Add the ability to change the working directory

pkg/pathos/test/pathos_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.
 
 library pathos_test;
 
 import 'dart:io' as io;
 
 import 'package:unittest/unittest.dart';
 import 'package:pathos/path.dart' as path;
@@ skipping 22 matching lines @@
       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('uses the current working directory if root is omitted', () {
       var builder = new path.Builder();
-      expect(builder.root, new io.Directory.current().path);
+      expect(builder.root, io.Directory.current.path);
     });
 
     test('uses the host OS if style is omitted', () {
       var builder = new path.Builder();
       if (io.Platform.operatingSystem == 'windows') {
         expect(builder.style, path.Style.windows);
       } else {
         expect(builder.style, path.Style.posix);
       }
     });
   });
 
   test('current', () {
-    expect(path.current, new io.Directory.current().path);
+    expect(path.current, io.Directory.current.path);
   });
 }