This isn't really 'testing' with the squelsh, but on radios with a mnaual squelsh adjustment the correct procedure is to change frequency and adjust the SQ so as the white noise cuts out.
I hope I didn't give the impression that I didn't know what the squelch was.
There are probably few new radios out there with a manual squelch so the new breed of 150 hour commercial pilots won't know much about squelch and what it's used for.
Does anyone know if the squelch is user adjustable on the G430's or similar from the front interface?