为什么Angular中的Jasmine间谍功能没有被回调触发？

Question

I want to test this.communication.subscribe() call which is having a callback in argument:

constructor (private communication: CommunicationProvider)

ngOnInit() {
    this.communication.subscribe(() => {
      this.router.navigate(["/success"]);
    });
  }

I have used callFake to mock the implementation to call callback()

beforeEach(async(() => {
    communicationSpy = jasmine.createSpyObj("CommunicationProvider", ["subscribe"]);
    routerSpy = jasmine.createSpyObj<Router>("Router", ["navigate"]);

    communicationSpy.subscribe.and.callFake((callback: any) => {
        callback();
    });
}));

it("should route on callback", (done: DoneFn) => {
    setTimeout(() => {
        expect(routerSpy.navigate).toHaveBeenCalledWith(["/success"]);
        done();
    }, 3000);
});

As per code coverage results, this.router.navigate(["/success"]); is being covered by callback() . But "should route on callback" test is failing as routerSpy.navigate is never being called.

Why?

Answer 1

Because you never trigger the subscription.

I don't know what your service is, but we'll take advantage of the fact that you don't use restriction operators such as take or takeUntil .

Start by mocking your observable as a hot stream with a Subject :

component['communication'] = new Subject() as any;

Now, you should have a new instance of your component in every test thanks to the fixture createComponentInstance called in the before each. This means you already have called ngOnInit and created the subscription.

Since the stream is hot, you can subscribe to it in your test :

it('should navigate', done => {
  component['communication'].subscribe(() => {
    expect(routerSpy.navigate).toHaveBeenCalledWith(["/success"]);
    done();
  });

  (component['communication'] as Subject).next(true);
});

With the next call, you trigger the subscriptions, launching the router and expecting it to have been called.

(PS : I have used array syntax and Subject to picture the issue, feel free to use whatever you want to trigger a subscription and to mock your dependencies)