test_py3kwarn had been overlooked when test.test_support.catch_warning() was
re-implemented to use warnings.catch_warnings() and had its API improved.

Closes issue #3768.
Code review by Benjamin Peterson.
diff --git a/Lib/test/test_py3kwarn.py b/Lib/test/test_py3kwarn.py
index 8fa6135..7bfe1e5 100644
--- a/Lib/test/test_py3kwarn.py
+++ b/Lib/test/test_py3kwarn.py
@@ -220,28 +220,28 @@
             # With object as the base class
             class WarnOnlyCmp(object):
                 def __cmp__(self, other): pass
-            self.assertEqual(len(w.warnings), 1)
+            self.assertEqual(len(w), 1)
             self.assertWarning(None, w,
                  "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
             w.reset()
             class WarnOnlyEq(object):
                 def __eq__(self, other): pass
-            self.assertEqual(len(w.warnings), 1)
+            self.assertEqual(len(w), 1)
             self.assertWarning(None, w,
                  "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
             w.reset()
             class WarnCmpAndEq(object):
                 def __cmp__(self, other): pass
                 def __eq__(self, other): pass
-            self.assertEqual(len(w.warnings), 2)
-            self.assertWarning(None, w.warnings[-2],
+            self.assertEqual(len(w), 2)
+            self.assertWarning(None, w[-2],
                  "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
             self.assertWarning(None, w,
                  "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
             w.reset()
             class NoWarningOnlyHash(object):
                 def __hash__(self): pass
-            self.assertEqual(len(w.warnings), 0)
+            self.assertEqual(len(w), 0)
             # With an intermediate class in the heirarchy
             class DefinesAllThree(object):
                 def __cmp__(self, other): pass
@@ -249,28 +249,28 @@
                 def __hash__(self): pass
             class WarnOnlyCmp(DefinesAllThree):
                 def __cmp__(self, other): pass
-            self.assertEqual(len(w.warnings), 1)
+            self.assertEqual(len(w), 1)
             self.assertWarning(None, w,
                  "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
             w.reset()
             class WarnOnlyEq(DefinesAllThree):
                 def __eq__(self, other): pass
-            self.assertEqual(len(w.warnings), 1)
+            self.assertEqual(len(w), 1)
             self.assertWarning(None, w,
                  "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
             w.reset()
             class WarnCmpAndEq(DefinesAllThree):
                 def __cmp__(self, other): pass
                 def __eq__(self, other): pass
-            self.assertEqual(len(w.warnings), 2)
-            self.assertWarning(None, w.warnings[-2],
+            self.assertEqual(len(w), 2)
+            self.assertWarning(None, w[-2],
                  "Overriding __cmp__ blocks inheritance of __hash__ in 3.x")
             self.assertWarning(None, w,
                  "Overriding __eq__ blocks inheritance of __hash__ in 3.x")
             w.reset()
             class NoWarningOnlyHash(DefinesAllThree):
                 def __hash__(self): pass
-            self.assertEqual(len(w.warnings), 0)
+            self.assertEqual(len(w), 0)
 
 
 class TestStdlibRemovals(unittest.TestCase):