为什么第一个 Jest 测试导致第二个测试失败？

Question

我有一个 React 组件，它呈现组件列表。我正在运行一些测试，这些测试模拟 axios 模块，该模块从 JSONPlaceHolder 加载到用户中。一切工作正常，包括异步测试和它的模拟数据如预期。但是，如果您查看下面的代码，只要第一个测试被注释掉，它就会通过？我错过了什么吗？多年来一直敲着我的头。测试之间是否需要进行一些清理工作？提前致谢。

import { waitForElement } from 'enzyme-async-helpers';
import UsersList from '../UsersList';
import axios from 'axios';

const mockUsers = [
    {
        "id": 1,
        "name": "Leanne Mock",
        "username": "Bret",
        "email": "Sincere@april.biz"
    },
    {
        "id": 2,
        "name": "John Mock",
        "username": "Jospeh",
        "email": "wacky@april.biz"
    }
]

axios.get.mockImplementationOnce(() => Promise.resolve({
    data: mockUsers
}))


describe('<UsersList /> tests:', () => {

        //WHEN I UNCOMMENT THIS TEST THE SECOND TEST FAILS?
        test('It renders without crashing', (done) => {
           // const wrapper = shallow(<UsersList />);
        });

        test('It renders out <User /> components after axios fetches users', async () => {
            const wrapper = shallow(<UsersList />);
            expect(wrapper.find('#loading').length).toBe(1); //loading div should be present


            await waitForElement(wrapper, 'User'); //When we have a User component found we know data has loaded
            expect(wrapper.find('#loading').length).toBe(0); //loading div should no longer be rendered
            expect(axios.get).toHaveBeenCalledTimes(1);

            expect(wrapper.state('users')).toEqual(mockUsers); //check the state is now equal to the mockUsers
            expect(wrapper.find('User').get(0).props.name).toBe(mockUsers[0].name); //check correct data is being sent down to User components
            expect(wrapper.find('User').get(1).props.name).toBe(mockUsers[1].name);
        })

})

我收到的错误消息是：

    The render tree at the time of timeout:
     <div
      id="loading"
    >
       Loading users
    </div>

  console.warn node_modules/enzyme-async-helpers/lib/wait.js:42
    As JSON:
     { node:
       { nodeType: 'host',
         type: 'div',
         props: { id: 'loading', children: ' Loading users ' },
         key: undefined,
         ref: null,
         instance: null,
         rendered: ' Loading users ' },
      type: 'div',
      props: { id: 'loading' },
      children: [ ' Loading users ' ],
      '$$typeof': Symbol(react.test.json) }

Test Suites: 1 failed, 1 total
Tests:       2 failed, 2 total

Answer 1

您只模拟第一次axios.get调用，因为您使用的是mockImplementationOnce。

当您shallow(<UsersList />)两次时，第二次是加载用户超时。

您可以添加一个beforeEach方法，其中包含一个mockResolvedValueOnce，以模拟axios.get每个测试之前的情况：

beforeEach(() => {
  axios.get.mockResolvedValueOnce({data: mockUsers});
}