Index: Lib/test/test_bytes.py
===================================================================
--- Lib/test/test_bytes.py	(revision 77287)
+++ Lib/test/test_bytes.py	(working copy)
@@ -927,7 +927,13 @@
             self.assertEqual(val, newval)
             self.assertTrue(val is not newval,
                             methname+' returned self on a mutable object')
-
+        for expr in ('val.split()[0]', 'val.rsplit()[0]',
+                     'val.partition(".")[0]', 'val.rpartition(".")[2]',
+                     'val.splitlines()[0]', 'val.replace("", "")'):
+            newval = eval(expr)
+            self.assertEqual(val, newval)
+            self.assertTrue(val is not newval,
+                            expr+' returned val on a mutable object')
 
 class FixedStringTest(test.string_tests.BaseTest):