"""Testing for the VotingClassifier and VotingRegressor"""

import pytest
import numpy as np

from sklearn.utils._testing import assert_almost_equal, assert_array_equal
from sklearn.utils._testing import assert_array_almost_equal
from sklearn.utils._testing import assert_raise_message
from sklearn.utils.estimator_checks import check_estimator
from sklearn.utils.estimator_checks import check_no_attributes_set_in_init
from sklearn.exceptions import NotFittedError
from sklearn.linear_model import LinearRegression
from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB
from sklearn.ensemble import RandomForestClassifier
from sklearn.ensemble import RandomForestRegressor
from sklearn.ensemble import VotingClassifier, VotingRegressor
from sklearn.tree import DecisionTreeClassifier
from sklearn.tree import DecisionTreeRegressor
from sklearn.model_selection import GridSearchCV
from sklearn import datasets
from sklearn.model_selection import cross_val_score, train_test_split
from sklearn.datasets import make_multilabel_classification
from sklearn.svm import SVC
from sklearn.multiclass import OneVsRestClassifier
from sklearn.neighbors import KNeighborsClassifier
from sklearn.base import BaseEstimator, ClassifierMixin, clone
from sklearn.dummy import DummyRegressor


# Load datasets
iris = datasets.load_iris()
X, y = iris.data[:, 1:3], iris.target

X_r, y_r = datasets.load_boston(return_X_y=True)


def test_estimator_init():
    eclf = VotingClassifier(estimators=[])
    msg = ("Invalid 'estimators' attribute, 'estimators' should be"
           " a list of (string, estimator) tuples.")
    assert_raise_message(ValueError, msg, eclf.fit, X, y)

    clf = LogisticRegression(random_state=1)

    eclf = VotingClassifier(estimators=[('lr', clf)], voting='error')
    msg = ('Voting must be \'soft\' or \'hard\'; got (voting=\'error\')')
    assert_raise_message(ValueError, msg, eclf.fit, X, y)

    eclf = VotingClassifier(estimators=[('lr', clf)], weights=[1, 2])
    msg = ('Number of `estimators` and weights must be equal'
           '; got 2 weights, 1 estimators')
    assert_raise_message(ValueError, msg, eclf.fit, X, y)

    eclf = VotingClassifier(estimators=[('lr', clf), ('lr', clf)],
                            weights=[1, 2])
    msg = "Names provided are not unique: ['lr', 'lr']"
    assert_raise_message(ValueError, msg, eclf.fit, X, y)

    eclf = VotingClassifier(estimators=[('lr__', clf)])
    msg = "Estimator names must not contain __: got ['lr__']"
    assert_raise_message(ValueError, msg, eclf.fit, X, y)

    eclf = VotingClassifier(estimators=[('estimators', clf)])
    msg = "Estimator names conflict with constructor arguments: ['estimators']"
    assert_raise_message(ValueError, msg, eclf.fit, X, y)


def test_predictproba_hardvoting():
    eclf = VotingClassifier(estimators=[('lr1', LogisticRegression()),
                                        ('lr2', LogisticRegression())],
                            voting='hard')
    msg = "predict_proba is not available when voting='hard'"
    with pytest.raises(AttributeError, match=msg):
        eclf.predict_proba

    assert not hasattr(eclf, "predict_proba")
    eclf.fit(X, y)
    assert not hasattr(eclf, "predict_proba")


def test_notfitted():
    eclf = VotingClassifier(estimators=[('lr1', LogisticRegression()),
                                        ('lr2', LogisticRegression())],
                            voting='soft')
    ereg = VotingRegressor([('dr', DummyRegressor())])
    msg = ("This %s instance is not fitted yet. Call \'fit\'"
           " with appropriate arguments before using this estimator.")
    assert_raise_message(NotFittedError, msg % 'VotingClassifier',
                         eclf.predict, X)
    assert_raise_message(NotFittedError, msg % 'VotingClassifier',
                         eclf.predict_proba, X)
    assert_raise_message(NotFittedError, msg % 'VotingClassifier',
                         eclf.transform, X)
    assert_raise_message(NotFittedError, msg % 'VotingRegressor',
                         ereg.predict, X_r)
    assert_raise_message(NotFittedError, msg % 'VotingRegressor',
                         ereg.transform, X_r)


def test_majority_label_iris():
    """Check classification by majority label on dataset iris."""
    clf1 = LogisticRegression(solver='liblinear', random_state=123)
    clf2 = RandomForestClassifier(n_estimators=10, random_state=123)
    clf3 = GaussianNB()
    eclf = VotingClassifier(estimators=[
                ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                voting='hard')
    scores = cross_val_score(eclf, X, y, scoring='accuracy')
    assert_almost_equal(scores.mean(), 0.95, decimal=2)


