code: def test_class_init_with_data_string(self):
      self.graph = DAG([("a", "b"), ("b", "c")])
      self.assertListEqual(sorted(self.graph.nodes()), ["a", "b", "c"])
      self.assertListEqual(
          hf.recursive_sorted(self.graph.edges()),
          [["a", "b"], ["b", "c"]],
      )
      self.assertEqual(self.graph.latents, set())
  
      self.graph = DAG([("a", "b"), ("b", "c")], latents=["b"])
      self.assertListEqual(sorted(self.graph.nodes()), ["a", "b", "c"])
      self.assertListEqual(
          hf.recursive_sorted(self.graph.edges()),
          [["a", "b"], ["b", "c"]],
      )
      self.assertEqual(self.graph.latents, set(["b"]))
  
imports: import unittest
  import networkx
  import numpy
  import pgmpy.tests.help_functions
  from pgmpy.base import DAG, PDAG
label_desc: Use image node_id 3 for calling the TestDAGCreation obj's underlying member method code with example usage: obj.test_class_init_with_data_string() without return types