async def METHOD_NAME(loop: Any, mocker: Any) -> None:
    """Ensure that the transport is set to None when the connection is lost.
    This ensures the writer knows that the connection is closed.
    """
    proto = ResponseHandler(loop=loop)
    proto.connection_made(mocker.Mock())
    assert proto.transport is not None
    proto.connection_lost(OSError())
    assert proto.transport is None