title: What's the advantage of using Sinon.js over Jasmine's built in Spys?
body: <p>I'm piecing together a jsTestDriver/Jasmine environment for testing our front end code and I'm seeing a lot of references to Sinon.js for stand-alone (or drop in) spies.  Could someone describe what Sinon.js brings to the table that Jasmine doesn't for testing the UI?</p>