code: def test_roundtrip_mrl(tmp_path):
      # Arrange
      tempfile = str(tmp_path / "temp.mrl")
      mop = ImageMorph.MorphOp(op_name="corner")
      initial_lut = mop.lut
  
      # Act
      mop.save_lut(tempfile)
      mop.load_lut(tempfile)
  
      # Act / Assert
      assert mop.lut == initial_lut
  
imports: from __future__ import annotations
  import pytest
  from PIL import Image, ImageMorph, _imagingmorph
  from .helper import assert_image_equal_tofile, hopper
label_desc: Use image node_id 20 for calling a global function with example usage: test_roundtrip_mrl(tmp_path) without return types