In article , Mike rock wrote:
*Pull out the GFI and use a pigtail socket and bulb to confirm that you have
a functional ground.


A GFI's operation has nothing to do with the ground. It monitors the
current flowing throught the hot and neutral.

If you'd read the entire thread, you would have seen that the OP stated that
the GFCI trips normally when he presses the test button on the GFCI, but fails
to trip when he presses the test button on his plug-in tester -- and you would
have also seen an explanation of why this is so: the plug-in tester shunts
current to *ground*, and *cannot* trip the GFCI unless there is a functional
ground at the outlet.