code: def test_zero_trend():
      """Test PolynomialTrendForecaster with degree zero."""
      _test_trend(degree=0, with_intercept=True)
  
file_path: sktime/sktime/forecasting/trend/tests/test_trend.py
imports: import numpy
  import pandas
  import pytest
  from sktime.datasets import load_airline
  from sktime.forecasting.trend import PolynomialTrendForecaster, TrendForecaster
  from sktime.forecasting.trend._util import _get_X_numpy_int_from_pandas
  from sktime.utils._testing.forecasting import make_forecasting_problem
label_desc: Use image node_id 5 for calling a global function with example usage: test_zero_trend() without return types