If you're doing the class with either Marc, Rich or John... give your instructor a call... all of them are perfectly capable of giving tips on how to manage the swimtest.
My personal favourite method is 1 length frontcrawl (I cant do this)/breaststroke and 1 length backstroke. The backstroke gives me time to fully breathe, and on the breaststroke I keep focus on gliiiiding... takes a bit of mental effort, but wow, when it works, it works.
Being a full-figured girl, I am above average buoyant in water. Ie. i can read a book in freshwater without stressing. The under water swim has always given me grief, but the trick is to get a good kick of the side of the pool and glide. Then slowly, and tucked in to your body bring your hands forward. No sharp movements.
(And, it is possible to do all the swimtests up to T2C2CCR in a breaststroke....)