code: def test_add_nodes_from_string(self):
      self.G.add_nodes_from(["a", "b", "c", "d"])
      self.assertCountEqual(list(self.G.nodes()), ["a", "b", "c", "d"])
  
imports: import unittest
  import networkx
  import pandas
  import numpy
  from pgmpy.models import NaiveBayes
  from pgmpy.independencies import Independencies
label_desc: Use image node_id 7 for calling the TestBaseModelCreation obj's underlying member method code with example usage: obj.test_add_nodes_from_string() without return types