Well, pyflakes will tell you about name clashes within a TestCase (unless you're shadowing a test on a base class which I guess is rarely the case)...
When we generate the tests we could add the parameter reprs to the docstring. A decorator factor that takes arguments and an optional name builder seem like a reasonable api to me.
Actually, name clashes *aren't* a problem - as we're generating TestCase instances these generated tests won't shadow existing tests (you'll just have two tests with the same name - does this mean id() may not be unique - worth checking).