我想用Jest in a Typescript Express env来模拟这个异步函数。

// src/helpers/user.ts
import { UserModel } from "../models";

export const getUserByUsername = async (username: string) => {
  return UserModel.findOne({ username }).exec()
}

个字符
以下是我失败的测试：

// src/helpers/user.test.ts
describe("getUserByUsername():", () => {
  test('should return a user if username matches', async () => {
    const mockUser: User = await userFactory.build("user");

    const spy = jest.spyOn(UserModel, "findOne");
    spy.mockImplementationOnce(() => Promise.resolve(mockUser))

    const userByUsernameResult = usersHelper.getUserByUsername(mockUser.username);

    await expect(userByUsernameResult).resolves.toEqual(expect.objectContaining({ username: mockUser.username })); 
  });
});

型
我得到的错误消息：
expect（received）.resolves.toEqual（）接收到的promise rejected而不是resolved Rejected的值：[类型错误：models_1.UserModel.findOne（...）.exec不是函数]
你能帮帮我吗？

UPDATE：我在其他一些测试中使用了在这种情况下也有效的MongoDB Memory Server方法（见下文）。然而，我真的很想知道如何通过模拟.exec()（见上文）来实现这一点。

// src/helpers/user.test.ts
beforeAll(async () => {
  await mongoose.connect(process.env.MONGO_URL as string, { useNewUrlParser: true, useUnifiedTopology: true } as ConnectOptions, (err) => {
    if(err) {
      console.error(err);
      process.exit(1);
    }
  })
});

afterAll(async () => {
  await mongoose.connection.close();
});

describe("getUserByUsername():", () => {
  test('should return a user if username matches', async () => {
    const mockUser: User = await userFactory.build("user", {}, { setId: false });

    const validUser = new UserModel(mockUser);
    await validUser.save();

    const userByUsernameResult = usersHelper.getUserByUsername(mockUser.username);

    await expect(userByUsernameResult).resolves.toEqual(expect.objectContaining({ username: mockUser.username }));
  });

型