code: def test_add_node_string(self):
      self.G.add_node("a")
      self.assertListEqual(list(self.G.nodes()), ["a"])
  
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 5 for calling the TestBaseModelCreation obj's underlying member method code with example usage: obj.test_add_node_string() without return types