A while back, we built an "experimental fork" here at Key of the venerable SUnit. I blogged about it quite a bit. I wasn't out to "take over" the SUnit effort. In fact, I'd be quite pleased if all/any/some of the "improvements" we made in SUnitToo and the associated IDE extension (ExtraRBForSUnitToo) made it back into the core. Just wanted that on record.
That said, we did recently find a bug with the tool and the way it interoperated with PDP's ability to "define method" when you get a MessageNotUnderstood. Much thanks to Terry Raymond for helping see the problem and finding a fix for it. It's been replicated to the Open Repository.