jest-css-modules-transform

Preprocessor css modules for Jest test framework

This preprocessor converts css files in modules like Webpack. If we have css files

1.class1, .class2, .class3 {
2    display: block;
3}

Webpack will transfrom it to object.

1{
2    class1: 'class1', //value may be different. It depends of localIndentName property
3    class2: 'class2',
4    class3: 'class3',
5}

In testing you need to mock all css modules to aviod exception. But use pure object {} for mocking is bad idea, because it makes wrong classNames in components. This preprocessor makes correct modules as if Webpack did.

Usage

In Jest config add option

1"transform": {
2  ".+\\.(css|styl|less|sass|scss)$": "jest-css-modules-transform"
3},

or

1"transform": {
2  ".+\\.(css|styl|less|sass|scss)$": "<rootDir>/node_modules/jest-css-modules-transform"
3},

It supports pure CSS, SCSS, SASS, STYLUS and LESS.

For PostCSS

For .css, .pcss, .postcss files used postcss.config.js from root folder(if file exist of course).
For tests you can rewrite your existed postcss.config.js. See options.

Options

You can save preproccessor options in file jest-css-modules-transform-config.js in root of your project(Where is the file package.json). You can pass options for your preprocessors.

example:

1const path = require('path');  
2const additionalResolvePath = path.resolve(__dirname, 'src', 'additional_modules');
3
4module.exports = {
5    sassConfig: {
6        includePaths: [additionalResolvePath],
7        precision: 5,
8    },
9    lessConfig: {
10        paths: [additionalResolvePath],
11    },
12    stylusConfig: {
13        paths: [additionalResolvePath],
14    },
15    postcssConfig: {
16        plugins: [
17            require('autoprefixer')({
18                browsers: ['Chrome 68', 'Firefox 62', 'Safari 12']
19            })
20        ]
21    },
22};

For all preprocessor options see offical documentations for Sass, Less, Stylus.

cssLoaderConfig

exportLocalsStyle

Webpack's cssLoader has option exportLocalsStyle.

1// file jest-css-modules-transform-config.js
2module.exports = {
3   cssLoaderConfig: {
4        exportLocalsStyle: 'camelCase'
5   }
6};

then this css code

1    .foo__bar{color: red;}
2    .foo__bar2{color: red;}

converted to

1    {
2        foo__bar: 'foo__bar',
3        fooBar: 'foo__bar',
4        foo__bar2: 'foo__bar2',
5        fooBar: 'foo__bar2',
6    }

Available values camelCase, camelCaseOnly, dashes, dashesOnly, asIs(by default)

prepend

Type: string, Function, Array<string | Function>
Default: null

Pass urls for prepend(before file content) to transformed files.
Useful in a situation where the module uses variables or mixins without explicit import.

For example you have vars in file, but without implicit import. You can prepend file with sass variables before convert module.

injectIntoDOM

Type: boolean Default: false

Inject the generated CSS into the head of the document.

This option could be useful for visual regression testing, where the output dom has the styles applied to it.

sassModuleName

Type: string Default: null

The default nodejs module for sass/scss files is sass. If not found in node_modules, then node-sass. You can define any another module.

Example with array of paths

1// file jest-css-modules-transform-config.js
2module.exports = {
3   prepend: [
4       'some/url/vars.scss',
5       'some/url/theme.scss',
6   ],
7};

Example with single string

1// file jest-css-modules-transform-config.js
2module.exports = {
3   prepend: 'some/url/vars.scss',
4};

Example with custom function

1// file jest-css-modules-transform-config.js
2module.exports = {
3   prepend: (filepath) => {
4       if (filepath.includes('components')) {
5           return [
6               'components/vars.scss',
7               'components2/vars.scss',
8           ];
9       }
10
11       return [
12            'common/vars.scss',
13            'common/vars2.scss',
14       ];
15   },
16};

It works with any preprocessors(Sass, Less, Styles, PostCSS, pure CSS)

Custom config path

By default option plugin's config file is jest-css-modules-transform-config.js from root. For specify custom path just add env JEST_CSS_MODULES_TRANSFORM_CONFIG. For example:

1JEST_CSS_MODULES_TRANSFORM_CONFIG=custom-config-path npm test

or

1JEST_CSS_MODULES_TRANSFORM_CONFIG=custom-config-path yarn test

Install

npm i jest-css-modules-transform