我有一個將HttpClient服務作為值的服務，我想監(jiān)視post那個類的方法，所以我創(chuàng)建了一個看起來像這樣的間諜：spyOn(httpClient, 'post').and.returnValue(() => new Subject<any>().asObservable());但是，我收到以下錯誤：Argument of type '() => Observable<any>' is not assignable to parameter of type 'Observable<unknown>'.  Type '() => Observable<any>' is missing the following properties from type 'Observable<unknown>': _isScalar, source, operator, lift, and 6 more.這是它來自的規(guī)范：describe('GraphQLClientService', () => {  let service: GraphQLClientService;  let httpClient: HttpClient;  let postSpy: any;  beforeEach(() => {    httpClient = jasmine.createSpyObj('HttpClient', []);    postSpy = spyOn(httpClient, 'post').and.returnValue(() => new Subject<any>().asObservable());    service = new GraphQLClientService(httpClient);  });});