Equipment

Ideally, testing would be performed with a standard medical oxigen tank, regulator, and humidifier similar to this one:

In the absence of real equipment, the following may be substituted with care to match the characteristics of medical equipment.

Air Supply

Air compressor with regulator, should be able to provide 15L/min @ 40 PSI

Flow limiter

Pressure compensated, should be able to limit to 15L/min to match standard medical equipment. Can be approximated with an 0.8mm printer nozzle @ 35 PSI. Calculator for airflow

To verify you're producing 15L/min, submerge a container of known volume in a large container of water. Place the air line (after the flow limiter) under the container and measure the amount of time it takes to make the container fill. E.G. with a 15L container that starts out completely full of water, the container should rise completely out of the water in about 1 minute, a 5L container should take 20 seconds. There is some wiggle room, but medical equipment is mostly limited to 15L, so accurate testing depends on accurate flow limiting.

Manometer

A manometer that can accurately show pressures in the 0-20cm H2O range is vital. A U-tube manometer is easily constructed out of clear vinyl tubing. A printable manometer can be found on thingiverse