You don't have to be eating everything for the York test.. it's just that if you have already cut something out it may not come up as an allergy/intolerance.
My husband did it last week. He has cut out potatoes and tomatoes and citrus from his diet so those things won't show up as intolerances.
We're looking forward to peace of mind from knowing for certain what he can and can't eat.. so at least we can rule those things out for sure. At the moment it's all guess work (if he gets more arthritis we try to figure out what it was he ate and then cut that out of his diet).