  a79: number,
+} |
+{
+  type: 'a783',
+  a79: number,
+} |
+{
+  type: 'a784',
+  a79: number,
+} |
+{
+  type: 'a785',
+  a79: number,
+} |
+{
+  type: 'a786',
+  a79: number,
+} |
+{
+  type: 'a787',
+  a79: number,
+} |
+{
+  type: 'a788',
+  a79: number,
+} |
+{
+  type: 'a789',
+  a79: number,
+} |
+{
+  type: 'a790',
+  a79: number,
+} |
+{
+  type: 'a791',
+  a80: number,
+} |
+{
+  type: 'a792',
+  a80: number,
+} |
+{
+  type: 'a793',
+  a80: number,
+} |
+{
+  type: 'a794',
+  a80: number,
+} |
+{
+  type: 'a795',
+  a80: number,
+} |
+{
+  type: 'a796',
+  a80: number,
+} |
+{
+  type: 'a797',
+  a80: number,
+} |
+{
+  type: 'a798',
+  a80: number,
+} |
+{
+  type: 'a799',
+  a80: number,
+} |
+{
+  type: 'a800',
+  a80: number,
+} |
+{
+  type: 'a801',
+  a81: number,
+} |
+{
+  type: 'a802',
+  a81: number,
+} |
+{
+  type: 'a803',
+  a81: number,
+} |
+{
+  type: 'a804',
+  a81: number,
+} |
+{
+  type: 'a805',
+  a81: number,
+} |
+{
+  type: 'a806',
+  a81: number,
+} |
+{
+  type: 'a807',
+  a81: number,
+} |
+{
+  type: 'a808',
+  a81: number,
+} |
+{
+  type: 'a809',
+  a81: number,
+} |
+{
+  type: 'a810',
+  a81: number,
+} |
+{
+  type: 'a811',
+  a82: number,
+} |
+{
+  type: 'a812',
+  a82: number,
+} |
+{
+  type: 'a813',
+  a82: number,
+} |
+{
+  type: 'a814',
+  a82: number,
+} |
+{
+  type: 'a815',
+  a82: number,
+} |
+{
+  type: 'a816',
+  a82: number,
+} |
+{
+  type: 'a817',
+  a82: number,
+} |
+{
+  type: 'a818',
+  a82: number,
+} |
+{
+  type: 'a819',
+  a82: number,
+} |
+{
+  type: 'a820',
+  a82: number,
+} |
+{
+  type: 'a821',
+  a83: number,
+} |
+{
+  type: 'a822',
+  a83: number,
+} |
+{
+  type: 'a823',
+  a83: number,
+} |
+{
+  type: 'a824',
+  a83: number,
+} |
+{
+  type: 'a825',
+  a83: number,
+} |
+{
+  type: 'a826',
+  a83: number,
+} |
+{
+  type: 'a827',
+  a83: number,
+} |
+{
+  type: 'a828',
+  a83: number,
+} |
+{
+  type: 'a829',
+  a83: number,
+} |
+{
+  type: 'a830',
+  a83: number,
+} |
+{
+  type: 'a831',
+  a84: number,
+} |
+{
+  type: 'a832',
+  a84: number,
+} |
+{
+  type: 'a833',
+  a84: number,
+} |
+{
+  type: 'a834',
+  a84: number,
+} |
+{
+  type: 'a835',
+  a84: number,
+} |
+{
+  type: 'a836',
+  a84: number,
+} |
+{
+  type: 'a837',
+  a84: number,
+} |
+{
+  type: 'a838',
+  a84: number,
+} |
+{
+  type: 'a839',
+  a84: number,
+} |
+{
+  type: 'a840',
+  a84: number,
+} |
+{
+  type: 'a841',
+  a85: number,
+} |
+{
+  type: 'a842',
+  a85: number,
+} |
+{
+  type: 'a843',
+  a85: number,
+} |
+{
+  type: 'a844',
+  a85: number,
+} |
+{
+  type: 'a845',
+  a85: number,
+} |
+{
+  type: 'a846',
+  a85: number,
+} |
+{
+  type: 'a847',
+  a85: number,
+} |
+{
+  type: 'a848',
+  a85: number,
+} |
+{
+  type: 'a849',
+  a85: number,
+} |
+{
+  type: 'a850',
+  a85: number,
+} |
+{
+  type: 'a851',
+  a86: number,
+} |
+{
+  type: 'a852',
+  a86: number,
+} |
+{
+  type: 'a853',
+  a86: number,
+} |
+{
+  type: 'a854',
+  a86: number,
+} |
+{
+  type: 'a855',
+  a86: number,
+} |
+{
+  type: 'a856',
+  a86: number,
+} |
+{
+  type: 'a857',
+  a86: number,
+} |
+{
+  type: 'a858',
+  a86: number,
+} |
+{
+  type: 'a859',
+  a86: number,
+} |
+{
+  type: 'a860',
+  a86: number,
+} |
+{
+  type: 'a861',
+  a87: number,
+} |
+{
+  type: 'a862',
+  a87: number,
+} |
+{
+  type: 'a863',
+  a87: number,
+} |
+{
+  type: 'a864',
+  a87: number,
+} |
+{
+  type: 'a865',
+  a87: number,
+} |
+{
+  type: 'a866',
+  a87: number,
+} |
+{
+  type: 'a867',
+  a87: number,
+} |
+{
+  type: 'a868',
+  a87: number,
+} |
+{
+  type: 'a869',
+  a87: number,
+} |
+{
+  type: 'a870',
+  a87: number,
+} |
+{
+  type: 'a871',
+  a88: number,
+} |
+{
+  type: 'a872',
+  a88: number,
+} |
+{
+  type: 'a873',
+  a88: number,
+} |
+{
+  type: 'a874',
+  a88: number,
+} |
+{
+  type: 'a875',
+  a88: number,
+} |
+{
+  type: 'a876',
+  a88: number,
+} |
+{
+  type: 'a877',
+  a88: number,
+} |
+{
+  type: 'a878',
+  a88: number,
+} |
+{
+  type: 'a879',
+  a88: number,
+} |
+{
+  type: 'a880',
+  a88: number,
+} |
+{
+  type: 'a881',
+  a89: number,
+} |
+{
+  type: 'a882',
+  a89: number,
+} |
+{
+  type: 'a883',
+  a89: number,
+} |
+{
+  type: 'a884',
+  a89: number,
+} |
+{
+  type: 'a885',
+  a89: number,
+} |
+{
+  type: 'a886',
+  a89: number,
+} |
+{
+  type: 'a887',
+  a89: number,
+} |
+{
+  type: 'a888',
+  a89: number,
+} |
+{
+  type: 'a889',
+  a89: number,
+} |
+{
+  type: 'a890',
+  a89: number,
+} |
+{
+  type: 'a891',
+  a90: number,
+} |
+{
+  type: 'a892',
+  a90: number,
+} |
+{
+  type: 'a893',
+  a90: number,
+} |
+{
+  type: 'a894',
+  a90: number,
+} |
+{
+  type: 'a895',
+  a90: number,
+} |
+{
+  type: 'a896',
+  a90: number,
+} |
+{
+  type: 'a897',
+  a90: number,
+} |
+{
+  type: 'a898',
+  a90: number,
+} |
+{
+  type: 'a899',
+  a90: number,
+} |
+{
+  type: 'a900',
+  a90: number,
+} |
+{
+  type: 'a901',
+  a91: number,
+} |
+{
+  type: 'a902',
+  a91: number,
+} |
+{
+  type: 'a903',
+  a91: number,
+} |
+{
+  type: 'a904',
+  a91: number,
+} |
+{
+  type: 'a905',
+  a91: number,
+} |
+{
+  type: 'a906',
+  a91: number,
+} |
+{
+  type: 'a907',
+  a91: number,
+} |
+{
+  type: 'a908',
+  a91: number,
+} |
+{
+  type: 'a909',
+  a91: number,
+} |
+{
+  type: 'a910',
+  a91: number,
+} |
+{
+  type: 'a911',
+  a92: number,
+} |
+{
+  type: 'a912',
+  a92: number,
+} |
+{
+  type: 'a913',
+  a92: number,
+} |
+{
+  type: 'a914',
+  a92: number,
+} |
+{
+  type: 'a915',
+  a92: number,
+} |
+{
+  type: 'a916',
+  a92: number,
+} |
+{
+  type: 'a917',
+  a92: number,
+} |
+{
+  type: 'a918',
+  a92: number,
+} |
+{
+  type: 'a919',
+  a92: number,
+} |
+{
+  type: 'a920',
+  a92: number,
+} |
+{
+  type: 'a921',
+  a93: number,
+} |
+{
+  type: 'a922',
+  a93: number,
+} |
+{
+  type: 'a923',
+  a93: number,
+} |
+{
+  type: 'a924',
+  a93: number,
+} |
+{
+  type: 'a925',
+  a93: number,
+} |
+{
+  type: 'a926',
+  a93: number,
+} |
+{
+  type: 'a927',
+  a93: number,
+} |
+{
+  type: 'a928',
+  a93: number,
+} |
+{
+  type: 'a929',
+  a93: number,
+} |
+{
+  type: 'a930',
+  a93: number,
+} |
+{
+  type: 'a931',
+  a94: number,
+} |
+{
+  type: 'a932',
+  a94: number,
+} |
+{
+  type: 'a933',
+  a94: number,
+} |
+{
+  type: 'a934',
+  a94: number,
+} |
+{
+  type: 'a935',
+  a94: number,
+} |
+{
+  type: 'a936',
+  a94: number,
+} |
+{
+  type: 'a937',
+  a94: number,
+} |
+{
+  type: 'a938',
+  a94: number,
+} |
+{
+  type: 'a939',
+  a94: number,
+} |
+{
+  type: 'a940',
+  a94: number,
+} |
+{
+  type: 'a941',
+  a95: number,
+} |
+{
+  type: 'a942',
+  a95: number,
+} |
+{
+  type: 'a943',
+  a95: number,
+} |
+{
+  type: 'a944',
+  a95: number,
+} |
+{
+  type: 'a945',
+  a95: number,
+} |
+{
+  type: 'a946',
+  a95: number,
+} |
+{
+  type: 'a947',
+  a95: number,
+} |
+{
+  type: 'a948',
+  a95: number,
+} |
+{
+  type: 'a949',
+  a95: number,
+} |
+{
+  type: 'a950',
+  a95: number,
+} |
+{
+  type: 'a951',
+  a96: number,
+} |
+{
+  type: 'a952',
+  a96: number,
+} |
+{
+  type: 'a953',
+  a96: number,
+} |
+{
+  type: 'a954',
+  a96: number,
+} |
+{
+  type: 'a955',
+  a96: number,
+} |
+{
+  type: 'a956',
+  a96: number,
+} |
+{
+  type: 'a957',
+  a96: number,
+} |
+{
+  type: 'a958',
+  a96: number,
+} |
+{
+  type: 'a959',
+  a96: number,
+} |
+{
+  type: 'a960',
+  a96: number,
+} |
+{
+  type: 'a961',
+  a97: number,
+} |
+{
+  type: 'a962',
+  a97: number,
+} |
+{
+  type: 'a963',
+  a97: number,
+} |
+{
+  type: 'a964',
+  a97: number,
+} |
+{
+  type: 'a965',
+  a97: number,
+} |
+{
+  type: 'a966',
+  a97: number,
+} |
+{
+  type: 'a967',
+  a97: number,
+} |
+{
+  type: 'a968',
+  a97: number,
+} |
+{
+  type: 'a969',
+  a97: number,
+} |
+{
+  type: 'a970',
+  a97: number,
+} |
+{
+  type: 'a971',
+  a98: number,
+} |
+{
+  type: 'a972',
+  a98: number,
+} |
+{
+  type: 'a973',
+  a98: number,
+} |
+{
+  type: 'a974',
+  a98: number,
+} |
+{
+  type: 'a975',
+  a98: number,
+} |
+{
+  type: 'a976',
+  a98: number,
+} |
+{
+  type: 'a977',
+  a98: number,
+} |
+{
+  type: 'a978',
+  a98: number,
+} |
+{
+  type: 'a979',
+  a98: number,
+} |
+{
+  type: 'a980',
+  a98: number,
+} |
+{
+  type: 'a981',
+  a99: number,
+} |
+{
+  type: 'a982',
+  a99: number,
+} |
+{
+  type: 'a983',
+  a99: number,
+} |
+{
+  type: 'a984',
+  a99: number,
+} |
+{
+  type: 'a985',
+  a99: number,
+} |
+{
+  type: 'a986',
+  a99: number,
+} |
+{
+  type: 'a987',
+  a99: number,
+} |
+{
+  type: 'a988',
+  a99: number,
+} |
+{
+  type: 'a989',
+  a99: number,
+} |
+{
+  type: 'a990',
+  a99: number,
+} |
+{
+  type: 'a991',
+  a100: number,
+} |
+{
+  type: 'a992',
+  a100: number,
+} |
+{
+  type: 'a993',
+  a100: number,
+} |
+{
+  type: 'a994',
+  a100: number,
+} |
+{
+  type: 'a995',
+  a100: number,
+} |
+{
+  type: 'a996',
+  a100: number,
+} |
+{
+  type: 'a997',
+  a100: number,
+} |
+{
+  type: 'a998',
+  a100: number,
+} |
+{
+  type: 'a999',
+  a100: number,
+} |
+{
+  type: 'a1000',
+  a100: number,
+};
+function foo(x: TAction): TAction { return x; }
diff --git a/tests/union-intersection/jsfmt.spec.js b/tests/union-intersection/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/union-intersection/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/union-intersection/test.js b/tests/union-intersection/test.js
new file mode 100644
index 000000000000..83655a3be56d
--- /dev/null
+++ b/tests/union-intersection/test.js
@@ -0,0 +1,15 @@
+type A = {a: number};
+type B = {b: number};
+type C = {c: number};
+
+type T1 = (A | B) & C;
+function f1(x: T1): T1 { return x; }
+
+type T2 = (A & B) | C;
+function f2(x: T2): T2 { return x; }
+
+type T3 = (A & C) | (B & C);
+function f3(x: T3): T3 { return x; }
+
+type T4 = (A | C) & (B | C);
+function f4(x: T4): T4 { return x; }
diff --git a/tests/union/__snapshots__/jsfmt.spec.js.snap b/tests/union/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..11f75a60dcfe
--- /dev/null
+++ b/tests/union/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,5533 @@
+exports[`test fields.js 1`] = `
+"class C {
+    x: ?number|string;
+    constructor() {
+        this.x = null;
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test fields2.js 1`] = `
+"class C { }
+
+class D {
+    content: string|C;
+    copyContent(content: C): string|C {
+        this.content = content;
+        return this.content;
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-17.js 1`] = `
+"/* @flow */
+
+type T =
+    {type: \"a\"; a: number} |
+    {type: \"b\"; b: string};
+
+var l: Array<T> = [
+    {type: \"a\", a: 1},
+    {type: \"a\", a: 2},
+    {type: \"a\", a: 3},
+    {type: \"a\", a: 4},
+    {type: \"b\", b: \"monkey\"},
+    {type: \"b\", b: \"gorilla\"},
+    {type: \"b\", b: \"giraffe\"},
+    {type: \"b\", b: \"penguin\"},
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-198.js 1`] = `
+"var p = new Promise(function(resolve, reject) {
+    resolve(5);
+})
+    .then(function(num) {
+        return num.toFixed();
+    })
+    .then(function(str) {
+        // This should fail because str is string, not number
+        return str.toFixed();
+    });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var p = new Promise(
+  function(resolve, reject) {
