you bought the rental insurance or your CC covers the rental.

But when you test drive, you can't have insurance, because it is not your car. So the dealer will go with you in these drive, they will pick the shortest and easiest road. most of time, you are not allowed to go on highway.

dealer has insurance to cover their cars on the lot. but who will prevent the insurance company to go after you for a damaged car?

just my 2 cents :)