code: def test_single():
      assert 1 == func.single([1])
      with pytest.raises(Exception):
          assert 1 == func.single([])
      with pytest.raises(Exception):
          assert 1 == func.single([1, 2])
  
file_path: catboost/library/python/func/ut/test_func.py
imports: import pytest
  import multiprocessing
  import random
  import threading
  import time
  import library.python.func
label_desc: Use image node_id 2 for calling a global function with example usage: test_single() without return types