code: def test_representation_length(self):
      input_array = self._sample_batch()
      representation = self._serializer.serialize(input_array)
      self.assertEqual(
          representation.shape,
          (1, self._serializer.representation_length),
      )
  
imports: import gin
  import gym
  import numpy
  from tensorflow import test
  from trax.rl import space_serializer
label_desc: Use image node_id 3 for calling the MultiDiscreteSpaceSerializerTest obj's underlying member method code with example usage: obj.test_representation_length() without return types