Improve str() and object.__str__() documentation (issue #13538).
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index c32992c..19d7c70 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1286,6 +1286,7 @@
         self.assertRaises(TypeError, setattr, sys, 1, 'spam')
         self.assertRaises(TypeError, setattr)
 
+    # test_str(): see test_unicode.py and test_bytes.py for str() tests.
 
     def test_sum(self):
         self.assertEqual(sum([]), 0)