I wore yoga pants and brought a hoodie so I could put it on in case it was cold. I think you might want to wear yoga capris or leggings instead of shorts, the seats can be cold and hard and it might be uncomfortable sitting in shorts. Good luck!
If yours are anything like my tests were you will be sitting for a while so I would say go comfy. Being a sweatshirt incase it's cold. Nothing worse than freezing while trying to take a test! Good luck!!