code: def img_atlas(shape_3d_default, affine_mni):
      """Return an atlas and its labels."""
      atlas = np.ones(shape_3d_default, dtype="int32")
      atlas[2:5, :, :] = 2
      atlas[5:8, :, :] = 3
      return {
          "img": Nifti1Image(atlas, affine_mni),
          "labels": {
              "gm": 1,
              "wm": 2,
              "csf": 3,
          },
      }
  
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 35 for calling a global function with example usage: img_atlas(shape_3d_default, affine_mni) and returns: dict