Install a game.
If it works, it's fine.
Really if you want to benchmark it to see it is working then a synthetic benchmark like 3DMark will work just fine.
03 or 05 will serve your purpose, 05 will be very jerky though, so use 03 for a smoother experience.
Just download, install and run the default benchmark.
you should get around 8000 points in 3Dmark 03.