code: def test_displacement_field():
      """Test that our matched point deformation works."""
      to = np.array(
          [[5, 4, 1], [6, 1, 0], [4, -1, 1], [3, 3, 0]], float
      )
      fro = np.array(
          [[0, 2, 2], [2, 2, 1], [2, 0, 2], [0, 0, 1]], float
      )
      interp = _MatchedDisplacementFieldInterpolator(fro, to)
      fro_t = interp(fro)
      assert_allclose(to, fro_t, atol=1e-12)
      # check midpoints (should all be decent)
      for a in range(len(to)):
          for b in range(a + 1, len(to)):
              to_ = np.mean(to[[a, b]], axis=0)
              fro_ = np.mean(fro[[a, b]], axis=0)
              fro_t = interp(fro_)
              assert_allclose(to_, fro_t, atol=1e-12)
  
imports: import itertools
  import os
  from pathlib import Path
  import numpy
  import pytest
  from numpy.testing import assert_allclose, assert_almost_equal, assert_array_equal, assert_array_less, assert_equal
  import mne
  from mne import read_trans, write_trans
  from mne.datasets import testing
  from mne.fixes import _get_img_fdata
  from mne.io import read_info
  from mne.transforms import _angle_between_quats, _average_quats, _cart_to_sph, _compute_r2, _euler_to_quat, _find_trans, _find_vector_rotation, _fit_matched_points, _get_trans, _MatchedDisplacementFieldInterpolator, _pol_to_cart, _quat_real, _quat_to_affine, _quat_to_euler, _read_fs_xfm, _sph_to_cart, _topo_to_sph, _validate_pipeline, _write_fs_xfm, apply_trans, combine_transforms, get_ras_to_neuromag_trans, invert_transform, quat_to_rot, rot_to_quat, rotation, rotation3d, rotation3d_align_z_axis, rotation_angles, translation
  from mne.transforms import _SphericalSurfaceWarp
label_desc: Use image node_id 24 for calling a global function with example usage: test_displacement_field() without return types