Version: 30.0

Using with 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の設定例

一般的な種類のwebpackの設定ファイルから始めて、Jestのセットアップに変換してみましょう。

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.

静的アセットの管理

次は、スタイルシートや画像などのアセットを簡潔に管理できるようにJestを設定しましょう。通常、これらのファイルはテストでは特に扱いづらいので、問題がないようにモックします。しかし、CSSモジュールを利用している場合はクラス名参照のためのプロキシをモックした方が良いでしょう。

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',
  },
};

そしてモックファイル自身は次のようになります:

__mocks__/styleMock.js
module.exports = {};

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

CSSモジュールのモック

You can use an ES6 Proxy to mock CSS Modules:

npm
Yarn
pnpm
Bun

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

yarn add --dev identity-obj-proxy

pnpm add --save-dev identity-obj-proxy

bun add --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',
  },
};

Jestがスタイルシートや画像の拡張子のあるファイルを無視して、代わりにモックファイルを読み込むように設定しました。 webpackの設定で扱うファイルタイプを照合する正規表現は調整することができます。

tip

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",
}

ソースファイルを探索できるようにJestを設定する

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',
  },
};

note

<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',
  },
};

以上です！ webpackは複雑で柔軟なツールなので、適用するアプリケーションが必要とすることに対応するためにいくらか調整をしなければならないでしょう。幸いにもほとんどのプロジェクトでは、Jestはwebpackの設定を調整するよりも十分な柔軟性を持っているはずです。

tip

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