fixed relative root tests

test/posix_test.dart

Index: test/posix_test.dart
diff --git a/test/posix_test.dart b/test/posix_test.dart
index 5b6d131518d00f1816f21ab6c8b9d35fb7fe650c..e6aaba4e786a0f916e84e04190deee38e789825c 100644
--- a/test/posix_test.dart
+++ b/test/posix_test.dart
@@ -421,11 +421,11 @@ main() {
 
     test('from a relative root', () {
       var r = new path.Context(style: path.Style.posix, current: 'foo/bar');
-      expect(context.isWithin('.', 'a/b/c'), isTrue);
-      expect(context.isWithin('.', '../a/b/c'), isFalse);
-      expect(context.isWithin('.', '../../a/foo/b/c'), isFalse);
-      expect(context.isWithin('/', '/baz/bang'), isTrue);
-      expect(context.isWithin('.', '/baz/bang'), isFalse);
+      expect(r.isWithin('.', 'a/b/c'), isTrue);
+      expect(r.isWithin('.', '../a/b/c'), isFalse);
+      expect(r.isWithin('.', '../../a/foo/b/c'), isFalse);
+      expect(r.isWithin('/', '/baz/bang'), isTrue);
+      expect(r.isWithin('.', '/baz/bang'), isFalse);
     });
   });