code: def test_is_d_separated(self):
      self.assertTrue(
          self.inference.model.is_dconnected("X", "Y", observed=None)
      )
      self.assertFalse(
          self.inference.model.is_dconnected(
              "B", "Y", observed=("C", "X")
          )
      )
  
imports: import unittest
  import numpy
  import numpy.testing
  import pandas
  from pgmpy.factors.discrete import TabularCPD
  from pgmpy.inference.CausalInference import CausalInference
  from pgmpy.models import BayesianNetwork
label_desc: Use image node_id 2 for calling the TestCausalGraphMethods obj's underlying member method code with example usage: obj.test_is_d_separated() without return types