Add a mock HTTP client class.

pkg/http/lib/testing.dart

+// Copyright (c) 2012, 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 testing;
+
+/// This library contains testing classes for the HTTP library.
+///
+/// The [MockClient] class is a drop-in replacement for `http.Client` that
+/// allows test code to set up a local request handler in order to fake a server
+/// that responds to HTTP requests:
+///
+///     import 'dart:json';
+///     import 'package:http/testing.dart';
+///
+///     var client = new MockClient((request) {
+///       if (request.url.path != "/data.json") {
+///         return new Response("", 404);
+///       }
+///       return new Response(JSON.stringify({
+///         'numbers': [1, 4, 15, 19, 214]
+///       }, 200, headers: {
+///         'content-type': 'application/json'
+///       });
+///     };
+
+export 'src/mock_client.dart';

[Bob Nystrom, 2012/11/05 23:25:15]

Is there any reason you're leaving the source there instead of just moving it
here?

[nweiz, 2012/11/05 23:40:15]

It indicates that this library isn't intended to just be the MockClient. In the
future I'll probably add other testing utilities, and they'll go here as well.