my_respond_with_json.js

//I put this next to the "respondWith" function inside sinon.js

         respondWithJson: function (url, responseObject){
            this.respondWith(url, [200, {
                "Content-Type": "application/json"
                }, JSON.stringify(responseObject)]);
         },

to_assert_the_request.js

this.server.requests = [];

//do something that will fire the request

assert... this.server.requests[0].requestBody, $.param({...});
assert... this.server.requests[0].url, my url..

to_set_a_mock_response.js

this.server.respondWithJson("/notification/123", [{
        Name: "NOTJOSE", Message: "FooBarBaz"}]);


something.doSomethingThatWillFetchTheUrl();

this.server.respond();