code: def test_predict_bootstrapping_output_when_forecaster_is_LinearRegression_steps_is_2_in_sample_residuals_True_exog_and_transformer_fixed_to_zero():
      """
      Test output of predict_bootstrapping when regressor is LinearRegression,
      2 steps are predicted, using in-sample residuals, exog is included, both
      inputs are transformed and in-sample residuals are fixed to 0.
      """
      forecaster = ForecasterAutoreg(
          regressor=LinearRegression(),
          lags=3,
          transformer_y=StandardScaler(),
          transformer_exog=StandardScaler(),
      )
      forecaster.fit(y=y, exog=exog)
      forecaster.in_sample_residuals = np.full_like(
          forecaster.in_sample_residuals, fill_value=0
      )
      results = forecaster.predict_bootstrapping(
          steps=2, exog=exog_predict, n_boot=4, in_sample_residuals=True
      )
      expected = pd.DataFrame(
          data=np.array(
              [
                  [0.67998879, 0.67998879, 0.67998879, 0.67998879],
                  [0.46135022, 0.46135022, 0.46135022, 0.46135022],
              ]
          ),
          columns=[f"pred_boot_{i}" for i in range(4)],
          index=pd.RangeIndex(start=50, stop=52),
      )
  
      pd.testing.assert_frame_equal(expected, results)
  
imports: import re
  import pytest
  import numpy
  import pandas
  from sklearn.exceptions import NotFittedError
  from skforecast.ForecasterAutoreg import ForecasterAutoreg
  from skforecast.preprocessing import TimeSeriesDifferentiator
  from sklearn.linear_model import LinearRegression
  from sklearn.preprocessing import StandardScaler
  from .fixtures_ForecasterAutoreg import y
  from .fixtures_ForecasterAutoreg import exog
  from .fixtures_ForecasterAutoreg import exog_predict
  from .fixtures_ForecasterAutoreg import data
label_desc: Use image node_id 7 for calling a global function with example usage: test_predict_bootstrapping_output_when_forecaster_is_LinearRegression_steps_is_2_in_sample_residuals_True_exog_and_transformer_fixed_to_zero() without return types