code: def mask_1(self):
      mask = Image.new("1", (self.size, self.size))
      px = mask.load()
      for y in range(mask.height):
          for x in range(mask.width):
              px[y, x] = (x + y) % 2
      return mask
  
imports: from __future__ import annotations
  import pytest
  from PIL import Image
  from .helper import CachedProperty, assert_image_equal
label_desc: Use image node_id 3 for calling the TestImagingPaste obj's underlying member method code with example usage: obj.mask_1() and returns: mask