BAEL-4648: How to debug Websockets (#11469)

* BAEL-4648: How to debug Websockets

* Formatted the code

* Incorporated comments from Kevin

spring-websockets/src/test/java/com/baeldung/debugwebsockets/WebSocketIntegrationTest.java

@@ -0,0 +1,114 @@
+package com.baeldung.debugwebsockets;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.web.server.LocalServerPort;
+import org.springframework.messaging.converter.MappingJackson2MessageConverter;
+import org.springframework.messaging.simp.stomp.StompCommand;
+import org.springframework.messaging.simp.stomp.StompFrameHandler;
+import org.springframework.messaging.simp.stomp.StompHeaders;
+import org.springframework.messaging.simp.stomp.StompSession;
+import org.springframework.messaging.simp.stomp.StompSessionHandler;
+import org.springframework.web.socket.client.WebSocketClient;
+import org.springframework.web.socket.client.standard.StandardWebSocketClient;
+import org.springframework.web.socket.messaging.WebSocketStompClient;
+
+import java.lang.reflect.Type;
+import java.util.Map;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicReference;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+/**
+ * This should be part of integration test suite.
+ * The test starts the server and then connects to the WebSocket. Then verifies if the messages are received from the
+ * WebSocket.
+ * This test is inspired from: https://github.com/spring-guides/gs-messaging-stomp-websocket/blob/main/complete/src/test/java/com/example/messagingstompwebsocket/GreetingIntegrationTests.java
+ */
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
+class WebSocketIntegrationTest{
+    WebSocketClient client;
+    WebSocketStompClient stompClient;
+    @LocalServerPort
+    private int port;
+    private static final Logger logger= LoggerFactory.getLogger(WebSocketIntegrationTest.class);
+
+    @BeforeEach
+    public void setup() {
+        logger.info("Setting up the tests ...");
+        client = new StandardWebSocketClient();
+        stompClient = new WebSocketStompClient(client);
+        stompClient.setMessageConverter(new MappingJackson2MessageConverter());
+    }
+
+    @Test
+    void givenWebSocket_whenMessage_thenVerifyMessage() throws Exception {
+        final CountDownLatch latch = new CountDownLatch(1);
+        final AtomicReference<Throwable> failure = new AtomicReference<>();
+        StompSessionHandler sessionHandler = new StompSessionHandler() {
+            @Override
+            public Type getPayloadType(StompHeaders headers) {
+                return null;
+            }
+
+            @Override
+            public void handleFrame(StompHeaders headers, Object payload) {
+            }
+
+            @Override
+            public void afterConnected(StompSession session, StompHeaders connectedHeaders) {
+                logger.info("Connected to the WebSocket ...");
+                session.subscribe("/topic/ticks", new StompFrameHandler() {
+                    @Override
+                    public Type getPayloadType(StompHeaders headers) {
+                        return Map.class;
+                    }
+
+                    @Override
+                    public void handleFrame(StompHeaders headers, Object payload) {
+                        try {
+
+                            assertThat(payload).isNotNull();
+                            assertThat(payload).isInstanceOf(Map.class);
+
+                            @SuppressWarnings("unchecked")
+                            Map<String, Integer> map = (Map<String, Integer>) payload;
+
+                            assertThat(map).containsKey("HPE");
+                            assertThat(map.get("HPE")).isInstanceOf(Integer.class);
+                        } catch (Throwable t) {
+                            failure.set(t);
+                            logger.error("There is an exception ", t);
+                        } finally {
+                            session.disconnect();
+                            latch.countDown();
+                        }
+
+                    }
+                });
+            }
+
+            @Override
+            public void handleException(StompSession session, StompCommand command, StompHeaders headers, byte[] payload, Throwable exception) {
+            }
+
+            @Override
+            public void handleTransportError(StompSession session, Throwable exception) {
+            }
+        };
+        stompClient.connect("ws://localhost:{port}/stock-ticks/websocket", sessionHandler, this.port);
+        if (latch.await(20, TimeUnit.SECONDS)) {
+            if (failure.get() != null) {
+                fail("Assertion Failed", failure.get());
+            }
+        } else {
+            fail("Could not receive the message on time");
+        }
+    }
+}