I opened an issue to discuss this back in September, but it was closed without anyone addressing the question: https://github.com/ansible/ansible-modules-core/issues/40
To paraphrase myself:
I opened a pull request on the original ansible project, which included a new option for a core module and corresponding tests. When modules were moved to the ansible-core-module project, no tests came along with them. It’s unclear to me how to submit tests for any new module functionality.
Is there any preferred approach?