"Chris Lewis" wrote in message

Three-light plug or neon testers are sufficient to tell you
that a ground _exists_ (in the former, the two green lights but not
the red one light up), but not how "good" the ground it is. If
they light up appropriately, the ground is almost guaranteed to be
good enough to trip a GFCI. But it's nowhere near a certainty that
a hot-ground short would trip the breaker.

So how do you test how good the ground is?
Connect a hair dryer across hot and ground (instead of neutral) and see if
it works just as well? Obviously this test would not work on a GFCI
receptacle.