def METHOD_NAME(self):
    self.nats_client.is_connected = True
    f = concurrent.Future()
    f.set_result(1)
    self.nats_client.subscribe_async.return_value = f
    yield self.subscriber_transport.subscribe('foo', None)
    self.nats_client.subscribe_async.assert_called()
    self.assertTrue(self.subscriber_transport.is_subscribed())