code: def test_dag(client):
      batch = create_batch(client)
      head = batch.create_job(
          DOCKER_ROOT_IMAGE, command=["echo", "head"]
      )
      left = batch.create_job(
          DOCKER_ROOT_IMAGE, command=["echo", "left"], parents=[head]
      )
      right = batch.create_job(
          DOCKER_ROOT_IMAGE, command=["echo", "right"], parents=[head]
      )
      tail = batch.create_job(
          DOCKER_ROOT_IMAGE,
          command=["echo", "tail"],
          parents=[left, right],
      )
      batch.submit()
      batch.wait()
      status = legacy_batch_status(batch)
  
      node_status_logs = []
      for node in [head, left, right, tail]:
          node_status_logs.append((node.status(), node.log()))
  
      assert batch_status_job_counter(status, "Success") == 4, str(
          (status, batch.debug_info())
      )
  
      for node in [head, left, right, tail]:
          status = node._status
          assert status["state"] == "Success", str(
              (status, batch.debug_info())
          )
          assert node._get_exit_code(status, "main") == 0, str(
              (status, batch.debug_info())
          )
  
imports: import asyncio
  import os
  import re
  import secrets
  import pytest
  from aiohttp import web
  from hailtop.batch_client import aioclient
  from hailtop.batch_client.client import BatchClient, Job
  from .utils import DOCKER_ROOT_IMAGE, batch_status_job_counter, create_batch, legacy_batch_status
label_desc: Use image node_id 4 for calling a global function with example usage: test_dag(client) without return types