茉莉花单元测试未进入订阅回调函数

Question

在ngOnInit上，我从数据库中获取用户权限。我无法测试订阅响应中的代码

component.ts：

subscription$: Subject<boolean> = new Subject<boolean>();

ngOnInit() {
    this.permissionsService.getUserPermissions().pipe(takeUntil(this.subscription$)).subscribe(res => {
        this.nodeTreeInitalization() // this never gets invoked
    });
}

component.spec.ts：

  beforeEach(() => {
    spectator = createComponent();

    permissionService = spectator.inject<PermissionService>(PermissionService);
    permissionService.getUserPermissions.and.returnValue(timer(0).pipe(
      mapTo({permissions: 3})
    ));
  });

  it('should call nodeTreeInitalization', () => {
    const nodeTreeInitSpy = spyOn(spectator.component, 'nodeTreeInitalization');

    spectator.fixture.detectChanges();

    expect(nodeTreeInitSpy).toHaveBeenCalled();        // Fails
  });

据我所知，我在模拟permissionService.getUserPermissions，然后通过detectChanges()调用ngOnInit，所以我不明白为什么我无法测试响应回调