def test_update_fn_gets_called(self):
        def _update(bdm):
            self.update_called = True

        self.block_device_mapping[1]['device_name'] = None
        compute_utils.default_device_names_for_instance(
            self.instance, self.root_device_name, _update, [], [],
            self.block_device_mapping)
        self.assertTrue(self.update_called)

 def _test_default_device_names(self, update_function, *block_device_lists):
     compute_utils.default_device_names_for_instance(self.instance,
                                                     self.root_device_name,
                                                     update_function,
                                                     *block_device_lists)