I have no idea what this term means to you. How can I therefore answer your question.
I suspect that you will have a problem with my answer, but here I go anyway.
The word "testify" as I am using it comes from John 15:26 (as I stated in an earlier post), and is followed by its own definition in verse 27: "And ye also shall bear witness [of Christ]."
I'll stick with that as the definition. A testifying moment is an event where someone bears a witness of Christ and/or of His mission.
BTW, I'm likely done for the night. Thanks for the chat. Have a happy new year.