Angular Jasmine中的模拟Firestore文档

我已经为使用AngularFirestore的Ionic 4应用程序创建了单元测试，但是我没有成功地模拟firestore，有人知道如何模拟它吗

我已经试过了一个

spyOn（firestore.doc.prototype，'set'）

但它返回此错误

：set（）方法不存在

[...]

angularFirestoreStub = {
  doc() {
    return {
      set() {
        return Promise.resolve();
      },
    };
  },
};

TestBed.configureTestingModule({
  providers: [
    UserService,
      { provide: AngularFireAuth, useValue: angularFireAuthStub },
      { provide: AngularFirestore, useValue: angularFirestoreStub }
    ],
}).compileComponents();

beforeEach(() => {
  service = TestBed.get(UserService);
  fireAuth = TestBed.get(AngularFireAuth);
  firestore = TestBed.get(AngularFirestore);
});

[...]

it('deve salvar um perfil de usuário no Firestore', () => {
  spyOn(firestore, 'doc').and.callThrough();
  spyOn(firestore.doc.prototype, 'set');
  service.createProfile('Wk4CvT5WpPPaQBgDTiPbY3MwED52', 'userName', 'userLastName')
    .then(() => {
      expect(firestore.doc).toHaveBeenCalledWith('users/Wk4CvT5WpPPaQBgDTiPbY3MwED52');
      expect(angularFireAuthStub.doc.set).toHaveBeenCalledWith({
        firstName: 'userName', lastName: 'userLastName'
      });
    });
});

我希望有人能帮我