avoid using mock.assert_called (py 3.5)

tests/tests_logging.py

@@ -54,7 +54,7 @@ def test_should_call_handle_error_if_exception_was_thrown(self):
         logger.handlers = [handler]
         with patch.object(handler, 'handleError') as mock:
             logger.info('test')
-            mock.assert_called()
+            assert mock.called
 
     @pytest.mark.parametrize('exception_class', [
         KeyboardInterrupt,