Upgrade unittest to be able to use isNotEmpty.

pkg/analysis_server/test/analysis_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.analysis_server;
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/domain_server.dart';
 import 'package:analysis_server/src/operation/operation.dart';
@@ skipping 23 matching lines @@
       AnalysisResult lastResult = new AnalysisResult(null, 1, '', 1);
       when(
           context.performAnalysisTask).thenReturnList(
               [firstResult, firstResult, firstResult, lastResult]);
       helper.server.serverServices.add(ServerService.STATUS);
       helper.server.schedulePerformAnalysisOperation(context);
       // Pump the event queue to make sure the server has finished any
       // analysis.
       return pumpEventQueue().then((_) {
         List<Notification> notifications = helper.channel.notificationsReceived;
-        expect(notifications, isNot(isEmpty));
+        expect(notifications, isNotEmpty);
         // expect at least one notification indicating analysis is in progress
         expect(notifications.any((Notification notification) {
           if (notification.event == SERVER_STATUS) {
             var params = new ServerStatusParams.fromNotification(notification);
             return params.analysis.isAnalyzing;
           }
           return false;
         }), isTrue);
         // the last notification should indicate that analysis is complete
         Notification notification = notifications[notifications.length - 1];
@@ skipping 162 matching lines @@
   @override
   Response handleRequest(Request request) {
     if (request.method == 'echo') {
       return new Response(request.id, result: {
         'echo': true
       });
     }
     return null;
   }
 }