def test_tie_situation():
    """Check voting classifier selects smaller class label in tie situation."""
    clf1 = LogisticRegression(random_state=123, solver='liblinear')
    clf2 = RandomForestClassifier(random_state=123)
    eclf = VotingClassifier(estimators=[('lr', clf1), ('rf', clf2)],
                            voting='hard')
    assert clf1.fit(X, y).predict(X)[73] == 2
    assert clf2.fit(X, y).predict(X)[73] == 1
    assert eclf.fit(X, y).predict(X)[73] == 1


def test_weights_iris():
    """Check classification by average probabilities on dataset iris."""
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    clf3 = GaussianNB()
    eclf = VotingClassifier(estimators=[
                            ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                            voting='soft',
                            weights=[1, 2, 10])
    scores = cross_val_score(eclf, X, y, scoring='accuracy')
    assert_almost_equal(scores.mean(), 0.93, decimal=2)


def test_weights_regressor():
    """Check weighted average regression prediction on boston dataset."""
    reg1 = DummyRegressor(strategy='mean')
    reg2 = DummyRegressor(strategy='median')
    reg3 = DummyRegressor(strategy='quantile', quantile=.2)
    ereg = VotingRegressor([('mean', reg1), ('median', reg2),
                            ('quantile', reg3)], weights=[1, 2, 10])

    X_r_train, X_r_test, y_r_train, y_r_test = \
        train_test_split(X_r, y_r, test_size=.25)

    reg1_pred = reg1.fit(X_r_train, y_r_train).predict(X_r_test)
    reg2_pred = reg2.fit(X_r_train, y_r_train).predict(X_r_test)
    reg3_pred = reg3.fit(X_r_train, y_r_train).predict(X_r_test)
    ereg_pred = ereg.fit(X_r_train, y_r_train).predict(X_r_test)

    avg = np.average(np.asarray([reg1_pred, reg2_pred, reg3_pred]), axis=0,
                     weights=[1, 2, 10])
    assert_almost_equal(ereg_pred, avg, decimal=2)

    ereg_weights_none = VotingRegressor([('mean', reg1), ('median', reg2),
                                         ('quantile', reg3)], weights=None)
    ereg_weights_equal = VotingRegressor([('mean', reg1), ('median', reg2),
                                          ('quantile', reg3)],
                                         weights=[1, 1, 1])
    ereg_weights_none.fit(X_r_train, y_r_train)
    ereg_weights_equal.fit(X_r_train, y_r_train)
    ereg_none_pred = ereg_weights_none.predict(X_r_test)
    ereg_equal_pred = ereg_weights_equal.predict(X_r_test)
    assert_almost_equal(ereg_none_pred, ereg_equal_pred, decimal=2)


def test_predict_on_toy_problem():
    """Manually check predicted class labels for toy dataset."""
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    clf3 = GaussianNB()

    X = np.array([[-1.1, -1.5],
                  [-1.2, -1.4],
                  [-3.4, -2.2],
                  [1.1, 1.2],
                  [2.1, 1.4],
                  [3.1, 2.3]])

    y = np.array([1, 1, 1, 2, 2, 2])

    assert all(clf1.fit(X, y).predict(X)) == all([1, 1, 1, 2, 2, 2])
    assert all(clf2.fit(X, y).predict(X)) == all([1, 1, 1, 2, 2, 2])
    assert all(clf3.fit(X, y).predict(X)) == all([1, 1, 1, 2, 2, 2])

    eclf = VotingClassifier(estimators=[
                            ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                            voting='hard',
                            weights=[1, 1, 1])
    assert all(eclf.fit(X, y).predict(X)) == all([1, 1, 1, 2, 2, 2])

    eclf = VotingClassifier(estimators=[
                            ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                            voting='soft',
                            weights=[1, 1, 1])
    assert all(eclf.fit(X, y).predict(X)) == all([1, 1, 1, 2, 2, 2])


def test_predict_proba_on_toy_problem():
    """Calculate predicted probabilities on toy dataset."""
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    clf3 = GaussianNB()
    X = np.array([[-1.1, -1.5], [-1.2, -1.4], [-3.4, -2.2], [1.1, 1.2]])
    y = np.array([1, 1, 2, 2])

    clf1_res = np.array([[0.59790391, 0.40209609],
                         [0.57622162, 0.42377838],
                         [0.50728456, 0.49271544],
                         [0.40241774, 0.59758226]])

    clf2_res = np.array([[0.8, 0.2],
                         [0.8, 0.2],
                         [0.2, 0.8],
                         [0.3, 0.7]])

    clf3_res = np.array([[0.9985082, 0.0014918],
                         [0.99845843, 0.00154157],
                         [0., 1.],
                         [0., 1.]])

