code: def test_add_initial_belief(self):
      expected_belief_xml = etree.XML(
          """
  <InitialStateBelief>
    <CondProb>
      <Var>rover_0</Var>
      <Parent>null</Parent>
      <Parameter type="TBL">
        <Entry>
          <Instance> - </Instance>
          <ProbTable>0.0 1.0 0.0</ProbTable>
        </Entry>
      </Parameter>
    </CondProb>
    <CondProb>
      <Var>rock_0</Var>
      <Parent>null</Parent>
      <Parameter type="TBL">
        <Entry>
          <Instance> - </Instance>
          <ProbTable>uniform</ProbTable>
        </Entry>
      </Parameter>
    </CondProb>
  </InitialStateBelief>"""
      )
      self.maxDiff = None
      self.assertEqual(
          str(self.writer.add_initial_belief()),
          str(etree.tostring(expected_belief_xml)),
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 3 for calling the TestPomdpXWriter obj's underlying member method code with example usage: obj.test_add_initial_belief() without return types