karma.conf.js

// Karma configuration

var webpackConfig = require('./webpack.conf/tests.js');

module.exports = function(config) {
  config.set({

    // 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', 'chai', 'sinon'
    ],

    webpack: webpackConfig,

    client: {
      mocha: {
        reporter: 'html'
      }
    },

    // list of files / patterns to load in the browser
    files: ['tests/index.js'],

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

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

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

    coverageReporter: {
      dir: './coverage',
      reporters: [
        {
          type: 'lcov',
          subdir: function(browser) {
            // We're using chrome as base for coverage
            const b = browser.toLowerCase().split(/[ /-]/)[0];

            return b === 'chrome'
              ? '.'
              : b;
          }
        }, {
          type: 'text-summary'
        }
      ]
    },

    // 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_ERROR,

    // 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', 'ChromeCanary', 'Firefox', 'Safari', 'PhantomJS', 'Opera', 'IE'],
    browsers: [
      'ChromeHeadless', 'FirefoxHeadless'
    ],

    customLaunchers: {
      FirefoxHeadless: {
        base: 'Firefox',
        flags: ['-headless']
      }
    },

    // 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: 1
  });
};