code: def test_get_decimated_surfaces(src, n, nv):
      """Test get_decimated_surfaces."""
      surfaces = get_decimated_surfaces(src)
      assert len(surfaces) == n
      if n == 0:
          return
      for s in surfaces:
          assert set(s) == {"rr", "tris"}
          assert len(s["rr"]) == nv
          assert_array_equal(np.unique(s["tris"]), np.arange(nv))
  
imports: from pathlib import Path
  from shutil import copytree
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_array_equal, assert_array_less, assert_equal
  import mne
  from mne import SourceEstimate, add_source_space_distances, compute_source_morph, get_volume_labels_from_src, make_sphere_model, morph_source_spaces, pick_types, read_bem_solution, read_bem_surfaces, read_freesurfer_lut, read_source_spaces, read_trans, setup_source_space, setup_volume_source_space, write_source_spaces
  from mne._fiff.constants import FIFF
  from mne._fiff.pick import _picks_to_idx
  from mne.datasets import testing
  from mne.fixes import _get_img_fdata
  from mne.source_estimate import _get_src_type
  from mne.source_space import compute_distance_to_sensors, get_decimated_surfaces
  from mne.source_space._source_space import _compare_source_spaces
  from mne.surface import _accumulate_normals, _triangle_neighbors
  from mne.utils import _record_warnings, requires_mne, run_subprocess
label_desc: Use image node_id 22 for calling a global function with example usage: test_get_decimated_surfaces(src, n, nv) without return types