Actually, you're overcomplicating the issue somewhat. Be careful not to rule out simple problems (software issues, bad RAM, etc) just because it looks like a graphics card issue.
That said, what type of computer do you have? If it's a MacBook Pro, not the current model but anywhere from about 1 1/2 years old to 3 years old, you might very likely be suffering from the known problem with the NVIDIA Graphics cards. Of course, the only way to know for sure would be to take it to a repair facility, either an Apple Store or an Authorized Service Center, as the tests for that sort of thing are internal, so you won't be able to get a copy to use. In fact, most hardware tests are internal, aside from the copy you get with your install disks.
I'd say try to rule out software or RAM, then take it in if the problems persist. If it's a MBP with a covered card, you should pay anything anyways, so you'd only lose the use of the computer for a while.
jW