The commit cbe72d842646ded2454784679231e3d1e6252e72 is a good example:

            deadline = time.monotonic() + 60
            t = 0.1
            while time.monotonic() < deadline:
                time.sleep(t)
                t = min(t*2, 5)
                try:
                    smm = shared_memory.SharedMemory(name, create=False)
                except FileNotFoundError:
                    break
            else:
                raise AssertionError("A SharedMemory segment was leaked after"
                                     " a process was abruptly terminated.")

It would be nice to convert this code pattern into an helper function in test.support. It's common to have to wait for something in tests.