code: def test_not_fitted_still_works_regression(estimator):
      X, _ = sk_datasets.make_regression(n_samples=500, n_features=4)
      X = pd.DataFrame(X)
      y_pred = estimator.predict_many(X)
      assert len(y_pred) == len(X)
      assert y_pred.eq(0).all()
  
file_path: river/river/compat/test_sklearn.py
imports: from __future__ import annotations
  import pandas
  import pytest
  from sklearn import datasets
  from sklearn import linear_model
  from sklearn.utils import estimator_checks
  from river import base, cluster, compat, linear_model, preprocessing
label_desc: Use image node_id 3 for calling a global function with example usage: test_not_fitted_still_works_regression(estimator) without return types