+    resolve(5);
+  }
+).then(
+  function(num) {
+    return num.toFixed();
+  }
+).then(
+  function(str) {
+    // This should fail because str is string, not number
+    return str.toFixed();
+  }
+);
+
+"
+`;
+
+exports[`test issue-256.js 1`] = `
+"declare class Myclass {
+    myfun(myarray: Array<Function | string>): any;
+}
+declare var myclass: Myclass;
+
+myclass.myfun([\"1\", \"2\", \"3\", \"4\", \"5\", \"6\", function (ar) {}])
+myclass.myfun([\"1\", \"2\", \"3\", \"4\", \"5\", \"6\", \"7\", function (ar) {}])
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-323.js 1`] = `
+"var Foo = require(\"./issue-323-lib\");
+var foo = new Foo();
+var foostr: Foo | string = foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-323-lib.js 1`] = `
+"/* @flow */
+class Foo {}
+module.exports = Foo;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+class Foo {}
+module.exports = Foo;
+
+"
+`;
+
+exports[`test issue-324.js 1`] = `
+"/* @flow */
+class Foo{};
+class Bar{};
+
+var foostr: Foo | string = new Foo();
+var barstr: Bar | string = new Bar();
+
+foostr = barstr;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-325.js 1`] = `
+"class Tag {
+    constructor() {
+        var a1: Array<Tag|string> = [];
+        var a2: Array<Tag|string> = a1;
+    }
+}
+
+type Node = Tag_ | string;
+class Tag_ {
+    constructor() {
+        var a1: Array<Node> = [new Tag_];
+        var a2: Array<Node> = a1;
+    }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-326.js 1`] = `
+"var numberAndStringArr:Array<number|string> = [1,2];
+var stringArr:Array<string> = [\'a\',\'b\'];
+
+var result = numberAndStringArr.concat(stringArr);  // no error
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-582.js 1`] = `
+"/***
+ * nested unions
+ * @flow
+ */
+
+// inline
+var nested1: (\'foo\' | \'bar\') | \'baz\' = \'baz\';
+
+// through tvars
+type FooBar = \'foo\' | \'bar\';
+type Baz = \'baz\';
+type FooBarBaz = FooBar | Baz;
+
+var nested2: FooBarBaz = \'baz\';
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-963.js 1`] = `
+"/***
+ * unions with embedded intersections
+ * @flow
+ */
+
+type t1 = {
+    p1 : number
+};
+
+type t2 = {
+    p2: number
+}
+
+type t3 = {
+    p3 : number
+}
+
+type intersected = t1 & t2;
+type union = intersected | t3;
+type union2 = t3 | intersected;
+
+const u1 : union = {
+    p3 : 3
+};
+
+const u2 : union = {
+    p1 : 1,
+    p2 : 2
+};
+
+const u3 : union2 = {
+    p1 : 1,
+    p2 : 2
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test.js 1`] = `
+"var C = require(\'test-lib\');
+
+// TODO: spurious error! (replacing C with number makes the error go away)
+// type Foo<X> = Array<C> | Array<?C>;
+type Foo<X:?C> = Array<X>; // workaround
+var x:Array<C> = [];
+var y:Array<?C> = [];
+function foo<X>(x:Foo<X>) {}
+foo(x);
+foo(y);
+
+// TODO: spurious error! (replacing C with number makes the error go away)
+// type Bar = (() => C) | (() => string);
+type Bar = () => (C | string); // workaround
+
+function f() { return \"\"; }
+function bar(x:Bar) { }
+bar(f);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test-lib.js 1`] = `
+"/* @providesModule test-lib */
+
+class C { }
+module.exports = C;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule test-lib */
+class C {}
+module.exports = C;
+
+"
+`;
+
+exports[`test type-app.js 1`] = `
+"/**
+ * @flow
+ */
+
+class LocalClass<T> {}
+
+var a: LocalClass<number> | number = 123;
+
+// Iterator is defined in a lib file, so the speculative algorithm for the
+// union type would incorrectly succeed for Iterator<number>. Only later during
+// the merge would we fine the error, but it would be too late. The diff that
+// introduces this test fixes this such that the speculative algorithm is
+// correctly delayed upon encountering a non-concrete TypeAppT
+var b: Iterator<number> | number = 123;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1172:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test union.js 1`] = `
+"function bar(x: Document | string): void { }
+bar(0);
+
+class C { }
+class D { }
+function CD(b) {
+  var E = b? C: D;
+  var c:C = new E(); // error, since E could be D, and D is not a subtype of C
+  function qux(e: E) { } // this annotation is an error: is it C, or is it D?
+  function qux2(e: C | D) { } // OK
+  qux2(new C);
+}
+
+declare class F {
+    foo(x: number):void;
+    foo(x: string):void;
+}
+function corge(b) {
+    var x = b ? \"\" : 0;
+    new F().foo(x);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test yuge.js 1`] = `
+"/**
+ * great big union used as type annotation will be flowed into itself.
+ * List.mem check avoids pathology, as long as singletons aren\'t converted.
+ * This is a band-aid, though: see second case.
+ * @flow
+ */
+\'use strict\';
+
+class SecurityCheckupTypedLogger {
+  _data: Data;
+
+  setError(value: ErrorCode) {
+    this._data[\'error\'] = value;
+  }
+
+  // Bug: right now, any incompatible type coming into a huge
+  // union might blow the recursion limit.
+  // TODO real solution is to specialize union reps for obvious cases,
+  // e.g. (base type, list in decl order, set). Of course we could do
+  // something quick to get the union size off the Ocaml call stack,
+  // but not sure it\'s worth doing that before the real solution.
+  ohThatsNotSoGood() {
+    (\"\": ErrorCode);  // also, error pos omits this line completely
+  }
+}
+
+type ErrorCode =
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+4818 |
+4819 |
+4820 |
+4821 |
+4822 |
+4823 |
+4824 |
+4825 |
+4826 |
+4827 |
+4828 |
+4829 |
+4830 |
+4831 |
+4832 |
+4833 |
+4834 |
+4835 |
+4836 |
+4837 |
+4838 |
+4839 |
+4840 |
+4841 |
+4842 |
+4843 |
+4844 |
+4845 |
+4846 |
+4847 |
+4848 |
+4849 |
+4850 |
+4851 |
+4852 |
+4853 |
+4854 |
+4855 |
+4856 |
+4857 |
+4858 |
+4859 |
+4860 |
+4861 |
+4862 |
+4863 |
+4864 |
+4865 |
+4866 |
+4867 |
+4868 |
+4869 |
+4870 |
+4871 |
+4872 |
+4873 |
+4874 |
+4875 |
+4876 |
+4877 |
+4878 |
+4879 |
+4880 |
+4881 |
+4882 |
+4883 |
+4884 |
+4885 |
+4886 |
+4887 |
+4888 |
+4889 |
+4890 |
+4891 |
+4892 |
+4893 |
+4894 |
+4895 |
+4896 |
+4897 |
+4898 |
+4899 |
+4900 |
+4901 |
+4902 |
+4903 |
+4904 |
+4905 |
+4906 |
+4907 |
+4908 |
+4909 |
+4910 |
+4911 |
+4912 |
+4913 |
+4914 |
+4915 |
+4916 |
+4917 |
+4918 |
+4919 |
+4920 |
+4921 |
+4922 |
+4923 |
+4924 |
+4925 |
+4926 |
+4927 |
+4928 |
+4929 |
+4930 |
+4931 |
+4932 |
+4933 |
+4934 |
+4935 |
+4936 |
+4937 |
+4938 |
+4939 |
+4940 |
+4941 |
+4942 |
+4943 |
+4944 |
+4945 |
+4946 |
+4947 |
+4948 |
+4949 |
+4950 |
+4951 |
+4952 |
+4953 |
+4954 |
+4955 |
+4956 |
+4957 |
+4958 |
+4959 |
+4960 |
+4961 |
+4962 |
+4963 |
+4964 |
+4965 |
+4966 |
+4967 |
+4968 |
+4969 |
+4970 |
+4971 |
+4972 |
+4973 |
+4974 |
+4975 |
+4976 |
+4977 |
+4978 |
+4979 |
+4980 |
+4981 |
+4982 |
+4983 |
+4984 |
+4985 |
+4986 |
+4987 |
+4988 |
+4989 |
+4990 |
+4991 |
+4992 |
+4993 |
+4994 |
+4995 |
+4996 |
+4997 |
+4998 |
+4999;
+
+type Data = {
+  error?: ErrorCode,
+};
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/ast-types/lib/types.js:60
+            throw new Error(str + \" does not match type \" + this);
+            ^
+
+Error: {type: NumericLiteralTypeAnnotation, start: 843, end: 844, loc: [object Object], value: 0, extra: [object Object]} does not match type Printable
+    at Type.Tp.assert (/node_modules/ast-types/lib/types.js:60:19)
+    at genericPrintNoParens (/src/printer.js:221:24)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+"
+`;
diff --git a/tests/union/fields.js b/tests/union/fields.js
new file mode 100644
index 000000000000..f3bb77b06f98
--- /dev/null
+++ b/tests/union/fields.js
@@ -0,0 +1,6 @@
+class C {
+    x: ?number|string;
+    constructor() {
+        this.x = null;
+    }
+}
diff --git a/tests/union/fields2.js b/tests/union/fields2.js
new file mode 100644
index 000000000000..b065e17fddb2
--- /dev/null
+++ b/tests/union/fields2.js
@@ -0,0 +1,9 @@
+class C { }
+
+class D {
+    content: string|C;
+    copyContent(content: C): string|C {
+        this.content = content;
+        return this.content;
+    }
+}
diff --git a/tests/union/issue-17.js b/tests/union/issue-17.js
new file mode 100644
index 000000000000..18c6dc49571c
--- /dev/null
+++ b/tests/union/issue-17.js
@@ -0,0 +1,16 @@
+/* @flow */
+
+type T =
+    {type: "a"; a: number} |
+    {type: "b"; b: string};
+
+var l: Array<T> = [
+    {type: "a", a: 1},
+    {type: "a", a: 2},
+    {type: "a", a: 3},
+    {type: "a", a: 4},
+    {type: "b", b: "monkey"},
+    {type: "b", b: "gorilla"},
+    {type: "b", b: "giraffe"},
+    {type: "b", b: "penguin"},
+];
diff --git a/tests/union/issue-198.js b/tests/union/issue-198.js
new file mode 100644
index 000000000000..72072f498088
--- /dev/null
+++ b/tests/union/issue-198.js
@@ -0,0 +1,10 @@
+var p = new Promise(function(resolve, reject) {
+    resolve(5);
+})
+    .then(function(num) {
+        return num.toFixed();
+    })
+    .then(function(str) {
+        // This should fail because str is string, not number
+        return str.toFixed();
+    });
diff --git a/tests/union/issue-256.js b/tests/union/issue-256.js
new file mode 100644
index 000000000000..5fc84c9519be
--- /dev/null
+++ b/tests/union/issue-256.js
@@ -0,0 +1,7 @@
+declare class Myclass {
+    myfun(myarray: Array<Function | string>): any;
+}
+declare var myclass: Myclass;
+
+myclass.myfun(["1", "2", "3", "4", "5", "6", function (ar) {}])
+myclass.myfun(["1", "2", "3", "4", "5", "6", "7", function (ar) {}])
diff --git a/tests/union/issue-323-lib.js b/tests/union/issue-323-lib.js
new file mode 100644
index 000000000000..8d0e73801568
--- /dev/null
+++ b/tests/union/issue-323-lib.js
@@ -0,0 +1,3 @@
+/* @flow */
+class Foo {}
+module.exports = Foo;
diff --git a/tests/union/issue-323.js b/tests/union/issue-323.js
new file mode 100644
index 000000000000..f5216b84e06c
--- /dev/null
+++ b/tests/union/issue-323.js
@@ -0,0 +1,3 @@
+var Foo = require("./issue-323-lib");
+var foo = new Foo();
+var foostr: Foo | string = foo;
diff --git a/tests/union/issue-324.js b/tests/union/issue-324.js
new file mode 100644
index 000000000000..a18cf7a8482f
--- /dev/null
+++ b/tests/union/issue-324.js
@@ -0,0 +1,8 @@
+/* @flow */
+class Foo{};
+class Bar{};
+
+var foostr: Foo | string = new Foo();
+var barstr: Bar | string = new Bar();
+
+foostr = barstr;
diff --git a/tests/union/issue-325.js b/tests/union/issue-325.js
new file mode 100644
index 000000000000..7fefbc251caa
--- /dev/null
+++ b/tests/union/issue-325.js
@@ -0,0 +1,14 @@
+class Tag {
+    constructor() {
+        var a1: Array<Tag|string> = [];
+        var a2: Array<Tag|string> = a1;
+    }
+}
+
+type Node = Tag_ | string;
+class Tag_ {
+    constructor() {
+        var a1: Array<Node> = [new Tag_];
+        var a2: Array<Node> = a1;
+    }
+}
diff --git a/tests/union/issue-326.js b/tests/union/issue-326.js
new file mode 100644
index 000000000000..d3de6e5f9616
--- /dev/null
+++ b/tests/union/issue-326.js
@@ -0,0 +1,4 @@
+var numberAndStringArr:Array<number|string> = [1,2];
+var stringArr:Array<string> = ['a','b'];
+
+var result = numberAndStringArr.concat(stringArr);  // no error
diff --git a/tests/union/issue-582.js b/tests/union/issue-582.js
