Kent Beck doesn’t aim for 100% test coverage. A reminder be wary of extreme statements and positions:

I get paid for code that works, not for tests, so my philosophy is to test as little as possible to reach a given level of confidence (I suspect this level of confidence is high compared to industry standards, but that could just be hubris). If I don’t typically make a kind of mistake (like setting the wrong variables in a constructor), I don’t test for it.

Link: tdd – How deep are your unit tests? – Stack Overflow via stackoverflow.com

Found via http://37signals.com/svn/posts/3159-testing-like-the-tsa