Sealed Plumbing roof vents

Inspection yesterday on a 1994 built home had 3 of 4 plumbing roof vents sealed off, 4th one has what appeared to be some sort of rubber expansion device inserted in the vent.

Is this part of some kind of test on the venting system?

Looks like a set up for a waterless air pressure test.

Thanks Derek

Radon testing?

someone forgot their equipment…how did the drains function ?

That’s it. Yeah, how did the drains function?