Unit testing a Typescript (Angular) subscription is essential to ensure its functionality and reliability

I have implemented a straightforward function that accomplishes this task.

ngOnInit() {
  if (this.session.getToken()) {
    this.isUserLogged = true;
  }

  this.loadingObserver = this.session.loadingObservable.subscribe(loading => this.isLoading = loading);
}

Here is the test scenario I have devised:

it('Testing ngOnInit() ...', async(() => {
  let spy = spyOn(services.session, 'getToken').and.returnValue('token');
  services.session.loadingObservable.subscribe(any => expect(component.isLoading).toEqual(false));
  component.ngOnInit();
  expect(component.isUserLogged).toEqual(true);
  expect(spy).toHaveBeenCalled();
}));

However, during code coverage analysis of my application, the subscribe portion remains uncovered. Interestingly, expecting false also seems to yield the desired result.

Does anyone have suggestions on how to effectively test a subscription in this context?

Answer №1

Understanding whether your handler code will be triggered upon subscription is determined by the "hotness" or "coldness" of the Observable being subscribed to. For further insight, take a look at this informative resource -- -- to classify where your "loadingObservable" stands. It may also be necessary, as previously mentioned, to manually activate it in your unit test.

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