Python PyTest running GitPython under Tox in Ubuntu Docker image: commit fails with Committer/Author identity unknown

Question

Q+A (I'm posting this in case someone else goes down this niche rabbit hole - as it took me a while to figure this out).

Scenario: You've decided to run a unit-test which 'plays' with creating a local git repo using GitPython. Your tests run in Tox in a GitHub action which runs an Ubuntu docker image - which has correct .gitconfig file with user.name and user.email. You can even see this correct config if you use GitPython's GitConfigParser or just read the file at git.config.get_config_path.
With all the above looking good, you run your tests, which contain something like:

with open(os.path.join(remote_repo.working_dir, 'readme.md'), 'w') as file:
    file.write('# Remote\n')
remote_repo.git.add(A=True)
remote_repo.git.commit(m=commit_text)

in GH and get failures with something like:

          raise GitCommandError(redacted_command, status, stderr_value, stdout_value)
  E           git.exc.GitCommandError: Cmd('git') failed due to: exit code(128)
  E             cmdline: git commit -m Initial commit
  E             stderr: 'Author identity unknown
  E           
  E           *** Please tell me who you are.
  E           
  E           Run
  E           
  E             git config --global user.email "[email protected]"
  E             git config --global user.name "Your Name"
  E           
  E           to set your account's default identity.
  E           Omit --global to set the identity only in this repository.
  E           
  E           fatal: unable to auto-detect email address (got '**********.(none)')'

EDIT Answer moved the answers below.

Answer 1

I tried so many things... but the last desperate attempt of calling remote_repo.git.config('--global', 'user.name', 'some user') failed with the message that '$HOME' wasn't set - which finally led me to the...

Solution: Add the following to tox.ini's testenv section [edited after comment]:

[testenv]
  passenv = HOME
  ...

Explanation: Tox doesn't set the HOME environment variable, and it appears GitPython's repo.git.commit command only reads the config if HOME is set.