code: def test_autocontrast_unsupported_mode():
      im = Image.new("RGBA", (1, 1))
      with pytest.raises(OSError):
          ImageOps.autocontrast(im)
  
imports: from __future__ import annotations
  import pytest
  from PIL import Image, ImageDraw, ImageOps, ImageStat, features
  from .helper import assert_image_equal, assert_image_similar, assert_image_similar_tofile, assert_tuple_approx_equal, hopper
label_desc: Use image node_id 18 for calling a global function with example usage: test_autocontrast_unsupported_mode() without return types