ES6类开玩笑的嘲笑 [英] ES6 class jest mocking

问题描述

我有一个ES6类，需要模拟它的方法.按照文档的说明，我对此进行了手动模拟，并使构造函数被调用和声明.

I have an ES6 class which I need to mock it's methods. Following the documentation i made a manual mock of this, and got the constructor to both be called and asserted.

我使用此类的函数只是一个运行类方法之一的基本函数.

My function that consumes this class is just a basic function that runs one of the class methods.

test.js

const mockConnect = jest.fn();
const mockAccess = jest.fn();
jest.mock('../../src/connection');
const connection = require('../../src/connection').default;

connection.mockImplementation(() => {
  return {
    connect: mockConnect,
    access: mockAccess.mockReturnValue(true),
  };
});

caller_function(); 
expect(connection).toHaveBeenCalled(); // works properly as the constructor is called
expect(connection).toHaveBeenCalledWith('something'); // works
expect(mockAccess).toHaveBeenCalled(); // says it was not called when it should have

caller_function.js

import connection from 'connection';
const conn = new connection('something');

export function caller_function() {
  conn.access(); // returns undefined when mock says it should return true
}

推荐答案

之所以发生这种情况，是因为您使用的是mockImplementation()而不是手动模拟或jest.mock()，和的工厂参数您的模拟对象是在模块加载过程中创建的，因为构造函数调用不在任何函数内部.发生了什么事:

This is happening because you're using mockImplementation() instead of a manual mock or the factory parameter to jest.mock(), and your mocked object is being created during the module loading process, since the constructor call is not inside of any function. What's happening is:

1. 运行对jest.mock('../../src/connection')的调用并将connection设置为自动模拟.
2. conn对象是使用自动模拟创建的.因此，它的access方法返回undefined.
3. 对mockImplementation()的调用发生，更改了connection模拟.但是，由于已经创建了conn对象，因此无法获得自定义实现.

1. The call to jest.mock('../../src/connection') runs and sets connection to be an automatic mock.
2. The conn object is created using the automatic mock. Therefore its access method returns undefined.
3. The call to mockImplementation() happens, changing the connection mock. However, since the conn object has already been created, it doesn't get the custom implementation.

将构造函数调用移至caller_function是修复它的一种方法:

Moving the constructor call into caller_function is one way to fix it:

export function caller_function() {
  const conn = new connection('something');
  conn.access();
}

您还可以在jest.mock()中使用factory参数，在此处指定实现，而不用调用mockImplementation().这样，您就不必更改实现代码:

You could also use the factory parameter to jest.mock(), specifying the implementation there, instead of calling mockImplementation(). That way you won't have to change your implementation code:

const mockConnect = jest.fn();
const mockAccess = jest.fn();
import connection from '../../src/connection';
jest.mock('./so-import', () => {
  return jest.fn().mockImplementation(() => {
    return {
      connect: mockConnect,
      access: mockAccess.mockReturnValue(true)
    };
  });
});

...

顺便说一句，ES6类名称的约定以大写字母开头.我暂时对小写字母connection感到困惑.

BTW the convention for ES6 class names is to begin with an uppercase letter. I was temporarily confused by the lowercase name connection.

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