code: def assert_difference(
      self, bistring_1: str, bitstring_2: str, target: str
  ):
      mask_a = BitMask.from_bin(bistring_1)
      mask_b = BitMask.from_bin(bitstring_2)
      mask_a.difference(mask_b)
      self.assertEqual(mask_a.x, int(target, 2))
  
imports: import unittest
  from copy import deepcopy
  from random import randint, random, seed
  from lightly.api.bitmask import BitMask
label_desc: Use image node_id 10 for calling the TestBitMask obj's underlying member method code with example usage: obj.assert_difference(bistring_1, bitstring_2, target) without return types