code: def random_bitstring(self, length: int):
      bitsting = "0b"
      for i in range(length):
          bitsting += str(randint(0, 1))
      return bitsting
  
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 12 for calling the TestBitMask obj's underlying member method code with example usage: obj.random_bitstring(length) and returns: bitsting