版本：30.0

测试React程序

At Facebook, we use Jest to test React applications.

安装

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。 We are using the babel-jest package and the react babel preset to transform our code inside of the test environment. Also see using babel.

运行

npm
Yarn
pnpm
Bun

npm install --save-dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

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

pnpm add --save-dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

bun add --dev jest babel-jest @babel/preset-env @babel/preset-react react-test-renderer

Your package.json should look something like this (where <current-version> is the actual latest version number for the package). 请添加脚本项目和 jest 配置：

{
  "dependencies": {
    "react": "<current-version>",
    "react-dom": "<current-version>"
  },
  "devDependencies": {
    "@babel/preset-env": "<current-version>",
    "@babel/preset-react": "<current-version>",
    "babel-jest": "<current-version>",
    "jest": "<current-version>",
    "react-test-renderer": "<current-version>"
  },
  "scripts": {
    "test": "jest"
  }
}

babel.config.js
module.exports = {
  presets: [
    '@babel/preset-env',
    ['@babel/preset-react', {runtime: 'automatic'}],
  ],
};

And you're good to go!

快照测试

Let's create a snapshot test for a Link component that renders hyperlinks:

Link.js
import {useState} from 'react';

const STATUS = {
  HOVERED: 'hovered',
  NORMAL: 'normal',
};

export default function Link({page, children}) {
  const [status, setStatus] = useState(STATUS.NORMAL);

  const onMouseEnter = () => {
    setStatus(STATUS.HOVERED);
  };

  const onMouseLeave = () => {
    setStatus(STATUS.NORMAL);
  };

  return (
    <a
      className={status}
      href={page || '#'}
      onMouseEnter={onMouseEnter}
      onMouseLeave={onMouseLeave}
    >
      {children}
    </a>
  );
}

备注

示例正在使用函数组件，但类组件可以同样方式测试。 See React: Function and Class Components. Reminders that with Class components, we expect Jest to be used to test props and not methods directly.

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：

Link.test.js
import renderer from 'react-test-renderer';
import Link from '../Link';

it('changes the class when hovered', () => {
  const component = renderer.create(
    <Link page="http://www.facebook.com">Facebook</Link>,
  );
  let tree = component.toJSON();
  expect(tree).toMatchSnapshot();

  // manually trigger the callback
  renderer.act(() => {
    tree.props.onMouseEnter();
  });
  // re-rendering
  tree = component.toJSON();
  expect(tree).toMatchSnapshot();

  // manually trigger the callback
  renderer.act(() => {
    tree.props.onMouseLeave();
  });
  // re-rendering
  tree = component.toJSON();
  expect(tree).toMatchSnapshot();
});

When you run yarn test or jest, this will produce an output file like this:

__tests__/__snapshots__/Link.test.js.snap
exports[`changes the class when hovered 1`] = `
<a
  className="normal"
  href="http://www.facebook.com"
  onMouseEnter={[Function]}
  onMouseLeave={[Function]}
>
  Facebook
</a>
`;

exports[`changes the class when hovered 2`] = `
<a
  className="hovered"
  href="http://www.facebook.com"
  onMouseEnter={[Function]}
  onMouseLeave={[Function]}
>
  Facebook
</a>
`;

exports[`changes the class when hovered 3`] = `
<a
  className="normal"
  href="http://www.facebook.com"
  onMouseEnter={[Function]}
  onMouseLeave={[Function]}
>
  Facebook
</a>
`;

下次你运行测试时，渲染的结果将会和之前创建的快照进行比较。代码变动时，快照也应该被提交。当快照测试失败，你需要去检查是否是你想要或不想要的变动。 If the change is expected you can invoke Jest with jest -u to overwrite the existing snapshot.

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

Snapshot Testing with Mocks, Enzyme and React 16+

快照测试在 Enzyme 和 React 16+ 中使用时有一个注意事项。如果您使用以下方式模拟模块：

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

然后您将在控制台中看到警告：

Warning: <SomeComponent /> is using uppercase HTML. Always use lowercase HTML tags in React.

