Well, basically check its behavior as mentioned in my post:
1. check that the valve is open when the engine is off
2. check that the valve is closed when you start the ignition and the engine is idling
3. have someone step on the gas pedal to around 3,000 - 4,000 rpm, and check that the valve shuts again
Also, when you drive, if you feel the car is sluggish when taking off from stationary, the valve might be stuck open.
And when you accelerate, if the car feel like it runs out of power too soon, revving high but not much pulling power, the valve might be stuck closed.
When it is working correctly, the engine will breathe and pull nicely from a standing start, and accelerate smoothly and powerfully to 3,000 rpm and beyond, without 'running out of breath'.