karma.config.js

//? our webpack config imports as a function, and running it returns the required object to be used below
const webpackConfig = require('./webpack.config.js')(null, { mode: 'test' });
// clear entry file config (if exists)
webpackConfig.entry = () => ({});

module.exports = (config) => {
    config.set({
        basePath: '',

        // frameworks: https://npmjs.org/browse/keyword/karma-adapter
        frameworks: ['jasmine'],

        // This will be the new entry to webpack so it should just be a single file
        files: ['src/index.tests.js'],

        // Preprocess test index and test files using webpack (will run babel)
        preprocessors: {
            'src/index.tests.js': ['webpack'],
            'src/**/*.test.js': ['webpack'],
        },

        // Reference webpack config (single object)
        webpack: webpackConfig,

        webpackMiddleware: {
            noInfo: true,
            stats: 'errors-only',
        },

        // test results reporter to use
        // possible values: 'dots', 'progress'
        // https://npmjs.org/browse/keyword/karma-reporter
        reporters: ['progress'],

        port: 9876,
        colors: true,
        logLevel: config.LOG_INFO, // possible values: LOG_DISABLE, LOG_ERROR, LOG_WARN, LOG_INFO, LOG_DEBUG
        autoWatch: true, // if true, Karma captures browsers, runs the tests and exits
        browsers: ['ChromeHeadless'],
        singleRun: false,
        concurrency: Infinity,
    });
};