code: def test_flatten_dict(dict_grouping_size):
      grouping, size = dict_grouping_size
      expected = list(range(size))
      result = flatten_grouping(grouping)
      assert expected == result
      assert len(result) == grouping_len(grouping)
  
imports: from dash.dependencies import Input
  from dash._grouping import flatten_grouping, make_grouping_by_index, grouping_len, map_grouping, make_grouping_by_key, validate_grouping, SchemaTypeValidationError, SchemaLengthValidationError, SchemaKeysValidationError
  from fixtures import scalar_grouping_size, list_grouping_size, dict_grouping_size, mixed_grouping_size
  import string
  import pytest
label_desc: Use image node_id 3 for calling a global function with example usage: test_flatten_dict(dict_grouping_size) without return types