Added note - Running a test with the WG cover plate also tells you the absolute earliest possible spool-up you are to aim for when you install and test WG spring(s) load and your boost solenoid. You should have same readings on spool-up with the cover plate as with your WG. Then you will learn what difference there is to achieve. Real valuable information right there! And of course the boost levels you test when immediately let go of gas pedal with a cover plate should of course be mapped safely beforehand so you don't go into detonation. Remember to close up the pressure hose that normally goes to WG, so you dont do the test with an added leak
When doing the system leak test the end cap mounts to the inlet cold side of the turbo (not all clear in text above). From here you get to pressure test the entire inlet system and the connected "accessories"