There are two major difference
1. there are high pressure test(75% working pressre) and low pressure test
2. after cooling down.Close the downstream valve.Open the test valve. then measure the external leakage.
Sometimes it's fail because the test valve can't open.
As I know, you weld the pipe onto the testing valve. The SwRI welcome you do that to avoid any unnecessary problem. That is not the real leakage, but avoid any confuse suituation happening.
