I use a plastic container with machine screws through the plastic lid. Internal wires on the inside and connect matches, LEDs. or what ever I want to test to the outside. I have a small plastic tubing through the cover to apply vacuum to simulate a flight. That tests the altimeter.
The ematches and charges for ground testing is a different process. It is to test the charge sizes, not the altimeter.
The only rocket I've ever use vacuum on the av-bay to test the deployment charges was on my L1 cert rocket. Even then I had tested charges with a controller to determine the charge size first. It was only the final test when I loaded every up and applied vacuum to the av-bay.
Now I test the charge sizes and seldom test the altimeters prior to first flight since manufactures are so good with testing. The advantage of doing all those tests on the L1 cert rocket was that by the time I was ready to make the DD cert flight, I was very well familiar with the altimeter, how it worked, and it became one of the minor things I worried about on the cert flight.
If you are testing ejection charges fired by ematches, you can just touch the wires to a 9V battery. Actually, a AA will probably work too, although I haven't tried that.