Cannot Read Property 'subscribe' of Angular Test Mock

Question

I'm trying to unit test an Angular component that has an injected service. In the component's constructor, a method on the injected service is called that returns an Observable. I'm trying to mock the service in my component's unit test, but I keep running into this error: TypeError: Cannot read property 'subscribe' of undefined.

I've tried to mock the service in the following ways:

const serviceStub = {
  getObservable: () => { return {subscribe: () => {}}; },
};

beforeEach(async(() => {
  TestBed.configureTestingModule({
    providers: [
      {provide: MyService, useValue: serviceStub}
    ]
})


it('should create', () => {
  spyOn(serviceStub, 'getObservable').and.returnValue({subscribe: () => {}});
  expect(component).toBeTruthy();
});

It feels like I'm missing something obvious. Can someone please point it out?

UPDATE

I get this error even when I inject the actual service in my test bed providers.

The component's constructor looks something like this:

private _subscription: Subscription;

constructor(private _service: MyService) {
  this._subscription = _service.getObservable().subscribe(console.log);
}

Answer 1

Use inject to inject the service and mock it not stub

it('should create', inject([MyService], (myService: MyService) => {
  spyOn(myService, 'getObservable').and.returnValue({subscribe: () => {}});
  expect(component).toBeTruthy();
}));

Here is full version:

component:

@Component({
  selector: 'my-cmp',
  template: 'my cmp {{x}}'
})
export class MyComponent {
  x;

  constructor(private myService: MyService) {
    this.myService.getObservable()
      .subscribe(x => {
        console.log(x);
        this.x = x;
      });
  }
}

test:

   describe('my component test', () => {
    let fixture: ComponentFixture<MyComponent>, comp: MyComponent, debugElement: DebugElement, element: HTMLElement;

    beforeEach(async(() => {
      TestBed.configureTestingModule({
        declarations: [MyComponent],
        providers: [MyService]
      });
    }));

    beforeEach(() => {
      fixture = TestBed.createComponent(MyComponent);
      comp = fixture.componentInstance;
      debugElement = fixture.debugElement;
      element = debugElement.nativeElement;
    });

    it('should create', inject([MyService], (myService: MyService) => {
      expect(comp).toBeTruthy();
    }));

    it('should set value', async(inject([MyService], (myService: MyService) => {
      spyOn(myService, 'getObservable').and.returnValue(Observable.of(1));

      fixture.detectChanges();

      fixture.whenStable().then(() => {
        expect(comp.x).toEqual(1);
      });
    })));
  });