new file mode 100644
index 000000000000..1793a84226dd
--- /dev/null
+++ b/tests/union/issue-582.js
@@ -0,0 +1,14 @@
+/***
+ * nested unions
+ * @flow
+ */
+
+// inline
+var nested1: ('foo' | 'bar') | 'baz' = 'baz';
+
+// through tvars
+type FooBar = 'foo' | 'bar';
+type Baz = 'baz';
+type FooBarBaz = FooBar | Baz;
+
+var nested2: FooBarBaz = 'baz';
diff --git a/tests/union/issue-963.js b/tests/union/issue-963.js
new file mode 100644
index 000000000000..b4803c6da641
--- /dev/null
+++ b/tests/union/issue-963.js
@@ -0,0 +1,34 @@
+/***
+ * unions with embedded intersections
+ * @flow
+ */
+
+type t1 = {
+    p1 : number
+};
+
+type t2 = {
+    p2: number
+}
+
+type t3 = {
+    p3 : number
+}
+
+type intersected = t1 & t2;
+type union = intersected | t3;
+type union2 = t3 | intersected;
+
+const u1 : union = {
+    p3 : 3
+};
+
+const u2 : union = {
+    p1 : 1,
+    p2 : 2
+};
+
+const u3 : union2 = {
+    p1 : 1,
+    p2 : 2
+};
diff --git a/tests/union/jsfmt.spec.js b/tests/union/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/union/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/union/test-lib.js b/tests/union/test-lib.js
new file mode 100644
index 000000000000..e994d2afd4dd
--- /dev/null
+++ b/tests/union/test-lib.js
@@ -0,0 +1,4 @@
+/* @providesModule test-lib */
+
+class C { }
+module.exports = C;
diff --git a/tests/union/test.js b/tests/union/test.js
new file mode 100644
index 000000000000..5acbee01e223
--- /dev/null
+++ b/tests/union/test.js
@@ -0,0 +1,18 @@
+var C = require('test-lib');
+
+// TODO: spurious error! (replacing C with number makes the error go away)
+// type Foo<X> = Array<C> | Array<?C>;
+type Foo<X:?C> = Array<X>; // workaround
+var x:Array<C> = [];
+var y:Array<?C> = [];
+function foo<X>(x:Foo<X>) {}
+foo(x);
+foo(y);
+
+// TODO: spurious error! (replacing C with number makes the error go away)
+// type Bar = (() => C) | (() => string);
+type Bar = () => (C | string); // workaround
+
+function f() { return ""; }
+function bar(x:Bar) { }
+bar(f);
diff --git a/tests/union/type-app.js b/tests/union/type-app.js
new file mode 100644
index 000000000000..21b4feffd7e7
--- /dev/null
+++ b/tests/union/type-app.js
@@ -0,0 +1,14 @@
+/**
+ * @flow
+ */
+
+class LocalClass<T> {}
+
+var a: LocalClass<number> | number = 123;
+
+// Iterator is defined in a lib file, so the speculative algorithm for the
+// union type would incorrectly succeed for Iterator<number>. Only later during
+// the merge would we fine the error, but it would be too late. The diff that
+// introduces this test fixes this such that the speculative algorithm is
+// correctly delayed upon encountering a non-concrete TypeAppT
+var b: Iterator<number> | number = 123;
diff --git a/tests/union/union.js b/tests/union/union.js
new file mode 100644
index 000000000000..1aa068b024de
--- /dev/null
+++ b/tests/union/union.js
@@ -0,0 +1,21 @@
+function bar(x: Document | string): void { }
+bar(0);
+
+class C { }
+class D { }
+function CD(b) {
+  var E = b? C: D;
+  var c:C = new E(); // error, since E could be D, and D is not a subtype of C
+  function qux(e: E) { } // this annotation is an error: is it C, or is it D?
+  function qux2(e: C | D) { } // OK
+  qux2(new C);
+}
+
+declare class F {
+    foo(x: number):void;
+    foo(x: string):void;
+}
+function corge(b) {
+    var x = b ? "" : 0;
+    new F().foo(x);
+}
diff --git a/tests/union/yuge.js b/tests/union/yuge.js
new file mode 100644
index 000000000000..ad2028252900
--- /dev/null
+++ b/tests/union/yuge.js
@@ -0,0 +1,5031 @@
+/**
+ * great big union used as type annotation will be flowed into itself.
+ * List.mem check avoids pathology, as long as singletons aren't converted.
+ * This is a band-aid, though: see second case.
+ * @flow
+ */
+'use strict';
+
+class SecurityCheckupTypedLogger {
+  _data: Data;
+
+  setError(value: ErrorCode) {
+    this._data['error'] = value;
+  }
+
+  // Bug: right now, any incompatible type coming into a huge
+  // union might blow the recursion limit.
+  // TODO real solution is to specialize union reps for obvious cases,
+  // e.g. (base type, list in decl order, set). Of course we could do
+  // something quick to get the union size off the Ocaml call stack,
+  // but not sure it's worth doing that before the real solution.
+  ohThatsNotSoGood() {
+    ("": ErrorCode);  // also, error pos omits this line completely
+  }
+}
+
+type ErrorCode =
+0 |
+1 |
+2 |
+3 |
+4 |
+5 |
+6 |
+7 |
+8 |
+9 |
+10 |
+11 |
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+4789 |
+4790 |
+4791 |
+4792 |
+4793 |
+4794 |
+4795 |
+4796 |
+4797 |
+4798 |
+4799 |
+4800 |
+4801 |
+4802 |
+4803 |
+4804 |
+4805 |
+4806 |
+4807 |
+4808 |
+4809 |
+4810 |
+4811 |
+4812 |
+4813 |
+4814 |
+4815 |
+4816 |
+4817 |
+4818 |
+4819 |
+4820 |
+4821 |
+4822 |
+4823 |
+4824 |
+4825 |
+4826 |
+4827 |
+4828 |
+4829 |
+4830 |
+4831 |
+4832 |
+4833 |
+4834 |
+4835 |
+4836 |
+4837 |
+4838 |
+4839 |
+4840 |
+4841 |
+4842 |
+4843 |
+4844 |
+4845 |
+4846 |
+4847 |
+4848 |
+4849 |
+4850 |
+4851 |
+4852 |
+4853 |
+4854 |
+4855 |
+4856 |
+4857 |
+4858 |
+4859 |
+4860 |
+4861 |
+4862 |
+4863 |
+4864 |
+4865 |
+4866 |
+4867 |
+4868 |
+4869 |
+4870 |
+4871 |
+4872 |
+4873 |
+4874 |
+4875 |
+4876 |
+4877 |
+4878 |
+4879 |
+4880 |
+4881 |
+4882 |
+4883 |
+4884 |
+4885 |
+4886 |
+4887 |
+4888 |
+4889 |
+4890 |
+4891 |
+4892 |
+4893 |
+4894 |
+4895 |
+4896 |
+4897 |
+4898 |
+4899 |
+4900 |
+4901 |
+4902 |
+4903 |
+4904 |
+4905 |
+4906 |
+4907 |
+4908 |
+4909 |
+4910 |
+4911 |
+4912 |
+4913 |
+4914 |
+4915 |
+4916 |
+4917 |
+4918 |
+4919 |
+4920 |
+4921 |
+4922 |
+4923 |
+4924 |
+4925 |
+4926 |
+4927 |
+4928 |
+4929 |
+4930 |
+4931 |
+4932 |
+4933 |
+4934 |
+4935 |
+4936 |
+4937 |
+4938 |
+4939 |
+4940 |
+4941 |
+4942 |
+4943 |
+4944 |
+4945 |
+4946 |
+4947 |
+4948 |
+4949 |
+4950 |
+4951 |
+4952 |
+4953 |
+4954 |
+4955 |
+4956 |
+4957 |
+4958 |
+4959 |
+4960 |
+4961 |
+4962 |
+4963 |
+4964 |
+4965 |
+4966 |
+4967 |
+4968 |
+4969 |
+4970 |
+4971 |
+4972 |
+4973 |
+4974 |
+4975 |
+4976 |
+4977 |
+4978 |
+4979 |
+4980 |
+4981 |
+4982 |
+4983 |
+4984 |
+4985 |
+4986 |
+4987 |
+4988 |
+4989 |
+4990 |
+4991 |
+4992 |
+4993 |
+4994 |
+4995 |
+4996 |
+4997 |
+4998 |
+4999;
+
+type Data = {
+  error?: ErrorCode,
+};
diff --git a/tests/union_new/__snapshots__/jsfmt.spec.js.snap b/tests/union_new/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..8c6fb30c46f7
--- /dev/null
+++ b/tests/union_new/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,1768 @@
+exports[`test issue-815.js 1`] = `
+"/* @flow */
+type T = A|B;
+class U {};
+declare var children: U;
+(children: T|U);
+class A {};
+class B {};
+
+type VirtualElement = Thunk|VirtualNode;
+type Child = VirtualElement;
+type Children = Array<Child>;
+
+
+class Thunk {}
+class VirtualNode {
+  children: Child|Children;
+  constructor(type, children/*:Children*/) {
+    this.children = children.length === 1 ? children[0] :
+      children;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-824.js 1`] = `
+"import { B, C } from \"./issue-824-helper\";
+
+type K = B | C;
+
+type I = {
+  which(): number;
+};
+
+export default class A {
+  static foo(p: K): bool {
+    return false;
+  }
+  static bar(p: I & K): bool {
+    return this.foo(p);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-824-helper.js 1`] = `
+"import A from \"./issue-824\";
+
+export class B extends A {
+  which(): number {
+    return 1;
+  }
+}
+export class C extends A {
+  which(): number {
+    return 2;
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+import A from \"./issue-824\";
+export class B extends A {
+  which(): number {
+    return 1;
+  }
+}
+export class C extends A {
+  which(): number {
+    return 2;
+  }
+}
+
+"
+`;
+
+exports[`test issue-1349.js 1`] = `
+"/* @flow */
+
+var bar: Array<{b: ?boolean, c: number} | {b: boolean}> = [
+  {b: true, c: 123},
+  {b: true}
+];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1497:36)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1371.js 1`] = `
+"function create(a: any): { type: \'B\', data: number } | { type: \'A\', data: string }
+{
+  return {
+    type: \'A\',
+    data: a
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1455.js 1`] = `
+"/* @flow */
+import type {Foobar} from \"./issue-1455-helper\"
+
+function create(content: ?Foobar | String | Array<String>) {
+}
+
+function node(content: ?Foobar | String | Array<String>) {
+  create(content)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1455-helper.js 1`] = `
+"/* @flow */
+
+export class Foobar { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+export class Foobar {}
+
+"
+`;
+
+exports[`test issue-1462-i.js 1`] = `
+"type Common = {
+};
+
+type A = Common & {
+  type: \'A\',
+  foo: number
+};
+
+type B = Common & {
+  type: \'B\',
+  foo: Array<number>
+}
+
+type MyType = A | B;
+
+function print(x: number) {
+  console.log(x);
+}
+
+function printAll(val: MyType) {
+  print(val.foo);  // <--- foo could be an array
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1462-ii.js 1`] = `
+"type Common = {
+};
+
+type A = {
+  type: \'A\',
+  foo: number
+} & Common;
+
+type B = {
+  type: \'B\',
+  foo: Array<number>
+} & Common;
+
+type MyType = A | B;
+
+
+function print(x: number) {
+  console.log(x);
+}
+
+function printAll(val: MyType) {
+  if (val.type === \'A\') {
+    print(val.foo);
+  } else {
+    val.foo.forEach(print);
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1664.js 1`] = `
+"/* @flow */
+
+type DataBase = {
+  id: string,
+  name: string,
+};
+
+type UserData = DataBase & {
+  kind: \"user\",
+};
+
+type SystemData = DataBase & {
+  kind: \"system\",
+}
+
+type Data = UserData | SystemData;
+
+const data: Data = {
+  id: \"\",
+  name: \"\",
+  kind: \"system\",
+}
+
+if (data.kind === \"system\") {
+  (data: SystemData);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-1759.js 1`] = `
+"// @flow
+
+type X = ({a:true} & {b:string}) | ({a:false} & {c:string});
+//type X = {a:true, b:string} | {a:false, c:string}; // this works.
+
+function hello(x:X): string {
+  if (x.a === true) return x.b; else return x.c;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test issue-2232.js 1`] = `
+"/* @flow */
+
+declare type Entity<T> = {
+  id: T,
+  name: string
+}
+
+declare type StringEntity = Entity<string>
+
+
+declare type Foo = StringEntity & {
+  bars: Object,
+  kind: 1
+}
+declare type EmptyFoo = StringEntity &  {
+  bars: null,
+  kind: 2
+}
+
+function test(f: Foo| EmptyFoo) {
+  if (f.kind === 1) {
+    (f: Foo)
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test1.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////////////
+// example with object types
+//////////////////////////////
+
+function obj(a: A1 | A2) {
+  return a.x;
+}
+
+const obj_result = obj({ x: \"\" }); // currently an error! (expect it to be OK)
+
+// Type definitions used above are defined below, but in an order that
+// deliberately makes their full resolution as lazy as possible. The call above
+// blocks until A1 is partially resolved. Since the argument partially matches
+// A1, that branch is selected. Later, that branch errors, but other branches
+// have been lost by then.
