What are you not sure about how to test that? OpenAI compatible API means, you have a base API url, like https://api.openai.com/v1 or https://api.ppq.ai (my favourite), and then /chat/completions is appended to that, and the JSON returned has the same structure as the ones from the official OpenAI API. But you can use much more LLMs than just the OpenAI ones.