Test mqtt connect void function via fake/in memory implementation

Question

I have the code that listens to a specific topic and a callback in managed in messageInboundHandler class, it works on manual tests but I did not find a good way to test it in automatic test using mockito, is there any fake/in memory mqtt implementation, like h2 for database?

final MqttConnectOptions options = generateMqttConnectOptions(urls, username, password);
final MqttClient mqttClient = generateSubscriberClient(urls.get(0), clientId);
mqttClient.connect(options);
mqttClient.subscribe(topic);
mqttClient.setCallback(messageInboundHandler);
return mqttClient;