code: def test_categorical(self):
      s = pd.Series(pd.Categorical(["a", "b", "a"]))
      s.index.name = "idx"
      result = s.to_json(orient="table", date_format="iso")
      result = json.loads(result, object_pairs_hook=OrderedDict)
      result["schema"].pop("pandas_version")
  
      fields = [
          {"name": "idx", "type": "integer"},
          {
              "constraints": {"enum": ["a", "b"]},
              "name": "values",
              "ordered": False,
              "type": "any",
          },
      ]
  
      expected = OrderedDict(
          [
              ("schema", {"fields": fields, "primaryKey": ["idx"]}),
              (
                  "data",
                  [
                      OrderedDict([("idx", 0), ("values", "a")]),
                      OrderedDict([("idx", 1), ("values", "b")]),
                      OrderedDict([("idx", 2), ("values", "a")]),
                  ],
              ),
          ]
      )
  
      assert result == expected
  
imports: from collections import OrderedDict
  from io import StringIO
  import json
  import numpy
  import pytest
  from pandas.core.dtypes.dtypes import CategoricalDtype, DatetimeTZDtype, PeriodDtype
  import pandas
  from pandas import DataFrame
  import pandas._testing
  from pandas.io.json._table_schema import as_json_table_type, build_table_schema, convert_json_field_to_pandas_type, convert_pandas_type_to_json_field, set_default_names
label_desc: Use image node_id 15 for calling the TestTableOrient obj's underlying member method code with example usage: obj.test_categorical() without return types