使用 Jest 进行测试时如何更改 const 值

Question

您好，我正在为我的 node.js API 编写测试，但遇到了问题。我正在使用“const = emailCount”验证我的代码中是否存在电子邮件。如果确实存在，则返回错误 JSON。如果它不存在，它会返回一个成功的 JSON。但是我不确定如何模拟我在代码中声明的内部常量。

代码如下：

    async function registerUser(req, res) {
       // Request
      const email = req.body.email;
      const password = req.body.password;
      const firstName = req.body.firstName;
      const lastName = req.body.lastName;
      const inviteCode = req.body.inviteCode;
      let errMessage = [];
 if (!firstName) {
    errMessage.push("first Name Required")
}

if (!lastName) {
    errMessage.push("last Name Required")
}
if (!inviteCode) {
    errMessage.push("inviteCode Required")
}
if (!email) {
    errMessage.push("email Required")
}
if (!password) {
    errMessage.push("password Required")
}

if (errMessage.length > 0) {
    res.json({ code: "422", message: errMessage })
}

const accessToken = jwt.sign({
    email: email,
    firstName: firstName,
    lastName: lastName
}, config.jwtSecret);

const emailCount = await db.doesEmailExists(email)

if (emailCount.doesEmailExists > 0) {
    res.json({ Errors: "Account already exists" })
} else {
    db.createUser({
        username: email,
        hashedPassword: password,
        firstName: firstName,
        lastName: lastName,
    }).then(data => {
        res.json({
            id: data.insertId,
            firstName: firstName,
            lastName: lastName,
            token: accessToken,
            role: 'user'
        })
    }).catch(err => res.json({ Error: err }))
}

}

这是我的测试代码

  test('POST /user/register', async () => {
     //use super test to send post method with json payload of newUser
     const res = await agent.post('/user/register').send(newUser);


     expect(res.statusCode).toEqual(200) 
     expect(res.body).toHaveProperty('Errors') || expect(res.body).toHaveProperty('token');
  })

如果可能的话，我最终想在我的测试中更改 emailCount 的值，以便在有用户和没有用户的情况下测试不同的响应。

Answer 1

您不应该模拟您的代码，而应该模拟您的依赖项，db 就是这样。

例如，您可以这样编写测试场景：

const db = require('./path/to/db.js');

// auto-create mock
jest.mock('./path/to/db.js')


describe('POST /user/register', () => {

  describe('when email Exists'), () => {
    // defining the "res" object here
    // will allow you to execute the request one
    // and separate the expectations in different
    // test cases, which will provide better visibility
    // on what exactly have failed (in the future)
    let res;
    beforeAll(async () => {
      db.doesEmailExists.mockResolvedValue({
        doesEmailExists: 789
      });
      res = await agent.post('/user/register').send(newUser);
    });

    it('should probably return something more than 200', () => {
      expect(res.statusCode).toBeGreaterThanOrEqual(200)
    });

    it('should return Error in response Body', () => {
      expect(res.body).toHaveProperty('Errors')
    });
  });


  describe('when email DOES NOT Exists'), () => {
    let res;
    beforeAll(async () => {
      db.doesEmailExists.mockResolvedValue({
        doesEmailExists: 0
      });
      res = await agent.post('/user/register').send(newUser);
    });

    it('should probably return statusCode 200', () => {
      expect(res.statusCode).toEqual(200)
    });

    it('should return token', () => {
      expect(res.body).toHaveProperty('token')
    });
  });
});

注意：您还需要模拟db.createUser 的返回值，因为自动模拟将生成一个jest.fn()，它返回undefined