karma.conf.js

// Karma configuration
const karmaWebpack = require('karma-webpack');

module.exports = function createConfig(config) {
  const configuration = {
    // base path that will be used to resolve all patterns (eg. files, exclude)
    basePath: '',

    // frameworks to use
    // available frameworks: https://npmjs.org/browse/keyword/karma-adapter
    frameworks: ['mocha', 'sinon-chai'],

    client: {
      mocha: {
        ui: 'bdd',
      },
    },

    // list of files / patterns to load in the browser
    files: ['test/**/*.spec.js'],

    webpack: {
      devtool: 'inline-source-map',

      module: {
        loaders: [
          {
            test: /\.jsx?$/,
            loader: 'babel-loader',
            exclude: /node_modules/,
          },
        ],
      },

      externals: {
        cheerio: 'window',
        'react/addons': true,
        'react/lib/ExecutionEnvironment': true,
        'react/lib/ReactContext': true,
        'react-addons-test-utils': true,
      },
    },

    // list of files to exclude
    exclude: [],

    plugins: [
      karmaWebpack,
      'karma-mocha',
      'karma-sinon-chai',
      'karma-sourcemap-loader',
      'karma-chrome-launcher',
      'karma-coverage',
    ],

    // preprocess matching files before serving them to the browser
    // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor
    preprocessors: {
      'src/**/*.js': ['webpack', 'sourcemap'],
      'test/**/*.js': ['webpack', 'sourcemap'],
    },

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

    // web server port
    port: 9876,

    // enable / disable colors in the output (reporters and logs)
    colors: true,

    // level of logging
    // possible values: config.LOG_DISABLE || config.LOG_ERROR || config.LOG_WARN || config.LOG_INFO || config.LOG_DEBUG
    logLevel: config.LOG_INFO,

    // enable / disable watching file and executing tests whenever any file changes
    autoWatch: true,

    // start these browsers
    // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher
    browsers: ['Chrome', 'ChromeHeadless', 'ChromeHeadlessNoSandbox'],

    customLaunchers: {
      ChromeHeadlessNoSandbox: {
        base: 'ChromeHeadless',
        flags: ['--no-sandbox'],
      },
    },

    // Continuous Integration mode
    // if true, Karma captures browsers, runs the tests and exits
    singleRun: false,

    // Concurrency level
    // how many browser should be started simultaneous
    concurrency: Infinity,
  };

  config.set(configuration);
};