code: function Ping(url, driver) {
    if (!(this instanceof Ping)) {
      return new Ping(url, driver);
    }
  
    driver = driver || request;
  
    this.url = url;
    this.driver = driver;
    this.successCodes = SUCCESS;
    this.started = false;
    this.validators = [];
    var self = this;
  
    var textCheck = function(err, res, body) {
      if (!self._text) return true;
      return ~body.indexOf(self._text);
    };
  
    var errorCheck = function(err, res) {
      return !err;
    };
  
    var statusCheck = function(err, res, body) {
      // If there is no result from the server, assume site is down.
      if (!res){
        return false;
      } else {
        return ~self.successCodes.indexOf(res.statusCode);
      }
    };
  
    var perfCheck = function(err, res, body, info) {
      if (typeof self._maxDuration !== 'number') return true;
      return info.duration <= self._maxDuration;
    };
  
    this.register(errorCheck, statusCheck, textCheck, perfCheck);
  }
docs: Ping class.
  
  @param {String} url
  @param {Object} driver
  @constructor