Yep, I worked for ASDA for about 6 months last year before coming back to uni. The Magic interview wasn't actually that bad. Dress smartly (don't need a full suit) and make an effort to get involved and you'll do fine.
We started by going round the group introducing ourselves, then watched a short video about ASDA, had a group exercise which involved making monsters out of craft materials (balloons, felt, etc) and finished with a tour of the store (which included rumbling one of the aisles). I got a call the day after asking me to come back for a one to one interview. Day after that I got a call saying I got the job and arranged a date for induction.