Testing React Apps

    如果你是 React 新手，我们建议使用 Create React App。 它已经包含了 ！ 您只需要添加 来渲染快照。

    运行

    如果你已经有一个应用，你仅需要安装一些包来使他们运行起来。 我们使用babel-jest包和babel-preset-react，从而在测试环境中转换我们代码。 可参考使用babel

    运行

    1. yarn add --dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

    你的package.json文件应该像下面这样(<current-version>是当前包的最新版本号) 请添加脚本项目和 jest 配置：

    1. // package.json
    2.   "dependencies": {
    3.     "react": "<current-version>",
    4.     "react-dom": "<current-version>"
    5.   },
    6.   "devDependencies": {
    7.     "@babel/preset-env": "<current-version>",
    8.     "@babel/preset-react": "<current-version>",
    9.     "babel-jest": "<current-version>",
    10.     "jest": "<current-version>",
    11.     "react-test-renderer": "<current-version>"
    12.   },
    13.   "scripts": {
    14.     "test": "jest"
    15.   }
    1. // babel.config.js
    2. module.exports = {
    3.   presets: ['@babel/preset-env', '@babel/preset-react'],
    4. };

    准备工作已经完成！

    让我们来为一个渲染超链接的 Link 组件创建

    1. // Link.react.js
    2. import React from 'react';
    4. const STATUS = {
    5.   HOVERED: 'hovered',
    6.   NORMAL: 'normal',
    7. };
    9. export default class Link extends React.Component {
    10.   constructor(props) {
    11.     super(props);
    13.     this._onMouseEnter = this._onMouseEnter.bind(this);
    14.     this._onMouseLeave = this._onMouseLeave.bind(this);
    16.     this.state = {
    17.       class: STATUS.NORMAL,
    18.     };
    19.   }
    21.   _onMouseEnter() {
    22.     this.setState({class: STATUS.HOVERED});
    23.   }
    25.   _onMouseLeave() {
    26.     this.setState({class: STATUS.NORMAL});
    27.   }
    29.   render() {
    30.     return (
    31.       <a
    32.         href={this.props.page || '#'}
    33.         onMouseEnter={this._onMouseEnter}
    34.         onMouseLeave={this._onMouseLeave}
    35.       >
    36.         {this.props.children}
    38.     );
    39.   }
    40. }

    现在，使用React的test renderer和Jest的快照特性来和组件交互，获得渲染结果和生成快照文件：

    当你运行 npm test 或者 jest，将产生一个像下面的文件：

    1. // __tests__/__snapshots__/Link.react.test.js.snap
    2. exports[`Link changes the class when hovered 1`] = `
    3. <a
    4.   className="normal"
    5.   href="http://www.facebook.com"
    6.   onMouseEnter={[Function]}
    7.   onMouseLeave={[Function]}>
    8.   Facebook
    9. </a>
    10. `;
    12. exports[`Link changes the class when hovered 2`] = `
    13. <a
    14.   className="hovered"
    15.   href="http://www.facebook.com"
    16.   onMouseEnter={[Function]}
    17.   onMouseLeave={[Function]}>
    18.   Facebook
    19. </a>
    20. `;
    22. exports[`Link changes the class when hovered 3`] = `
    23. <a
    24.   className="normal"
    25.   href="http://www.facebook.com"
    26.   onMouseEnter={[Function]}
    27.   onMouseLeave={[Function]}>
    28.   Facebook
    29. </a>
    30. `;

    该示例代码在 examples/snapshot

    快照测试与 Mocks, Enzyme 和 React 16

    There’s a caveat around snapshot testing when using Enzyme and React 16+. If you mock out a module using the following style:

    1. jest.mock('../SomeDirectory/SomeComponent', () => 'SomeComponent');

    Then you will see warnings in the console:

    1. Warning: <SomeComponent /> is using uppercase HTML. Always use lowercase HTML tags in React.
    3. # Or:
    4. Warning: The tag <SomeComponent> is unrecognized in this browser. If you meant to render a React component, start its name with an uppercase letter.

