I think that my left hand shoulder button is faulty on my new DSi XL, is there any test I can do or what is a game that uses the left hand shoulder button just to make sure if it is or is not faulty
Just close your mouth around the button and blow (prefferably in a place where you're not liley to draw attention - assuming you're at home, you should be fine
).
...but any FPS will do, such as Metroid: Hunters.