Testing with BehaviourSubject and debounceTime.

Hello there! I cannot unit test a component which uses rxjs observable built with BehaviourSubject and which uses debounceTime.

Component example:

public gg = 1;
private subject = new BehaviorSubject("blabla");
private please = this.subject.asObservable();
// private please = of("blabla"); // it works

public wp$ = this.please.pipe(
    debounceTime(300),
    switchMap(() => {
      this.gg = 2;
      return of("new blabla");
    })
);

Test example:

describe('test', () => {
  let fixture: ComponentFixture<AppComponent>;
  let component: AppComponent;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [AppModule]
    })
    
    fixture = TestBed.createComponent(AppComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  })

  it('works', fakeAsync(() => {
    tick(300);
    expect(component.gg).toBe(2);
  }))
});

I subscribe to wp$ in html file using async pipe. The test does not pass. However, interestingly, if I change the source observable to something like of('blabla'), i.e. observable which completed right away, the test would pass.

🔬 Full example reproduction

https://stackblitz.com/edit/angular-ivy-ue7wkw?file=src%2Fapp%2Fapp.component.ts

[JoostK]

That is because of completes the observable, which means that the debounceTime operator no longer awaits the timer as it certain there won’t be any additional values. This means that the switchMap callback is triggered synchronously, during the completion of the of observable.

[angular-automatic-lock-bot[bot]]

This issue has been automatically locked due to inactivity. Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}