code: def img_4D():
      data_4d = np.zeros((40, 40, 40, 3))
      data_4d[20, 20, 20] = 1
      return Nifti1Image(data_4d, affine=np.eye(4))
  
imports: import numpy
  import pytest
  from nibabel import Nifti1Image
  from numpy.testing import assert_almost_equal
  from nilearn._utils.testing import write_imgs_to_path
  from nilearn.conftest import _affine_eye, _rng
  from nilearn.decomposition._multi_pca import _MultiPCA
  from nilearn.maskers import MultiNiftiMasker, NiftiMasker
label_desc: Use image node_id 1 for calling a global function with example usage: img_4D() and returns: Nifti1Image