title: Sinon JS "Attempted to wrap ajax which is already wrapped"
body: <p>I got the above error message when I ran my test. Below is my code (I'm using Backbone JS and Jasmine for testing). Does anyone know why this happens?</p>
  
  <pre><code>$(function() {
    describe("Category", function() {
       beforeEach(function() {
        category = new Category;
        sinon.spy(jQuery, "ajax");
       }
  
       it("should fetch notes", function() {
        category.set({code: 123});
        category.fetchNotes();
        expect(category.trigger).toHaveBeenCalled();
       }
    })
  }
  </code></pre>