diff -r d24befb680d6 Lib/test/test_os.py
--- a/Lib/test/test_os.py	Tue Oct 30 20:20:54 2012 -0400
+++ b/Lib/test/test_os.py	Tue Oct 30 23:52:40 2012 -0400
@@ -54,7 +54,16 @@
     def setUp(self):
         if os.path.exists(support.TESTFN):
             os.unlink(support.TESTFN)
-    tearDown = setUp
+        self.rename_dest_file = "%s_%d_tmp" % ("test_rename_dest_file", \
+            os.getpid())
+        if os.path.exists(self.rename_dest_file):
+            os.unlink(self.rename_dest_file)
+
+    def tearDown(self):
+        if os.path.exists(support.TESTFN):
+            os.unlink(support.TESTFN)
+        if os.path.exists(self.rename_dest_file):
+            os.unlink(self.rename_dest_file)
 
     def test_access(self):
         f = os.open(support.TESTFN, os.O_CREAT|os.O_RDWR)
@@ -90,6 +99,41 @@
         new = sys.getrefcount(path)
         self.assertEqual(old, new)
 
+    def test_rename_src_file_dest_file_not_exist(self):
+        source = support.TESTFN
+        destination = self.rename_dest_file
+        fd = os.open(source, os.O_CREAT | os.O_WRONLY)
+        os.write(fd, b"beans\n")
+        os.write(fd, b"bacon\n")
+        os.write(fd, b"eggs\n")
+        os.write(fd, b"spam\n")
+        os.close(fd)
+        os.rename(source, destination)
+        with open(destination, "rb") as fobj:
+            self.assertEqual(fobj.read().splitlines(),
+                [b"beans", b"bacon", b"eggs", b"spam"])
+
+    # the file name in variable destination should not be replaced because it
+    # already exists
+    # this test case actually makes the source file disapear which might be
+    # a bug
+    def test_rename_src_file_dest_file_exists(self):
+        source = support.TESTFN
+        destination = self.rename_dest_file
+        fd = os.open(source, os.O_CREAT | os.O_WRONLY)
+        os.write(fd, b"beans\n")
+        os.write(fd, b"bacon\n")
+        os.write(fd, b"eggs\n")
+        os.write(fd, b"spam\n")
+        os.close(fd)
+        fd = os.open(source, os.O_CREAT | os.O_WRONLY)
+        os.write(fd, b"destination file already exists and has data\n")
+        os.close(fd)
+        os.rename(source, destination)       
+        with open(destination, "rb") as fobj:
+            self.assertNotEqual(fobj.read().splitlines(),
+                [b"beans", b"bacon", b"eggs", b"spam"])
+
     def test_read(self):
         with open(support.TESTFN, "w+b") as fobj:
             fobj.write(b"spam")