code: def test_operator_minus(self):
      mask_a = BitMask.from_bin("0b10111")
      mask_a_old = deepcopy(mask_a)
      mask_b = BitMask.from_bin("0b01100")
      mask_target = BitMask.from_bin("0b10011")
      diff = mask_a - mask_b
      self.assertEqual(diff, mask_target)
      self.assertEqual(mask_a_old, mask_a)
  
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 14 for calling the TestBitMask obj's underlying member method code with example usage: obj.test_operator_minus() without return types