Definitely worth testing when hot (with usual precautions) as well as cold, have come across external leaks that didn't show when cold even when pressurised at operating pressure and did leak when pressurised hot.
5:13 - I spy, with my beady little eye, someone left the transport bung in, on that battery right by your fingerooney! As a home DIY-er I made my own pressure tester for the car. 3 DIFFERENT mechanics didn't have a coolant pressure tester either!