def METHOD_NAME(self, Popen):
    manager = ListenerManager()
    backend1 = Backend.objects.create(name="foo")
    manager.start = MagicMock()
    manager.stop = MagicMock()
    # start existing backends
    manager.keep_listeners_running()
    manager.start.assert_called_with(backend1)
    # new backend, start it too
    backend2 = Backend.objects.create(name="bar")
    manager.keep_listeners_running()
    manager.start.assert_has_calls([call(backend1), call(backend2)], any_order=True)
    manager.stop.assert_not_called()