How to test callbacks for MqttClientConnection when mocking

[mogambo100]

I have a MqttClientConnection object created like this

            HostResolver hostResolver = new HostResolver(eventLoopGroup);
            ClientBootstrap clientBootstrap = new ClientBootstrap(eventLoopGroup, hostResolver)) {
            MqttClientConnectionEvents callbacks = new MqttClientConnectionEvents() {
                @Override
                public void onConnectionInterrupted(int errorCode) {
                    mqttClientConnectedStatus = "DISCONNECTED";
                    if (errorCode != 0) {
                        log.warn("Connection interrupted: " + errorCode + ": " + CRT.awsErrorString(errorCode));
                    }
                }

                @Override
                public void onConnectionResumed(boolean sessionPresent) {
                    mqttClientConnectedStatus = "CONNECTED";
                    log.warn("Connection resumed: " + (sessionPresent ? "existing session" : "clean session"));
                }
            };

            MqttClientConnection mqttClientConnection = AwsIotMqttConnectionBuilder.newDefaultBuilder()
                    .withConnectionEventCallbacks(callbacks)
                    .withBootstrap(clientBootstrap)
                    .withCertificateAuthority(getRootCA())
                    .withCleanSession(true)
                    .withClientId(randomInstanceId)
                    .withEndpoint(iotEndpoint)
                    .withSocketOptions(new SocketOptions())
                    .withTimeoutMs((int)CONNECT_TO_IOTBROKER_TIMEOUT)
                    .withWebsockets(true)
                    .withWebsocketCredentialsProvider(populateCredentials(awsSessionCredentials))
                    .withWebsocketSigningRegion(AWS_REGION)
                    .build();

            //connect
            try {
                CompletableFuture<Boolean> connectFuture = mqttClientConnection.connect();

I want to mock the callbacks so that when mqttClientConnection.connect is hit we can verify our callbacks functionality.

I tried mocking via doAnswer but resulted in OutOfBoundException

doAnswer(answerVoid((MqttClientConnectionEvents mqttCallback)-> mqttCallback.onConnectionResumed(true)))
                .when(awsIotMqttClient).connect();

Whats should be the correct way to verify. Post callbacks we will be checking value of mqttClientConnectedStatus variable.

[jmklix]

This is a question of which third party tool to use to mock callbacks, and we don't have any suggestions for what works well with this sdk. But I would encourage anyone else to recommend what they are using.