code: def test_apply(self):
      lut = ImageFilter.Color3DLUT.generate(
          5, lambda r, g, b: (r, g, b)
      )
  
      g = Image.linear_gradient("L")
      im = Image.merge(
          "RGB",
          [
              g,
              g.transpose(Image.ROTATE_90),
              g.transpose(Image.ROTATE_180),
          ],
      )
      assert im == im.filter(lut)
  
imports: from array import array
  import pytest
  from PIL import Image, ImageFilter
  from .helper import assert_image_equal
label_desc: Use image node_id 4 for calling the TestGenerateColorLut3D obj's underlying member method code with example usage: obj.test_apply() without return types