Buy a test kit because there is a chance it's not MDMA at all. Don't consume an unknown chemical based on someone's word. Especially with all of these research chemicals/bathsalts flooding the US and you can't tell the difference by sight. Good luck.
One additional piece of advice: A testing kit will not tell you how cut the product is. It will only in general give a ballpark indication of what the product might be. The only way to do this and get an actual purity value would be some form of separation method like chromatography. (Which unless you are an amateur chemist and can perform TLC, or have access and the knowledge to operate a GC machine, you won't be able to accomplish this.)
It is possible for someone at home to purify the product via some form of solvent wash, however (eg acetone wash). That will give you a rough idea of how pure the original product was, sort of.
Color, shape, size, smell, taste, etc. of the crystal are not useful ways of determining the purity or content. "Molly" could be anything - methylone, methamphetamine, caffeine, aspirin...