code: def test_assert_valid_estimator_fails_class():
      """[Utils] assert_valid_estimator: check fails uninstantiated estimator."""
      np.testing.assert_raises(TypeError, assert_valid_estimator, OLS)
  
imports: import numpy
  from mlens.externals.sklearn.base import clone
  from mlens.utils.checks import check_ensemble_build, assert_valid_estimator, assert_correct_format, check_initialized
  from mlens.utils.dummy import OLS, Scale
  from mlens.testing import EstimatorContainer
  from mlens.utils.exceptions import LayerSpecificationError, LayerSpecificationWarning, NotFittedError, ParallelProcessingError, ParallelProcessingWarning
label_desc: Use image node_id 6 for calling a global function with example usage: test_assert_valid_estimator_fails_class() without return types