code: def test_eulernumber(tmpdir):
      # grab a surface from fsaverage
      fssrc = FreeSurferSource(
          subjects_dir=fs.Info.subjectsdir(),
          subject_id="fsaverage",
          hemi="lh",
      )
      pial = fssrc.run().outputs.pial
      assert isinstance(pial, str), "Problem when fetching surface file"
  
      eu = fs.EulerNumber()
      eu.inputs.in_file = pial
      res = eu.run()
      assert res.outputs.defects == 0
      assert res.outputs.euler == 2
  
file_path: nipype/nipype/interfaces/freesurfer/tests/test_utils.py
imports: import os
  import os.path
  import pytest
  from nipype.testing.fixtures import create_files_in_directory_plus_dummy_file, create_surf_file_in_directory
  from nipype.pipeline import engine
  from nipype.interfaces import freesurfer
  from nipype.interfaces.base import TraitError
  from nipype.interfaces.io import FreeSurferSource
label_desc: Use image node_id 6 for calling a global function with example usage: test_eulernumber(tmpdir) without return types