code: function (clientArguments) {
    var grepRegex = /^--grep=(.*)$/;
  
    if (Object.prototype.toString.call(clientArguments) === '[object Array]') {
      var indexOfGrep = indexOf(clientArguments, '--grep');
  
      if (indexOfGrep !== -1) {
        return clientArguments[indexOfGrep + 1]
      }
  
      return map(filter(clientArguments, function (arg) {
        return grepRegex.test(arg)
      }), function (arg) {
        return arg.replace(grepRegex, '$1')
      })[0] || ''
    } else if (typeof clientArguments === 'string') {
      var match = /--grep=([^=]+)/.exec(clientArguments);
  
      return match ? match[1] : ''
    }
  }
docs: Extract grep option from karma config
  @param {[Array|string]} clientArguments The karma client arguments
  @return {string} The value of grep option by default empty string