code: def test_get_file_units(caplog):
      """Test get the file-units from the dataset info."""
      did = make_dataid(name="some_variable", modifiers=())
      ds_info = {"file_units": None}
      with caplog.at_level(logging.DEBUG):
          file_units = _get_file_units(did, ds_info)
  
      assert file_units is None
      log_output = "Unknown units for file key 'DataID(name='some_variable', modifiers=())'"
      assert log_output in caplog.text
  
file_path: satpy/satpy/tests/reader_tests/test_viirs_atms_utils.py
imports: import logging
  import dask.array
  import numpy
  import pytest
  import xarray
  from satpy.readers.viirs_atms_sdr_base import _get_file_units, _get_scale_factors_for_units
  from satpy.tests.utils import make_dataid
label_desc: Use image node_id 1 for calling a global function with example usage: test_get_file_units(caplog) without return types