# Or:
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 触发这些警告，取决于它是如何检查元素类型的，在这些检查中模拟模块会失败。您可以：

渲染为纯文本。这种方式你看不到传递给模拟组件的Props，但最直观。
```
jest.mock('./SomeComponent', () => () => 'SomeComponent');
```
渲染为自定义元素。 DOM的“自定义元素“不会检查任何属性，所以也不会触发warnings。他们都是小写的、中划线分割的单词。
```
jest.mock('./Widget', () => () => <mock-widget />);
```
Use react-test-renderer. The test renderer doesn't care about element types and will happily accept e.g. SomeComponent. 你可以使用react-test-renderer进行快照检测，使用单独使用Enzyme进行组件行为监测。
禁用所有警告（在jest setup file中）：
```
jest.mock('fbjs/lib/warning', () => require('fbjs/lib/emptyFunction'));
```
这是下策，因为所有有用的警告也都会丢失。不过，依然有其适用场景。例如我们需要测试 react-native的组件编译为DOM，很多警告是无关紧要的。另一个方式是使用控制台忽略特定的警告信息。

DOM测试

If you'd like to assert, and manipulate your rendered components you can use @testing-library/react, Enzyme, or React's TestUtils. The following example use @testing-library/react.

@testing-library/react

npm
Yarn
pnpm
Bun

npm install --save-dev @testing-library/react

yarn add --dev @testing-library/react

pnpm add --save-dev @testing-library/react

bun add --dev @testing-library/react

这里我们实现一个在两个标签之间切换的复选框。

CheckboxWithLabel.js
import {useState} from 'react';

export default function CheckboxWithLabel({labelOn, labelOff}) {
  const [isChecked, setIsChecked] = useState(false);

  const onChange = () => {
    setIsChecked(!isChecked);
  };

  return (
    <label>
      <input type="checkbox" checked={isChecked} onChange={onChange} />
      {isChecked ? labelOn : labelOff}
    </label>
  );
}

__tests__/CheckboxWithLabel-test.js
import {cleanup, fireEvent, render} from '@testing-library/react';
import CheckboxWithLabel from '../CheckboxWithLabel';

// Note: running cleanup afterEach is done automatically for you in @testing-library/react@9.0.0 or higher
// unmount and cleanup DOM after the test is finished.
afterEach(cleanup);

it('CheckboxWithLabel changes the text after click', () => {
  const {queryByLabelText, getByLabelText} = render(
    <CheckboxWithLabel labelOn="On" labelOff="Off" />,
  );

  expect(queryByLabelText(/off/i)).toBeTruthy();

  fireEvent.click(getByLabelText(/off/i));

  expect(queryByLabelText(/on/i)).toBeTruthy();
});

The code for this example is available at examples/react-testing-library.

自定义转译器

如果你需要更多高级功能，你也可以自定义你的转译器。 Instead of using babel-jest, here is an example of using @babel/core:

custom-transformer.js
'use strict';

const {transform} = require('@babel/core');
const jestPreset = require('babel-preset-jest');

module.exports = {
  process(src, filename) {
    const result = transform(src, {
      filename,
      presets: [jestPreset],
    });

    return result || src;
  },
};

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

To make this work with Jest you need to update your Jest configuration with this: "transform": {"\\.js$": "path/to/custom-transformer.js"}.

If you'd like to build a transformer with babel support, you can also use babel-jest to compose one and pass in your custom configuration options:

const babelJest = require('babel-jest');

module.exports = babelJest.createTransformer({
  presets: ['my-custom-preset'],
});

See dedicated docs for more details.

安装​

快照测试​

Snapshot Testing with Mocks, Enzyme and React 16+​

DOM测试​

@testing-library/react​

自定义转译器​

安装

快照测试

Snapshot Testing with Mocks, Enzyme and React 16+

DOM测试

@testing-library/react

自定义转译器