def test_custom_fc_support_fit_a_linreg(self, model):
        """AutoETS does not support future covariates natively. Check that Darts' OLS trick is applied."""
        model.fit(series=self.series, future_covariates=self.ts_trend)

        # check if linear regression was fit
        assert model._linreg is not None
        assert model._linreg._fit_called

        # fit a linear regression
        linreg = LinearRegressionModel(lags_future_covariates=[0])
        linreg.fit(series=self.series, future_covariates=self.ts_trend)

        # check if the linear regression was fit on the same data by checking if the coefficients are equal
        assert model._linreg.model.coef_ == linreg.model.coef_
AutoETS does not support future covariates natively. Check that Darts' OLS trick is applied.
darts/tests/models/forecasting/test_sf_models.py