code: def mini_mask(mini_img) -> SurfaceImage:
      data = {k: (v > v.ravel()[0]) for k, v in mini_img.data.items()}
      return SurfaceImage(mini_img.mesh, data)
  
file_path: nilearn/nilearn/experimental/surface/tests/conftest.py
imports: from typing import Callable
  import numpy
  import pytest
  from nilearn.experimental.surface import InMemoryMesh, PolyMesh, SurfaceImage, load_fsaverage
label_desc: Use image node_id 3 for calling a global function with example usage: mini_mask(mini_img) and returns: SurfaceImage