Add a spot check for directories that don't contain tests (#1791)

Closes #1433

lib-js/spec-directory/spec-directory.ts

@@ -159,4 +159,8 @@ export default abstract class SpecDirectory {
       }
     }
   }
+
+  toString(): string {
+    return this.path;
+  }
 }

spec/core_functions/list/zip.hrx

@@ -1,3 +1,11 @@
+<===> README.md
+`zip()` is unique among built-in functions in that there's no possible
+invocation that produces an error, since it can take any number of arguments and
+any argument can be interpreted as a list. Since we don't normally test for
+passing invalid named parameters, it has no error tests.
+
+<===>
+================================================================================
 <===> no_lists/input.scss
 @import "core_functions/list/utils";
 
@@ -191,11 +199,3 @@ a {b: zip(c, d, e)}
 a {
   b: c d e;
 }
-
-<===>
-================================================================================
-<===> error/README.md
-`zip()` is unique among built-in functions in that there's no possible
-invocation that produces an error, since it can take any number of arguments and
-any argument can be interpreted as a list. Since we don't normally test for
-passing invalid named parameters, it has no error tests.

spec/libsass-closed-issues/issue_2863.hrx

@@ -1,4 +1,4 @@
-<===> input.scss 
+<===> input.scss
 $squoted: "'dquoted'";
 $dquoted: "\"squoted\"";
 
@@ -10,7 +10,8 @@ test {
     str-insert-single: str-insert( $squoted, "p", 2 );
     str-insert-double: str-insert( $dquoted, "p", 2 );
 }
-<===> output.css 
+
+<===> output.css
 test {
   str-slice-single: "'d";
   str-slice-double: '"s';

test/spot-check.test.ts

@@ -0,0 +1,29 @@
+import * as p from 'path';
+import * as specDirectory from '../lib-js/spec-directory';
+
+// Spot checks for common spec errors.
+
+it('every directory contains or is contained by a test', async () => {
+  // Verifies that `dir` either is a test, or that all its children are tests.
+  async function verifyDirectory(
+    dir: specDirectory.SpecDirectory
+  ): Promise<void> {
+    if (dir.isTestDir()) return;
+
+    const subdirs = await dir.subdirs();
+    if (subdirs.length === 0) {
+      // Empty directories aren't recorded by Git, so we allow them.
+      if ((await dir.listFiles()).length === 0) return;
+
+      const path = p.relative(process.cwd(), dir.path);
+      throw new Error(
+        `Directory ${path} is neither a test, the child of a test, nor the ` +
+          'parent of a test.'
+      );
+    } else {
+      await Promise.all(subdirs.map(verifyDirectory));
+    }
+  }
+
+  await verifyDirectory(await specDirectory.fromPath('spec'));
+});