Fix a couple test timeouts.

test/server/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 json_rpc_2.test.server.server_test;
 
 import 'dart:convert';
 
 import 'package:unittest/unittest.dart';
 import 'package:json_rpc_2/error_code.dart' as error_code;
@@ skipping 71 matching lines @@
     }));
   });
 
   test("doesn't return a result for a notification", () {
     controller.server.registerMethod('foo', (args) => 'result');
 
     expect(controller.handleRequest({
       'jsonrpc': '2.0',
       'method': 'foo',
       'params': {}
-    }), completion(isNull));
+    }), doesNotComplete);
   });
 
   test("includes the error data in the response", () {
     controller.server.registerMethod('foo', (params) {
       throw new json_rpc.RpcException(5, 'Error message.', data: 'data value');
     });
 
     expectErrorResponse(controller, {
       'jsonrpc': '2.0',
       'method': 'foo',
@@ skipping 79 matching lines @@
       }));
     });
   });
 
   test("disallows multiple methods with the same name", () {
     controller.server.registerMethod('foo', () => null);
     expect(() => controller.server.registerMethod('foo', () => null),
         throwsArgumentError);
   });
 }