TypeError: .subscribe 不是函数 Jasmine Angular

Question

我正在尝试为我的角度组件编写单元测试。 我能够使用 spyon 成功模拟 2 种方法。 但是即使在我模拟并使用 callFake 之后，一种方法 (_paymentStateService.getMakePaymentState$) 也会出错。 它在这些行中给出错误（this._payStateService.getMakePaymentState$.subscribe is not a function）： spyOn(mockMakePaymentState, 'getMakePaymentState$')

fdescribe('DetailsComponent', () => {
  let component: DetailsComponent;
  let fixture: ComponentFixture<DetailsComponent>;
  let httpMock: HttpTestingController;  
  let formModule: FormsModule;

  let form = new FormGroup({
    username: new FormControl('', Validators.required),
    dob: new FormControl('')
  });

  let mockbillingService = {
    getDetails: () => {},
    getBankDetails: () => {}
  }

  
  let mockMakePaymentState = {
    getPaymentDetails$: () => of({} as IPaymentDetails),    
    getDetails: () => {},
    getUserInfo: () => {}
  
  };

   class MatDialogMock {
    // When the component calls this.dialog.open(...) we'll return an object
    // with an afterClosed method that allows to subscribe to the dialog result observable.
    open() {
      return {
        afterClosed: () => of({action: true})
      };
    }
  }

  let paymentInfoDetails = <PaymentInfoDetails>{};
  let paymentBankDetails = <PaymentBankDetails>{};
  let makePaymentState = <IPaymentDetails> {}
  
  paymentInfoDetails.banks = [paymentBankDetails];
  
  beforeEach(async () => {     

    await TestBed.configureTestingModule({
      declarations: [ ],
      imports: [ FormsModule, ReactiveFormsModule],
      providers: [
        { provide: BillingService, useValue: mockbillingService },
        {provide: PayState, useValue: mockMakePaymentState},
        { provide: MatDialog, useClass: MatDialogMock } 
      ]
    })
    .compileComponents();

    fixture = TestBed.createComponent(DetailsComponent);
    component = fixture.componentInstance;
     httpMock = TestBed.inject(HttpTestingController);
     formModule = TestBed.inject(FormsModule);
    // fixture.detectChanges();



  });


  it('should call ngOnInit', () => {
     spyOn(mockMakePaymentState, 'getDetails').and.callFake(() => {
      return of(
        paymentInfoDetails
      );
    });
    spyOn(mockMakePaymentState, 'getBankPayments').and.callFake(() => {
      return of(
        paymentBankDetails
      );
    });
    
    

   spyOn(mockMakePaymentState, 'getMakePaymentState$').and.callFake(() => {
      return of(makePaymentState);
  })

   

    fixture.detectChanges();
  });



});