cant speak for all agencies, but for PADI its: (12 points total to pass)
1: 400 yard swim with no swimming aids.
8 to 10 mins = 3 points
2: 15 minute tread
passed but hands not out of the water last 2 mins = 3 points
3: 800 yard snorkel swim (no arms)
15 to 17 mins = 3 points
4: 100 yard inert tired diver tow
3 to 4 mins = 3 points
Its not that easy of a test to pass, but it can be done but you should prepare and swim as much as you can in a local pool if you have access to one. Also if you fail one then you will need to do better on another to get the 12 points, its scored 1 to 5 and 5 being the best. 3 points is a avg score.