It's good to see others with the same idea as me. I just wrote https://github.com/python/cpython/pull/6005/commits/4d7e1837f235687c875e985e97701609fc1ac458 . In my opinion, there is no need for another test class. I completely agree with Zachary Ware that the current TestCase class is more or less broken (or at least easily misused) with respect to coroutines. Fixing TestCase would not break existing code. The customization of event loop would not be hard to add.