Somehow I fail to see why you would want to do invalid radio button selection, sounds more like hacking to me. ;-)
Exactly! I want to make sure that my application can handle an enduser hacking the HTML. When I validate my parameters on the server side I always check to make sure that the user hasn't fudged any data, and I want to add a test to make sure that code is always working correctly. I know it is working right now, but I may break it in the future for all I know. Hence the need for a test.