code: def test_optode_names():
      """Ensure optode name extraction is correct."""
      ch_names = [
          "S11_D2 760",
          "S11_D2 850",
          "S3_D1 760",
          "S3_D1 850",
          "S2_D13 760",
          "S2_D13 850",
      ]
      ch_types = np.repeat("fnirs_od", 6)
      info = create_info(
          ch_names=ch_names, ch_types=ch_types, sfreq=1.0
      )
      src_names, det_names = _fnirs_optode_names(info)
      assert_array_equal(src_names, [f"S{n}" for n in ["2", "3", "11"]])
      assert_array_equal(det_names, [f"D{n}" for n in ["1", "2", "13"]])
  
      ch_names = [
          "S1_D11 hbo",
          "S1_D11 hbr",
          "S2_D17 hbo",
          "S2_D17 hbr",
          "S3_D1 hbo",
          "S3_D1 hbr",
      ]
      ch_types = np.tile(["hbo", "hbr"], 3)
      info = create_info(
          ch_names=ch_names, ch_types=ch_types, sfreq=1.0
      )
      src_names, det_names = _fnirs_optode_names(info)
      assert_array_equal(src_names, [f"S{n}" for n in range(1, 4)])
      assert_array_equal(
          det_names, [f"D{n}" for n in ["1", "11", "17"]]
      )
  
imports: import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_almost_equal, assert_array_equal
  from mne import create_info
  from mne._fiff.constants import FIFF
  from mne._fiff.pick import _picks_to_idx
  from mne.datasets import testing
  from mne.datasets.testing import data_path
  from mne.io import RawArray, read_raw_nirx
  from mne.preprocessing.nirs import _channel_chromophore, _channel_frequencies, _check_channels_ordered, _fnirs_optode_names, _fnirs_spread_bads, _optode_position, _validate_nirs_info, beer_lambert_law, optical_density, scalp_coupling_index, tddr
label_desc: Use image node_id 9 for calling a global function with example usage: test_optode_names() without return types