code: def test_reward_function(self):
      reward_function_expected = [
          {
              "Var": "reward_rover",
              "Parent": ["action_rover", "rover_0", "rock_0"],
              "Type": "TBL",
              "Parameter": [
                  {
                      "Instance": ["ame", "s1", "*"],
                      "ValueTable": ["10"],
                  },
                  {
                      "Instance": ["amw", "s0", "*"],
                      "ValueTable": ["-100"],
                  },
                  {
                      "Instance": ["as", "s1", "*"],
                      "ValueTable": ["-100"],
                  },
                  {
                      "Instance": ["as", "s0", "good"],
                      "ValueTable": ["10"],
                  },
                  {
                      "Instance": ["as", "s0", "bad"],
                      "ValueTable": ["-10"],
                  },
              ],
          }
      ]
      self.maxDiff = None
      self.assertEqual(
          self.reader_string.get_reward_function(),
          reward_function_expected,
      )
      self.assertEqual(
          self.reader_file.get_reward_function(),
          reward_function_expected,
      )
  
imports: import io
  import sys
  import unittest
  import xml.etree.ElementTree
  from pgmpy.readwrite import PomdpXReader, PomdpXWriter
label_desc: Use image node_id 6 for calling the TestPomdpXReaderStringTorch obj's underlying member method code with example usage: obj.test_reward_function() without return types