Please don't do that. The testnet is not intended for "testing rigs". It's meant for new feature development and trying out experimental patches. When the difficulty gets high it's harder to do that. Mining on the testnet with a GPU makes it useless for anyone else.
Hello,
is it possible to setup "testnet in a box" on a computer and mine with a miner (cgminer, DiabloMiner, ...) on a second one? With such a configuration one could easily test modifications on the SHA algorithm.
Regards,
Gilles