Angular 2单元测试不等待承诺返回

Question

我有以下组件方法：

onSignup() {
    if (this.form.valid) {
      let email = this.form.value.email;
      let password = this.form.value.password;
      this.usersService.signup(email, password)
        .then(() => {
          console.log('1')
          this.router.navigate(['/app/home']);
        })
        .catch(err => {
          this.mdlSnackbarService.showToast(err);
        });
    }
  }

以下单元测试：

it('should navigate on success', async(() => {
    spyOn(usersService, 'signup').and.returnValue(Promise.resolve());

    component.form.setValue({'email': 'mail@mail.com', 'password': '123456'});

    component.onSignup();

    fixture.whenStable().then(() => {
        console.log('2')
        expect(router.navigate).toHaveBeenCalledWith(['/app/home']);
    })
  }))

我添加了几个console.log以找出失败的原因，结果证明1从未打印过，所以它不会等待承诺得到解决，尽管使用fixture.whenStable()。这是我的beforeEach：

beforeEach(inject([Router],(_router: Router) => {
    router = _router;
    router.navigate = jasmine.createSpy('navigate');
    fixture = TestBed.createComponent(SignupComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  }));

有谁知道我在这里做错了什么？