code: def test_multistage_model_config():
      """Tests the default parameters in ``MultistageForecastModelConfig``."""
      config = MultistageForecastModelConfig()
      assert config.train_length == f"{7 * 56}D"
      assert config.fit_length is None
      assert config.agg_func == "nanmean"
      assert config.agg_freq is None
      assert config.estimator == SimpleSilverkiteEstimator
      assert config.estimator_params is None
  
imports: import datetime
  import numpy
  import pandas
  import pytest
  from testfixtures import LogCapture
  import greykite.common.constants
  from greykite.common.testing_utils import generate_df_for_tests
  from greykite.sklearn.estimator.lag_based_estimator import LagBasedEstimator
  from greykite.sklearn.estimator.multistage_forecast_estimator import MultistageForecastEstimator
  from greykite.sklearn.estimator.multistage_forecast_estimator import MultistageForecastModelConfig
  from greykite.sklearn.estimator.simple_silverkite_estimator import SimpleSilverkiteEstimator
  from greykite.sklearn.uncertainty.uncertainty_methods import UncertaintyMethodEnum
label_desc: Use image node_id 7 for calling a global function with example usage: test_multistage_model_config() without return types