Christians: what would you do if you accidentally found out your formerly Christian friend is wiccan?

I'm not Christian but maybe I can give some advice nonetheless. accept it, it is the friends believes and not yours so believe what you believe and let your friend believe what they believe. If it bothers you I would sugest talking to your friend and have them explain their believes to you so you don't make umptions. believes are believes and you can't change your friends just as they can't change yours so don't loose a friendship by trying. Wicca is a very peaceful religion and all religions can co-exist peacefuly if given the chance to understand eachother.