Angular testing async pipe does not trigger the observable

I want to test a component that uses the async pipe. This is my code:

@Component({
  selector: 'test',
  template: `
    <div></div>
  `
})
class AsyncComponent {
  number = Observable.interval(1000).take(3)
}

fdescribe('Async Compnent', () => {
  let component : AsyncComponent;
  let fixture : ComponentFixture<AsyncComponent>;

  beforeEach(
    async(() => {
      TestBed.configureTestingModule({
        declarations: [ AsyncComponent ]
      }).compileComponents();
    })
  );

  beforeEach(() => {
    fixture = TestBed.createComponent(AsyncComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });


  it('should emit values', fakeAsync(() => {

    tick(1000);
    fixture.detectChanges();
    expect(fixture.debugElement.query(By.css('div')).nativeElement.innerHTML).toBe('0');

});

But the test failed. It's seems Angular does not execute to Observable from some reason. What I am missing?

When I'm trying to log the observable with the do operator, I don't see any output in the browser console.