Given old two-prong (ungrounded) wiring where a GFCI is installed nearest the panel and other two-prong outlets are attached to the load side of that GFCI, how does one confirm that all the outlets are properly protected?
As far as I understand things, a GFCI tester must leak some current to earth to confirm that it triggers a fault. With the earth pin unconnected that test can't be done with a conventional three-prong tester.
Is there a more sophisticated test? Or is there simply no such thing as downstream protection in ungrounded circuits? Must every outlet have its own GFCI?