The machine can vary depending on where you take the exam. The club I tested at uses Babolat machines and I ended up stringing on a Star 5 for my MRT exam.
I believe you can also arrange to bring your own machine if you feel more comfortable. You get maximum points for finishing your string job in under 45 minutes, which should allow you to take your time and make sure you get everything right, even on an unfamiliar machine.
USRSA MRT - Gamma 6004 + Wise 2086
Pro Staff 97 - Natural Gut/Black Magic