Fix a couple test timeouts.

test/server/batch_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 json_rpc_2.test.server.batch_test;
 
 import 'dart:convert';
 
 import 'package:unittest/unittest.dart';
 import 'package:json_rpc_2/error_code.dart' as error_code;
@@ skipping 52 matching lines @@
       {'jsonrpc': '2.0', 'result': 'foo', 'id': 1},
       {'jsonrpc': '2.0', 'result': 'value', 'id': 3}
     ])));
   });
 
   test('returns nothing if every request is a notification', () {
     expect(controller.handleRequest([
       {'jsonrpc': '2.0', 'method': 'foo'},
       {'jsonrpc': '2.0', 'method': 'id', 'params': ['value']},
       {'jsonrpc': '2.0', 'method': 'arg', 'params': {'arg': 'value'}}
-    ]), completion(isNull));
+    ]), doesNotComplete);
   });
 
   test('returns an error if the batch is empty', () {
     expectErrorResponse(controller, [], error_code.INVALID_REQUEST,
         'A batch must contain at least one request.');
   });
 
   test('disallows nested batches', () {
     expect(controller.handleRequest([
       [{'jsonrpc': '2.0', 'method': 'foo', 'id': 1}]
     ]), completion(equals([{
       'jsonrpc': '2.0',
       'id': null,
       'error': {
         'code': error_code.INVALID_REQUEST,
         'message': 'Request must be an Array or an Object.',
         'data': {'request': [{'jsonrpc': '2.0', 'method': 'foo', 'id': 1}]}
       }
     }])));
   });
 }