make sure os.symlink presence is tested before running some shutil tests --...

make sure os.symlink presence is tested before running some shutil tests -- also refactored the tests to use unittest.skipUnless

Lib/test/test_shutil.py

@@ -263,7 +263,7 @@ class TestShutil(unittest.TestCase):
             shutil.rmtree(src_dir)
             shutil.rmtree(os.path.dirname(dst_dir))
 
-    if hasattr(os, "symlink"):
+    @unittest.skipUnless(hasattr(os, 'symlink'), 'requires os.symlink')
     def test_dont_copy_file_onto_link_to_itself(self):
         # bug 851123.
         os.mkdir(TESTFN)
@@ -292,6 +292,7 @@ class TestShutil(unittest.TestCase):
             except OSError:
                 pass
 
+        @unittest.skipUnless(hasattr(os, 'symlink'), 'requires os.symlink')
         def test_rmtree_on_symlink(self):
             # bug 1669.
             os.mkdir(TESTFN)
@@ -304,7 +305,7 @@ class TestShutil(unittest.TestCase):
             finally:
                 shutil.rmtree(TESTFN, ignore_errors=True)
 
-    if hasattr(os, "mkfifo"):
+    @unittest.skipUnless(hasattr(os, 'mkfifo'), 'requires os.mkfifo')
     # Issue #3002: copyfile and copytree block indefinitely on named pipes
     def test_copyfile_named_pipe(self):
         os.mkfifo(TESTFN)
@@ -316,6 +317,7 @@ class TestShutil(unittest.TestCase):
         finally:
             os.remove(TESTFN)
 
+    @unittest.skipUnless(hasattr(os, 'mkfifo'), 'requires os.mkfifo')
     def test_copytree_named_pipe(self):
         os.mkdir(TESTFN)
         try:
@@ -351,6 +353,7 @@ class TestShutil(unittest.TestCase):
         shutil.copytree(src_dir, dst_dir, copy_function=_copy)
         self.assertEquals(len(copied), 2)
 
+    @unittest.skipUnless(hasattr(os, 'symlink'), 'requires os.symlink')
     def test_copytree_dangling_symlinks(self):
 
         # a dangling symlink raises an error at the end