I should have mentioned that we were doing the circuit breathing test in a pool that was only 5 feet deep, so there was minimal risk. Also, the test came at the end of the class which included 32 hours of pool time, 36 hours of class time, passing the written test with a minimum score of 90%, so we'd had a reasonable amount of training at the point when we took the water tests.
The head of the aquatics program (tenured professor) taught the class and had zero financial incentive to pass anyone. You could pass the tests and get college credit, but still not get certified. Our class had about 105 students of which 4 actually got certified; the other three were all on the U of Mo swim team.
My point is that it wasn't like we did it after a session or two in the pool. Also he had teaching assistants galore, so we were very closely supervised.