code: def masker():
      return MultiNiftiMasker(mask_img=_img_3d_ones()).fit()
  
file_path: nilearn/nilearn/decomposition/tests/test_base.py
imports: import numpy
  import pytest
  from nibabel import Nifti1Image
  from numpy.testing import assert_array_almost_equal
  from scipy import linalg
  from nilearn.conftest import _affine_eye, _img_3d_ones, _rng
  from nilearn.decomposition._base import _fast_svd, _mask_and_reduce
  from nilearn.maskers import MultiNiftiMasker
label_desc: Use image node_id 2 for calling a global function with example usage: masker() and returns: MultiNiftiMasker