+
+type A1 = { x: B1 };
+type A2 = { x: B2 };
+
+type B1 = number;
+type B2 = string;
+
+(obj_result: B1 | B2);
+
+///////////////////////////////////////
+// similar example with function types
+///////////////////////////////////////
+
+function fun(a: A3 | A4) {
+  return a();
+}
+
+const fun_result = fun(() => \"\");
+
+type A3 = () => B3;
+type A4 = () => B4;
+
+type B3 = number;
+type B4 = string;
+
+(fun_result: B3 | B4);
+
+/////////////////////////////////////////////
+// similar example with class instance types
+/////////////////////////////////////////////
+
+function inst(a: A5 | A6) { }
+
+class B5 { }
+class B6 { }
+inst([new B6]);
+
+type A5 = B5[];
+type A6 = B6[];
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test2.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////////////
+// example with object types
+//////////////////////////////
+
+function obj(a: { x: number } | { x: string }) { }
+
+obj(({ x: \"\" }: A1));
+
+type A1 = { x: B1 };
+
+type B1 = string;
+
+///////////////////////////////////////
+// similar example with function types
+///////////////////////////////////////
+
+function fun(a: (() => number) | (() => string)) { }
+
+fun(((() => \"\"): A2));
+
+type A2 = () => B2;
+
+type B2 = string;
+
+/////////////////////////////////////////////////////
+// similar example with generic class instance types
+/////////////////////////////////////////////////////
+
+class C<X> { }
+
+function inst(a: C<number> | C<string>) { }
+
+inst((new C: A3));
+
+type A3 = C<B3>;
+
+type B3 = string;
+
+/////////////////////////////////////////////
+// similar example with generic type aliases
+/////////////////////////////////////////////
+
+function alias(a: T<number> | T<string>) { }
+alias({ x: (x: V<B4>) => { } });
+
+type T<X> = { x: U<X> }
+type U<X> = (x: V<X>) => void;
+type V<X> = X;
+
+type B4 = string;
+
+// class statics
+
+function stat(a: { x: number } | { x: string }) { }
+
+class D {
+  static x: B5;
+}
+
+stat(D);
+
+type B5 = string;
+
+// tuples
+
+function tup(a: [number,boolean] | [string,boolean]) { }
+
+tup(([\"\",false]: A6));
+
+type A6 = [B6,boolean];
+type B6 = string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test3.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+///////////////////////////////
+// example with function types
+///////////////////////////////
+
+function fun(a: ((x: number) => void) | ((x: string) => void)) { }
+
+fun((((x) => {}): A1));
+
+type A1 = (x: B1) => void;
+
+type B1 = string;
+
+////////////////////////////
+// example with array types
+////////////////////////////
+
+function arr(a: number[] | string[]) { }
+
+arr(([]: A2));
+
+type A2 = B2[];
+
+type B2 = string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test4.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+///////////////////////////////
+// example with function types
+///////////////////////////////
+
+function fun(a: ((x: number) => void) | ((x: string) => void)) { }
+
+const a1 = ((x) => {}: A1);
+fun(a1);
+
+function fun_call(x: string) { a1(x); }
+
+type A1 = (x: B1) => void;
+
+type B1 = string;
+
+////////////////////////////
+// example with array types
+////////////////////////////
+
+function arr(a: number[] | string[]) { }
+
+const a2 = ([]: A2);
+arr(a2);
+
+function arr_set(x: string, i: number) { a2[i] = x; }
+function arr_get(i: number): string { return a2[i]; }
+
+type A2 = B2[];
+
+type B2 = string;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test5.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+///////////////////////////////
+// example with function types
+///////////////////////////////
+
+function fun(a: ((x: number) => number) | ((x: string) => string)) { }
+
+function a1(x) { return x; }
+fun(a1);
+
+function fun_call(x: string): string { return a1(x); }
+
+/////////////////////////////
+// example with array types
+/////////////////////////////
+
+function arr(a: number[] | string[]) { }
+
+var a2 = [];
+arr(a2);
+
+function arr_set(x: string, i: number) { a2[i] = x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test6.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////////////////////////
+// example with generic class inheritance
+//////////////////////////////////////////
+
+function inst(a: E<B4>): C<number> | C<string> { return a; }
+
+const mk_C = () => C;
+const mk_D = () => D;
+const mk_E = () => E;
+
+type B4 = string;
+
+const _D = mk_D();
+class E<X> extends _D<X> { }
+
+const _C = mk_C();
+class D<X> extends _C<X> { }
+
+class C<X> { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test7.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+////////////////////
+// recursive types
+////////////////////
+
+function rec(x: F1 | F2) { }
+rec({ x: 0 });
+
+type F1 = G1;
+type F2 = G2;
+type G1 = { x: H1, y?: G1 };
+type G2 = { x: H2, y?: G2 };
+type H1 = string;
+type H2 = number;
+
+///////////////////////////////
+// polymorphic recursive types
+///////////////////////////////
+
+function polyrec(x: PF<number> | PF<string>) { }
+rec({ x: 0 });
+
+type PF<X> = PG<X>;
+type PG<X> = { x: X, y?: PG<X> };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test8.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////
+// nested union types
+//////////////////////
+
+function rec(x: F1 | F2) { }
+rec({ x: 0 });
+
+type F1 = G1 | G1_;
+type F2 = G2 | G2_;
+type G1 = { x: H1 };
+type G1_ = { x: H1_ };
+type G2 = { x: H2 };
+type G2_ = { x: H2_ };
+type H1 = boolean;
+type H1_ = string;
+type H2 = boolean;
+type H2_ = number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test9.js 1`] = `
+"// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+////////////////
+// interference
+////////////////
+
+function square(x? = 0) {
+  return x * x;
+}
+
+function foo(f: ((_: ?number) => ?number) | (() => void)) { }
+foo((x): number => square(x))
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test10.js 1`] = `
+"// @noflow
+
+function id<X>(x: X): X { return x; }
+
+/////////////////////////
+// primitive annotations
+/////////////////////////
+
+function check_prim(_: number | string) { }
+
+// ok
+check_prim(\"\");
+
+// ...even when they \"flow\" in
+check_prim(id(\"\"));
+
+//////////////////////////////
+// class instance annotations
+//////////////////////////////
+
+class C { }
+class D { }
+function check_inst(_: C | D) { }
+
+// ok
+check_inst(new D);
+
+// ...even when they \"flow\" in
+check_inst(id(new C));
+
+////////////////////////
+// function annotations
+////////////////////////
+
+function check_fun(_: ((_: number) => number) | ((_: string) => string)) { }
+
+// help!
+check_fun((x) => x);
+
+//////////////////////
+// object annotations
+//////////////////////
+
+function check_obj(_: { x: number } | { x: string }) { }
+
+// ok
+check_obj({ x: \"\" });
+
+// help!
+check_obj({ x: id(\"\") });
+
+/////////////////////
+// array annotations
+/////////////////////
+
+function check_arr(_: number[] | string[]) { }
+
+// ok
+check_arr([\"\"]);
+
+// help!
+check_arr([id(\"\")]);
+
+//////////////////////////////////////
+// generic class instance annotations
+//////////////////////////////////////
+
+class P<X> { }
+function check_poly_inst(_: P<number> | P<string>) { }
+
+// help!
+check_poly_inst(new P);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test11.js 1`] = `
+"// @noflow
+
+// disjoint unions
+
+function length(list: List) {
+  if (list.kind === \"cons\") return length(list.next) + 1;
+  else return 0;
+}
+
+
+length({ kind: \"nil\" });
+length({ kind: \"cons\" }); // missing \`next\`
+length({ kind: \"cons\", next: { kind: \"nil\" } });
+length({ kind: \"empty\" }); // \`kind\` not found
+
+type List = Nil | Cons;
+type Nil = { kind: \"nil\" };
+type Cons = { kind: \"cons\", next: List };
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test12.js 1`] = `
+"// @noflow
+
+// polymorphic recursive types
+
+type F<X> = { f: F<X>, x: X }
+type G = { x: number }
+type H = { x: string }
+
+function rec(x: F<string>): G | H { return x; }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test13.js 1`] = `
+"// @noflow
+
+/* ensure there are no unintended side effects when trying branches */
+
+({type: \'B\', id: \'hi\'}: {
+  type: \'A\';
+  id: ?string;
+} | {
+  type: \'B\';
+  id: string;
+});
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test14.js 1`] = `
+"// @noflow
+
+// annotations
+
+declare class C<X> {
+  get(): X;
+}
+
+function union(o: { x: string } | { x: number }) { }
+
+function foo(c: C<number>) {
+  union({ x: c.get() });
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test15.js 1`] = `
+"// @noflow
+
+// functions as objects
+
+function foo<X>(target: EventTarget) {
+  target.addEventListener(\'click\', (e) => {});
+}
+
+declare class EventTarget {
+  addEventListener(type: \'foo\', listener: KeyboardEventHandler): void;
+  addEventListener(type: string, listener: EventHandler): void;
+}
+
+declare class Event { }
+declare class KeyboardEvent { }
+
+type EventHandler = (event: Event) => mixed
+type KeyboardEventHandler = (event: KeyboardEvent) => mixed
+
+// example where globals are not yet resolved
+
+function bar(x: (() => void) | { x: number }) { }
+
+bar(() => { });
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test16.js 1`] = `
+"// @noflow
+
+// annotations
+
+type T = number | (() => string);
+type Foo = T | (() => bool);
+
+type Bar = number | (() => string) | (() => bool);
+
+function foo(x: Foo) { }
+foo(() => qux());
+
+function bar(x: Bar) { }
+bar(() => qux());
+
+var x = false;
+function qux() { return x; }
+x = \"\";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test17.js 1`] = `
+"// @noflow
+
+// Array#concat
+
+[].concat([]);
+
+([].concat([0,1])[1]: string)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @noflow
+// Array#concat
+[  ].concat([  ]);
+([  ].concat([ 0, 1 ])[1]: string);
+
+"
+`;
+
+exports[`test test18.js 1`] = `
+"// @noflow
+
+// method overloads
+
+declare class C {
+  m(x: number): void;
+  m(x: string): void;
+}
+
+function f() { return 0; }
+
+new C().m(f());
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test19.js 1`] = `
+"// @noflow
+
+// constructor overloads
+
+function m<X>() {
+  return new D();
+}
+
+declare class D {
+  constructor(_: void): void;
+  constructor(_: null): void;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:340:16)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test20.js 1`] = `
+"// @noflow
+
+// Array#reduce
+
+[0,1].reduce((x,y,i) => y);
+
+[\"a\", \"b\"].reduce(
+  (regex, representation, index) => {
+    return regex + (index ? \'|\' : \'\') + \'(\' + representation + \')\';
+  },
+  \'\',
+);
+
+[\"\"].reduce((acc,str) => acc * str.length);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @noflow
+// Array#reduce
+[ 0, 1 ].reduce((x, y, i) => y);
+[ \"a\", \"b\" ].reduce(
+  (regex, representation, index) => {
+    return regex + ((index ? \"|\" : \"\")) + \"(\" + representation + \")\";
+  },
+  \"\"
+);
+[ \"\" ].reduce((acc, str) => acc * str.length);
+
+"
+`;
+
+exports[`test test21.js 1`] = `
+"// @noflow
+
+// annotations for disjoint unions
+
+type T =
+  | { type: \"FOO\", x: number }
+  | { type: \"BAR\", x: string }
+
+({ type: (bar(): \"BAR\"), x: str() }: T);
+
+({ type: bar(), x: str() }: T);
+
+({ type: bar(), x: (str(): string) }: T);
+
+function bar() {
+  return \"BAR\";
+}
+
+function str() {
+  return \"hello\";
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test22.js 1`] = `
+"// @noflow
+
+// refinement of disjoint unions
+
+type Empty = { }
+
+type Success = {
+  type: \'SUCCESS\';
+  result: string;
+};
+
+type Error = {
+  type: \'ERROR\';
+} & Empty;
+
+export type T = Success | Error;
+
+function foo(x: T) {
+  if (x.type === \'SUCCESS\') return x.result;
+  else return x.result;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test23.js 1`] = `
+"// @noflow
+
+// nested intersections (see also lib/test23_lib.js)
+
+type NestedObj = { } & { dummy: SomeLibClass };
+
+type Obj = NestedObj & { x: string };
+
+function foo(obj: Obj) {
+  obj.x; // should be OK
+  obj.x; // should also be OK (the check above shouldn\'t affect anything)
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test24.js 1`] = `
+"// @noflow
+
+// scaling test for full type resolution
+
+declare class C {
+  addListener(event: string, listener: Function): C;
+  emit(event: string, ...args:Array<any>): boolean;
+  listeners(event: string): Array<Function>;
+  listenerCount(event: string): number;
+  on(event: string, listener: Function): C;
+  once(event: string, listener: Function): C;
+  removeAllListeners(event?: string): C;
+  removeListener(event: string, listener: Function): C;
+  setMaxListeners(n: number): void;
+}
+
+declare class D extends C {
+  listen(port: number, hostname?: string, backlog?: number, callback?: Function): D;
+  listen(path: string, callback?: Function): D;
+  listen(handle: Object, callback?: Function): D;
+  close(callback?: Function): D;
+  address(): number;
+  connections: number;
+  maxConnections: number;
+  getConnections(callback: Function): void;
+  ref():  D;
+  unref():  D;
+}
+
+(0: D | number);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test25.js 1`] = `
+"// @noflow
+
+// termination test (see also lib/test25_lib.js)
+
+function foo(rows: Rows, set: Set<number>) {
+  return rows.reduce_rows(
+    (set, row) => row.reduce_row(
+      (set, i) => set.add(i),
+      set,
+    ),
+    set,
+  );
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test26.js 1`] = `
+"// @noflow
+
+declare function foo(x: number): number;
+declare function foo(x: string): string;
+
+declare var x: number | string;
+
+(foo(x): number | string);
+
+type T = number | string;
+declare var y: T;
+
+(foo(y): T);
+
+declare class Record {
+  set(x: \'foo\', y: number): void;
+  set(x: \'bar\', y: string): void;
+}
+
+new Record().set(\'foo\', \"42\");
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1254:25)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test27.js 1`] = `
+"// @noflow
+
+type X = ({a:true} & {b:string}) | ({a:false} & {c:string});
+//type X = {a:true, b:string} | {a:false, c:string}; // this works.
