It's not hard, you just need a container big enough to hold what is being tested and strong enough to hold the pressure. Drill 2 holes in the lid, one for a pressure gauge and one for a quick-connect air hose. The air line needs a 1/4 turn ball valve to control pressurizing the container.
Depending on the size of the object, a pressure cooker is a great starting point. You can often find them at garage sales for very cheap.