code: def f(x):
      # A simple test function
      return x
  
file_path: nilearn/nilearn/_utils/tests/test_cache_mixin.py
imports: import os
  import shutil
  from pathlib import Path
  import pytest
  from joblib import Memory
  import nilearn
  from nilearn._utils import CacheMixin, cache_mixin
label_desc: Use image node_id 2 for calling a global function with example usage: f(x) and returns: x