code: def test_add_transition_function(self):
      expected_transition_xml = etree.XML(
          """
  <StateTransitionFunction>
    <CondProb>
      <Var>rover_1</Var>
      <Parent>action_rover rover_0</Parent>
      <Parameter type="TBL">
        <Entry>
          <Instance>amw s0 s2</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>amw s1 s0</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>ame s0 s1</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>ame s1 s2</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>ac s0 s0</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>ac s1 s1</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>as s0 s0</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>as s1 s2</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>* s2 s2</Instance>
          <ProbTable>1.0</ProbTable>
        </Entry>
      </Parameter>
    </CondProb>
    <CondProb>
      <Var>rock_1</Var>
      <Parent>action_rover rover_0 rock_0</Parent>
      <Parameter type="TBL">
        <Entry>
          <Instance>amw * - - </Instance>
          <ProbTable>1.0 0.0 0.0 1.0</ProbTable>
        </Entry>
        <Entry>
          <Instance>ame * - - </Instance>
          <ProbTable>identity</ProbTable>
        </Entry>
        <Entry>
          <Instance>ac * - - </Instance>
          <ProbTable>identity</ProbTable>
        </Entry>
        <Entry>
          <Instance>as * - - </Instance>
          <ProbTable>identity</ProbTable>
        </Entry>
        <Entry>
          <Instance>as s0 * - </Instance>
          <ProbTable>0.0 1.0</ProbTable>
        </Entry>
      </Parameter>
    </CondProb>
  </StateTransitionFunction>"""
      )
      self.maxDiff = None
      self.assertEqual(
          self.writer.add_state_transition_function(),
          etree.tostring(expected_transition_xml),
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 4 for calling the TestPomdpXWriter obj's underlying member method code with example usage: obj.test_add_transition_function() without return types