Bench checking wastegate opening pressure (boost)

Have an external wastegate and will like to know how I can check wastegate opening without the engine running.
Was planning to use compressed air and an ol boost gauge to have an estimate...
Any pointers??
Yea that would work. Is there a reason you don’t want to just tear it on the car? Are u putting in a super heavy spring or something?
I use an old manual boost control valve, a small gauge w/ very good resolution at low psi, in line, and regulate shop air to test it.
Under heavy load exhaust pressure will be trying to open the gate also. Exhaust pressure can be as high as 2x the boost so maybe 40psi and higher. Smarter people than me have logged and proved this. I think you will get some info from bench testing but on the car you should see something different. Try to set it for a low boost and add more gradually.