public class WebSocketIntegrationTest {

    @LocalServerPort
    private int port;

    @Autowired
    private MockMvc mockMvc;

    @Autowired
    private ObjectMapper objectMapper;

    private String url;

    private WebSocketStompClient stompClient;
    private WebSocketHandler webSocketHandler;
    private CompletableFuture<NotificationDto> completableFuture = new CompletableFuture<>();

    @Autowired
    private NotificationService notificationService;



    @BeforeEach
    public void setUp() {
        this.stompClient = new WebSocketStompClient(
            new SockJsClient(
                List.of(new WebSocketTransport(new StandardWebSocketClient()))
            )
        );
        var messageConverter = new MappingJackson2MessageConverter();
        messageConverter.setObjectMapper(objectMapper); 
        this.stompClient.setMessageConverter(messageConverter);
        this.url = "ws://localhost:" + port + "/ws";
        this.webSocketHandler = new WebSocketHandler(new CompletableFuture<NotificationDto>());
    }
   
    @Test
    @Transactional
    public void likeArticle_shouldSendNotification() throws Exception {

        StompSession session = stompClient.connectAsync(url, new StompSessionHandlerAdapter() {
                @Override
                public void afterConnected(StompSession session, StompHeaders connectedHeaders) {

                    session.subscribe("/user/testId/topic/notification",
                        new StompFrameHandler() {
                            @Override
                            public Type getPayloadType(StompHeaders headers) {
                                logger.info("Received STOMP Headers: {}", headers);
                                return NotificationDto.class;
                            }

                            @Override
                            public void handleFrame(StompHeaders headers, Object o) {
                                logger.info("Received notification: {}", o);
                                if (o instanceof NotificationDto) {
                                    completableFuture.complete((NotificationDto) o);
                                } else {
                                    logger.error("Unexpected payload type: {}", o.getClass());
                                }
                            }
                        }
                    );
                }
            }
        ).get(5, TimeUnit.SECONDS);

        //when
        notificationService.sendNotification(
            Notification.builder().message("test").user(user).build(), user);

        TimeUnit.SECONDS.sleep(1);

        //then
        var notificationDto = completableFuture.get(20, TimeUnit.SECONDS);
        assertThat(notificationDto).isNotNull();
    }
}

this is my test code for testing websocket message send and transfer server to client but I got always TimeoutException on var notificationDto = completableFuture.get(20, TimeUnit.SECONDS);

According to chatGPT4o mini,

1. check the path. so I checked the Config.class, and NotificationService.sendNotification()

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {

    @Override
    public void configureMessageBroker(MessageBrokerRegistry config) {
        config.enableSimpleBroker("/topic", "/queue");
        config.setApplicationDestinationPrefixes("/app");
        config.setUserDestinationPrefix("/user");
    }

    @Override
    public void registerStompEndpoints(StompEndpointRegistry registry) {
        registry.addEndpoint("/ws")
            .addInterceptors(new HttpSessionHandshakeInterceptor())
            .setAllowedOrigins("*")
            .withSockJS();
    }

@Service
@RequiredArgsConstructor
@Slf4j
public class NotificationService {

    private final NotificationRepository notificationRepository;
    private final SimpMessagingTemplate messagingTemplate; 

    @Transactional
    public void createNotification(Notification notification) {
        notificationRepository.save(notification);
    }

    public void sendNotification(Notification notification, User receiver) {
        NotificationDto notificationDto = NotificationDto.from(notification);

        messagingTemplate.
            convertAndSendToUser(
                receiver.getLoginId(), 
                "/topic/notification",
                notificationDto 
            );
        log.info("Notification sent to /user/{}{}", receiver.getLoginId(), "/topic/notification");
    }

I subscribe the end-point thru session.subscribe("/user/testId/topic/notification", new StompFrameHandler()...

I checked so many times but I’m sure the path is great. log.info("Notification sent to /user/{}{}", receiver.getLoginId(), "/topic/notification"); prints out the same destination with session.subscribe("/user/testId/topic/notification",...

2. check port number -> no problem

3. make longer the timeout of var notificationDto = completableFuture.get(20, TimeUnit.SECONDS); -> no work (only longer time to wait to get failure)

I really want to know how to work it. and I guess the subscribe() method is something wrong bcs the new StompFrameHandler() has 2 override method and I log the two but not working. that means the getPayloadType() and handleFrame() is not computed

everything I can do. I’m sure for 2 days