How to test appliance for ground fault?
@CactusCake has the right idea but you don't have to go to the bathroom. Per the NEC all dwellings built in the US have to have at least 2 small appliance circuits in the Kitchen/Dining/Breakfast Nook areas and they will all be GFCI protected in the kitchen. So try the other circuit and see if you get a trip. 

I will say that some GFCI's do go bad, usually due to over tripping. The bad news is that it is usually not the case.

Good luck and stay safe.