The cooling system can be pressurized using a cooling system pressure tester. When engine is cool remove the fill cap and attach the tester, since caps are different styles on many vehicles an adapter may be needed. Pump the tester up until the maximum pressure (most caps have max psi on them) of the cooling sytem is reached. If there is a fast leak the max psi may not need to be obtained before the leak is revealed. There is a video at DenLorsTools.com in the tech article section that shows a pressure tester being used, it also has information about purging air from the cooling system after the leak has been repaired.