code: def test_serial(self):
      num_threads = 5
      long_delay = TAG_BATCH_DELAY * 1.2
      batches_sent, tags_updated = batch_test(
          num_threads, delay=long_delay
      )
      self.assertEqual(batches_sent, num_threads)
      self.assertEqual(tags_updated, num_threads)
  
file_path: ray/python/ray/tests/aws/test_aws_batch_tag_update.py
imports: import threading
  import time
  import unittest
  from unittest import mock
  import pytest
  from ray.autoscaler._private.aws.node_provider import AWSNodeProvider
  from ray.autoscaler._private.aws.node_provider import TAG_BATCH_DELAY
label_desc: Use image node_id 2 for calling the TagBatchTest obj's underlying member method code with example usage: obj.test_serial() without return types