code: def test_obs_function_dd(self):
      self.model_data = {
          "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.writer = PomdpXWriter(model_data=self.model_data)
      expected_xml = etree.XML(
          """
  <ObsFunction>
    <CondProb>
      <Var>obs_sensor</Var>
      <Parent>action_rover rover_1 rock_1</Parent>
      <Parameter type="DD">
        <DAG>
          <Node var="action_rover">
            <Edge val="ac">
              <Node var="rover_1">
                <Edge val="s0">
                  <Node var="rock_1">
                    <Edge val="bad">
                      <SubDAG type="deterministic" val="obad" var="obs_sensor" />
                    </Edge>
                    <Edge val="good">
                      <SubDAG type="deterministic" val="ogood" var="obs_sensor"/>
                    </Edge>
                  </Node>
                </Edge>
                <Edge val="s1">
                  <SubDAG idref="obs_rock" type="template"/>
                </Edge>
                <Edge val="s2">
                  <SubDAG idref="obs_rock" type="template"/>
                </Edge>
              </Node>
            </Edge>
            <Edge val="ame">
              <SubDAG type="deterministic" val="ogood" var="obs_sensor"/>
            </Edge>
            <Edge val="amw">
              <SubDAG type="deterministic" val="ogood" var="obs_sensor" />
            </Edge>
            <Edge val="as">
              <SubDAG type="deterministic" val="ogood" var="obs_sensor"/>
            </Edge>
          </Node>
        </DAG>
        <SubDAGTemplate id="obs_rock">
          <Node var="rock_1">
            <Edge val="bad">
              <Node var="obs_sensor">
                <Edge val="obad">
                  <Terminal>0.8</Terminal>
                </Edge>
                <Edge val="ogood">
                  <Terminal>0.2</Terminal>
                </Edge>
              </Node>
            </Edge>
            <Edge val="good">
              <Node var="obs_sensor">
                <Edge val="obad">
                  <Terminal>0.2</Terminal>
                </Edge>
                <Edge val="ogood">
                  <Terminal>0.8</Terminal>
                </Edge>
              </Node>
            </Edge>
          </Node>
        </SubDAGTemplate>
      </Parameter>
    </CondProb>
  </ObsFunction>"""
      )
      self.maxDiff = None
      self.assertEqual(
          str(self.writer.add_obs_function()),
          str(etree.tostring(expected_xml)),
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 9 for calling the TestPomdpXWriter obj's underlying member method code with example usage: obj.test_obs_function_dd() without return types