code: def test_layer_fit():
      """[Module | LayerEstimator] test fit"""
      out = est.fit(X, y)
      assert out is est
  
      p = est.fit_transform(X, y, refit=False)
      np.testing.assert_array_equal(p, F)
  
imports: import numpy
  from mlens.index import FullIndex, FoldIndex
  from mlens.testing import Data
  from mlens.testing.dummy import ESTIMATORS, PREPROCESSING
  from mlens.utils.dummy import OLS, Scale
  from mlens.utils.exceptions import NotFittedError, ParameterChangeWarning
  from mlens.parallel import make_group
  from mlens.estimators import LearnerEstimator, TransformerEstimator, LayerEnsemble
  from mlens.externals.sklearn.base import clone
label_desc: Use image node_id 1 for calling a global function with example usage: test_layer_fit() without return types