If you are certified and have a log book showing that you dove in the past year you shouldn't have to do anything besides sign up. I think if you haven't been diving in over a year they require you show your skills in the pool -- I'm not sure if that requires a swim test or not.
The only swim test I'm familiar with is for the resort course and consists of 8 lengths in a small pool. You have to do a crawl (or in my case an ugly, crawl-like stroke) without stopping but can go as slowly as you like. You couldn't wear fins, but the pool is not long. It's challenging, but not too bad if you take your time. It sounds like you won't have to do this though if you're certified.
verknid is correct, if you have a c card and logged a dive within the last year, you should be all set to just to sign up and dive. Even if you are asked to prove some skills, I don't believe the swim is part of it.