code: def test_private_vs_public(func):
      public_only = set(func(return_private=False))
      private_and_public = set(func(return_private=True))
      assert public_only.issubset(private_and_public)
      assert np.all(
          [
              elt[0].startswith("_")
              for elt in private_and_public - public_only
          ]
      )
  
imports: import numpy
  import pytest
  from nilearn._utils import all_classes, all_functions, all_modules
label_desc: Use image node_id 2 for calling a global function with example usage: test_private_vs_public(func) without return types