Angular - Unit testing Subject()?

Question

I have a Angular service that simply uses a Subject, but I am unsure of how to write unit tests for it.

I saw [this thread][1], but I didn't find it terribly helpful.

I have attempted to mock next() but I am more than a little lost.

Solution

You should spy on service.serviceMsg and not service, because next() method appears to be on serviceMsg subject.

it('should catch what is emitted', () => {
    const nextSpy = spyOn(service.serviceMsg, 'next');
    service.confirm(ACTION);
    expect(nextSpy).toHaveBeenCalled();
});

EDIT :

You should also change the way you are creating service instance. What you show in your code is applicable only for component instance creation

beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [MessageService]
    });
    service = TestBed.get(MessageService); // get service instance
    httpMock = TestBed.get(HttpTestingController);
});

Comments

[Admin]

By doing that you rely on the implementation of Subject, which is not what a unit test should do. You should instead mock it like he tried to do.

[Buczkowski]

I believe it is not unit test since it includes things like creating module or injecting. It is true that it will rely on Subject implementation.

[physicsboy]

I see what you mean. Although I am getting the error: Error: Illegal state: Could not load the summary for directive MessageService.

[physicsboy]

@trichetriche - Do you have any knowledge of this issue?

[Amit Chigadani]

You cannot create service instance like fixture = TestBed.createComponent(MessageService); service = fixture.componentInstance;. That is applicable for component only. Instead you should be doing service = TestBed.get(MessageService)

[physicsboy]

Ah amazing! Thank you for your help @Amit :-)

[Admin]

@physicsboy if you want to notify me, it has to be on a question/answer I already commented on, otherwise I don't receive a notification !

[physicsboy]

@trichetriche - Whoops. Better just giving me your email XD