The point of a swimtest is not to create a hurdle that you must jump over, it is there for two purposes: the first is to assure that you are not wasting your time and money, that is to say, that you have the comfort in the water and waterskills needed to learn to dive with minimal risk; the second is to assure the instructor of the same things so that he or she will be able to assume that you will be able to keep up with the class and not be an undue burden on the instructor's time and energy.
If you are not a comfortable swimmer, if you can not swim 200 yards (actually I'd say 400 yards) comfortably and in some semblance of style (side-stroke is fine, breast-stroke is fine, free-style is fine, a combination is fine), I think that you would be doing everyone a favor to work on your basic waterskills at the local Y with a swim class before trying to learn to dive.
Actually I'm not a big believer in doing a specific set distance, frankly I can tell in way less than one lenght if you are actually ready. If physical condition is an issue, I'd much rather have that judged by a physician with a stress test than try to do that myself with a distance swim.