code: def test_head():
      """Test loading the head surface."""
      surf_1 = get_head_surf("sample", subjects_dir=subjects_dir)
      surf_2 = get_head_surf(
          "sample", "head", subjects_dir=subjects_dir
      )
      assert len(surf_1["rr"]) < len(surf_2["rr"])  # BEM vs dense head
      pytest.raises(
          TypeError,
          get_head_surf,
          subject=None,
          subjects_dir=subjects_dir,
      )
  
imports: from pathlib import Path
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal, assert_equal
  from mne import decimate_surface, dig_mri_distances, get_montage_volume_labels, pick_types, read_surface, write_surface
  from mne._fiff.constants import FIFF
  from mne.channels import make_dig_montage
  from mne.datasets import testing
  from mne.io import read_info
  from mne.surface import _compute_nearest, _get_ico_surface, _marching_cubes, _normal_orth, _project_onto_surface, _read_patch, _tessellate_sphere, _voxel_neighbors, fast_cross_3d, get_head_surf, get_meg_helmet_surf, read_curvature
  from mne.transforms import _get_trans
  from mne.utils import _record_warnings, catch_logging, object_diff, requires_freesurfer
label_desc: Use image node_id 2 for calling a global function with example usage: test_head() without return types