code: def test_variables(self):
      expected_variables = etree.XML(
          """
  <Variable>
    <StateVar fullyObs="true" vnameCurr="rover_1" vnamePrev="rover_0">
      <NumValues>3</NumValues>
    </StateVar>
    <StateVar fullyObs="false" vnameCurr="rock_1" vnamePrev="rock_0">
      <ValueEnum>good bad</ValueEnum>
    </StateVar>
    <ObsVar vname="obs_sensor">
      <ValueEnum>ogood obad</ValueEnum>
    </ObsVar>
    <ActionVar vname="action_rover">
      <ValueEnum>amw ame ac as</ValueEnum>
    </ActionVar>
    <RewardVar vname="reward_rover" />
  </Variable>"""
      )
      self.maxDiff = None
      self.assertEqual(
          self.writer.get_variables(),
          etree.tostring(expected_variables),
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 2 for calling the TestPomdpXWriter obj's underlying member method code with example usage: obj.test_variables() without return types