Add a Server interface.

test/io_server_test.dart

+// Copyright (c) 2015, 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.
+
+@TestOn('vm')
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:http/http.dart' as http;
+import 'package:shelf/shelf_io.dart';
+import 'package:test/test.dart';
+
+import 'test_util.dart';
+
+void main() {
+  var server;
+  setUp(() async {
+    server = await IOServer.bind(InternetAddress.LOOPBACK_IP_V4, 0);
+  });
+
+  tearDown(() => server.close());
+
+  test("serves HTTP requests with the mounted handler", () async {
+    server.mount(syncHandler);
+    expect(await http.read(server.url), equals('Hello from /'));
+  });
+
+  test("delays HTTP requests until a handler is mounted", () async {
+    expect(http.read(server.url), completion(equals('Hello from /')));
+    await new Future.delayed(Duration.ZERO);
+
+    server.mount(asyncHandler);
+  });
+
+  test("disallows more than one handler from being mounted", () async {
+    server.mount((_) {});
+    expect(() => server.mount((_) {}), throwsStateError);
+    expect(() => server.mount((_) {}), throwsStateError);
+  });
+}