Add unit tests for Python argument options

[koesie10]

This adds unit tests for Python argument options and fixes some bugs that I found while writing the unit tests. Suggested in #3540 (review)

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.