code: def test_copy_alpha_channel(self):
      g = Image.linear_gradient("L")
      im = Image.merge(
          "RGBA",
          [
              g,
              g.transpose(Image.Transpose.ROTATE_90),
              g.transpose(Image.Transpose.ROTATE_180),
              g.transpose(Image.Transpose.ROTATE_270),
          ],
      )
  
      assert_image_equal(
          im,
          im._new(
              im.im.color_lut_3d(
                  "RGBA",
                  Image.Resampling.BILINEAR,
                  *self.generate_identity_table(3, 17),
              )
          ),
      )
  
imports: from __future__ import annotations
  from array import array
  import pytest
  from PIL import Image, ImageFilter
  from .helper import assert_image_equal
label_desc: Use image node_id 8 for calling the TestColorLut3DCoreAPI obj's underlying member method code with example usage: obj.test_copy_alpha_channel() without return types