角度单元测试用例中的错误：TypeError: this.userService.currentUser.subscribe is not a function

Question

我在运行 Angular 单元测试用例时遇到此错误：

测试结果

SidebarComponent
   × should create
    TypeError: this.userService.currentUser.subscribe is not a function

sidebar.component.spec.ts

describe('SidebarComponent', () => {
  let fixture: ComponentFixture<SidebarComponent>;
  let mockUserService;

  beforeEach(() => {
    mockUserService = jasmine.createSpyObj(['currentUser']);

    TestBed.configureTestingModule({
      imports: [HttpClientTestingModule],
      declarations: [SidebarComponent],
      schemas: [NO_ERRORS_SCHEMA],
      providers: [{ provide: UserService, useValue: mockUserService }]
    });

    fixture = TestBed.createComponent(SidebarComponent);
  });

  fit('should create', () => {
    mockUserService.currentUser.and.returnValue(of('Here goes an object'));
    fixture.detectChanges();
    expect(SidebarComponent).toBeTruthy();
  });
});

sidebar.component.ts

ngOnInit() {
    this.userService.currentUser.subscribe(currentUser => {
        // Some code here
    });
}

package.json

"devDependencies": {
    "@types/jasmine": "2.8.8",
    "@types/jasminewd2": "2.0.3",
    "@types/node": "9.6.23",
    "jasmine-core": "2.99.1",
    "jasmine-spec-reporter": "4.2.1",
    "karma": "4.2.0",
    "karma-chrome-launcher": "2.2.0",
    "karma-cli": "2.0.0",
    "karma-coverage-istanbul-reporter": "1.4.3",
    "karma-jasmine": "2.0.1",
    "karma-jasmine-html-reporter": "1.4.0",
    "karma-junit-reporter": "1.2.0",
    "karma-spec-reporter": "0.0.32",
    "protractor": "6.0.0",
    "rxjs-tslint": "0.1.7",
}

user.service.ts

@Injectable({ providedIn: 'root'})
export class UserService {
  private currentUserSubject = new BehaviorSubject({});
  public currentUser: Observable<User> = this.currentUserSubject.asObservable().pipe(distinctUntilChanged());

  setUser(user) {
      this.currentUserSubject.next({ ...newUser });
  }
}

据我所知，要解决这个问题，我们需要在以下语句中使用：

mockUserService.currentUser.and.returnValue(of('Here going an object'));

其中 of 是从 'rxjs' 导入的。当我记录 of('Here going an object') 的值时，它表明它是可观察的。

我该如何解决这个问题？

Answer 1

用spyOn模拟具体的服务方法怎么样：

const userService = TestBed.get(UserService);
const mockedResponse = {}; // Modify as per your need
spyOn(userService, 'currentUser').and.callFake(() => {
  return of(mockedResponse);
});

这对我有用。

Answer 2

在对这个测试做了一些工作之后，我发现我们不能使用 spyOn(userService, 'currentUser')。原因很明显，currentUser 不是一个函数，而是一个变量，我们在其中分配了一个 observable。 SpyOn 将在此创建一个假函数，但我们需要的是一个 observable。所以我们可以使用 userService.setUser 方法来适当地设置 currentUser 的值。

sidebar.component.spec.ts

describe('SidebarComponent', () => {
  let component: SidebarComponent;
  let fixture: ComponentFixture<SidebarComponent>;
  let userService: UserService;

  beforeEach(done => {
    TestBed.configureTestingModule({
    imports: [HttpClientTestingModule, RouterTestingModule],
    declarations: [SidebarComponent],
    schemas: [NO_ERRORS_SCHEMA]
  })
  .compileComponents()
  .then(() => {
    fixture = TestBed.createComponent(SidebarComponent);
    component = fixture.componentInstance;

    userService = TestBed.get(UserService);
    userService.setUser(userInfo);

    fixture.detectChanges();
    done();
  });
 });

 it('should create', done => {
   expect(component).toBeTruthy();
   done();
 });
})

Answer 3

你可以做类似的嘲笑：

export const mockUserService= {
    currentUser = {
        subscribe() {
          return of({ 
              // whatever here
          });
        }
    }
};

代码创建了一个虚假服务。这个假服务可以添加被测试的组件使用的所有功能和成员。