Add OpenAI provider unit test code

[tomfrombayesians]

Hello!

Thank you for creating such a great package. We really appreciate it and are using it well. We’re developing open-source Agent Tom, that automates codebase maintenance tasks like unit test management.

This PR is a simple one—it’s our first contribution, so we’ve only added a small unit test without any associated issues. The code was developed in collaboration with Tom, our AI agent. For now, our project is still private, but if you’re interested, you can sign up for our Beta Release Waitlist through this link.

I carefully followed the CONTRIBUTING guidelines, but please let us know if there’s anything we should adjust. Thanks again!