使用 webpack
- Webpack 示例
- 使用 webpack

使用 webpack

Jest 可以用于使用 webpack 来管理资源、样式和编译的项目中。 webpack 确实相比超过其他类似工具来说，展示出一些特有的优势，因为它直接与你的app整合，允许管理资源文件，如图像和字体，并带有可以将系统编译为JavaScript 语言和工具。

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. 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

你可以使用 ES6 Proxy来模拟一个 CSS:

npm
Yarn

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

yarn add --dev identity-obj-proxy

然后在样式对象上，你的所有className查找都会原样返回 (如 styles.foobar === 'foobar') 这对React的Snapshot Testing是相当方便的. 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',
  },
};

如果 moduleNameMapper 不能满足你的需要，你就需要使用Jest的transform 来自定义对那些文件后缀应该如何转译。例如，一个输出不带文件后缀的文件名 (such that require('logo. jpg'); returns 'logo') 应该这样写:

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。

tip

记住，如果你想将它和其他代码预处理器一起使用，那必须要显式地引入默认的 babel-jest 转译器，

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

配置Jest来搜寻文件

现在Jest知道如何处理我们的文件了，接下来我们需要告诉它如何找到它们。 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',
  },
};

最后，我们关注一下Webpack的alias。在这里，我们可以再次使用 moduleNameMapper。

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。

tip

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
Yarn

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

yarn add --dev @babel/preset-env

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

.babelrc

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

tip

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.

tip

如果你使用动态加载 (import('some-file.js').then(module => ...))，你还需要引入Babel的动态加载插件（ dynamic-import-node ）。

.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.