When I did my "Toytown PAT course" which "qualifies" me to do PATs, one of the tips given is to open up the plug and inspect the internals, then put a "Fitted with nnA fuse" sticker across the screw. Next time, if the sticker is intact, and the cord is still in the grips with no sign of having been pulled out, then it's a reasonable assumption that the internals haven't been messed with and you can skip opening up the plug to check.