code: def check_panel_expsmooth():
      """Test exponential smoothing on panel data with datetime index."""
      # make panel with hour of day panel and datetime index
      y = load_airline()
      y.index = pd.date_range(
          start="1960-01-01", periods=len(y.index), freq="H"
      )
      y.index.names = ["datetime"]
      y.name = "passengers"
      y = y.to_frame()
      y["hour_of_day"] = y.index.hour
      y = (
          y.reset_index()
          .set_index(["hour_of_day", "datetime"])
          .sort_index()
      )
  
      forecaster = ExponentialSmoothing(trend="add", sp=1)
      forecaster.fit(y)
      forecaster.predict(fh=[1, 3])
  
file_path: sktime/sktime/forecasting/tests/test_exp_smoothing.py
imports: import pandas
  import pytest
  from numpy.testing import assert_array_equal
  from sktime.datasets import load_airline
  from sktime.forecasting.exp_smoothing import ExponentialSmoothing
  from sktime.split import temporal_train_test_split
  from sktime.utils._testing.forecasting import make_forecasting_problem
  from sktime.utils.validation._dependencies import _check_soft_dependencies
label_desc: Use image node_id 2 for calling a global function with example usage: check_panel_expsmooth() without return types