Angular2 - Test a function that calls a http service inside

I am currently trying to test a function which calls a http request service and then does something in the subscribe part (calls a function and sets a variable). My approach so far was to just call the function and I thought the request-service will be called automatically and so the subscribe part will be executed. However, I feel like this is not the way of doing it as it's not working.

The function I want to test:

  public trainBot() {
    this.isTraining = true;
    this.requestsService.trainModel(this.botId, false)
      .subscribe(response => {
        this.trainingStatus = this.trainingStatusMapping[response['status']];
        this.pollTrainingStatus();
      });
  }

My test so far (which does not work).

it('should poll the training status', () => {
    spyOn(component, 'pollTrainingStatus').and.callThrough();
    component.trainBot();
    fixture.detectChanges();
    expect(component.pollTrainingStatus).toHaveBeenCalled();
  });

So, can anyone tell me how to test that part inside the .subscribe(... part?

Update:

as someone suggested I added returnValue and async to my test. They are still not working, but looking like that now:

it('should poll the training status', fakeAsync(() => {
    component.trainBot();
    spyOn(service, 'trainModel').and.returnValue(Observable.of({'status': 'training'}));
    spyOn(component, 'pollTrainingStatus').and.callThrough();
    fixture.detectChanges();
    tick(1);
    expect(service.trainModel).toHaveBeenCalled();
    expect(component.pollTrainingStatus).toHaveBeenCalled();
  }));

The Error is the same