code: def test_set_start_state_none(self):
      model = MC()
      model.state = "state"
      model.set_start_state(None)
      self.assertIsNone(model.state)
  
imports: import sys
  import unittest
  import numpy
  from mock import call, patch
  from pandas import DataFrame
  from pgmpy.factors.discrete import State
  from pgmpy.models import MarkovChain
label_desc: Use image node_id 8 for calling the TestMarkovChain obj's underlying member method code with example usage: obj.test_set_start_state_none() without return types