2nd Gen R56 Cooper Troubleshooting Rear Window Defrost

Here is a question from someone with ZERO automotive electrical knowledge. My 2008 MC is still under warranty (37K miles)--I am sure that the rear window defrost is not working--i.e., nothing melts and no discernable warming of the glass. The indicator light does come on when I turn the defrost on. So...is there a simple technique for verifying that no current is reaching the elements? Another way of saying this: if I take the car to the BMW dealership for a warranty repair, can it be demonstrated that the defrost is not functioning, even if it's a warm day?