diff -r 0ebc9005cb00 Lib/test/test_collections.py
--- a/Lib/test/test_collections.py	Thu May 30 21:08:49 2013 -0400
+++ b/Lib/test/test_collections.py	Fri May 31 18:28:10 2013 +0800
@@ -930,11 +930,11 @@
                     update_test,
                     Counter(words),
                     ]):
-            msg = (i, dup, words)
-            self.assertTrue(dup is not words)
-            self.assertEqual(dup, words)
-            self.assertEqual(len(dup), len(words))
-            self.assertEqual(type(dup), type(words))
+            with self.subTest(i=i):
+                self.assertTrue(dup is not words)
+                self.assertEqual(dup, words)
+                self.assertEqual(len(dup), len(words))
+                self.assertEqual(type(dup), type(words))
 
     def test_copy_subclass(self):
         class MyCounter(Counter):
@@ -1226,11 +1226,12 @@
                     update_test,
                     OrderedDict(od),
                     ]):
-            self.assertTrue(dup is not od)
-            self.assertEqual(dup, od)
-            self.assertEqual(list(dup.items()), list(od.items()))
-            self.assertEqual(len(dup), len(od))
-            self.assertEqual(type(dup), type(od))
+            with self.subTest(i=i):
+                self.assertTrue(dup is not od)
+                self.assertEqual(dup, od)
+                self.assertEqual(list(dup.items()), list(od.items()))
+                self.assertEqual(len(dup), len(od))
+                self.assertEqual(type(dup), type(od))
 
     def test_yaml_linkage(self):
         # Verify that __reduce__ is setup in a way that supports PyYAML's dump() feature.