code: def test_get_variables(self):
      self.assertListEqual(
          self.writer.get_variables(),
          [
              "asia",
              "tub",
              "smoke",
              "lung",
              "bronc",
              "either",
              "xray",
              "dysp",
          ],
      )
  
imports: import unittest
  import numpy
  from pgmpy import config
  from pgmpy.readwrite import NETReader, NETWriter
  from pgmpy.utils import compat_fns, get_example_model
label_desc: Use image node_id 2 for calling the TestNETWriter obj's underlying member method code with example usage: obj.test_get_variables() without return types