code: def X():
      """dataset for test cases"""
      size = 20
      return pd.DataFrame(
          {
              TIME_COL: pd.date_range(
                  start="2018-01-01", periods=size, freq="H"
              ),
              ACTUAL_COL: np.random.normal(scale=10, size=size),
              VALUE_COL: np.random.normal(scale=10, size=size),
          }
      )
  
imports: import numpy
  import pandas
  import pytest
  from sklearn.metrics import mean_squared_error
  from sklearn.pipeline import Pipeline
  from greykite.common.constants import ACTUAL_COL
  from greykite.common.constants import TIME_COL
  from greykite.common.constants import VALUE_COL
  from greykite.common.python_utils import assert_equal
  from greykite.sklearn.estimator.null_model import DummyEstimator
  from greykite.sklearn.estimator.simple_silverkite_estimator import SimpleSilverkiteEstimator
  from greykite.sklearn.transform.column_selector import ColumnSelector
  from greykite.sklearn.transform.difference_based_outlier_transformer import DifferenceBasedOutlierTransformer
  from greykite.sklearn.transform.null_transformer import NullTransformer
  from greykite.sklearn.transform.pandas_feature_union import PandasFeatureUnion
  from greykite.sklearn.transform.zscore_outlier_transformer import ZscoreOutlierTransformer
label_desc: Use image node_id 1 for calling a global function with example usage: X() and returns: pd