code: def test_LAB(self):
      self.assert_unpack(
          "LAB", "LAB", 3, (1, 130, 131), (4, 133, 134), (7, 136, 137)
      )
      self.assert_unpack("LAB", "L", 1, (1, 0, 0), (2, 0, 0), (3, 0, 0))
      self.assert_unpack("LAB", "A", 1, (0, 1, 0), (0, 2, 0), (0, 3, 0))
      self.assert_unpack("LAB", "B", 1, (0, 0, 1), (0, 0, 2), (0, 0, 3))
  
imports: from __future__ import annotations
  import sys
  import pytest
  from PIL import Image
label_desc: Use image node_id 15 for calling the TestLibUnpack obj's underlying member method code with example usage: obj.test_LAB() without return types