    React 16 triggers these warnings due to how it checks element types, and the mocked module fails these checks. Your options are:

    1. Render as text. This way you won’t see the props passed to the mock component in the snapshot, but it’s straightforward:

      1. jest.mock('./SomeComponent', () => () => 'SomeComponent');

    2. Render as a custom element. DOM “custom elements” aren’t checked for anything and shouldn’t fire warnings. They are lowercase and have a dash in the name.

    3. Use react-test-renderer. The test renderer doesn’t care about element types and will happily accept e.g. SomeComponent. You could check snapshots using the test renderer, and check component behavior separately using Enzyme.

    4. Disable warnings all together (should be done in your jest setup file):

      1. jest.mock('fbjs/lib/warning', () => require('fbjs/lib/emptyFunction'));

      This shouldn’t normally be your option of choice as useful warnings could be lost. However, in some cases, for example when testing react-native’s components we are rendering react-native tags into the DOM and many warnings are irrelevant. Another option is to swizzle the console.warn and suppress specific warnings.

    react-testing-library

    You have to run yarn add --dev @testing-library/react to use react-testing-library.

    Let’s implement a checkbox which swaps between two labels:

    1. // CheckboxWithLabel.js
    3. import React from 'react';
    5. export default class CheckboxWithLabel extends React.Component {
    6.   constructor(props) {
    7.     super(props);
    8.     this.state = {isChecked: false};
    10.     // bind manually because React class components don't auto-bind
    11.     this.onChange = this.onChange.bind(this);
    12.   }
    14.   onChange() {
    16.   }
    18.   render() {
    19.     return (
    20.       <label>
    21.         <input
    22.           type="checkbox"
    23.           checked={this.state.isChecked}
    24.           onChange={this.onChange}
    25.         />
    26.         {this.state.isChecked ? this.props.labelOn : this.props.labelOff}
    27.       </label>
    28.     );
    29.   }
    30. }
    1. // __tests__/CheckboxWithLabel-test.js
    2. import React from 'react';
    3. import {cleanup, fireEvent, render} from '@testing-library/react';
    4. import CheckboxWithLabel from '../CheckboxWithLabel';
    6. // Note: running cleanup afterEach is done automatically for you in @testing-library/react@9.0.0 or higher
    7. // unmount and cleanup DOM after the test is finished.
    8. afterEach(cleanup);
    10. it('CheckboxWithLabel changes the text after click', () => {
    11.   const {queryByLabelText, getByLabelText} = render(
    12.     <CheckboxWithLabel labelOn="On" labelOff="Off" />,
    13.   );
    15.   expect(queryByLabelText(/off/i)).toBeTruthy();
    17.   fireEvent.click(getByLabelText(/off/i));
    19.   expect(queryByLabelText(/on/i)).toBeTruthy();
    20. });

    The code for this example is available at .

    Enzyme

    You have to run yarn add --dev enzyme to use Enzyme. If you are using a React version below 15.5.0, you will also need to install react-addons-test-utils.

    Let’s rewrite the test from above using Enzyme instead of react-testing-library. 在这个例子中我们使用了 Enzyme 的。

    1. // __tests__/CheckboxWithLabel-test.js
    3. import React from 'react';
    4. import {shallow} from 'enzyme';
    5. import CheckboxWithLabel from '../CheckboxWithLabel';
    7. test('CheckboxWithLabel changes the text after click', () => {
    8.   // Render a checkbox with label in the document
    9.   const checkbox = shallow(<CheckboxWithLabel labelOn="On" labelOff="Off" />);
    11.   expect(checkbox.text()).toEqual('Off');
    13.   checkbox.find('input').simulate('change');
    15.   expect(checkbox.text()).toEqual('On');
    16. });

    The code for this example is available at examples/enzyme.

    If you need more advanced functionality, you can also build your own transformer. Instead of using babel-jest, here is an example of using babel:

    Don’t forget to install the @babel/core and babel-preset-jest packages for this example to work.

    为了使这个与 Jest 一起工作，您需要更新您的 Jest 配置："transform": {"\\.js$": "path/to/custom-transformer.js"}。

    1. const babelJest = require('babel-jest');
    3. module.exports = babelJest.createTransformer({
    4.   presets: ['my-custom-preset'],