+
+function hello1(x:X): string {
+  if (x.a === true) return x.b; else return x.c;
+}
+
+function hello2(x:X): string {
+  if (x.a === false) return x.c; else return x.b;
+}
+
+function hello3(x:X): string {
+  if (x.a) { return x.b; } else { return x.c; }
+}
+
+function hello4(x:X): string {
+  if (!x.a) { return x.c; } else { return x.b; }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1407
+      return fromString(\" & \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1407:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.map (/src/fast-path.js:167:19)
+    at genericPrintNoParens (/src/printer.js:1530:42)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test29.js 1`] = `
+"// @noflow
+
+// Make sure caching doesn\'t cause a spurious successful match (e.g., when a
+// failed match is tried again). This may happen, e.g., when checking
+// polymorphic definitions, where the same code may be checked multiple times
+// with different instantiations.
+
+type Row = { x: string };
+
+declare class D<T> {
+  reduce(
+    callbackfn: (previousValue: T, currentValue: T) => T,
+    initialValue: void
+  ): T;
+  reduce<U>(
+    callbackfn: (previousValue: U, currentValue: T) => U,
+    initialValue: U
+  ): U;
+}
+
+class C {
+  foo(
+    rows: D<Row>,
+    minWidth: number,
+  ): number {
+    return rows.reduce(
+      (length, row) => 0,
+      minWidth,
+    );
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1368:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test30.js 1`] = `
+"// @noflow
+
+const Constants = require(\'./test30-helper\');
+
+type ActionType =
+  | { type: \'foo\', x: number }
+  | { type: \'bar\', x: number }
+
+({ type: Constants.BAR, x: 0 }: ActionType);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1530
+      return fromString(\" | \").join(path.map(print, \"types\"));
+                               ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1530:32)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1481:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test30-helper.js 1`] = `
+"// @noflow
+
+module.exports = {
+  FOO: \'foo\',
+  BAR: \'bar\',
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @noflow
+module.exports = { FOO: \"foo\", BAR: \"bar\" };
+
+"
+`;
+
+exports[`test test31.js 1`] = `
+"// @noflow
+
+// make sure tuples are type arguments (as used e.g. when viewing maps as
+// key/value iterables) work
+
+interface SomeIterator<T> { }
+
+interface SomeIterable<T> {
+  it(): SomeIterator<T>;
+}
+
+declare class SomeMap<K,V> {
+  it(): SomeIterator<[K,V]>;
+  set(k: K, v: V): void;
+}
+
+declare class ImmutableMap<K,V> { }
+
+declare function convert<K,V>(iter: SomeIterable<[K,V]>): ImmutableMap<K,V>;
+
+function foo(): ImmutableMap<string, boolean> {
+  const countersGlobalMap = new SomeMap();
+  countersGlobalMap.set(\"\", false);
+  return convert(countersGlobalMap);
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1384:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test32.js 1`] = `
+"// @flow
+
+// make sure that full resolution jobs don\'t cache improperly to signal success
+// when they have failed earlier
+
+function foo(value: Indirect<string> | number): Indirect<string> | number {
+  const castedValue: number = typeof value === \'number\' ? value : 0;
+  return castedValue;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1374:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/union_new/issue-1349.js b/tests/union_new/issue-1349.js
new file mode 100644
index 000000000000..3bb5c9f3ba3c
--- /dev/null
+++ b/tests/union_new/issue-1349.js
@@ -0,0 +1,6 @@
+/* @flow */
+
+var bar: Array<{b: ?boolean, c: number} | {b: boolean}> = [
+  {b: true, c: 123},
+  {b: true}
+];
diff --git a/tests/union_new/issue-1371.js b/tests/union_new/issue-1371.js
new file mode 100644
index 000000000000..e46b4059ea6b
--- /dev/null
+++ b/tests/union_new/issue-1371.js
@@ -0,0 +1,7 @@
+function create(a: any): { type: 'B', data: number } | { type: 'A', data: string }
+{
+  return {
+    type: 'A',
+    data: a
+  }
+}
diff --git a/tests/union_new/issue-1455-helper.js b/tests/union_new/issue-1455-helper.js
new file mode 100644
index 000000000000..a483642f8423
--- /dev/null
+++ b/tests/union_new/issue-1455-helper.js
@@ -0,0 +1,3 @@
+/* @flow */
+
+export class Foobar { }
diff --git a/tests/union_new/issue-1455.js b/tests/union_new/issue-1455.js
new file mode 100644
index 000000000000..1163aaf93311
--- /dev/null
+++ b/tests/union_new/issue-1455.js
@@ -0,0 +1,9 @@
+/* @flow */
+import type {Foobar} from "./issue-1455-helper"
+
+function create(content: ?Foobar | String | Array<String>) {
+}
+
+function node(content: ?Foobar | String | Array<String>) {
+  create(content)
+}
diff --git a/tests/union_new/issue-1462-i.js b/tests/union_new/issue-1462-i.js
new file mode 100644
index 000000000000..e844d3b78221
--- /dev/null
+++ b/tests/union_new/issue-1462-i.js
@@ -0,0 +1,22 @@
+type Common = {
+};
+
+type A = Common & {
+  type: 'A',
+  foo: number
+};
+
+type B = Common & {
+  type: 'B',
+  foo: Array<number>
+}
+
+type MyType = A | B;
+
+function print(x: number) {
+  console.log(x);
+}
+
+function printAll(val: MyType) {
+  print(val.foo);  // <--- foo could be an array
+}
diff --git a/tests/union_new/issue-1462-ii.js b/tests/union_new/issue-1462-ii.js
new file mode 100644
index 000000000000..260eb7c19017
--- /dev/null
+++ b/tests/union_new/issue-1462-ii.js
@@ -0,0 +1,27 @@
+type Common = {
+};
+
+type A = {
+  type: 'A',
+  foo: number
+} & Common;
+
+type B = {
+  type: 'B',
+  foo: Array<number>
+} & Common;
+
+type MyType = A | B;
+
+
+function print(x: number) {
+  console.log(x);
+}
+
+function printAll(val: MyType) {
+  if (val.type === 'A') {
+    print(val.foo);
+  } else {
+    val.foo.forEach(print);
+  }
+}
diff --git a/tests/union_new/issue-1664.js b/tests/union_new/issue-1664.js
new file mode 100644
index 000000000000..e2d1e2d50425
--- /dev/null
+++ b/tests/union_new/issue-1664.js
@@ -0,0 +1,26 @@
+/* @flow */
+
+type DataBase = {
+  id: string,
+  name: string,
+};
+
+type UserData = DataBase & {
+  kind: "user",
+};
+
+type SystemData = DataBase & {
+  kind: "system",
+}
+
+type Data = UserData | SystemData;
+
+const data: Data = {
+  id: "",
+  name: "",
+  kind: "system",
+}
+
+if (data.kind === "system") {
+  (data: SystemData);
+}
diff --git a/tests/union_new/issue-1759.js b/tests/union_new/issue-1759.js
new file mode 100644
index 000000000000..af3a1a3fe51f
--- /dev/null
+++ b/tests/union_new/issue-1759.js
@@ -0,0 +1,8 @@
+// @flow
+
+type X = ({a:true} & {b:string}) | ({a:false} & {c:string});
+//type X = {a:true, b:string} | {a:false, c:string}; // this works.
+
+function hello(x:X): string {
+  if (x.a === true) return x.b; else return x.c;
+}
diff --git a/tests/union_new/issue-2232.js b/tests/union_new/issue-2232.js
new file mode 100644
index 000000000000..2401f36058f5
--- /dev/null
+++ b/tests/union_new/issue-2232.js
@@ -0,0 +1,24 @@
+/* @flow */
+
+declare type Entity<T> = {
+  id: T,
+  name: string
+}
+
+declare type StringEntity = Entity<string>
+
+
+declare type Foo = StringEntity & {
+  bars: Object,
+  kind: 1
+}
+declare type EmptyFoo = StringEntity &  {
+  bars: null,
+  kind: 2
+}
+
+function test(f: Foo| EmptyFoo) {
+  if (f.kind === 1) {
+    (f: Foo)
+  }
+}
diff --git a/tests/union_new/issue-815.js b/tests/union_new/issue-815.js
new file mode 100644
index 000000000000..44f2bed4b095
--- /dev/null
+++ b/tests/union_new/issue-815.js
@@ -0,0 +1,21 @@
+/* @flow */
+type T = A|B;
+class U {};
+declare var children: U;
+(children: T|U);
+class A {};
+class B {};
+
+type VirtualElement = Thunk|VirtualNode;
+type Child = VirtualElement;
+type Children = Array<Child>;
+
+
+class Thunk {}
+class VirtualNode {
+  children: Child|Children;
+  constructor(type, children/*:Children*/) {
+    this.children = children.length === 1 ? children[0] :
+      children;
+  }
+}
diff --git a/tests/union_new/issue-824-helper.js b/tests/union_new/issue-824-helper.js
new file mode 100644
index 000000000000..289eb998e500
--- /dev/null
+++ b/tests/union_new/issue-824-helper.js
@@ -0,0 +1,12 @@
+import A from "./issue-824";
+
+export class B extends A {
+  which(): number {
+    return 1;
+  }
+}
+export class C extends A {
+  which(): number {
+    return 2;
+  }
+}
diff --git a/tests/union_new/issue-824.js b/tests/union_new/issue-824.js
new file mode 100644
index 000000000000..655e03d1391b
--- /dev/null
+++ b/tests/union_new/issue-824.js
@@ -0,0 +1,16 @@
+import { B, C } from "./issue-824-helper";
+
+type K = B | C;
+
+type I = {
+  which(): number;
+};
+
+export default class A {
+  static foo(p: K): bool {
+    return false;
+  }
+  static bar(p: I & K): bool {
+    return this.foo(p);
+  }
+}
diff --git a/tests/union_new/jsfmt.spec.js b/tests/union_new/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/union_new/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/union_new/lib/__snapshots__/jsfmt.spec.js.snap b/tests/union_new/lib/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fe17b3fb98ef
--- /dev/null
+++ b/tests/union_new/lib/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,69 @@
+exports[`test test23_lib.js 1`] = `
+"declare class SomeLibClass { }
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare class SomeLibClass {}
+
+"
+`;
+
+exports[`test test25_lib.js 1`] = `
+"declare class Set<T> {
+    add(): Set<T>;
+}
+
+declare class Row {
+    reduce_row(
+      callbackfn: (previousValue: number, currentValue: number) => number,
+      initialValue: void
+    ): number;
+    reduce_row<U>(
+      callbackfn: (previousValue: U, currentValue: number) => U,
+      initialValue: U
+    ): U;
+}
+
+declare class Rows {
+    reduce_rows<X>(
+      callbackfn: (previousValue: X, currentValue: Row) => X,
+      initialValue: X
+    ): X;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1348
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1348:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1452:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
+
+exports[`test test32_lib.js 1`] = `
+"type Indirect<T> = Array<T>;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/src/printer.js:1497
+        fromString(\", \").join(path.map(print, \"params\")),
+                         ^
+
+TypeError: fromString(...).join is not a function
+    at genericPrintNoParens (/src/printer.js:1497:26)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+    at printGenerically (/src/printer.js:111:12)
+    at FastPath.call (/src/fast-path.js:113:16)
+    at genericPrintNoParens (/src/printer.js:1479:14)
+    at genericPrint (/src/printer.js:166:7)
+    at p (/src/printer.js:111:37)
+    at exports.printComments (/src/comments.js:327:20)
+"
+`;
diff --git a/tests/union_new/lib/jsfmt.spec.js b/tests/union_new/lib/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/union_new/lib/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/union_new/lib/test23_lib.js b/tests/union_new/lib/test23_lib.js
new file mode 100644
index 000000000000..a0b41766ae6e
--- /dev/null
+++ b/tests/union_new/lib/test23_lib.js
@@ -0,0 +1 @@
+declare class SomeLibClass { }
diff --git a/tests/union_new/lib/test25_lib.js b/tests/union_new/lib/test25_lib.js
new file mode 100644
index 000000000000..d79c71a20c19
--- /dev/null
+++ b/tests/union_new/lib/test25_lib.js
@@ -0,0 +1,21 @@
+declare class Set<T> {
+    add(): Set<T>;
+}
+
+declare class Row {
+    reduce_row(
+      callbackfn: (previousValue: number, currentValue: number) => number,
+      initialValue: void
+    ): number;
+    reduce_row<U>(
+      callbackfn: (previousValue: U, currentValue: number) => U,
+      initialValue: U
+    ): U;
+}
+
+declare class Rows {
+    reduce_rows<X>(
+      callbackfn: (previousValue: X, currentValue: Row) => X,
+      initialValue: X
+    ): X;
+}
diff --git a/tests/union_new/lib/test32_lib.js b/tests/union_new/lib/test32_lib.js
new file mode 100644
index 000000000000..e0daf1518b2f
--- /dev/null
+++ b/tests/union_new/lib/test32_lib.js
@@ -0,0 +1 @@
+type Indirect<T> = Array<T>;
diff --git a/tests/union_new/test1.js b/tests/union_new/test1.js
new file mode 100644
index 000000000000..10758e4134b2
--- /dev/null
+++ b/tests/union_new/test1.js
@@ -0,0 +1,60 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////////////
+// example with object types
+//////////////////////////////
+
+function obj(a: A1 | A2) {
+  return a.x;
+}
+
+const obj_result = obj({ x: "" }); // currently an error! (expect it to be OK)
+
+// Type definitions used above are defined below, but in an order that
+// deliberately makes their full resolution as lazy as possible. The call above
+// blocks until A1 is partially resolved. Since the argument partially matches
+// A1, that branch is selected. Later, that branch errors, but other branches
+// have been lost by then.
