Use the @LocalServerPort annotation.

complete/src/test/java/com/example/messagingstompwebsocket/GreetingIntegrationTests.java

@@ -22,12 +22,13 @@ import org.springframework.web.socket.WebSocketHttpHeaders;
 import org.springframework.web.socket.client.WebSocketClient;
 import org.springframework.web.socket.client.standard.StandardWebSocketClient;
 import org.springframework.web.socket.messaging.WebSocketStompClient;
-import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.web.server.LocalServerPort;
+
 
 @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
 public class GreetingIntegrationTests {
 
-	@Value(value="${local.server.port}")
+	@LocalServerPort
 	private int port;
 
 	private WebSocketStompClient stompClient;