It's the one thing I like about testing your code.... it's generally something of a challenge.
That was meant to be a compliment. A testing challenge means you haven't left me any of the easy, "silly mistake" style bugs. At the heart of it, a good tester likes the interesting problems, too. Finding "yet another non-validated input" is kind of like a developer implementing "yet another login dialog".... boring.
I'm all for more challenges!