Hey Goose, I don't know if Glenny ended up sending you a PM but I'll say my bit regardless. You'll want to rock up to ASP in smart casual, i.e. collared shirt and chinos/suit trousers but for the 2 days you're actually on base you'll be wearing PT gear underneath a flight suit. The smart casual is only for arriving/departing.
As for the testing itself, there's some great links posted earlier which goes into it in more detail than I could possibly hope to, but something I haven't seen mentioned so far but I feel ought to be - get a really good nights sleep and eat well in the lead up. In my opinion that'll make more of a difference than studying every detail of the testing will.
Otherwise, just do your best and you'll be fine. Good luck.