code: def test_as_flat_dict(self):
      params = Params(
          {"a": 10, "b": {"c": 20, "d": "stuff"}}
      ).as_flat_dict()
  
      assert params == {"a": 10, "b.c": 20, "b.d": "stuff"}
  
imports: import json
  import os
  import re
  from collections import OrderedDict
  import pytest
  from allennlp.common.checks import ConfigurationError
  from allennlp.common.params import infer_and_cast, Params, remove_keys_from_params, with_overrides
  from allennlp.common.testing import AllenNlpTestCase
label_desc: Use image node_id 7 for calling the TestParams obj's underlying member method code with example usage: obj.test_as_flat_dict() without return types