code: def test_surface_source_morph_shortcut():
      """Test that our shortcut for smooth=0 works."""
      stc = mne.read_source_estimate(fname_smorph)
      morph_identity = compute_source_morph(
          stc,
          "sample",
          "sample",
          spacing=stc.vertices,
          smooth=0,
          subjects_dir=subjects_dir,
      )
      stc_back = morph_identity.apply(stc)
      assert_allclose(stc_back.data, stc.data, rtol=1e-4)
      abs_sum = morph_identity.morph_mat - speye(
          len(stc.data), format="csc"
      )
      abs_sum = np.abs(abs_sum.data).sum()
      assert abs_sum < 1e-4
  
imports: from inspect import signature
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal, assert_array_less
  from scipy.sparse import csr_matrix
  from scipy.sparse import eye
  from scipy.spatial.distance import cdist
  import mne
  from mne import SourceEstimate, SourceMorph, VectorSourceEstimate, VolSourceEstimate, VolVectorSourceEstimate, compute_source_morph, get_volume_labels_from_aseg, grade_to_vertices, make_ad_hoc_cov, make_forward_solution, make_sphere_model, read_evokeds, read_forward_solution, read_freesurfer_lut, read_source_estimate, read_source_morph, setup_volume_source_space
  from mne._freesurfer import _get_atlas_values, _get_mri_info_data
  from mne.datasets import testing
  from mne.fixes import _get_img_fdata
  from mne.minimum_norm import apply_inverse, make_inverse_operator, read_inverse_operator
  from mne.source_space._source_space import _add_interpolator, _grid_interp
  from mne.transforms import quat_to_rot
  from mne.utils import _record_warnings, catch_logging
label_desc: Use image node_id 6 for calling a global function with example usage: test_surface_source_morph_shortcut() without return types