J.K. Rowling wrote this quiz herself!
https://my.pottermore.com/patronus

More info here:
http://www.nytimes.com/2016/09/23/business/media/expecto-patronum-patronus-test-keeps-harry-potter-marketing-alive.html

Taking the quiz now; I hope I'm not a rat or a weasel. Expecto Patronum!!