What does a pressure test for 2004 ES330 coolant system reveal?

Pressure testing is used to check for leaks in the cooling system and to test the radiator cap. The most common pressure tester is the hand-pump device with adaptors to fit different size caps and the filler neck of the radiator. Another style of pressure tester uses shop air connected to the coolant overflow hose. https://macsworldwide.wordpress.com/2010/10/04/why-pressure-test-an-engine-cooling-system/