Without an official test procedure, I have just pulled all the plugs, stuck them back in their cap's hanging off the PH, then I wrapped a length of solder looping each plugs base making a series stringer of plugs. Then ground the solder stringer with a clip lead. Then crank it over (with a jumper wire or have someone help) and inspect all the plugs at once...Probably other ways but, this worked for me to get a quick and dirty idea of how things looked. Plugs all should light up nice and white/blue'ish all in turn and sound snappy........
