code: def test_pdag_to_dag(self):
      # PDAG no: 1  Possibility of creating a v-structure
      pdag = PDAG(
          directed_ebunch=[("A", "B"), ("C", "B")],
          undirected_ebunch=[("C", "D"), ("D", "A")],
      )
      dag = pdag.to_dag()
      self.assertTrue(("A", "B") in dag.edges())
      self.assertTrue(("C", "B") in dag.edges())
      self.assertFalse(
          (("A", "D") in dag.edges()) and (("C", "D") in dag.edges())
      )
      self.assertTrue(len(dag.edges()) == 4)
  
      # With latents
      pdag = PDAG(
          directed_ebunch=[("A", "B"), ("C", "B")],
          undirected_ebunch=[("C", "D"), ("D", "A")],
          latents=["A"],
      )
      dag = pdag.to_dag()
      self.assertTrue(("A", "B") in dag.edges())
      self.assertTrue(("C", "B") in dag.edges())
      self.assertFalse(
          (("A", "D") in dag.edges()) and (("C", "D") in dag.edges())
      )
      self.assertEqual(dag.latents, set(["A"]))
      self.assertTrue(len(dag.edges()) == 4)
  
      # PDAG no: 2  No possibility of creation of v-structure.
      pdag = PDAG(
          directed_ebunch=[("B", "C"), ("A", "C")],
          undirected_ebunch=[("A", "D")],
      )
      dag = pdag.to_dag()
      self.assertTrue(("B", "C") in dag.edges())
      self.assertTrue(("A", "C") in dag.edges())
      self.assertTrue(
          (("A", "D") in dag.edges()) or (("D", "A") in dag.edges())
      )
  
      # With latents
      pdag = PDAG(
          directed_ebunch=[("B", "C"), ("A", "C")],
          undirected_ebunch=[("A", "D")],
          latents=["A"],
      )
      dag = pdag.to_dag()
      self.assertTrue(("B", "C") in dag.edges())
      self.assertTrue(("A", "C") in dag.edges())
      self.assertTrue(
          (("A", "D") in dag.edges()) or (("D", "A") in dag.edges())
      )
      self.assertEqual(dag.latents, set(["A"]))
  
      # PDAG no: 3  Already existing v-structure, possibility to add another
      pdag = PDAG(
          directed_ebunch=[("B", "C"), ("A", "C")],
          undirected_ebunch=[("C", "D")],
      )
      dag = pdag.to_dag()
      expected_edges = {("B", "C"), ("C", "D"), ("A", "C")}
      self.assertEqual(expected_edges, set(dag.edges()))
  
      # With latents
      pdag = PDAG(
          directed_ebunch=[("B", "C"), ("A", "C")],
          undirected_ebunch=[("C", "D")],
          latents=["A"],
      )
      dag = pdag.to_dag()
      expected_edges = {("B", "C"), ("C", "D"), ("A", "C")}
      self.assertEqual(expected_edges, set(dag.edges()))
      self.assertEqual(dag.latents, set(["A"]))
  
imports: import unittest
  import networkx
  import numpy
  import pgmpy.tests.help_functions
  from pgmpy.base import DAG, PDAG
label_desc: Use image node_id 4 for calling the TestPDAG obj's underlying member method code with example usage: obj.test_pdag_to_dag() without return types