code: def test_obs_function_dd(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>
          <ObsFunction>
          <CondProb>
              <Var>obs_sensor</Var>
              <Parent>action_rover rover_1 rock_1</Parent>
              <Parameter type="DD">
                  <DAG>
                      <Node var="action_rover">
                          <Edge val="amw">
                              <SubDAG type="deterministic" var="obs_sensor" val="ogood"/>
                          </Edge>
                          <Edge val="ame">
                              <SubDAG type="deterministic" var="obs_sensor" val="ogood"/>
                          </Edge>
                          <Edge val="ac">
                              <Node var="rover_1">
                                  <Edge val="s0">
                                      <Node var="rock_1">
                                          <Edge val="good">
                                              <SubDAG type="deterministic" var="obs_sensor" val="ogood"/>
                                          </Edge>
                                          <Edge val="bad">
                                              <SubDAG type="deterministic" var="obs_sensor" val="obad"/>
                                          </Edge>
                                      </Node>
                                  </Edge>
                                  <Edge val="s1">
                                      <SubDAG type="template" idref="obs_rock"/>
                                  </Edge>
                                  <Edge val="s2">
                                      <SubDAG type="template" idref="obs_rock"/>
                                  </Edge>
                              </Node>
                          </Edge>
                          <Edge val="as">
                              <SubDAG type="deterministic" var="obs_sensor" val="ogood"/>
                          </Edge>
                      </Node>
                  </DAG>
                  <SubDAGTemplate id="obs_rock">
                      <Node var="rock_1">
                          <Edge val="good">
                              <Node var="obs_sensor">
                                  <Edge val="ogood">
                                      <Terminal>0.8</Terminal>
                                  </Edge>
                                  <Edge val="obad">
                                      <Terminal>0.2</Terminal>
                                  </Edge>
                              </Node>
                          </Edge>
                          <Edge val="bad">
                              <Node var="obs_sensor">
                                  <Edge val="ogood">
                                      <Terminal>0.2</Terminal>
                                  </Edge>
                                  <Edge val="obad">
                                      <Terminal>0.8</Terminal>
                                  </Edge>
                              </Node>
                          </Edge>
                      </Node>
                  </SubDAGTemplate>
              </Parameter>
          </CondProb>
      </ObsFunction>
      </pomdpx>
          """
      self.reader_string = PomdpXReader(string=string)
      self.reader_file = PomdpXReader(path=io.StringIO(string))
      expected_obs_function = [
          {
              "Var": "obs_sensor",
              "Parent": ["action_rover", "rover_1", "rock_1"],
              "Type": "DD",
              "Parameter": {
                  "action_rover": {
                      "amw": {
                          "type": "deterministic",
                          "var": "obs_sensor",
                          "val": "ogood",
                      },
                      "ame": {
                          "type": "deterministic",
                          "var": "obs_sensor",
                          "val": "ogood",
                      },
                      "ac": {
                          "rover_1": {
                              "s0": {
                                  "rock_1": {
                                      "good": {
                                          "type": "deterministic",
                                          "var": "obs_sensor",
                                          "val": "ogood",
                                      },
                                      "bad": {
                                          "type": "deterministic",
                                          "var": "obs_sensor",
                                          "val": "obad",
                                      },
                                  }
                              },
                              "s1": {
                                  "type": "template",
                                  "idref": "obs_rock",
                              },
                              "s2": {
                                  "type": "template",
                                  "idref": "obs_rock",
                              },
                          }
                      },
                      "as": {
                          "type": "deterministic",
                          "var": "obs_sensor",
                          "val": "ogood",
                      },
                  },
                  "SubDAGTemplate": {
                      "rock_1": {
                          "good": {
                              "obs_sensor": {
                                  "ogood": "0.8",
                                  "obad": "0.2",
                              }
                          },
                          "bad": {
                              "obs_sensor": {
                                  "ogood": "0.2",
                                  "obad": "0.8",
                              }
                          },
                      }
                  },
                  "id": "obs_rock",
              },
          }
      ]
      self.maxDiff = None
      self.assertEqual(
          self.reader_string.get_obs_function(), expected_obs_function
      )
      self.assertEqual(
          self.reader_file.get_obs_function(), expected_obs_function
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 11 for calling the TestPomdpXReaderString obj's underlying member method code with example usage: obj.test_obs_function_dd() without return types