I can see how monkey patching could be useful in mocking or something similar. I've never really used a language that supports it though.
I'm not entirely sure what Eclipse's code generation has to do with testing, but given the other examples I'll assume I'm being stupid again ;) I'm actually working with a lot of EMF generation stuff at the minute which can be quite painful.
(I don't disagree with your main point, but I don't quite see where those techniques fit in).