[Core] Add test cases

Add test cases for model cache to ensure it maintains a single
instance of each model. WTD-1033.

platform/core/test/models/CachingModelDecoratorSpec.js

@@ -19,6 +19,25 @@ define(
                 };
             }
 
+            function fakePromise() {
+                var chains = [],
+                    callbacks = [];
+
+                return {
+                    then: function (callback) {
+                        var next = fakePromise();
+                        callbacks.push(callback);
+                        chains.push(next);
+                        return next;
+                    },
+                    resolve: function (value) {
+                        callbacks.forEach(function (cb, i) {
+                            chains[i].resolve(cb(value));
+                        });
+                    }
+                };
+            }
+
             beforeEach(function () {
                 mockCallback = jasmine.createSpy();
                 mockModelService = jasmine.createSpyObj('modelService', ['getModels']);
@@ -54,6 +73,59 @@ define(
                 expect(mockCallback).toHaveBeenCalledWith(testModels);
             });
 
+            it("ensures a single object instance, even for multiple concurrent calls", function () {
+                var promiseA, promiseB, mockCallback = jasmine.createSpy();
+
+                promiseA = fakePromise();
+                promiseB = fakePromise();
+
+                // Issue two calls before those promises resolve
+                mockModelService.getModels.andReturn(promiseA);
+                decorator.getModels(['a']);
+                mockModelService.getModels.andReturn(promiseB);
+                decorator.getModels(['a']).then(mockCallback);
+
+                // Then resolve those promises. Note that we're whiteboxing here
+                // to figure out which promises to resolve (that is, we know that
+                // two thens are chained after each getModels)
+                promiseA.resolve(testModels);
+                promiseB.resolve({
+                    a: { someNewKey: "some other value" }
+                });
+
+                // Ensure that we have a pointer-identical instance
+                expect(mockCallback.mostRecentCall.args[0].a)
+                    .toEqual({ someNewKey: "some other value" });
+                expect(mockCallback.mostRecentCall.args[0].a)
+                    .toBe(testModels.a);
+            });
+
+            it("is robust against updating with undefined values", function () {
+                var promiseA, promiseB, mockCallback = jasmine.createSpy();
+
+                promiseA = fakePromise();
+                promiseB = fakePromise();
+
+                // Issue two calls before those promises resolve
+                mockModelService.getModels.andReturn(promiseA);
+                decorator.getModels(['a']);
+                mockModelService.getModels.andReturn(promiseB);
+                decorator.getModels(['a']).then(mockCallback);
+
+                // Some model providers might erroneously add undefined values
+                // under requested keys, so handle that
+                promiseA.resolve({
+                    a: undefined
+                });
+                promiseB.resolve({
+                    a: { someNewKey: "some other value" }
+                });
+
+                // Should still have gotten the model
+                expect(mockCallback.mostRecentCall.args[0].a)
+                    .toEqual({ someNewKey: "some other value" });
+            });
+
 
         });
     }