code: def test_dict_flattening_preprocessor(self):
      space = Dict(
          {
              "a": Discrete(2),
              "b": Tuple([Discrete(3), Box(-1.0, 1.0, (4,))]),
          }
      )
      pp = get_preprocessor(space)(space)
      self.assertTrue(isinstance(pp, DictFlatteningPreprocessor))
      self.assertEqual(pp.shape, (9,))
      check(
          pp.transform(
              {
                  "a": 1,
                  "b": (1, np.array([0.0, -0.5, 0.1, 0.6], np.float32)),
              }
          ),
          [0.0, 1.0, 0.0, 1.0, 0.0, 0.0, -0.5, 0.1, 0.6],
      )
  
imports: import gymnasium
  from gymnasium.spaces import Box, Dict, Discrete, MultiDiscrete, Tuple, MultiBinary
  import numpy
  import unittest
  import ray
  import ray.rllib.algorithms.ppo
  from ray.rllib.models.catalog import ModelCatalog
  from ray.rllib.models.preprocessors import DictFlatteningPreprocessor, get_preprocessor, NoPreprocessor, TupleFlatteningPreprocessor, OneHotPreprocessor, AtariRamPreprocessor, GenericPixelPreprocessor, MultiBinaryPreprocessor
  from ray.rllib.utils.test_utils import check, check_compute_single_action, check_train_results, framework_iterator
  from ray.rllib.utils.framework import try_import_tf
label_desc: Use image node_id 8 for calling the TestPreprocessors obj's underlying member method code with example usage: obj.test_dict_flattening_preprocessor() without return types