First stab at a dev server in pub using barback.

pkg/path/test/path_test.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.
 
 import 'package:unittest/unittest.dart';
 import 'package:path/path.dart' as path;
 
 main() {
   group('path.Style', () {
     test('name', () {
@@ skipping 16 matching lines @@
     test('uses the given root directory', () {
       var builder = new path.Builder(root: '/a/b/c');
       expect(builder.root, '/a/b/c');
     });
 
     test('uses the given style', () {
       var builder = new path.Builder(style: path.Style.windows);
       expect(builder.style, path.Style.windows);
     });
   });
+
+  test('posix is a default Builder for the POSIX style', () {
+    expect(path.posix.style, path.Style.posix);
+    expect(path.posix.root, ".");
+  });
+
+  test('windows is a default Builder for the Windows style', () {
+    expect(path.windows.style, path.Style.windows);
+    expect(path.windows.root, ".");
+  });
+
+  test('url is a default Builder for the URL style', () {
+    expect(path.url.style, path.Style.url);
+    expect(path.url.root, ".");
+  });
 }