code: def test_env_var():
      os.environ["RAPIDS_DATASET_ROOT_DIR"] = "custom_storage_location"
      datasets.set_download_dir(None)
  
      expected_path = Path("custom_storage_location").absolute()
      assert datasets.get_download_dir() == expected_path
  
      del os.environ["RAPIDS_DATASET_ROOT_DIR"]
  
imports: import os
  import gc
  from pathlib import Path
  from tempfile import TemporaryDirectory
  import pandas
  import pytest
  import cudf
  import dask_cudf
  from cugraph.structure import Graph
  from cugraph.testing import RAPIDS_DATASET_ROOT_DIR_PATH, ALL_DATASETS, WEIGHTED_DATASETS, SMALL_DATASETS, BENCHMARKING_DATASETS
  from cugraph import datasets
  from cugraph.dask.common.mg_utils import is_single_gpu
label_desc: Use image node_id 5 for calling a global function with example usage: test_env_var() without return types