Using jQuery MockAjax https://github.com/appendto/jquery-mockjax

mockjax

$.mockjax({
  url: '/foo',
  responseTime: 100,
  responseText: {
    status: 'success',
    message: 'well done, you!'
  }
});

$.ajax({
  url: "/foo",
  type: "POST",
  data: data,
  success: function(response, status, xhr){
    //do successy stuff
  },
  error: (xhr, status, error){
    //do errory stuff
  }
});