I'd go so far as to say if your test is doing something crafty, you're doing tests wrong. Maybe in a mock or fixture, but that's a write-once sort of affair.

I also don't apply DRY (don't repeat yourself) to tests. Tests should be independently readable beginning to end, no context needed. After all, the true value of a unit test is to take a block of code too complicated to easily fit in your mind, and break it down into a series of examples simple enough to fit.