code: def test_add_node_nonstring(self):
      self.graph.add_node(1)
      self.assertListEqual(list(self.graph.nodes()), [1])
  
imports: from pgmpy.base import UndirectedGraph
  from pgmpy.tests import help_functions
  import unittest
label_desc: Use image node_id 5 for calling the TestUndirectedGraphCreation obj's underlying member method code with example usage: obj.test_add_node_nonstring() without return types