code: def img_3d_mni():
      """Return a default random 3D Nifti1Image in MNI space."""
      return _img_3d_mni()
  
imports: import warnings
  import nibabel
  import numpy
  import pytest
  from nibabel import Nifti1Image
  from nilearn import image
  from nilearn.datasets.tests._testing import request_mocker
  from nilearn.datasets.tests._testing import temp_nilearn_data_dir
  from nilearn.experimental.surface.tests.conftest import make_mini_img, mini_img, mini_mesh
label_desc: Use image node_id 22 for calling a global function with example usage: img_3d_mni() and returns: _img_3d_mni