Showing how to fake server requests with Sinon.JS and Jasmine

gistfile1.js

/*
  Load Sinon.JS in the SpecRunner:

  <script type="text/javascript" src="lib/jasmine-1.0.1/jasmine.js"></script>
  <script type="text/javascript" src="lib/jasmine-1.0.1/jasmine-html.js"></script>
  <script type="text/javascript" src="sinon-1.0.0.js"></script>
  <script type="text/javascript" src="sinon-ie-1.0.0.js"></script>

  http://cjohansen.no/sinon/
*/

describe("SinonFakeServerWithJasmine", function() {
  var server;

  beforeEach(function() {
    server = sinon.fakeServer.create();
  });

  afterEach(function () {
    server.restore();
  });

  it("should fake a jQuery ajax request", function () {
    server.respondWith("GET", "/something",
                       [200, { "Content-Type": "application/json" },
                        '{ "stuff": "is", "awesome": "in here" }']);

    var callbacks = [sinon.spy(), sinon.spy()];

    jQuery.ajax({
      url: "/something",
      success: callbacks[0]
    });

    jQuery.ajax({
      url: "/other",
      success: callbacks[1]
    });

    console.log(server.requests); // Logs all requests so far
    server.respond(); // Process all requests so far

    expect(callbacks[0].calledOnce).toBeTruthy();
    expect(callbacks[0].calledWith({
      stuff: "is",
      awesome: "in here"
    })).toBeTruthy();

    expect(callbacks[1].calledOnce).toBeFalsy(); // Unknown URL /other received 404
  });
});

I used this code with a little modification; i made the xmlhttprequest call from the test file using the instance of the class where the htpp call is written. But it is not calling my callback function. Any idea why is that happening?