+
+type A1 = { x: B1 };
+type A2 = { x: B2 };
+
+type B1 = number;
+type B2 = string;
+
+(obj_result: B1 | B2);
+
+///////////////////////////////////////
+// similar example with function types
+///////////////////////////////////////
+
+function fun(a: A3 | A4) {
+  return a();
+}
+
+const fun_result = fun(() => "");
+
+type A3 = () => B3;
+type A4 = () => B4;
+
+type B3 = number;
+type B4 = string;
+
+(fun_result: B3 | B4);
+
+/////////////////////////////////////////////
+// similar example with class instance types
+/////////////////////////////////////////////
+
+function inst(a: A5 | A6) { }
+
+class B5 { }
+class B6 { }
+inst([new B6]);
+
+type A5 = B5[];
+type A6 = B6[];
diff --git a/tests/union_new/test10.js b/tests/union_new/test10.js
new file mode 100644
index 000000000000..deaa835fe346
--- /dev/null
+++ b/tests/union_new/test10.js
@@ -0,0 +1,72 @@
+// @noflow
+
+function id<X>(x: X): X { return x; }
+
+/////////////////////////
+// primitive annotations
+/////////////////////////
+
+function check_prim(_: number | string) { }
+
+// ok
+check_prim("");
+
+// ...even when they "flow" in
+check_prim(id(""));
+
+//////////////////////////////
+// class instance annotations
+//////////////////////////////
+
+class C { }
+class D { }
+function check_inst(_: C | D) { }
+
+// ok
+check_inst(new D);
+
+// ...even when they "flow" in
+check_inst(id(new C));
+
+////////////////////////
+// function annotations
+////////////////////////
+
+function check_fun(_: ((_: number) => number) | ((_: string) => string)) { }
+
+// help!
+check_fun((x) => x);
+
+//////////////////////
+// object annotations
+//////////////////////
+
+function check_obj(_: { x: number } | { x: string }) { }
+
+// ok
+check_obj({ x: "" });
+
+// help!
+check_obj({ x: id("") });
+
+/////////////////////
+// array annotations
+/////////////////////
+
+function check_arr(_: number[] | string[]) { }
+
+// ok
+check_arr([""]);
+
+// help!
+check_arr([id("")]);
+
+//////////////////////////////////////
+// generic class instance annotations
+//////////////////////////////////////
+
+class P<X> { }
+function check_poly_inst(_: P<number> | P<string>) { }
+
+// help!
+check_poly_inst(new P);
diff --git a/tests/union_new/test11.js b/tests/union_new/test11.js
new file mode 100644
index 000000000000..c5a02b7fbf81
--- /dev/null
+++ b/tests/union_new/test11.js
@@ -0,0 +1,18 @@
+// @noflow
+
+// disjoint unions
+
+function length(list: List) {
+  if (list.kind === "cons") return length(list.next) + 1;
+  else return 0;
+}
+
+
+length({ kind: "nil" });
+length({ kind: "cons" }); // missing `next`
+length({ kind: "cons", next: { kind: "nil" } });
+length({ kind: "empty" }); // `kind` not found
+
+type List = Nil | Cons;
+type Nil = { kind: "nil" };
+type Cons = { kind: "cons", next: List };
diff --git a/tests/union_new/test12.js b/tests/union_new/test12.js
new file mode 100644
index 000000000000..45aff3456d35
--- /dev/null
+++ b/tests/union_new/test12.js
@@ -0,0 +1,9 @@
+// @noflow
+
+// polymorphic recursive types
+
+type F<X> = { f: F<X>, x: X }
+type G = { x: number }
+type H = { x: string }
+
+function rec(x: F<string>): G | H { return x; }
diff --git a/tests/union_new/test13.js b/tests/union_new/test13.js
new file mode 100644
index 000000000000..89333fc536a4
--- /dev/null
+++ b/tests/union_new/test13.js
@@ -0,0 +1,11 @@
+// @noflow
+
+/* ensure there are no unintended side effects when trying branches */
+
+({type: 'B', id: 'hi'}: {
+  type: 'A';
+  id: ?string;
+} | {
+  type: 'B';
+  id: string;
+});
diff --git a/tests/union_new/test14.js b/tests/union_new/test14.js
new file mode 100644
index 000000000000..8b69352cd591
--- /dev/null
+++ b/tests/union_new/test14.js
@@ -0,0 +1,13 @@
+// @noflow
+
+// annotations
+
+declare class C<X> {
+  get(): X;
+}
+
+function union(o: { x: string } | { x: number }) { }
+
+function foo(c: C<number>) {
+  union({ x: c.get() });
+}
diff --git a/tests/union_new/test15.js b/tests/union_new/test15.js
new file mode 100644
index 000000000000..c5660df4e330
--- /dev/null
+++ b/tests/union_new/test15.js
@@ -0,0 +1,24 @@
+// @noflow
+
+// functions as objects
+
+function foo<X>(target: EventTarget) {
+  target.addEventListener('click', (e) => {});
+}
+
+declare class EventTarget {
+  addEventListener(type: 'foo', listener: KeyboardEventHandler): void;
+  addEventListener(type: string, listener: EventHandler): void;
+}
+
+declare class Event { }
+declare class KeyboardEvent { }
+
+type EventHandler = (event: Event) => mixed
+type KeyboardEventHandler = (event: KeyboardEvent) => mixed
+
+// example where globals are not yet resolved
+
+function bar(x: (() => void) | { x: number }) { }
+
+bar(() => { });
diff --git a/tests/union_new/test16.js b/tests/union_new/test16.js
new file mode 100644
index 000000000000..0debe2bd0a86
--- /dev/null
+++ b/tests/union_new/test16.js
@@ -0,0 +1,18 @@
+// @noflow
+
+// annotations
+
+type T = number | (() => string);
+type Foo = T | (() => bool);
+
+type Bar = number | (() => string) | (() => bool);
+
+function foo(x: Foo) { }
+foo(() => qux());
+
+function bar(x: Bar) { }
+bar(() => qux());
+
+var x = false;
+function qux() { return x; }
+x = "";
diff --git a/tests/union_new/test17.js b/tests/union_new/test17.js
new file mode 100644
index 000000000000..919fa91246c5
--- /dev/null
+++ b/tests/union_new/test17.js
@@ -0,0 +1,7 @@
+// @noflow
+
+// Array#concat
+
+[].concat([]);
+
+([].concat([0,1])[1]: string)
diff --git a/tests/union_new/test18.js b/tests/union_new/test18.js
new file mode 100644
index 000000000000..6ae2bbd21c8c
--- /dev/null
+++ b/tests/union_new/test18.js
@@ -0,0 +1,12 @@
+// @noflow
+
+// method overloads
+
+declare class C {
+  m(x: number): void;
+  m(x: string): void;
+}
+
+function f() { return 0; }
+
+new C().m(f());
diff --git a/tests/union_new/test19.js b/tests/union_new/test19.js
new file mode 100644
index 000000000000..2178cdf8a7d0
--- /dev/null
+++ b/tests/union_new/test19.js
@@ -0,0 +1,12 @@
+// @noflow
+
+// constructor overloads
+
+function m<X>() {
+  return new D();
+}
+
+declare class D {
+  constructor(_: void): void;
+  constructor(_: null): void;
+}
diff --git a/tests/union_new/test2.js b/tests/union_new/test2.js
new file mode 100644
index 000000000000..4647de3ccdfb
--- /dev/null
+++ b/tests/union_new/test2.js
@@ -0,0 +1,77 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////////////
+// example with object types
+//////////////////////////////
+
+function obj(a: { x: number } | { x: string }) { }
+
+obj(({ x: "" }: A1));
+
+type A1 = { x: B1 };
+
+type B1 = string;
+
+///////////////////////////////////////
+// similar example with function types
+///////////////////////////////////////
+
+function fun(a: (() => number) | (() => string)) { }
+
+fun(((() => ""): A2));
+
+type A2 = () => B2;
+
+type B2 = string;
+
+/////////////////////////////////////////////////////
+// similar example with generic class instance types
+/////////////////////////////////////////////////////
+
+class C<X> { }
+
+function inst(a: C<number> | C<string>) { }
+
+inst((new C: A3));
+
+type A3 = C<B3>;
+
+type B3 = string;
+
+/////////////////////////////////////////////
+// similar example with generic type aliases
+/////////////////////////////////////////////
+
+function alias(a: T<number> | T<string>) { }
+alias({ x: (x: V<B4>) => { } });
+
+type T<X> = { x: U<X> }
+type U<X> = (x: V<X>) => void;
+type V<X> = X;
+
+type B4 = string;
+
+// class statics
+
+function stat(a: { x: number } | { x: string }) { }
+
+class D {
+  static x: B5;
+}
+
+stat(D);
+
+type B5 = string;
+
+// tuples
+
+function tup(a: [number,boolean] | [string,boolean]) { }
+
+tup((["",false]: A6));
+
+type A6 = [B6,boolean];
+type B6 = string;
diff --git a/tests/union_new/test20.js b/tests/union_new/test20.js
new file mode 100644
index 000000000000..1aaab84f7941
--- /dev/null
+++ b/tests/union_new/test20.js
@@ -0,0 +1,14 @@
+// @noflow
+
+// Array#reduce
+
+[0,1].reduce((x,y,i) => y);
+
+["a", "b"].reduce(
+  (regex, representation, index) => {
+    return regex + (index ? '|' : '') + '(' + representation + ')';
+  },
+  '',
+);
+
+[""].reduce((acc,str) => acc * str.length);
diff --git a/tests/union_new/test21.js b/tests/union_new/test21.js
new file mode 100644
index 000000000000..9f68c9485371
--- /dev/null
+++ b/tests/union_new/test21.js
@@ -0,0 +1,21 @@
+// @noflow
+
+// annotations for disjoint unions
+
+type T =
+  | { type: "FOO", x: number }
+  | { type: "BAR", x: string }
+
+({ type: (bar(): "BAR"), x: str() }: T);
+
+({ type: bar(), x: str() }: T);
+
+({ type: bar(), x: (str(): string) }: T);
+
+function bar() {
+  return "BAR";
+}
+
+function str() {
+  return "hello";
+}
diff --git a/tests/union_new/test22.js b/tests/union_new/test22.js
new file mode 100644
index 000000000000..2b7a263f859b
--- /dev/null
+++ b/tests/union_new/test22.js
@@ -0,0 +1,21 @@
+// @noflow
+
+// refinement of disjoint unions
+
+type Empty = { }
+
+type Success = {
+  type: 'SUCCESS';
+  result: string;
+};
+
+type Error = {
+  type: 'ERROR';
+} & Empty;
+
+export type T = Success | Error;
+
+function foo(x: T) {
+  if (x.type === 'SUCCESS') return x.result;
+  else return x.result;
+}
diff --git a/tests/union_new/test23.js b/tests/union_new/test23.js
new file mode 100644
index 000000000000..ad65416fcffa
--- /dev/null
+++ b/tests/union_new/test23.js
@@ -0,0 +1,12 @@
+// @noflow
+
+// nested intersections (see also lib/test23_lib.js)
+
+type NestedObj = { } & { dummy: SomeLibClass };
+
+type Obj = NestedObj & { x: string };
+
+function foo(obj: Obj) {
+  obj.x; // should be OK
+  obj.x; // should also be OK (the check above shouldn't affect anything)
+}
diff --git a/tests/union_new/test24.js b/tests/union_new/test24.js
new file mode 100644
index 000000000000..98d2d704242d
--- /dev/null
+++ b/tests/union_new/test24.js
@@ -0,0 +1,30 @@
+// @noflow
+
+// scaling test for full type resolution
+
+declare class C {
+  addListener(event: string, listener: Function): C;
+  emit(event: string, ...args:Array<any>): boolean;
+  listeners(event: string): Array<Function>;
+  listenerCount(event: string): number;
+  on(event: string, listener: Function): C;
+  once(event: string, listener: Function): C;
+  removeAllListeners(event?: string): C;
+  removeListener(event: string, listener: Function): C;
+  setMaxListeners(n: number): void;
+}
+
+declare class D extends C {
+  listen(port: number, hostname?: string, backlog?: number, callback?: Function): D;
+  listen(path: string, callback?: Function): D;
+  listen(handle: Object, callback?: Function): D;
+  close(callback?: Function): D;
+  address(): number;
+  connections: number;
+  maxConnections: number;
+  getConnections(callback: Function): void;
+  ref():  D;
+  unref():  D;
+}
+
+(0: D | number);
diff --git a/tests/union_new/test25.js b/tests/union_new/test25.js
new file mode 100644
index 000000000000..581bed11d031
--- /dev/null
+++ b/tests/union_new/test25.js
@@ -0,0 +1,13 @@
+// @noflow
+
+// termination test (see also lib/test25_lib.js)
+
+function foo(rows: Rows, set: Set<number>) {
+  return rows.reduce_rows(
+    (set, row) => row.reduce_row(
+      (set, i) => set.add(i),
+      set,
+    ),
+    set,
+  );
+}
diff --git a/tests/union_new/test26.js b/tests/union_new/test26.js
new file mode 100644
index 000000000000..501c49c1eaa2
--- /dev/null
+++ b/tests/union_new/test26.js
@@ -0,0 +1,20 @@
+// @noflow
+
+declare function foo(x: number): number;
+declare function foo(x: string): string;
+
+declare var x: number | string;
+
+(foo(x): number | string);
+
+type T = number | string;
+declare var y: T;
+
+(foo(y): T);
+
+declare class Record {
+  set(x: 'foo', y: number): void;
+  set(x: 'bar', y: string): void;
+}
+
+new Record().set('foo', "42");
diff --git a/tests/union_new/test27.js b/tests/union_new/test27.js
new file mode 100644
index 000000000000..823609224da8
--- /dev/null
+++ b/tests/union_new/test27.js
@@ -0,0 +1,20 @@
+// @noflow
+
+type X = ({a:true} & {b:string}) | ({a:false} & {c:string});
+//type X = {a:true, b:string} | {a:false, c:string}; // this works.
+
+function hello1(x:X): string {
+  if (x.a === true) return x.b; else return x.c;
+}
+
+function hello2(x:X): string {
+  if (x.a === false) return x.c; else return x.b;
+}
+
+function hello3(x:X): string {
+  if (x.a) { return x.b; } else { return x.c; }
+}
+
+function hello4(x:X): string {
+  if (!x.a) { return x.c; } else { return x.b; }
+}
diff --git a/tests/union_new/test29.js b/tests/union_new/test29.js
new file mode 100644
index 000000000000..5db89360ada5
--- /dev/null
+++ b/tests/union_new/test29.js
@@ -0,0 +1,31 @@
+// @noflow
+
+// Make sure caching doesn't cause a spurious successful match (e.g., when a
+// failed match is tried again). This may happen, e.g., when checking
+// polymorphic definitions, where the same code may be checked multiple times
+// with different instantiations.
