Mike, the reason I asked is because I have run into circuits that have shared or slaved GFCI devices or receptacles with configurations that would make your head spin let alone wear you out testing the configurations. One occasion, 5 GFCI receptacles and lots of slaves including to other GFCI receptacles. The licensed electrician that wired the residence, a 3 level condo with 2.5 bathrooms, was there wring another unit. The builders representative was conducting the warranty inspection. He said the electrician was present. I called him over to look at the work he installed.
I said that home was wired incorrectly at several circuits. His excuse. That’s what the new homeowner ordered/wanted.
I said, sir the reset for one of the GFCI protected circuit slaves was on the exterior patio. Lovely to have to reset the device when it’s minus 20 or during a storm. As well, too much drop voltage. 2/12 cable would have reduced the voltage drop at the end of circuit. Then I asked the electrician, “That’s what the client ordered?” He looked at me, then the client and said he could put the reset in the home IF the client wished. 
Give me a break.
Personally, I never assume the wiring was correctly installed and test every receptacle I can stab and write up excessive Vd, Drop Voltage.
As for 3 bulb testers. I have 3 in my main tool box. The only time I use a three bulb testers is verify a finding with a third test.
Best regards, Mike.
Keep well.
Robert