Stubbing Backbone.js's fetch method with Jasmine & Sinon.js

spec.js

beforeEach(function() {
  var self = this; 
  //contacts
  this.contacts = new App.Collections.Contacts();
  _.each(this.fixtures.Contacts.valid, function(c) {
    self.contacts.add(new Contact(c));
  });
  this.contactsCollectionStub = 
      sinon.stub(App.Collections, 'Contacts')
         .returns(this.contacts);
  this.contactsFetchStub = 
      sinon.stub(this.contacts, 'fetch')
         .yieldsTo('success', this.contacts); 
});
afterEach(function() {
  this.contactsCollectionStub.restore();
  this.contactsFetchStub.restore();
});