One of the keys to preventing ACL injuries is to display control of the hip, knee, and ankle during dynamic movements. In particular we want to pay attention to this in the deceleration phases. During this test you will be watching or video taping the client from the front. What you are looking for is an inward collapse of the knee upon landing on the ground. You should notice minimal to no inward collapse of the knee. If the knee frequently caves inward or does so excessively, that would be considered a failed test.
The second part of this test is repeatability. You should be able to jump up and bring the heel to the back of the thigh x10 reps in a row without having to reset, loose your balance, or loose explosiveness. This portion of the test forces the client to demonstrate control of the knee while maintaining explosiveness and resisting fatigue.
This test could be used as a component of return to play testing or just general screening for your clients to see what exactly needs to be worked on during your workouts.