How do you debug git credential helpers?

I have read:

• https://git-scm.com/book/en/v2/Git-Tools-Credential-Storage
• https://git-scm.com/book/en/v2/Git-Internals-Environment-Variables
  • Specifically in "Debugging", GIT_TRACE_SETUP and GIT_TRACE
• https://pratz.github.io/custom-git-credential-helper
• https://stackoverflow.com/a/28007050/117471
  • …which taught me to test my credential-osxkeychain helper via echo -e "host=git-codecommit.us-east-1.amazonaws.com\nprotocol=https\n\n" | git credential-osxkeychain get
• https://kgrz.io/using-git-credential-helpers.html

Unfortunately, I cannot get the most basic Scientific Method™ test to work. I have used my stand-in command to try and log what happens when git calls the helper. Unfortunately, my command logs nothing. Therefore I'm forced to conclude that git is not calling its helper. What can I do?