To test air leakage the air valves should be?

A Trailer air supply in, parking brake in, trolley released, and pressure on brake pedal.

explanation

To properly test the air leakage you will need a trailer air supply to supply air to the trailer, a parking brake in filling the red line with air, steady pressure applied to the brake pedal filling the blue line with air, and the trolley released so no extra air is supplied to the blue line.