Upgrade unittest to be able to use isNotEmpty.

pkg/analysis_server/test/socket_server_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test.socket.server;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
@@ skipping 77 matching lines @@
     expect(channel.notificationsReceived[0].event, SERVER_CONNECTED);
     _MockRequestHandler handler = new _MockRequestHandler(false);
     server.analysisServer.handlers = [handler];
     var request = new ServerGetVersionParams().toRequest('0');
     return channel.sendRequest(request).then((Response response) {
       expect(response.id, equals('0'));
       expect(response.error, isNotNull);
       expect(response.error.code, equals(RequestErrorCode.SERVER_ERROR));
       expect(response.error.message, equals('mock request exception'));
       expect(response.error.stackTrace, isNotNull);
-      expect(response.error.stackTrace, isNot(isEmpty));
+      expect(response.error.stackTrace, isNotEmpty);
       channel.expectMsgCount(responseCount: 1, notificationCount: 1);
     });
   }
 
   static Future requestHandler_futureException() {
     SocketServer server = new SocketServer(
         new AnalysisServerOptions(),
         DirectoryBasedDartSdk.defaultSdk,
         InstrumentationService.NULL_SERVICE);
     MockServerChannel channel = new MockServerChannel();
@@ skipping 21 matching lines @@
       new Future(throwException);
       return new Response(request.id);
     }
     throw 'mock request exception';
   }
 
   void throwException() {
     throw 'mock future exception';
   }
 }