Recommended way to test Python extensions written in X language

I have some class A that is part of a Python extension I wrote in Rust using PyO3. class A is imported and used as is, as well as being as being subclassed in my Python code.

I want to make tests for class A but I'm not sure if tests should be written in Rust, in Python or both.

What's the recommended way for testing Python extensions written in another language like Rust?