Really, like all computers, you need to test the components, rather than the software. The software works or it doesn't, and that is pretty obvious.
You need to check the wireless / bluetooth and GPS work. GPS you can use wayfinder (takes a while), bluetooth you can use your phone, wireless there should be something around (hit the connect icon on the top, and see what is there).
The easiest thing to check is just the condition - scratches on the body or screen, memory card cover ok. USB port not damaged.