Added the test cases I actually meant to add.
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index c5bb54a..b10caf5 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -562,6 +562,11 @@
self.assertRaises(TypeError, format, object(), 4)
self.assertRaises(TypeError, format, object(), object())
+ # first argument to object.__format__ must be string
+ self.assertRaises(TypeError, object().__format__, 3)
+ self.assertRaises(TypeError, object().__format__, object())
+ self.assertRaises(TypeError, object().__format__, None)
+
# make sure we can take a subclass of str as a format spec
self.assertEqual(format(0, C('10')), ' 0')