+
+type Row = { x: string };
+
+declare class D<T> {
+  reduce(
+    callbackfn: (previousValue: T, currentValue: T) => T,
+    initialValue: void
+  ): T;
+  reduce<U>(
+    callbackfn: (previousValue: U, currentValue: T) => U,
+    initialValue: U
+  ): U;
+}
+
+class C {
+  foo(
+    rows: D<Row>,
+    minWidth: number,
+  ): number {
+    return rows.reduce(
+      (length, row) => 0,
+      minWidth,
+    );
+  }
+}
diff --git a/tests/union_new/test3.js b/tests/union_new/test3.js
new file mode 100644
index 000000000000..fd12e5fd150f
--- /dev/null
+++ b/tests/union_new/test3.js
@@ -0,0 +1,29 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+///////////////////////////////
+// example with function types
+///////////////////////////////
+
+function fun(a: ((x: number) => void) | ((x: string) => void)) { }
+
+fun((((x) => {}): A1));
+
+type A1 = (x: B1) => void;
+
+type B1 = string;
+
+////////////////////////////
+// example with array types
+////////////////////////////
+
+function arr(a: number[] | string[]) { }
+
+arr(([]: A2));
+
+type A2 = B2[];
+
+type B2 = string;
diff --git a/tests/union_new/test30-helper.js b/tests/union_new/test30-helper.js
new file mode 100644
index 000000000000..b4eccdb14226
--- /dev/null
+++ b/tests/union_new/test30-helper.js
@@ -0,0 +1,6 @@
+// @noflow
+
+module.exports = {
+  FOO: 'foo',
+  BAR: 'bar',
+}
diff --git a/tests/union_new/test30.js b/tests/union_new/test30.js
new file mode 100644
index 000000000000..96ec6ec5618c
--- /dev/null
+++ b/tests/union_new/test30.js
@@ -0,0 +1,9 @@
+// @noflow
+
+const Constants = require('./test30-helper');
+
+type ActionType =
+  | { type: 'foo', x: number }
+  | { type: 'bar', x: number }
+
+({ type: Constants.BAR, x: 0 }: ActionType);
diff --git a/tests/union_new/test31.js b/tests/union_new/test31.js
new file mode 100644
index 000000000000..23c2642bb22f
--- /dev/null
+++ b/tests/union_new/test31.js
@@ -0,0 +1,25 @@
+// @noflow
+
+// make sure tuples are type arguments (as used e.g. when viewing maps as
+// key/value iterables) work
+
+interface SomeIterator<T> { }
+
+interface SomeIterable<T> {
+  it(): SomeIterator<T>;
+}
+
+declare class SomeMap<K,V> {
+  it(): SomeIterator<[K,V]>;
+  set(k: K, v: V): void;
+}
+
+declare class ImmutableMap<K,V> { }
+
+declare function convert<K,V>(iter: SomeIterable<[K,V]>): ImmutableMap<K,V>;
+
+function foo(): ImmutableMap<string, boolean> {
+  const countersGlobalMap = new SomeMap();
+  countersGlobalMap.set("", false);
+  return convert(countersGlobalMap);
+}
diff --git a/tests/union_new/test32.js b/tests/union_new/test32.js
new file mode 100644
index 000000000000..b6f730ec9a37
--- /dev/null
+++ b/tests/union_new/test32.js
@@ -0,0 +1,9 @@
+// @flow
+
+// make sure that full resolution jobs don't cache improperly to signal success
+// when they have failed earlier
+
+function foo(value: Indirect<string> | number): Indirect<string> | number {
+  const castedValue: number = typeof value === 'number' ? value : 0;
+  return castedValue;
+}
diff --git a/tests/union_new/test4.js b/tests/union_new/test4.js
new file mode 100644
index 000000000000..93dd1dccaac4
--- /dev/null
+++ b/tests/union_new/test4.js
@@ -0,0 +1,36 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+///////////////////////////////
+// example with function types
+///////////////////////////////
+
+function fun(a: ((x: number) => void) | ((x: string) => void)) { }
+
+const a1 = ((x) => {}: A1);
+fun(a1);
+
+function fun_call(x: string) { a1(x); }
+
+type A1 = (x: B1) => void;
+
+type B1 = string;
+
+////////////////////////////
+// example with array types
+////////////////////////////
+
+function arr(a: number[] | string[]) { }
+
+const a2 = ([]: A2);
+arr(a2);
+
+function arr_set(x: string, i: number) { a2[i] = x; }
+function arr_get(i: number): string { return a2[i]; }
+
+type A2 = B2[];
+
+type B2 = string;
diff --git a/tests/union_new/test5.js b/tests/union_new/test5.js
new file mode 100644
index 000000000000..0222e8f934fc
--- /dev/null
+++ b/tests/union_new/test5.js
@@ -0,0 +1,27 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+///////////////////////////////
+// example with function types
+///////////////////////////////
+
+function fun(a: ((x: number) => number) | ((x: string) => string)) { }
+
+function a1(x) { return x; }
+fun(a1);
+
+function fun_call(x: string): string { return a1(x); }
+
+/////////////////////////////
+// example with array types
+/////////////////////////////
+
+function arr(a: number[] | string[]) { }
+
+var a2 = [];
+arr(a2);
+
+function arr_set(x: string, i: number) { a2[i] = x; }
diff --git a/tests/union_new/test6.js b/tests/union_new/test6.js
new file mode 100644
index 000000000000..c780bb848351
--- /dev/null
+++ b/tests/union_new/test6.js
@@ -0,0 +1,25 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////////////////////////
+// example with generic class inheritance
+//////////////////////////////////////////
+
+function inst(a: E<B4>): C<number> | C<string> { return a; }
+
+const mk_C = () => C;
+const mk_D = () => D;
+const mk_E = () => E;
+
+type B4 = string;
+
+const _D = mk_D();
+class E<X> extends _D<X> { }
+
+const _C = mk_C();
+class D<X> extends _C<X> { }
+
+class C<X> { }
diff --git a/tests/union_new/test7.js b/tests/union_new/test7.js
new file mode 100644
index 000000000000..1f9f5713b938
--- /dev/null
+++ b/tests/union_new/test7.js
@@ -0,0 +1,29 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+////////////////////
+// recursive types
+////////////////////
+
+function rec(x: F1 | F2) { }
+rec({ x: 0 });
+
+type F1 = G1;
+type F2 = G2;
+type G1 = { x: H1, y?: G1 };
+type G2 = { x: H2, y?: G2 };
+type H1 = string;
+type H2 = number;
+
+///////////////////////////////
+// polymorphic recursive types
+///////////////////////////////
+
+function polyrec(x: PF<number> | PF<string>) { }
+rec({ x: 0 });
+
+type PF<X> = PG<X>;
+type PG<X> = { x: X, y?: PG<X> };
diff --git a/tests/union_new/test8.js b/tests/union_new/test8.js
new file mode 100644
index 000000000000..4afbc4c62b5f
--- /dev/null
+++ b/tests/union_new/test8.js
@@ -0,0 +1,23 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+//////////////////////
+// nested union types
+//////////////////////
+
+function rec(x: F1 | F2) { }
+rec({ x: 0 });
+
+type F1 = G1 | G1_;
+type F2 = G2 | G2_;
+type G1 = { x: H1 };
+type G1_ = { x: H1_ };
+type G2 = { x: H2 };
+type G2_ = { x: H2_ };
+type H1 = boolean;
+type H1_ = string;
+type H2 = boolean;
+type H2_ = number;
diff --git a/tests/union_new/test9.js b/tests/union_new/test9.js
new file mode 100644
index 000000000000..18221e5d82cd
--- /dev/null
+++ b/tests/union_new/test9.js
@@ -0,0 +1,16 @@
+// @noflow
+
+/**
+ * Test that shows how the implementation of union types is broken
+ */
+
+////////////////
+// interference
+////////////////
+
+function square(x? = 0) {
+  return x * x;
+}
+
+function foo(f: ((_: ?number) => ?number) | (() => void)) { }
+foo((x): number => square(x))
diff --git a/tests/unreachable/__snapshots__/jsfmt.spec.js.snap b/tests/unreachable/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..dc6dbc6e22a9
--- /dev/null
+++ b/tests/unreachable/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,95 @@
+exports[`test typecheck.js 1`] = `
+"/* @flow */
+
+function test1(): string {
+  return bar();
+
+  function bar() {
+    return 0;
+  }
+}
+
+// regression test for analysis after abnormal control flow:
+// consts must not become bot (EmptyT).
+
+function test2() {
+  const n = 0;
+
+  return;
+
+  function f() {
+    var x: typeof n = 0;  // no error, n is still number
+    var y: string = n;    // error, n is number (EmptyT would work)
+  }
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function test1(): string {
+  return bar();
+  function bar() {
+    return 0;
+  }
+}
+// regression test for analysis after abnormal control flow:
+// consts must not become bot (EmptyT).
+function test2() {
+  const n = 0;
+  return;
+  function f() {
+    var x: typeof n = 0;// no error, n is still number
+    var y: string = n;// error, n is number (EmptyT would work)
+  }
+}
+
+"
+`;
+
+exports[`test unreachable.js 1`] = `
+"/* @flow */
+
+function foo(x, y) {
+  "use strict";
+  return bar(x) + baz(y);
+
+  // function declaration is hoisted, should not generate warning
+  function bar (ecks) {
+    return x + ecks;
+  }
+
+  // assignment is not hoisted, should generate warning
+  var baz = function (why) {
+    return y + why;
+  };
+
+  // variable declaration is hoisted, should not generate warning
+  var x, y, z;
+
+  // assignments are not hoisted, should generate 2 warnings
+  var t,
+      u = 5,
+      v,
+      w = 7;
+}
+
+foo(1, 2);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo(x, y) { "use strict"; 
+  return bar(x) + baz(y);
+  // function declaration is hoisted, should not generate warning
+  function bar(ecks) {
+    return x + ecks;
+  }
+  // assignment is not hoisted, should generate warning
+  var baz = function(why) {
+    return y + why;
+  };
+  // variable declaration is hoisted, should not generate warning
+  var xy,z;
+  // assignments are not hoisted, should generate 2 warnings
+  var tu = 5,v,w = 7;
+}
+foo(1, 2);
+
+"
+`;
diff --git a/tests/unreachable/jsfmt.spec.js b/tests/unreachable/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/unreachable/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/unreachable/typecheck.js b/tests/unreachable/typecheck.js
new file mode 100644
index 000000000000..78c517f82e75
--- /dev/null
+++ b/tests/unreachable/typecheck.js
@@ -0,0 +1,23 @@
+/* @flow */
+
+function test1(): string {
+  return bar();
+
+  function bar() {
+    return 0;
+  }
+}
+
+// regression test for analysis after abnormal control flow:
+// consts must not become bot (EmptyT).
+
+function test2() {
+  const n = 0;
+
+  return;
+
+  function f() {
+    var x: typeof n = 0;  // no error, n is still number
+    var y: string = n;    // error, n is number (EmptyT would work)
+  }
+}
diff --git a/tests/unreachable/unreachable.js b/tests/unreachable/unreachable.js
new file mode 100644
index 000000000000..84cee2a9e380
--- /dev/null
+++ b/tests/unreachable/unreachable.js
@@ -0,0 +1,27 @@
+/* @flow */
+
+function foo(x, y) {
+  "use strict";
+  return bar(x) + baz(y);
+
+  // function declaration is hoisted, should not generate warning
+  function bar (ecks) {
+    return x + ecks;
+  }
+
+  // assignment is not hoisted, should generate warning
+  var baz = function (why) {
+    return y + why;
+  };
+
+  // variable declaration is hoisted, should not generate warning
+  var x, y, z;
+
+  // assignments are not hoisted, should generate 2 warnings
+  var t,
+      u = 5,
+      v,
+      w = 7;
+}
+
+foo(1, 2);
diff --git a/tests/value/__snapshots__/jsfmt.spec.js.snap b/tests/value/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..778376ff6508
--- /dev/null
+++ b/tests/value/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,16 @@
+exports[`test value.js 1`] = `
+"var o = {};
+o["x"] = 4;
+var y:string = o["x"];
+
+var table: { [_: string]: number } = {};
+table["x"] = "hello";
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+var o = {};
+o["x"] = 4;
+var y: string = o["x"];
+var table: { [_: string]: number } = {};
+table["x"] = "hello";
+
+"
+`;
diff --git a/tests/value/jsfmt.spec.js b/tests/value/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/value/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/value/value.js b/tests/value/value.js
new file mode 100644
index 000000000000..ef7f957c6fe0
--- /dev/null
+++ b/tests/value/value.js
@@ -0,0 +1,6 @@
+var o = {};
+o["x"] = 4;
+var y:string = o["x"];
+
+var table: { [_: string]: number } = {};
+table["x"] = "hello";
diff --git a/tests/vim_emacs_errors/__snapshots__/jsfmt.spec.js.snap b/tests/vim_emacs_errors/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fc4cf2d5fc7f
--- /dev/null
+++ b/tests/vim_emacs_errors/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,10 @@
+exports[`test test.js 1`] = `
+"// @flow
+
+(123: string);
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+// @flow
+(123: string);
+
+"
+`;
diff --git a/tests/vim_emacs_errors/jsfmt.spec.js b/tests/vim_emacs_errors/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/vim_emacs_errors/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/vim_emacs_errors/test.js b/tests/vim_emacs_errors/test.js
new file mode 100644
index 000000000000..aa418762398d
--- /dev/null
+++ b/tests/vim_emacs_errors/test.js
@@ -0,0 +1,3 @@
+// @flow
+
+(123: string);
diff --git a/tests/weakmode/__snapshots__/jsfmt.spec.js.snap b/tests/weakmode/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..82293afbb43f
--- /dev/null
+++ b/tests/weakmode/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,47 @@
+exports[`test should_fail_without_weak.js 1`] = `
+"/* @flow */
+// This should fail without weak mode, because of the glaring type error.
+
+function returns_a_string() {
+  return "Hello";
+}
+
+function expects_an_int() {
+  return returns_a_string() * 10;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+// This should fail without weak mode, because of the glaring type error.
