Minimal Karma config for use with React & Babel & Browserify

karma.conf.js

// you need to $ npm i -D babel-preset-es2015 babel-preset-react babel-preset-stage-0 babelify karma karma-browserify karma-chai karma-mocha karma-mocha-reporter karma-phantomjs-launcher phantomjs-polyfill array.from

module.exports = function conf(config) {
    config.set({
        frameworks: ['browserify', 'mocha', 'chai'],
        plugins: [
            'karma-browserify',
            'karma-mocha',
            'karma-chai',
            'karma-phantomjs-launcher',
            'karma-mocha-reporter'
        ],
        files: [
            './node_modules/phantomjs-polyfill/bind-polyfill.js',
            './node_modules/array.from/array-from.js',
            'src/*.js',
            'src/__tests__/*-test.js'
        ],
        preprocessors: {
            'src/**/*.js': ['browserify']
        },
        browserify: {
            configure: function browserify(bundle) {
                bundle.once('prebundle', function prebundle() {
                    bundle.transform('babelify', {presets: ['es2015', 'react', 'stage-0']});
                });
            }
        },
        reporters: ['mocha'],
        port: 9876,
        colors: true,
        logLevel: config.LOG_INFO,
        autoWatch: true,
        browsers: ['PhantomJS'],
        singleRun: false,
        concurrency: Infinity
    });
};

for webpack deps would be:

$ npm i -D karma mocha chai phantomjs-prebuilt karma-chai karma-mocha karma-mocha-reporter karma-phantomjs-launcher phantomjs-polyfill array.from karma-webpack