为什么第一个 Jest 测试会导致第二个测试失败？

Question

我有一个渲染组件列表的 React 组件。我正在运行一些测试来模拟从 JSONPlaceHolder 加载用户的 axios 模块。一切正常，包括异步测试，它按预期模拟数据。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？多年来一直在敲我的头。测试之间是否需要进行一些清理？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);
        })

})

我得到的错误信息是：

    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

您只模拟了第一个axios.get 调用，因为您使用的是mockImplementationOnce。

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

您可以添加一个带有mockResolvedValueOnce 的beforeEach 方法，以在每次测试之前模拟axios.get：

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

Answer 2

有同样的问题，但我没有提出请求。我正在构建一个客户端 React 应用程序并测试子组件的渲染。我有一个加载到我的 Home 组件上的图像轮播，我正在为它编写测试。如果我注释掉除一个测试（任何测试）之外的所有测试，它就会通过。如果我有多个测试（任何测试组合），它就会失败。我已经尝试过 async/await/waitFor、react-test-renderer、使用 done() - 似乎没有任何改变这种行为。

import { render, screen } from '@testing-library/react';
import ImageCarousel from '../carousel/ImageCarousel';
import localPhotos from '../../data/localPhotos';

// passing in the full array of images is not necessary, it will cause the test to time out
const testArray = localPhotos.slice(0, 3);

describe('Image Carousel', () => {
    it('renders without error', () => {
      render(<ImageCarousel images={testArray} />);
      const imageCarousel = screen.getByTestId('image-carousel');
      expect(imageCarousel).toBeInTheDocument();
    });
    // it('displays the proper alt text for images', () => {
    //   render(<ImageCarousel images={testArray} />);
    //   const photo1 = screen.getByAltText(localPhotos[0].alt);
    //   const photo2 = screen.getByAltText(localPhotos[1].alt);
    //   expect(photo1.alt).toBe(localPhotos[0].alt);
    //   expect(photo2.alt).toBe(localPhotos[1].alt);
    // });
    // it("displays full-screen icons", () => {
    //   render(<ImageCarousel images={testArray} />);
    //   const fullScreenIcons = screen.getAllByTestId('full-screen-icon');
    //   expect(fullScreenIcons.length).toBe(testArray.length);
    // })
  // shows controls when showControls is true
  // does not show controls when showControls is false
  //   it('displays the proper number of images', () => {
  //     render(<ImageCarousel images={testArray} />);
  //     const carousel_images = screen.getAllByTestId('carousel_image');
  //     expect(carousel_images.length).toBe(testArray.length);
  //   });
  // calls next when clicked
  // calls previous when clicked
  // returns to first image when next is clicked and last image is shown
  // moves to last image when previous is clicked and first image is shown
});