Check that a failed deletion does not change the value

Author: serhiy-storchaka

Lib/test/test_ssl.py

@@ -5518,9 +5518,11 @@ def test_keylog_defaults(self):
         with self.assertRaises(TypeError):
             ctx.keylog_filename = 1
 
+        ctx.keylog_filename = os_helper.TESTFN
         with self.assertRaisesRegex(AttributeError, 'cannot be deleted'):
             del ctx.keylog_filename
-        self.assertEqual(ctx.keylog_filename, None)
+        # a failed deletion does not change the value
+        self.assertEqual(ctx.keylog_filename, os_helper.TESTFN)
 
     def test_keylog_filename(self):
         self.addCleanup(os_helper.unlink, os_helper.TESTFN)