code: def test_check_model(self):
      self.assertRaises(ValueError, self.graph2.check_model)
      self.assertRaises(ValueError, self.graph3.check_model)
      self.assertTrue(self.graph1.check_model())
      self.assertTrue(self.graph4.check_model())
  
imports: import unittest
  import numpy
  from pgmpy.factors.discrete import DiscreteFactor
  from pgmpy.models import JunctionTree
  from pgmpy.tests import help_functions
label_desc: Use image node_id 2 for calling the TestJunctionTreeMethods obj's underlying member method code with example usage: obj.test_check_model() without return types