code: def test_postprocessor_default_implementation(self):
      assert self.postprocessor.to_params().params == {"type": "simple"}
      assert isinstance(self.postprocessor, SimpleSerializer)
  
imports: from typing import Iterator, List
  import torch
  import pytest
  import json
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.common import Params
  from allennlp.common.util import sanitize
  from allennlp.data.data_loaders import TensorDict
  from allennlp.evaluation import Serializer
  from allennlp.evaluation.serializers import SimpleSerializer
label_desc: Use image node_id 2 for calling the TestSerializer obj's underlying member method code with example usage: obj.test_postprocessor_default_implementation() without return types