That's a good tip for most things, but for this test dress comfortably. There were a few people who dressed business casual and one person who dressed for an interview. Personally I wore jeans and a t-shirt because it was in the mid 90 ' all day.
5 bucks if someone does this and posts pics.you could wear a clown suit.... go change on break... come back in as a scuba steve... go change on break.... come back in a trench coat and thong and nobody in the FAA will care... no one with any impact on your hiring will be there. they are contractors.