A leak will be present at ANY boost level, not just over boost. If you want to test how much pressure the system can hold then you want to do as you said. But thats not what the OP wants to test. The OP wants to see if the system can hold pressure, not how much. Even at 1 psi the air will leak if he has a leak, there just wont be much air to help find the leak. 10 psi is a safe level where if the tester slips out it will wont have much momentum. At 30 psi its more like a ballistic object.
If your gonna be an *******, at least be a correct
*******. Because your wrong.
1psi of boost is nothing... thats like sticking your mouth to the IC piping and blowing into it. If you pulled your IC piping and blew into it, do you really think your body would have enough pressure to pressurize the system?
I'll help you out. No, your body wont even phase the gargantuan IC setup.
You need to pressurize to the PSI that truck typically runs at. 32psi is going to have a lot more force behind it than say, 1psi or 10psi. Thats a huge difference in pressure. When your turbo is pushing max boost and your driving down the road, the IC lines are moving, radiator/ic moving, the motor is torqueing etc... which can create boost leaks. You have to do everything you can do to simulate driving down the road to find the stubborn boost leaks.
For instance. My TDI I boost about 30psi. If I juice the IC up to 30psi w/ my leak down setup, nothing will leak. Now, simulating driving down the road, shaking the IC lines and the IC, all of a sudden I have a boost leak popping up that ONLY shows when the motor is tweaking and allowing the boost leak to show.
When you test at pressures this high, put a very heavy rag/towel over the boost fitting incase it pops off.
And lastly, if
your IC is sealed off as well as it should be, there should be very little to no
boost leaking out w/ the compressor shut off. The gauge should barely move on the decrease when sitting idle.