Allow providing stubs overrides for sinon.createStubInstance (sinonjs…

…#1864)

docs/release-source/release/stubs.md

@@ -95,7 +95,37 @@ Stubbing individual methods tests intent more precisely and is less susceptible
 If you want to create a stub object of `MyConstructor`, but don't want the constructor to be invoked, use this utility function.
 
 ```javascript
-var stub = sinon.createStubInstance(MyConstructor)
+var stub = sinon.createStubInstance(MyConstructor, overrides);
+```
+
+`overrides` is an optional map overriding created stubs, for example:
+
+```javascript
+
+var stub = sinon.createStubInstance(MyConstructor, {
+    foo: sinon.stub().returnsThis()
+});
+```
+
+is the same as:
+
+```javascript
+var stub = sinon.createStubInstance(MyConstructor);
+stub.foo.returnsThis();
+```
+
+If provided value is not a stub, it will be used as the returned value:
+
+```javascript
+var stub = sinon.createStubInstance(MyConstructor, {
+    foo: 3
+});
+```
+is the same as:
+
+```javascript
+var stub = sinon.createStubInstance(MyConstructor);
+stub.foo.returns(3);
 ```
 
 #### `stub.withArgs(arg1[, arg2, ...]);`

lib/sinon/stub.js

@@ -71,11 +71,28 @@ function stub(object, property) {
     return isStubbingNonFuncProperty ? s : wrapMethod(object, property, s);
 }
 
-stub.createStubInstance = function (constructor) {
+stub.createStubInstance = function (constructor, overrides) {
     if (typeof constructor !== "function") {
         throw new TypeError("The constructor should be a function.");
     }
-    return stub(Object.create(constructor.prototype));
+
+    var stubbedObject = stub(Object.create(constructor.prototype));
+
+    Object.keys(overrides || {}).forEach(function (propertyName) {
+        if (propertyName in stubbedObject) {
+            var value = overrides[propertyName];
+            if (value.createStubInstance) {
+                stubbedObject[propertyName] = value;
+            }
+            else {
+                stubbedObject[propertyName].returns(value);
+            }
+        }
+        else {
+            throw new Error("Cannot stub " + propertyName + ". Property does not exist!");
+        }
+    });
+    return stubbedObject;
 };
 
 /*eslint-disable no-use-before-define*/

test/stub-test.js

@@ -2755,6 +2755,39 @@ describe("stub", function () {
                 });
             }
         });
+
+        it("allows providing optional overrides", function () {
+            var Class = function () {};
+            Class.prototype.method = function () {};
+
+            var stub = createStubInstance(Class, {
+                method: createStub().returns(3)
+            });
+
+            assert.equals(3, stub.method());
+        });
+
+        it("allows providing optional returned values", function () {
+            var Class = function () {};
+            Class.prototype.method = function () {};
+
+            var stub = createStubInstance(Class, {
+                method: 3
+            });
+
+            assert.equals(3, stub.method());
+        });
+
+        it("throws an exception when trying to override non-existing property", function () {
+            var Class = function () {};
+            Class.prototype.method = function () {};
+
+            assert.exception(function () {
+                createStubInstance(Class, {
+                    foo: createStub().returns(3)
+                });
+            }, {message: "Cannot stub foo. Property does not exist!"});
+        });
     });
 
     describe(".callThrough", function () {