code: def test_add_variable_new(self):
      model = MC(["a"], [2])
      model.add_variable("p", 3)
      self.assertIn("p", model.variables)
      self.assertEqual(model.cardinalities["p"], 3)
      self.assertDictEqual(model.transition_models["p"], {})
  
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 13 for calling the TestMarkovChain obj's underlying member method code with example usage: obj.test_add_variable_new() without return types