Enzyme/Jest：如何测试是否调用了模拟函数

Question

我正在尝试使用 jest/enzyme 在我的 changeIt() 函数中测试对 fetch() 的调用。 但显然我做错了什么：

example.js

import fetch from 'node-fetch'

export default class Example extends Component {
  changeIt (id, value) {
    fetch('http://localhost/set-status?id=' + id + '&value=' + value)
  }

  render () {
    return (
      <div>something </div>
    )
  }
}

example.test.js

jest.mock('node-fetch')
test('should call fetch()', () => {
  const id = 1
  const value = 50
  const fetch = jest.fn() // <- This is wrong
  const wrapper = shallow(<Example />)
  wrapper.instance().changeIt(id, value)
  expect(fetch).toHaveBeenCalled() // <- This is wrong
})

Answer 1

您需要正确模拟 node-fetch 模块。因为它在node_modules中，所以你需要将node-fetch放在与node_modules同级的__mocks__文件夹中，例如：

├── node_modules/
│   ├── node-fetch/
├── __mocks__/
│   ├── node-fetch.js

在node-fetch.js里面放：

export default jest.fn();

最后在您的测试文件中导入fetch 并像这样模拟它：

import Example from './Bla';
import { shallow } from 'enzyme';
import React from 'react';
import fetch from 'node-fetch';
/**
 * Important! Import the mocked function.
 * Start the mocking with jest.mock('node-fetch').
 * Stop the mocking with jest.unmock('node-fetch').
 */    
jest.mock('node-fetch');

test('should call fetch()', () => {
  const id = 1
  const value = 50
  const wrapper = shallow(<Example />)
  wrapper.instance().changeIt(id, value)
  expect(fetch).toHaveBeenCalled() // now it works
})

Read more about mocking node_modules packages in jest here.