code: def test_get_id__correct_dict(self):
      df_dict = {
          "a": pd.DataFrame(
              {"_value": [1, 2, 3, 4, 10, 11], "id": [1, 1, 1, 1, 2, 2]}
          ),
          "b": pd.DataFrame(
              {"_value": [5, 6, 7, 8, 12, 13], "id": [4, 4, 3, 3, 2, 2]}
          ),
      }
      self.assertEqual(
          dataframe_functions.get_ids(df_dict, "id"), {1, 2, 3, 4}
      )
  
imports: import warnings
  from unittest import TestCase
  import numpy
  import pandas
  from pandas.testing import assert_frame_equal, assert_series_equal
  from tests.fixtures import warning_free
  from tsfresh import extract_relevant_features
  from tsfresh.feature_extraction.settings import MinimalFCParameters
  from tsfresh.utilities import dataframe_functions
label_desc: Use image node_id 2 for calling the GetIDsTestCase obj's underlying member method code with example usage: obj.test_get_id__correct_dict() without return types