Depends on the reason for it all. If your test is cancelled, then AAMC will pay for your travels to another location and hotel rooms if necessary. However, I heard they cap out the payments at $1000 and you have to prove the amounts (i.e. give them receipts). This is complete and utter bull because buy a ticket the night before will cost well over $1000.
It is very rare for all this to happen, but it has happened.