This is a bad thing. You're overusing DRY here to avoid rewriting the test cases from its superclass, but what you have in those test cases are different behaviours, because they're under different conditions, and if you happen to break one of those tests they will break as many times as there are subclasses that inherit those tests, which is really a bad thing.

Take a look here: http://c2.com/cgi/wiki?UnitTestIsolation