karma.conf.js

let browsers = ['ChromeHeadless'];
let coverageType = 'text';

if (process.env.CONTINUOUS_INTEGRATION) {
  browsers = ['Firefox'];
  coverageType = 'lcovonly';
}

module.exports = function(config) {
  config.set({
    frameworks: ['mocha'],

    preprocessors: {
      './src/*.js': ['coverage'],
      './src/**/*.js': ['coverage'],
      './specs/index.js': ['webpack', 'sourcemap']
    },

    files: ['./specs/index.js'],

    webpack: require('./scripts/webpack.test.config'),

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

    reporters: ['mocha', 'coverage'],

    mochaReporter: { showDiff: true },

    coverageReporter: {
      type : coverageType,
      dir : 'coverage/',
      subdir: '.'
    },

    port: 9876,

    colors: true,

    logLevel: config.LOG_INFO,

    autoWatch: true,

    browsers,

    // Increase timeouts to prevent the issue with disconnected tests (https://goo.gl/nstA69)
    captureTimeout: 4 * 60 * 1000,

    singleRun: (process.env.CONTINUOUS_INTEGRATION)
  });
};