How to easily mock ajax calls using Jasmine's spies. Binds on success callback to the custom object to simulate get('responseData') method.

jasmine_yui_ajax_mock.js

                it('test AJAX mock', function() {

                    spyOn(Y.io, 'request')
                        .andCallFake(function(url, config) {
                            console.log('fake ajax', arguments);

                            var bound = config.on.success.bind({
                                'get' : function(name) {
                                    if (name === 'responseData') {
                                        return {
                                            'some' : {
                                                'fake' : {
                                                    'response' : {

                                                    }
                                                }
                                            }
                                        };
                                    }
                                }
                            });

                            bound();
                        });

                    Y.io.request('http://localhost:1248', {
                        data    : 'json',
                        method  : 'post',
                        on      : {
                            success : function() {
                                console.log('success', this.get('responseData'));
                            }
                        }
                    });

                });