code: def test_add_transition_model_success(self):
      model = MC(["var"], [2])
      transition_model = {0: {0: 0.3, 1: 0.7}, 1: {0: 0.5, 1: 0.5}}
      model.add_transition_model("var", transition_model)
      self.assertDictEqual(
          model.transition_models["var"], transition_model
      )
  
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 21 for calling the TestMarkovChain obj's underlying member method code with example usage: obj.test_add_transition_model_success() without return types