I found the most amazing articles! Apparently, many ancient physicians including Pliny the Elder advocated the following as a virginity test: they would give the bride to be a diuretic, and if she could hold it in long enough without wetting, she was announced a virgin. They believed that sex weakened bladder control and the more sex a woman had, the less she could hold it. This was apparently very widely practiced throughout the middle ages and renaissance. Is this a story waiting to be written or what!?
http://www.encyclopedia.com/topic/virginity.aspx#1-1O128:virginitytests-full
http://books.google.com/books?id=KNi7eVPlXC8C&pg=PA40&lpg=PA40&dq