var MockXhr = Class.create({
  initialize: function(desiredResults) {
    this._desiredResults = Object.extend(Object.clone(MockXhr.defaultResults), desiredResults);
    this._headers = {};
    this.overrideMimeType = false;
    this.status = undefined;
    this.responseText = undefined;
    this.onreadystatechange = undefined;
    this.readyState = 0;
    this.responseXML = undefined;
    this.statusText = undefined;
  },
  open: function(method, url, async, username, password) {
    this._method = method;
    this._url = url;
    this._async = async;
    this._username = username;
    this._password = password;
  },
  send: function(postVars) {
    var me = this;
    if (callback) {
      $w('1 2 3 4').each(function(readyState, state) {
        var fn = function() {
          me.state = state + 1;
          if (me.state == 4) {
            // set to desired result
            Object.extend(this, this._desiredResults);
            this.statusText = MockXhr.statusTextLookup[this.status];
          }
          me.onreadystatechange();
        };
        if (me._async) {
          me._timeout = window.setTimeout(fn, state * 100);
        }
        else {
          fn();
        }
      });
    }
  },
  abort: function() {
    window.clearTimeout(this._timeout);
  },
  setRequestHeader: function(name, value) {
    this._headers[name] = value;
  },
  getAllRequestHeaders: function() {
    return Object.extend({}, this._headers);
  },
  getRequestHeader: function(name) {
    return this._headers[name];
  }
})
Object.extend(MockXhr, {
  statusTextLookup: {
    200: "Ok",
    301: "Moved Permanently",
    304: "Not Modified",
    404: "Not Found",
    403: "Forbidden",
    401: "Unauthorized"
  },
  defaultResults: {
    status: 200,
    responseText: 'success',
    responseXML: undefined
  }
});

// usage
var transport = new MockXhr({status: 12029, responseText: undefined});