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Использование с Webpack

Jest может использоваться в проектах, использующих webpack для управления ресурсами, стилями и компиляцией. 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 пример

Давйте начнем с привычной конфигурации webpack и адаптируем ее для использования с Jest.

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',
],
},
};

Если вы располагаете файлами, которые трансформируются Babel, вы можете включить поддержку Babel путем установки плагина babel-jest. Non-Babel JavaScript transformations can be handled with Jest's transform config option.

Обработка статических активов

Далее, настроим Jest для корректной обработки активов стилей и изображений. Обычно эти файлы не особо полезны в тестах, так что мы можем безопасно их имитировать. However, if you are using CSS Modules then it's better to mock a proxy for your className lookups.

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',
},
};

And the mock files themselves:

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

Мокинг CSS модулей

Можно использовать ES6 Proxy для имитации CSS модулей:

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

Тогда доступ к className в объектах стилей будет возвращаться как есть (т.е. styles.foobar === 'foobar'). Это довольно удобно при тестировании с использованием снимков в 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',
},
};

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',
},
};

Мы указали Jest на необходимость игнорировать файлы расширения которых совпадают с расширениями таблиц стилей и изображений, и на необходимость использовать имитационные файлы вместо них. Вы можете корректировать регулярное выражение так, чтобы оно совпадало с типами файлов, которые обрабатывает ваша webpack конфигурация.

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",
}

Конфигурация Jest для поиска наших файлов

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',
},
};

Вот и все! webpack is a complex and flexible tool, so you may have to make some adjustments to handle your specific application's needs. Luckily for most projects, Jest should be more than flexible enough to handle your webpack config.

tip

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

Использование с 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"]
}
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

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.