Originally Posted by
smearcase
What are you testing for?
Did the outside outlet trip without your pushing the test button-- before you started doing testing? Had you just plugged in something (other than the tester) and that tripped the gfci and that caused you to start checking with a tester?
Are you checking for voltage and if so, are you testing with probes in hot and neutral openings or one in hot and one in ground?
If you push the test button on the gfci, does it trip and then reset OK?
I can't tell if you have a real problem or are just experimenting with the tester.
The gfci should trip just like you say it does when you push the test button, whether you have a tester plugged in that moment or not.