How can hydraulic brakes be checked for leaks?

A Pump the brake pedal three times, then hold down the pedal for five seconds. If the pedal moves, there may be a problem.

explanation

If the vehicle has hydraulic brakes, pump the brake pedal 3 times. Then apply firm pressure to the pedal and hold for 5 seconds. The pedal should not move. If it does, there may be a leak or other problem. Get it fixed before driving. [Commercial Driver Handbook]