code: def test_init():
      """Tests model initialization"""
      model = DummyEstimator()
      assert model.strategy == "mean"
      assert model.constant is None
      assert model.quantile is None
      assert model.score_func == mean_squared_error
      assert model.coverage is None
  
      model = DummyEstimator(
          strategy="quantile",
          quantile=0.9,
          score_func=mean_absolute_error,
      )
      assert model.strategy == "quantile"
      assert model.constant is None
      assert model.quantile == 0.9
      assert model.score_func == mean_absolute_error
  
      model = DummyEstimator(strategy="median")
      assert model.strategy == "median"
      assert model.constant is None
      assert model.quantile is None
      # No additional variables should be set in init
      assert model.model is None
      assert model.time_col_ is None
      assert model.value_col_ is None
  
      # set_params must be able to replicate the init
      model2 = DummyEstimator()
      model2.set_params(strategy="median")
      assert model2.__dict__ == model.__dict__
  
file_path: greykite/greykite/tests/sklearn/estimator/test_null_model.py
imports: import numpy
  import pandas
  from sklearn.metrics import mean_absolute_error
  from sklearn.metrics import mean_squared_error
  from greykite.common.constants import PREDICTED_COL
  from greykite.common.constants import TIME_COL
  from greykite.common.constants import VALUE_COL
  from greykite.sklearn.estimator.null_model import DummyEstimator
label_desc: Use image node_id 1 for calling a global function with example usage: test_init() without return types