模拟导出为对象的 ES6 类模块答案

【问题标题】：Mocking ES6 Class Modules exported as objects模拟导出为对象的 ES6 类模块
【发布时间】：2020-11-08 01:41:54
【问题描述】：

考虑下面的例子

//AuthenticatorService.js
const UserService = require("./UserService");
class AuthenticatorService{
   constructor(){
      //Some initialisation
   }
//Some methods
}
module.exports = new AuthenticatorService();

//UserService.js
class UserService{
   constructor(){
     //Again some initialisations
   }
}
module.exports = new UserService();

因此，当我尝试在 AuthenticatorService.spec.js 文件中模拟 UserService 类时，UserService 的构造函数正在以这种方式导出时被执行。但我不希望那被执行。是否可以在不调用其构造函数的情况下模拟 AuthenticatorService.spec.js 文件中的 UserService 模块。

【问题讨论】：

标签： javascript node.js ecmascript-6 mocking jestjs

【解决方案1】：

您可以使用jest.mock(moduleName, factory, options) 来执行此操作。

例如

UserService.js:

class UserService {
  constructor() {
    console.log('initialize UserService');
  }
  hello() {
    console.log('user hello real implementation');
  }
}
module.exports = new UserService();

AuthenticatorService.js:

const userService = require('./UserService');

class AuthenticatorService {
  constructor() {
    console.log('initialize AuthenticatorService');
  }
  hello() {
    userService.hello();
  }
}

module.exports = new AuthenticatorService();

AuthenticatorService.test.js:

const authenticatorService = require('./AuthenticatorService');
const userService = require('./UserService');

jest.mock('./UserService', () => {
  return { hello: jest.fn() };
});

describe('62967707', () => {
  afterAll(() => {
    jest.resetAllMocks();
  });
  it('should pass', () => {
    userService.hello.mockImplementationOnce(() => console.log('user hello mocked implementation'));
    authenticatorService.hello();
    expect(userService.hello).toBeCalledTimes(1);
  });
});

单元测试结果：

 PASS  stackoverflow/62967707/AuthenticatorService.test.js (12.636s)
  62967707
    ✓ should pass (11ms)

  console.log
    initialize AuthenticatorService

      at new AuthenticatorService (stackoverflow/62967707/AuthenticatorService.js:5:13)

  console.log
    user hello mocked implementation

      at Object.<anonymous> (stackoverflow/62967707/AuthenticatorService.test.js:13:60)

-------------------------|---------|----------|---------|---------|-------------------
File                     | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
-------------------------|---------|----------|---------|---------|-------------------
All files                |     100 |      100 |     100 |     100 |                   
 AuthenticatorService.js |     100 |      100 |     100 |     100 |                   
-------------------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        14.703s

从日志中可以看到，UserService 的真正构造函数不会执行。我们模拟了UserService 类实例的hello 方法。

【讨论】：