code: def test_sample(self):
      model = MC(["a", "b"], [2, 2])
      model.transition_models["a"] = {
          0: {0: 0.1, 1: 0.9},
          1: {0: 0.2, 1: 0.8},
      }
      model.transition_models["b"] = {
          0: {0: 0.3, 1: 0.7},
          1: {0: 0.4, 1: 0.6},
      }
      sample = model.sample(
          start_state=[State("a", 0), State("b", 1)], size=2
      )
      self.assertEqual(len(sample), 2)
      self.assertEqual(list(sample.columns), ["a", "b"])
      self.assertTrue(
          list(sample.loc[0]) in [[0, 0], [0, 1], [1, 0], [1, 1]]
      )
      self.assertTrue(
          list(sample.loc[1]) in [[0, 0], [0, 1], [1, 0], [1, 1]]
      )
  
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 24 for calling the TestMarkovChain obj's underlying member method code with example usage: obj.test_sample() without return types