code: function exitIfDisabled () {
    var CI = process.env.CI === 'true';
    var KARMA = process.env.KARMA === 'true';
  
    if (CI && !KARMA) {
      console.warn('Karma is not enabled');
      process.exit();
    }
  }
docs: If this is a CI job, and Karma is not enabled, then exit.
  (useful for CI jobs that are only testing Node.js, not web browsers)