code: def test_summary():
      """Tests summary function returns without error"""
      model = DummyEstimator(
          strategy="quantile", constant=None, quantile=0.99
      )
      model.summary()
  
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 6 for calling a global function with example usage: test_summary() without return types