Jest Mock Service 参数不可分配

Question

我的 NestJs 应用程序中有一个简单的控制器。

@Post('/')
async create(@Body() createUserRequest: CreateUserRequest): Promise<User> {
  return await this.userService.create(createUserRequest);
}

我的目标是使用笑话来测试这个功能。正如您所看到的，控制器注入了一个UserService. 所以我尝试在单元测试中模拟此服务。测试用例如下所示。

describe('User Controller', () => {
  let userService: UserService;
  let userController: UserController;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      controllers: [UserController],
      providers: [UserService],
    }).compile();

    userService = module.get<UserService>(UserService);
    userController = module.get<UserController>(UserController);
  });

  describe('create', () => {
    it('should return a user', async () => {
      const result = new User();

      jest.spyOn(userService, 'create').mockImplementation(() => result);

      expect(await userController.create(new CreateUserRequest())).toBe(result);
    });
  });
});

我的问题是，jest.spyOn模拟发生的地方会产生错误。

No overload matches this call.
Overload 1 of 4, '(object: UserService, method: never): SpyInstance<never, never>', gave the following error.
Argument of type '"create"' is not assignable to parameter of type 'never'.
Overload 2 of 4, '(object: UserService, method: never): SpyInstance<never, never>', gave the following error.
Argument of type '"create"' is not assignable to parameter of type 'never'.

有人知道我的模拟有什么问题吗？我从文档中采用了这种方法。

Answer 1

这可能不是您期望的响应，但是，您可以实现相同的结果，如下所示：

// ...
describe('create', () => {
  it('should return a user', async () => {
    const result = new User();

    ((userService as unknown) as any).create = jest.fn().mockResolvedValue(result);
    // Or to ensure that the value is only called once, 
    // go ahead and use 'mockResolvedValueOnce'

    expect(await userController.create(new CreateUserRequest())).toBe(result);
  });
});
// ...