code: def test_scalp_coupling_index(fname, fmt, tmp_path):
      """Test converting NIRX files."""
      assert fmt in ("nirx", "fif")
      raw = read_raw_nirx(fname)
      with pytest.raises(RuntimeError, match="Scalp"):
          scalp_coupling_index(raw)
  
      raw = optical_density(raw)
      sci = scalp_coupling_index(raw)
  
      # All values should be between -1 and +1
      assert_array_less(sci, 1.0)
      assert_array_less(sci * -1.0, 1.0)
  
      # Fill in some data with known correlation values
      rng = np.random.RandomState(0)
      new_data = rng.rand(raw._data[0].shape[0])
      # Set first two channels to perfect correlation
      raw._data[0] = new_data
      raw._data[1] = new_data
      # Set next two channels to perfect correlation
      raw._data[2] = new_data
      raw._data[3] = new_data * 0.3  # check scale invariance
      # Set next two channels to anti correlation
      raw._data[4] = new_data
      raw._data[5] = new_data * -1.0
      # Set next two channels to be uncorrelated
      raw._data[6] = new_data
      raw._data[7] = rng.rand(raw._data[0].shape[0])
      # Set next channel to have zero std
      raw._data[8] = 0.0
      raw._data[9] = 1.0
      raw._data[10] = 2.0
      raw._data[11] = 3.0
      # Check values
      sci = scalp_coupling_index(raw)
      assert_allclose(sci[0:6], [1, 1, 1, 1, -1, -1], atol=0.01)
      assert np.abs(sci[6]) < 0.5
      assert np.abs(sci[7]) < 0.5
      assert_allclose(sci[8:12], 0, atol=1e-10)
  
      # Ensure function errors if wrong type is passed in
      raw = beer_lambert_law(raw, ppf=6)
      with pytest.raises(RuntimeError, match="Scalp"):
          scalp_coupling_index(raw)
  
imports: import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_less
  from mne.datasets import testing
  from mne.datasets.testing import data_path
  from mne.io import read_raw_nirx
  from mne.preprocessing.nirs import beer_lambert_law, optical_density, scalp_coupling_index
label_desc: Use image node_id 1 for calling a global function with example usage: test_scalp_coupling_index(fname, fmt, tmp_path) without return types