code: def test_add_reward_function(self):
      expected_reward_xml = etree.XML(
          """
  <RewardFunction>
    <Func>
      <Var>reward_rover</Var>
      <Parent>action_rover rover_0 rock_0</Parent>
      <Parameter type="TBL">
        <Entry>
          <Instance>ame s1 * </Instance>
          <ValueTable>10</ValueTable>
        </Entry>
        <Entry>
          <Instance>amw s0 * </Instance>
          <ValueTable>-100</ValueTable>
        </Entry>
        <Entry>
          <Instance>as s1 * </Instance>
          <ValueTable>-100</ValueTable>
        </Entry>
        <Entry>
          <Instance>as s0 good</Instance>
          <ValueTable>10</ValueTable>
        </Entry>
        <Entry>
          <Instance>as s0 bad</Instance>
          <ValueTable>-10</ValueTable>
        </Entry>
      </Parameter>
    </Func>
  </RewardFunction>"""
      )
      self.maxDiff = None
      self.assertEqual(
          self.writer.add_reward_function(),
          etree.tostring(expected_reward_xml),
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 6 for calling the TestPomdpXWriter obj's underlying member method code with example usage: obj.test_add_reward_function() without return types