chakram.addRawPlugin("unavailable", function (chai, utils) {
                utils.addProperty(chai.Assertion.prototype, 'unavailable', function () {
                    var statusCode = this._obj.response.statusCode;
                    this.assert(statusCode === 503, 'expected status code '+statusCode+' to equal 503', 'expected '+statusCode+' to not be equal to 503');
                });