Last year I noticed I was low on antifreeze. I took the pickup truck to a garage for a check up. After 10 minutes the service manager asked me to come and see what was the cause of my truck losing antifreeze. The mechanic had run a pressure test and he showed me plenty of liquid around the water pump. I needed a new water pump. The price was a over 600$.
I went to another garage for a second opinion. After about 15 minutes, I was again led to my pickup truck to see the result of their pressure test. I could not see a single drop of liquid.
Since I was still losing antifreeze, a few months later and almost 1800 miles further, I took it to another garage who ran the same pressure test. No leaking!
Finally, at a 4th garage, after I talked to the manager about my experience/results of pressure test, he proposed to run a test while the motor was cold! He had found the problem and sold me a water pump that cost me 186$.