Most of the big racing pool at De Anza College is 6 to 7 feet deep (the west end and the center).
I give this deep water swim test to people in my classes who want to swim in the deeper sections of the pool.
(For novice swim classes there is no swim test at all.
For beginning classes, when we have shallow water, there is no deep water swim test for most students, except those who want to swim in the deep parts of the pool.)
We give the deep water swim test (usually the first class session, after needed paperwork, discussions, etc.), in the lane at the far west end of the pool.
People swim one at a time,
one 25 yard lap of backstroke and one 25 yard lap of freestyle, (the width of the big pool)
then tread water for at least one minute, using a real treading water kick (such as a whip kick, eggbeater or a scissors kick such as used in sidestroke), not just a flutter kick.
Your strokes do not have to have perfect form, but you will need to complete each of the laps without stopping (you will not go to the wall or grab a lane line for support).
(You will not use a flip turn or dive into the pool during this testing.)
There is a great video of the De Anza College pool complex