pkg/shelf: include the original `onHijack` callback for Request.change

pkg/shelf/test/hijack_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 shelf.hijack_test;
 
 import 'dart:async';
 
 import 'package:unittest/unittest.dart';
 import 'package:shelf/shelf.dart';
@@ skipping 30 matching lines @@
   test('hijacking a hijackable request twice throws a StateError', () {
     // Assert that the [onHijack] callback is only called once.
     var request = new Request('GET', LOCALHOST_URI,
         onHijack: expectAsync((_) => null, count: 1));
 
     expect(() => request.hijack((_, __) => null),
         throwsA(new isInstanceOf<HijackException>()));
 
     expect(() => request.hijack((_, __) => null), throwsStateError);
   });
+
+  group('calling change', () {
+    test('hijacking a non-hijackable request throws a StateError', () {
+      var request = new Request('GET', LOCALHOST_URI);
+      var newRequest = request.change();
+      expect(() => newRequest.hijack((_, __) => null),
+          throwsStateError);
+    });
+
+    test('hijacking a hijackable request throws a HijackException and calls '
+        'onHijack', () {
+      var request = new Request('GET', LOCALHOST_URI,
+          onHijack: expectAsync((callback) {
+        var streamController = new StreamController();
+        streamController.add([1, 2, 3]);
+        streamController.close();
+
+        var sinkController = new StreamController();
+        expect(sinkController.stream.first, completion(equals([4, 5, 6])));
+
+        callback(streamController.stream, sinkController);
+      }));
+
+      var newRequest = request.change();
+
+      expect(() => newRequest.hijack(expectAsync((stream, sink) {
+        expect(stream.first, completion(equals([1, 2, 3])));
+        sink.add([4, 5, 6]);
+        sink.close();
+      })), throwsA(new isInstanceOf<HijackException>()));
+    });
+
+    test('hijacking the original request after calling change throws a '
+        'StateError', () {
+      // Assert that the [onHijack] callback is only called once.
+      var request = new Request('GET', LOCALHOST_URI,
+          onHijack: expectAsync((_) => null, count: 1));
+
+      var newRequest = request.change();
+
+      expect(() => newRequest.hijack((_, __) => null),
+          throwsA(new isInstanceOf<HijackException>()));
+
+      expect(() => request.hijack((_, __) => null), throwsStateError);
+    });
+  });
 }