istanbul-instrumenter-loader

istanbul-instrumenter-loader

Instrument JS files with istanbul-lib-instrument for subsequent code coverage reporting.

Install

npm install --save-dev istanbul-instrumenter-loader
# or
yarn add --dev istanbul-instrumenter-loader

Usage

References

• Loaders
• karma-webpack
• karma-coverage-istanbul-reporter

Project structure

Let's say you have the following:

├── src/
│   └── components/
│       ├── bar/
│       │   └── index.js
│       └── foo/
│           └── index.js
└── test/
    └── src/
        └── components/
            └── foo/
                └── index.js

To create a code coverage report for all components (even for those for which you have no tests yet) you have to require all the 1) sources and 2) tests. Something like it's described in "alternative usage" of karma-webpack:

test/index.js

// require all `project/test/src/components/**/index.js`
const testsContext = require.context('./src/components/', true, /index\.js$/);

testsContext.keys().forEach(testsContext);

// require all `project/src/components/**/index.js`
const componentsContext = require.context('../src/components/', true, /index\.js$/);

componentsContext.keys().forEach(componentsContext);

This file will be the only entry point for Karma.

karma.conf.js

config.set({
    …
    files: [
        'test/index.js'
    ],
    preprocessors: {
        'test/index.js': 'webpack'
    },
    webpack: {
        …
        module: {
            rules: [
                // instrument only testing sources with Istanbul
                {
                    test: /\.js$/,
                    include: path.resolve('src/components/'),
                    loader: 'istanbul-instrumenter-loader'
                }
            ]
        }
        …
    },
    reporters: [ 'progress', 'coverage-istanbul' ],
    coverageIstanbulReporter: {
        reports: [ 'text-summary' ],
        fixWebpackSourcePaths: true
    },
    …
});

Options

The loader supports all options supported by istanbul-lib-instrument.

Contributing

Don't hesitate to create a pull request. Every contribution is appreciated. In development you can start the tests by calling npm test.