Add a context field to Message in shelf.

pkg/shelf/test/message_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.message_test;
 
 import 'dart:async';
 import 'dart:convert';
 
 import 'package:shelf/src/message.dart';
 import 'package:unittest/unittest.dart';
 
 class _TestMessage extends Message {
-  _TestMessage(Map<String, String> headers, Stream<List<int>> body)
-      : super(body, headers: headers);
+  _TestMessage(Map<String, String> headers, Map<String, Object> context,
+        Stream<List<int>> body)
+      : super(body, headers: headers, context: context);
 }
 
-Message _createMessage({Map<String, String> headers, Stream<List<int>> body}) {
+Message _createMessage({Map<String, String> headers,
+    Map<String, Object> context, Stream<List<int>> body}) {
   if (body == null) body = new Stream.fromIterable([]);
-  return new _TestMessage(headers, body);
+  return new _TestMessage(headers, context, body);
 }
 
 void main() {
   group('headers', () {
     test('message headers are case insensitive', () {
       var message = _createMessage(headers: {'foo': 'bar'});
 
       expect(message.headers, containsPair('foo', 'bar'));
       expect(message.headers, containsPair('Foo', 'bar'));
       expect(message.headers, containsPair('FOO', 'bar'));
     });
 
     test('null header value becomes empty, immutable', () {
       var message = _createMessage();
       expect(message.headers, isEmpty);
       expect(() => message.headers['h1'] = 'value1', throwsUnsupportedError);
     });
 
     test('headers are immutable', () {
       var message = _createMessage(headers: {'h1': 'value1'});
       expect(() => message.headers['h1'] = 'value1', throwsUnsupportedError);
       expect(() => message.headers['h1'] = 'value2', throwsUnsupportedError);
       expect(() => message.headers['h2'] = 'value2', throwsUnsupportedError);
     });
   });
+
+  group('context', () {
+    test('is accessible', () {
+      var message = _createMessage(context: {'foo': 'bar'});
+      expect(message.context, containsPair('foo', 'bar'));
+    });
+
+    test('null context value becomes empty and immutable', () {
+      var message = _createMessage();
+      expect(message.context, isEmpty);
+      expect(() => message.context['key'] = 'value', throwsUnsupportedError);
+    });
+
+    test('is immutable', () {
+      var message = _createMessage(context: {'key': 'value'});
+      expect(() => message.context['key'] = 'value', throwsUnsupportedError);
+      expect(() => message.context['key2'] = 'value', throwsUnsupportedError);
+    });
+  });
+
   group("readAsString", () {
     test("supports a null body", () {
       var request = _createMessage();
       expect(request.readAsString(), completion(equals("")));
     });
 
     test("supports a Stream<List<int>> body", () {
       var controller = new StreamController();
       var request = _createMessage(body: controller.stream);
       expect(request.readAsString(), completion(equals("hello, world")));
@@ skipping 98 matching lines @@
       }).encoding, isNull);
     });
 
     test("comes from the content-type charset parameter", () {
       expect(_createMessage(headers: {
         'content-type': 'text/plain; charset=iso-8859-1'
       }).encoding, equals(LATIN1));
     });
   });
 }