How to troubleshoot pressure drops in water pipe pressure tests?

When a water pipe pressure test shows a pressure drop, don't immediately assume the pipe is leaking. I've seen it several times on-site where the real issue was a loose pressure gauge connection, a leaking temporary plug, or air not being fully bled from the pipes. It looks normal right after pressurizing, but then it drops a bit, and everyone starts tearing down walls to find a leak, only to…