code: def test_against_statsmodels_3():
      """Compare sktime's ARDL interface with statsmodels ARDL with X=None."""
      from statsmodels.datasets import longley
      from statsmodels.tsa.ardl import ARDL as _ARDL
  
      # data
      data = longley.load_pandas().data
      data = data.iloc[:-5, :]
      y = data.TOTEMP
      X = None
      X_oos = None
      # fit
      sm_ardl = _ARDL(y, lags=2, exog=None, trend="c")
      res = sm_ardl.fit()
      ardl_sktime = ARDL(lags=2, trend="c")
      ardl_sktime.fit(y=y, X=X, fh=None)
      # predict
      fh = ForecastingHorizon([1, 2, 3])
      start, end = y.shape[0] + fh[0] - 1, y.shape[0] + fh[-1] - 1
      y_pred_stats = sm_ardl.predict(
          res.params, start=start, end=end, exog_oos=X_oos
      )
      y_pred = ardl_sktime.predict(fh=fh, X=X_oos)
      return assert_allclose(y_pred, y_pred_stats)
  
file_path: sktime/sktime/forecasting/tests/test_ardl.py
imports: import pytest
  from numpy.testing import assert_allclose
  from sktime.datasets import load_macroeconomic
  from sktime.forecasting.ardl import ARDL
  from sktime.forecasting.base import ForecastingHorizon
  from sktime.tests.test_switch import run_test_for_class
label_desc: Use image node_id 3 for calling a global function with example usage: test_against_statsmodels_3() and returns: assert_allclose