code: def gradient_L(self):
      gradient = Image.new("L", (self.size, self.size))
      px = gradient.load()
      for y in range(gradient.height):
          for x in range(gradient.width):
              px[y, x] = (x + y) % 255
      return gradient
  
imports: from PIL import Image
  from .helper import assert_image_equal, cached_property
label_desc: Use image node_id 5 for calling the TestImagingPaste obj's underlying member method code with example usage: obj.gradient_L() and returns: gradient