### Initial Checks - [x] I confirm that I'm using the latest version of Pydantic AI - [x] I confirm that I searched for my issue in https://github.com/pydantic/pydantic-ai/issues before opening this issue ### Description I think registered Mimetypes might be OS specific and `.md` is not registered on macos by default so the test fails when running locally ### Example Code ```Python ``` ### Python, Pydantic AI & LLM client version ```Text latest ```