docstr: Test helper function responsible for retrieving indices of categorical features
code: def test_get_categorical_features_helper(self):
      """Test helper function responsible for retrieving indices of categorical features"""
      (
          series,
          past_covariates,
          future_covariates,
      ) = self.inputs_for_tests_categorical_covariates
      (
          indices,
          column_names,
      ) = self.lgbm_w_categorical_covariates._get_categorical_features(
          series=series,
          past_covariates=past_covariates,
          future_covariates=future_covariates,
      )
      assert indices == [2, 3, 5]
      assert column_names == [
          "past_cov_past_cov_cat_dummy_lag-1",
          "fut_cov_fut_cov_promo_mechanism_lag1",
          "product_id",
      ]
  
imports: import copy
  import functools
  import itertools
  import math
  from unittest.mock import patch
  import numpy
  import pandas
  import pytest
  from sklearn.ensemble import HistGradientBoostingRegressor, RandomForestRegressor
  from sklearn.linear_model import LinearRegression
  import darts
  from darts import TimeSeries
  from darts.dataprocessing.encoders import FutureCyclicEncoder, PastDatetimeAttributeEncoder
  from darts.logging import get_logger
  from darts.metrics import mae, rmse
  from darts.models import CatBoostModel, LightGBMModel, LinearRegressionModel, NotImportedModule, RandomForest, RegressionModel, XGBModel
  from darts.utils import timeseries_generation
  from darts.utils.multioutput import MultiOutputRegressor
label_desc: Use image node_id 33 for calling the TestRegressionModels obj's underlying member method code with example usage: obj.test_get_categorical_features_helper() without return types