+function returns_a_string() {
+  return "Hello";
+}
+function expects_an_int() {
+  return returns_a_string() * 10;
+}
+
+"
+`;
+
+exports[`test should_pass_with_weak.js 1`] = `
+"/* @flow weak */
+// This should fail without weak mode, because of the glaring type error.
+
+function returns_a_string() {
+  return "Hello";
+}
+
+function expects_an_int() {
+  return returns_a_string() * 10;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow weak */
+// This should fail without weak mode, because of the glaring type error.
+function returns_a_string() {
+  return "Hello";
+}
+function expects_an_int() {
+  return returns_a_string() * 10;
+}
+
+"
+`;
diff --git a/tests/weakmode/jsfmt.spec.js b/tests/weakmode/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/weakmode/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/weakmode/should_fail_without_weak.js b/tests/weakmode/should_fail_without_weak.js
new file mode 100644
index 000000000000..9dcc0c64d334
--- /dev/null
+++ b/tests/weakmode/should_fail_without_weak.js
@@ -0,0 +1,10 @@
+/* @flow */
+// This should fail without weak mode, because of the glaring type error.
+
+function returns_a_string() {
+  return "Hello";
+}
+
+function expects_an_int() {
+  return returns_a_string() * 10;
+}
diff --git a/tests/weakmode/should_pass_with_weak.js b/tests/weakmode/should_pass_with_weak.js
new file mode 100644
index 000000000000..14fce153d528
--- /dev/null
+++ b/tests/weakmode/should_pass_with_weak.js
@@ -0,0 +1,10 @@
+/* @flow weak */
+// This should fail without weak mode, because of the glaring type error.
+
+function returns_a_string() {
+  return "Hello";
+}
+
+function expects_an_int() {
+  return returns_a_string() * 10;
+}
diff --git a/tests/while/__snapshots__/jsfmt.spec.js.snap b/tests/while/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..5b99d486fc53
--- /dev/null
+++ b/tests/while/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,73 @@
+exports[`test abnormal.js 1`] = `
+"/* @flow */
+
+function foo(x: boolean) {
+  var ii = 10;
+  while (ii-- >= 0) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  //console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  var ii = 0;
+  while (ii > 0) {
+    return;
+  }
+  //console.log('this is still reachable');
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @flow */
+function foo(x: boolean) {
+  var ii = 10;
+  while (ii-- >= 0) {
+    if (x) {
+      continue;
+    }
+    return;
+  }//console.log('this is still reachable');
+}
+function bar(x: boolean) {
+  var ii = 0;
+  while (ii > 0) {
+    return;
+  }//console.log('this is still reachable');
+}
+
+"
+`;
+
+exports[`test test.js 1`] = `
+"class C {
+    m() { return new C; }
+}
+function blah() {}
+var node: ?C = new C;
+while (node) {
+    var parent = node.m();
+    var cloneable: C = node;
+    blah();
+    node = parent.m();
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+class C {
+  m() {
+    return new C();
+  }
+}
+function blah() {
+  
+}
+var node: ?C = new C();
+while (node) {
+  var parent = node.m();
+  var cloneable: C = node;
+  blah();
+  node = parent.m();
+}
+
+"
+`;
diff --git a/tests/while/abnormal.js b/tests/while/abnormal.js
new file mode 100644
index 000000000000..35431642a482
--- /dev/null
+++ b/tests/while/abnormal.js
@@ -0,0 +1,20 @@
+/* @flow */
+
+function foo(x: boolean) {
+  var ii = 10;
+  while (ii-- >= 0) {
+    if (x) {
+      continue;
+    }
+    return;
+  }
+  //console.log('this is still reachable');
+}
+
+function bar(x: boolean) {
+  var ii = 0;
+  while (ii > 0) {
+    return;
+  }
+  //console.log('this is still reachable');
+}
diff --git a/tests/while/jsfmt.spec.js b/tests/while/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/while/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/while/test.js b/tests/while/test.js
new file mode 100644
index 000000000000..16f55038cdb7
--- /dev/null
+++ b/tests/while/test.js
@@ -0,0 +1,11 @@
+class C {
+    m() { return new C; }
+}
+function blah() {}
+var node: ?C = new C;
+while (node) {
+    var parent = node.m();
+    var cloneable: C = node;
+    blah();
+    node = parent.m();
+}
diff --git a/tests/window/__snapshots__/jsfmt.spec.js.snap b/tests/window/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..fd3a6302ffdf
--- /dev/null
+++ b/tests/window/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,24 @@
+exports[`test window1.js 1`] = `
+"/*
+@providesModule Window1
+*/
+module.exports = window.history;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/*
+@providesModule Window1
+*/
+module.exports = window.history;
+
+"
+`;
+
+exports[`test window2.js 1`] = `
+"/* @providesModule Window2 */
+
+module.exports = window.parent;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/* @providesModule Window2 */
+module.exports = window.parent;
+
+"
+`;
diff --git a/tests/window/jsfmt.spec.js b/tests/window/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/window/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/window/window1.js b/tests/window/window1.js
new file mode 100644
index 000000000000..c5e6ac93949d
--- /dev/null
+++ b/tests/window/window1.js
@@ -0,0 +1,4 @@
+/*
+@providesModule Window1
+*/
+module.exports = window.history;
diff --git a/tests/window/window2.js b/tests/window/window2.js
new file mode 100644
index 000000000000..b16e6aa9eb88
--- /dev/null
+++ b/tests/window/window2.js
@@ -0,0 +1,3 @@
+/* @providesModule Window2 */
+
+module.exports = window.parent;
diff --git a/tests/x/XControllerURIBuilder.js b/tests/x/XControllerURIBuilder.js
new file mode 100644
index 000000000000..78429106b236
--- /dev/null
+++ b/tests/x/XControllerURIBuilder.js
@@ -0,0 +1,30 @@
+/**
+ * @generated SignedSource<<13ca42bbc7fe91f15057861e18a77d88>>
+ *
+ * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+ * !! This file is a check-in of a static_upstream project!      !!
+ * !!                                                            !!
+ * !! You should not modify this file directly. Instead:         !!
+ * !! 1) Use `fjs use-upstream` to temporarily replace this with !!
+ * !!    the latest version from upstream.                       !!
+ * !! 2) Make your changes, test them, etc.                      !!
+ * !! 3) Use `fjs push-upstream` to copy your changes back to    !!
+ * !!    static_upstream.                                        !!
+ * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+ *
+ * @providesModule XControllerURIBuilder
+ * @typechecks
+ */
+
+// ...
+class XControllerURIBuilder {
+
+  // ...
+  getURI() {
+    // ...
+    var tokenRegex = new RegExp(/^\{(\?)?(.+?)\}$/);
+    // ...
+  }
+}
+
+module.exports = XControllerURIBuilder;
diff --git a/tests/x/__snapshots__/jsfmt.spec.js.snap b/tests/x/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..2dc029c12a2e
--- /dev/null
+++ b/tests/x/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,61 @@
+exports[`test XControllerURIBuilder.js 1`] = `
+"/**
+ * @generated SignedSource<<13ca42bbc7fe91f15057861e18a77d88>>
+ *
+ * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+ * !! This file is a check-in of a static_upstream project!      !!
+ * !!                                                            !!
+ * !! You should not modify this file directly. Instead:         !!
+ * !! 1) Use \`fjs use-upstream\` to temporarily replace this with !!
+ * !!    the latest version from upstream.                       !!
+ * !! 2) Make your changes, test them, etc.                      !!
+ * !! 3) Use \`fjs push-upstream\` to copy your changes back to    !!
+ * !!    static_upstream.                                        !!
+ * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+ *
+ * @providesModule XControllerURIBuilder
+ * @typechecks
+ */
+
+// ...
+class XControllerURIBuilder {
+
+  // ...
+  getURI() {
+    // ...
+    var tokenRegex = new RegExp(/^\\{(\\?)?(.+?)\\}$/);
+    // ...
+  }
+}
+
+module.exports = XControllerURIBuilder;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/**
+ * @generated SignedSource<<13ca42bbc7fe91f15057861e18a77d88>>
+ *
+ * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+ * !! This file is a check-in of a static_upstream project!      !!
+ * !!                                                            !!
+ * !! You should not modify this file directly. Instead:         !!
+ * !! 1) Use \`fjs use-upstream\` to temporarily replace this with !!
+ * !!    the latest version from upstream.                       !!
+ * !! 2) Make your changes, test them, etc.                      !!
+ * !! 3) Use \`fjs push-upstream\` to copy your changes back to    !!
+ * !!    static_upstream.                                        !!
+ * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+ *
+ * @providesModule XControllerURIBuilder
+ * @typechecks
+ */
+// ...
+class XControllerURIBuilder {
+  // ...
+  getURI() {
+    // ...
+    var tokenRegex = new RegExp(/^\\{(\\?)?(.+?)\\}$/);// ...
+  }
+}
+module.exports = XControllerURIBuilder;
+
+"
+`;
diff --git a/tests/x/jsfmt.spec.js b/tests/x/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/x/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/yield/__snapshots__/jsfmt.spec.js.snap b/tests/yield/__snapshots__/jsfmt.spec.js.snap
new file mode 100644
index 000000000000..18bae5f5cf57
--- /dev/null
+++ b/tests/yield/__snapshots__/jsfmt.spec.js.snap
@@ -0,0 +1,34 @@
+exports[`test yield_arrow_error.js 1`] = `
+"function * f () {
+  var e = () => { yield 1; };
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+/node_modules/babylon/lib/index.js:4255
+  throw err;
+  ^
+
+SyntaxError: Unexpected token (2:18)
+    at Parser.pp$5.raise (/node_modules/babylon/lib/index.js:4252:13)
+    at Parser.pp.unexpected (/node_modules/babylon/lib/index.js:1633:8)
+    at Parser.pp$3.parseIdentifier (/node_modules/babylon/lib/index.js:4128:10)
+    at Parser.pp$3.parseExprAtom (/node_modules/babylon/lib/index.js:3490:21)
+    at Parser.parseExprAtom (/node_modules/babylon/lib/index.js:6408:22)
+    at Parser.pp$3.parseExprSubscripts (/node_modules/babylon/lib/index.js:3337:19)
+    at Parser.pp$3.parseMaybeUnary (/node_modules/babylon/lib/index.js:3317:19)
+    at Parser.pp$3.parseExprOps (/node_modules/babylon/lib/index.js:3247:19)
+    at Parser.pp$3.parseMaybeConditional (/node_modules/babylon/lib/index.js:3224:19)
+    at Parser.pp$3.parseMaybeAssign (/node_modules/babylon/lib/index.js:3187:19)
+"
+`;
+
+exports[`test yield_arrow_error2.js 1`] = `
+"function * f () {
+  var e = () => yield 1;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+function* f() {
+  var e = () => yield 1;
+}
+
+"
+`;
diff --git a/tests/yield/jsfmt.spec.js b/tests/yield/jsfmt.spec.js
new file mode 100644
index 000000000000..989047bccc52
--- /dev/null
+++ b/tests/yield/jsfmt.spec.js
@@ -0,0 +1 @@
+run_spec(__dirname);
diff --git a/tests/yield/yield_arrow_error.js b/tests/yield/yield_arrow_error.js
new file mode 100644
index 000000000000..330a07e8ad02
--- /dev/null
+++ b/tests/yield/yield_arrow_error.js
@@ -0,0 +1,3 @@
+function * f () {
+  var e = () => { yield 1; };
+}
diff --git a/tests/yield/yield_arrow_error2.js b/tests/yield/yield_arrow_error2.js
new file mode 100644
index 000000000000..243ac23ee67c
--- /dev/null
+++ b/tests/yield/yield_arrow_error2.js
@@ -0,0 +1,3 @@
+function * f () {
+  var e = () => yield 1;
+}
diff --git a/tests_config/run_spec.js b/tests_config/run_spec.js
new file mode 100644
index 000000000000..a7345bb42fb0
--- /dev/null
+++ b/tests_config/run_spec.js
@@ -0,0 +1,80 @@
+const fs = require('fs');
+const child_process = require('child_process');
+
+function run_spec(dirname) {
+  fs.readdirSync(dirname).forEach(filename => {
+    if (filename.endsWith('.js') && filename !== 'jsfmt.spec.js') {
+      const path = dirname + '/' + filename;
+
+      const RUN_AST_TESTS =
+        // true || // UNCOMMENT!
+        false;
+
+      if (!RUN_AST_TESTS) {
+        const source = read(path);
+        const output = prettyprint(path);
+        test(filename, () => {
+          expect(source + '~'.repeat(80) + '\n' + output).toMatchSnapshot();
+        });
+      }
+
+      if (RUN_AST_TESTS) {
+        test(path + ' parse', () => {
+          const file = read(dirname + '/' + filename);
+          const ast = parse(file);
+          const ppfile = pp(file);
+          const ppast = parse(ppfile);
+          expect(ast).toEqual(ppast);
+        });
+      }
+
+    }
+  });
+}
+global.run_spec = run_spec;
+
+function stripLocation(ast) {
+  if (Array.isArray(ast)) {
+    return ast.map(e => stripLocation(e));
+  }
+  if (typeof ast === 'object') {
+    const newObj = {};
+    for (var key in ast) {
+      if (key === 'loc' || key === 'range' || key === 'raw' || key === 'comments') {
+        continue;
+      }
+      newObj[key] = stripLocation(ast[key]);
+    }
+    return newObj;
+  }
+  return ast;
+}
+
+function parse(string) {
+  const flowParser = require('flow-parser');
+  return stripLocation(flowParser.parse(string));
+}
+
+function prettyprint(path) {
+  const result = child_process.spawnSync(
+    './bin/jscodefmt',
+    [path],
+  );
+  return (
+    result.stdout.toString() ||
+    result.stderr.toString()
+      .replace(new RegExp(process.cwd(), 'g'), '')
+  );
+}
+
+function pp(string) {
+  const tmp = 'tmp' + Math.random() + '.js';
+  fs.writeFileSync(tmp, string);
+  const result = prettyprint(tmp);
+  fs.unlinkSync(tmp);
+  return result;
+}
+
+function read(filename) {
+  return fs.readFileSync(filename, 'utf8');
+}