Expanding WebSocket test

tests/html/websocket_test.dart

 library WebSocketTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 main() {
 
   useHtmlIndividualConfiguration();
 
   group('supported', () {
     test('supported', () {
       expect(WebSocket.supported, true);
     });
   });
 
   group('websocket', () {
     var isWebSocket = predicate((x) => x is WebSocket, 'is a WebSocket');
     var expectation = WebSocket.supported ? returnsNormally : throws;
 
     test('constructorTest', () {
       expect(() {
         var socket = new WebSocket('ws://localhost');
         expect(socket, isNotNull);
         expect(socket, isWebSocket);
         }, expectation);
     });
+
+    if (WebSocket.supported) {
+      test('echo', () {
+        var socket = new WebSocket('ws://${window.location.host}/ws', 'chat');
+        socket.onOpen.first.then((_) {
+          socket.send('hello!');
+        });
+
+        return socket.onMessage.first.then((MessageEvent e) {
+          expect(e.data, 'hello!');
+        });
+      });
+    }
   });
 }