code: def test_snirf_fieldtrip_od():
      """Test reading FieldTrip SNIRF files with optical density data."""
      raw = read_raw_snirf(ft_od, preload=True)
  
      # Test data import
      assert raw._data.shape == (72, 500)
      assert raw.copy().pick("fnirs")._data.shape == (72, 500)
      assert raw.copy().pick("fnirs_od")._data.shape == (72, 500)
      with pytest.raises(
          ValueError, match="not be interpreted as channel"
      ):
          raw.copy().pick("hbo")
      with pytest.raises(
          ValueError, match="not be interpreted as channel"
      ):
          raw.copy().pick("hbr")
  
      assert_allclose(raw.info["sfreq"], 50)
  
imports: import shutil
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_almost_equal, assert_equal
  from mne._fiff.constants import FIFF
  from mne.datasets.testing import data_path, requires_testing_data
  from mne.io import read_raw_nirx, read_raw_snirf
  from mne.io.tests.test_raw import _test_raw_reader
  from mne.preprocessing.nirs import _reorder_nirx, beer_lambert_law, optical_density, short_channels, source_detector_distances
  from mne.transforms import _get_trans, apply_trans
  from mne.utils import catch_logging
label_desc: Use image node_id 10 for calling a global function with example usage: test_snirf_fieldtrip_od() without return types