Fake async test.ts

// Actual code
...
  public ngOnInit() {
    Observable.interval(3000)
      .takeUntil(this._componentDestroyed)
      .subscribe(() => this._statusStore.refreshStatus());
  }
  
  // Test Code
  import { fakeAsync, tick, discardPeriodicTasks } from '@angular/core/testing';
  ...
  it('polls statusStore.refreshStatus on an interval', fakeAsync(() => {
    spyOn(mockStatusStore, 'refreshStatus').and.callThrough();
    sut.ngOnInit();
    expect(mockStatusStore.refreshStatus).not.toHaveBeenCalled();
    tick(3001);
    expect(mockStatusStore.refreshStatus).toHaveBeenCalled();
    tick(3001);
    expect(mockStatusStore.refreshStatus).toHaveBeenCalledTimes(2);
    discardPeriodicTasks();
  }));