code: def dummy_map(x):
      """Dummy function used in calls to map_batches in these tests."""
      return x
  
imports: import os
  from typing import List
  import numpy
  import pandas
  import pytest
  import ray
  from ray._private.internal_api import memory_summary
  from ray.data import Dataset
  from ray.data.block import BlockMetadata
  from ray.data.context import DataContext
  from ray.data.datasource import Datasource, ReadTask
  from ray.data.datasource.csv_datasource import CSVDatasource
  from ray.data.tests.util import column_udf, extract_values
  from ray.tests.conftest import *
label_desc: Use image node_id 2 for calling a global function with example usage: dummy_map(x) and returns: x