In honesty it doesn't matter for the RT what you wear. However, remember that the person testing you my be interviewing you later in the process. For the interview you will need to be smartly dressed, for the RT wear something that you feel comfortable in, but that at least says you have made an effort.
I wore a smart fitted pair of trousers, black shoes and a smart jumper for my recruit test mate, a suit is probs a bit unnecessary tbh. I am going for officer as well, a suit for the interview is probably the best option, I wore one for mine. Remeber think quickly when doing the tests and keep cool. im sure youll ace them no worries.
When I did mine a couple of months ago there were 15-20 people and you could tell the difference between people going for officer (suit) and rating (most smart casual, some just casual).
At first I felt a bit over dressed being the only one in a suit out of the first 5 to arrive, but then I guess some of them felt under dressed in the test room.
I would say go smart.
From reading many of the threads giving advice in the Newbie forum one underlying theme comes through whenever anyone asks about what to wear - first impressions count, shinny shoes and smart dress do get noticed.
I am treating each part of the application process and one long job interview. I would always go to a job interview in a suit so I will attend all parts of my application process in a suit as well.
Good luck - its not very hard, time is a bit tight on a couple of the sections. Pass mark is around 50%, but Officer applications are expected to get much higher.
I went to my test in a pair of jeans and a smart polo shirt, I was the best dressed there by quite a margin but I suppose it was Newcastle... I'm glad I didn't wear a suit because I would have felt awkward, 7 out of the nine were in tracksuits! I'm definitely wearing a suit for the interview. I think as long as you look like you've made an effort to look presentable you'll be fine; that said, I'm not in yet!