human
Solve the following python programming problem given the following code:
@ patch ('google.appengine.api.taskqueue.Queue.add', auto_spec = True) 
def test_batches_get_split_dont_reinsert_enqueued(self, queue_add_mock) : 
    'Ensure a batch gets split and retried on error but only tasks which
        were not enqueued are retried.
        ' 
    from furious.context.context import _insert_tasks 
    from google.appengine.api import taskqueue 
    def raise_error(* args, **kwargs) : 
        raise taskqueue.TombstonedTaskError () 
queue_add_mock.side_effect = tasks 
    tasks = (Mock (), taskqueue.Task ('1'), taskqueue.Task ('B')) 
    tasks [0].was_enqueued = True 
    inserted = _insert_tasks (tasks, 'AbCd') 
    self.assertEqual (3, queue_add_mock.call_count) 
    self.assertEqual (1, inserted) 

    
    

    Fix the buggy line: queue_add_mock.side_effect = tasks
assistant
#Here is Python code to fix the buggy line: queue_add_mock.

queue_add_mock.side_effect = def raise_error(