code: def test_state_transition_function(self):
      string = """
           <pomdpx version="1.0" id="rockSample"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="pomdpx.xsd">
           <Description>RockSample problem for map size 1 x 3.
             Rock is at 0, Rover’s initial position is at 1.
             Exit is at 2.
           </Description>
           <Discount>0.95</Discount>
          <StateTransitionFunction>
          <CondProb>
              <Var>rover_1</Var>
              <Parent>action_rover rover_0</Parent>
              <Parameter type="DD">
                  <DAG>
                      <Node var="action_rover">
                          <Edge val="amw">
                              <Node var="rover_0">
                                  <Edge val="s0">
                                      <SubDAG type="deterministic" var="rover_1" val="s2"/>
                                  </Edge>
                                  <Edge val="s1">
                                      <SubDAG type="deterministic" var="rover_1" val="s0"/>
                                  </Edge>
                                  <Edge val="s2">
                                      <SubDAG type="deterministic" var="rover_1" val="s2"/>
                                  </Edge>
                              </Node>
                          </Edge>
                          <Edge val="ame">
                              <Node var="rover_0">
                                  <Edge val="s0">
                                      <SubDAG type="deterministic" var="rover_1" val="s1"/>
                                  </Edge>
                                  <Edge val="s1">
                                      <SubDAG type="deterministic" var="rover_1" val="s2"/>
                                  </Edge>
                                  <Edge val="s2">
                                      <SubDAG type="deterministic" var="rover_1" val="s2"/>
                                  </Edge>
                              </Node>
                          </Edge>
                          <Edge val="ac">
                              <SubDAG type="persistent" var="rover_1"/>
                          </Edge>
                          <Edge val="as">
                              <Node var="rover_0">
                                  <Edge val="s0">
                                      <SubDAG type="deterministic" var="rover_1" val="s0"/>
                                  </Edge>
                                  <Edge val="s1">
                                      <SubDAG type="deterministic" var="rover_1" val="s2"/>
                                  </Edge>
                                  <Edge val="s2">
                                      <SubDAG type="deterministic" var="rover_1" val="s2"/>
                                  </Edge>
                              </Node>
                          </Edge>
                      </Node>
                  </DAG>
              </Parameter>
          </CondProb>
          <CondProb>
              <Var>rock_1</Var>
              <Parent>action_rover rover_0 rock_0</Parent>
              <Parameter type="DD">
                  <DAG>
                      <Node var="action_rover">
                          <Edge val="amw">
                              <SubDAG type="persistent" var="rock_1"/>
                          </Edge>
                          <Edge val="ame">
                              <SubDAG type="persistent" var="rock_1"/>
                          </Edge>
                          <Edge val="ac">
                              <SubDAG type="persistent" var="rock_1"/>
                          </Edge>
                          <Edge val="as">
                              <Node var="rover_0">
                                  <Edge val="s0">
                                      <SubDAG type="deterministic" var="rock_1" val="bad"/>
                                  </Edge>
                                  <Edge val="s1">
                                      <SubDAG type="persistent" var="rock_1"/>
                                  </Edge>
                                  <Edge val="s2">
                                      <SubDAG type="persistent" var="rock_1"/>
                                  </Edge>
                              </Node>
                          </Edge>
                      </Node>
                  </DAG>
              </Parameter>
          </CondProb>
      </StateTransitionFunction>
  </pomdpx>
          """
      self.reader_string = PomdpXReader(string=string)
      self.reader_file = PomdpXReader(path=io.StringIO(string))
      expected_state_transition_function = [
          {
              "Var": "rover_1",
              "Parent": ["action_rover", "rover_0"],
              "Type": "DD",
              "Parameter": {
                  "action_rover": {
                      "amw": {
                          "rover_0": {
                              "s0": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s2",
                              },
                              "s1": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s0",
                              },
                              "s2": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s2",
                              },
                          }
                      },
                      "ame": {
                          "rover_0": {
                              "s0": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s1",
                              },
                              "s1": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s2",
                              },
                              "s2": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s2",
                              },
                          }
                      },
                      "ac": {"type": "persistent", "var": "rover_1"},
                      "as": {
                          "rover_0": {
                              "s0": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s0",
                              },
                              "s1": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s2",
                              },
                              "s2": {
                                  "type": "deterministic",
                                  "var": "rover_1",
                                  "val": "s2",
                              },
                          }
                      },
                  }
              },
          },
          {
              "Var": "rock_1",
              "Parent": ["action_rover", "rover_0", "rock_0"],
              "Type": "DD",
              "Parameter": {
                  "action_rover": {
                      "amw": {"type": "persistent", "var": "rock_1"},
                      "ame": {"type": "persistent", "var": "rock_1"},
                      "ac": {"type": "persistent", "var": "rock_1"},
                      "as": {
                          "rover_0": {
                              "s0": {
                                  "type": "deterministic",
                                  "var": "rock_1",
                                  "val": "bad",
                              },
                              "s1": {
                                  "type": "persistent",
                                  "var": "rock_1",
                              },
                              "s2": {
                                  "type": "persistent",
                                  "var": "rock_1",
                              },
                          }
                      },
                  }
              },
          },
      ]
      self.maxDiff = None
      self.assertEqual(
          self.reader_string.get_state_transition_function(),
          expected_state_transition_function,
      )
      self.assertEqual(
          self.reader_file.get_state_transition_function(),
          expected_state_transition_function,
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 10 for calling the TestPomdpXReaderString obj's underlying member method code with example usage: obj.test_state_transition_function() without return types