code: def test_update_node_parents(self):
      self.graph.add_nodes_from(["a", "b", "c"])
      self.graph.add_edges_from([("a", "b"), ("b", "c")])
      self.assertListEqual(list(self.graph.predecessors("a")), [])
      self.assertListEqual(list(self.graph.predecessors("b")), ["a"])
      self.assertListEqual(list(self.graph.predecessors("c")), ["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 17 for calling the TestDAGCreation obj's underlying member method code with example usage: obj.test_update_node_parents() without return types