code: def test_alpha(op):
      # Issue https://github.com/python-pillow/Pillow/issues/899
      # Is alpha preserved through image enhancement?
  
      original = _half_transparent_image()
  
      for amount in [0, 0.5, 1.0]:
          _check_alpha(
              getattr(ImageEnhance, op)(original).enhance(amount),
              original,
              op,
              amount,
          )
  
file_path: pillow/Tests/test_imageenhance.py
imports: from __future__ import annotations
  import pytest
  from PIL import Image, ImageEnhance
  from .helper import assert_image_equal, hopper
label_desc: Use image node_id 5 for calling a global function with example usage: test_alpha(op) without return types