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版本：29.7

使用 webpack

Jest can be used in projects that use webpack to manage assets, styles, and compilation. webpack does offer some unique challenges over other tools because it integrates directly with your application to allow managing stylesheets, assets like images and fonts, along with the expansive ecosystem of compile-to-JavaScript languages and tools.

Webpack 示例​

我们通过以下常见的webpack 配置文件，将其转化为符合Jest使用的配置。

webpack.config.js
module.exports = {
  module: {
    rules: [
      {
        test: /\.jsx?$/,
        exclude: ['node_modules'],
        use: ['babel-loader'],
      },
      {
        test: /\.css$/,
        use: ['style-loader', 'css-loader'],
      },
      {
        test: /\.gif$/,
        type: 'asset/inline',
      },
      {
        test: /\.(ttf|eot|svg)$/,
        type: 'asset/resource',
      },
    ],
  },
  resolve: {
    alias: {
      config$: './configs/app-config.js',
      react: './vendor/react-master',
    },
    extensions: ['.js', '.jsx'],
    modules: [
      'node_modules',
      'bower_components',
      'shared',
      '/shared/vendor/modules',
    ],
  },
};

If you have JavaScript files that are transformed by Babel, you can enable support for Babel by installing the babel-jest plugin. Non-Babel JavaScript transformations can be handled with Jest's transform config option.

处理静态文件​

接下来，让我们配置Jest，使其优雅地处理资源文件，如样式表和图像。 通常，这些文件在测试中无足轻重，因为我们可以安全地mock他们。 然而， 如果你使用CSS模块，那么最好是给你的类名查找模拟一个代理。

jest.config.js
module.exports = {
  moduleNameMapper: {
    '\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
      '<rootDir>/__mocks__/fileMock.js',
    '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
  },
};

所有mock文件本身:

__mocks__/styleMock.js
module.exports = {};
__mocks__/fileMock.js
module.exports = 'test-file-stub';

模拟 CSS 模块​

You can use an ES6 Proxy to mock CSS Modules:

npm install --save-dev identity-obj-proxy

Then all your className lookups on the styles object will be returned as-is (e.g., styles.foobar === 'foobar'). This is pretty handy for React Snapshot Testing.

jest.config.js (for CSS Modules)
module.exports = {
  moduleNameMapper: {
    '\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
      '<rootDir>/__mocks__/fileMock.js',
    '\\.(css|less)$': 'identity-obj-proxy',
  },
};

If moduleNameMapper cannot fulfill your requirements, you can use Jest's transform config option to specify how assets are transformed. For example, a transformer that returns the basename of a file (such that require('logo.jpg'); returns 'logo') can be written as:

fileTransformer.js
const path = require('path');

module.exports = {
  process(sourceText, sourcePath, options) {
    return {
      code: `module.exports = ${JSON.stringify(path.basename(sourcePath))};`,
    };
  },
};
jest.config.js (for custom transformers and CSS Modules)
module.exports = {
  moduleNameMapper: {
    '\\.(css|less)$': 'identity-obj-proxy',
  },
  transform: {
    '\\.(jpg|jpeg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm|wav|mp3|m4a|aac|oga)$':
      '<rootDir>/fileTransformer.js',
  },
};

我们已经告知Jest忽略相关匹配的样式表或者图像文件，相反，导入我们的模拟文件。 你可以通过调整正规表达式来匹配webpack可以处理的文件类型。

提示

Remember to include the default babel-jest transformer explicitly, if you wish to use it alongside with additional code preprocessors:

"transform": {
  "\\.[jt]sx?$": "babel-jest",
  "\\.css$": "some-css-transformer",
}

配置Jest来搜寻文件​

Now that Jest knows how to process our files, we need to tell it how to find them. For webpack's modules, and extensions options there are direct analogs in Jest's moduleDirectories and moduleFileExtensions options.

jest.config.js
module.exports = {
  moduleFileExtensions: ['js', 'jsx'],
  moduleDirectories: ['node_modules', 'bower_components', 'shared'],

  moduleNameMapper: {
    '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
    '\\.(gif|ttf|eot|svg)$': '<rootDir>/__mocks__/fileMock.js',
  },
};
备注

<rootDir> is a special token that gets replaced by Jest with the root of your project. Most of the time this will be the folder where your package.json is located unless you specify a custom rootDir option in your configuration.

Similarly, Jest's counterpart for Webpack's resolve.roots (an alternative to setting NODE_PATH) is modulePaths.

jest.config.js
module.exports = {
  modulePaths: ['/shared/vendor/modules'],
  moduleFileExtensions: ['js', 'jsx'],
  moduleDirectories: ['node_modules', 'bower_components', 'shared'],
  moduleNameMapper: {
    '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
    '\\.(gif|ttf|eot|svg)$': '<rootDir>/__mocks__/fileMock.js',
  },
};

And finally, we have to handle the webpack alias. For that, we can make use of the moduleNameMapper option again.

jest.config.js
module.exports = {
  modulePaths: ['/shared/vendor/modules'],
  moduleFileExtensions: ['js', 'jsx'],
  moduleDirectories: ['node_modules', 'bower_components', 'shared'],

  moduleNameMapper: {
    '\\.(css|less)$': '<rootDir>/__mocks__/styleMock.js',
    '\\.(gif|ttf|eot|svg)$': '<rootDir>/__mocks__/fileMock.js',

    '^react(.*)$': '<rootDir>/vendor/react-master$1',
    '^config$': '<rootDir>/configs/app-config.js',
  },
};

配置完成。 webpack 是一个复杂和灵活的工具，所以你可能需要做一些调整，以符合你的特定应用的需要。 幸运的是对于大多数项目来说，使用Jest来处理webpack配置，应该会更灵活。

提示

For more complex webpack configurations, you may also want to investigate projects such as: babel-plugin-webpack-loaders.

使用 webpack​

In addition to installing babel-jest as described earlier, you'll need to add @babel/preset-env like so:

npm install --save-dev @babel/preset-env

Then, you'll want to configure Babel as follows:

.babelrc
{
  "presets": ["@babel/preset-env"]
}
提示

Jest caches files to speed up test execution. If you updated .babelrc and Jest is not working as expected, try clearing the cache by running jest --clearCache.

提示

If you use dynamic imports (import('some-file.js').then(module => ...)), you need to enable the dynamic-import-node plugin.

.babelrc
{
  "presets": [["env", {"modules": false}]],

  "plugins": ["syntax-dynamic-import"],

  "env": {
    "test": {
      "plugins": ["dynamic-import-node"]
    }
  }
}

For an example of how to use Jest with webpack with React, you can view one here.