使用 webpack

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

If you have JavaScript files that are transformed by Babel, you can by installing the plugin. Non-Babel JavaScript transformations can be handled with Jest’s transform config option. Non-Babel JavaScript transformations can be handled with Jest’s config option.

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';

你可以使用 ES6 Proxy来模拟一个 :

npm
Yarn

npm install --save-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 .

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',
  },
};

fileTransformer.js

const path = require('path');
  process(src, filename, config, options) {
    return `module.exports = ${JSON.stringify(path.basename(filename))};`;
  },
};

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",
  ...
}

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

info

<rootDir> is a special token that gets replaced by Jest with the root of your project. 大多数情况下，这代表你的package.json所在的位置，除非你在项目配置中自定义了rootDir 。

类似的，Webpack的resolve.root、 NODE_PATH环境变量都可以使用 modulePaths选项。

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',
  },

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: .

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

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 ）。

{
  "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 .