    t00 = (2*clf1_res[0][0] + clf2_res[0][0] + clf3_res[0][0]) / 4
    t11 = (2*clf1_res[1][1] + clf2_res[1][1] + clf3_res[1][1]) / 4
    t21 = (2*clf1_res[2][1] + clf2_res[2][1] + clf3_res[2][1]) / 4
    t31 = (2*clf1_res[3][1] + clf2_res[3][1] + clf3_res[3][1]) / 4

    eclf = VotingClassifier(estimators=[
                            ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                            voting='soft',
                            weights=[2, 1, 1])
    eclf_res = eclf.fit(X, y).predict_proba(X)

    assert_almost_equal(t00, eclf_res[0][0], decimal=1)
    assert_almost_equal(t11, eclf_res[1][1], decimal=1)
    assert_almost_equal(t21, eclf_res[2][1], decimal=1)
    assert_almost_equal(t31, eclf_res[3][1], decimal=1)

    with pytest.raises(
            AttributeError,
            match="predict_proba is not available when voting='hard'"):
        eclf = VotingClassifier(estimators=[
                                ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                                voting='hard')
        eclf.fit(X, y).predict_proba(X)


def test_multilabel():
    """Check if error is raised for multilabel classification."""
    X, y = make_multilabel_classification(n_classes=2, n_labels=1,
                                          allow_unlabeled=False,
                                          random_state=123)
    clf = OneVsRestClassifier(SVC(kernel='linear'))

    eclf = VotingClassifier(estimators=[('ovr', clf)], voting='hard')

    try:
        eclf.fit(X, y)
    except NotImplementedError:
        return


def test_gridsearch():
    """Check GridSearch support."""
    clf1 = LogisticRegression(random_state=1)
    clf2 = RandomForestClassifier(random_state=1)
    clf3 = GaussianNB()
    eclf = VotingClassifier(estimators=[
                ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
                voting='soft')

    params = {'lr__C': [1.0, 100.0],
              'voting': ['soft', 'hard'],
              'weights': [[0.5, 0.5, 0.5], [1.0, 0.5, 0.5]]}

    grid = GridSearchCV(estimator=eclf, param_grid=params)
    grid.fit(iris.data, iris.target)


def test_parallel_fit():
    """Check parallel backend of VotingClassifier on toy dataset."""
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    clf3 = GaussianNB()
    X = np.array([[-1.1, -1.5], [-1.2, -1.4], [-3.4, -2.2], [1.1, 1.2]])
    y = np.array([1, 1, 2, 2])

    eclf1 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
        voting='soft',
        n_jobs=1).fit(X, y)
    eclf2 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
        voting='soft',
        n_jobs=2).fit(X, y)

    assert_array_equal(eclf1.predict(X), eclf2.predict(X))
    assert_array_almost_equal(eclf1.predict_proba(X), eclf2.predict_proba(X))


def test_sample_weight():
    """Tests sample_weight parameter of VotingClassifier"""
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    clf3 = SVC(probability=True, random_state=123)
    eclf1 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('svc', clf3)],
        voting='soft').fit(X, y, sample_weight=np.ones((len(y),)))
    eclf2 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('svc', clf3)],
        voting='soft').fit(X, y)
    assert_array_equal(eclf1.predict(X), eclf2.predict(X))
    assert_array_almost_equal(eclf1.predict_proba(X), eclf2.predict_proba(X))

    sample_weight = np.random.RandomState(123).uniform(size=(len(y),))
    eclf3 = VotingClassifier(estimators=[('lr', clf1)], voting='soft')
    eclf3.fit(X, y, sample_weight)
    clf1.fit(X, y, sample_weight)
    assert_array_equal(eclf3.predict(X), clf1.predict(X))
    assert_array_almost_equal(eclf3.predict_proba(X), clf1.predict_proba(X))

    # check that an error is raised and indicative if sample_weight is not
    # supported.
    clf4 = KNeighborsClassifier()
    eclf3 = VotingClassifier(estimators=[
        ('lr', clf1), ('svc', clf3), ('knn', clf4)],
        voting='soft')
    msg = ('Underlying estimator KNeighborsClassifier does not support '
           'sample weights.')
    with pytest.raises(TypeError, match=msg):
        eclf3.fit(X, y, sample_weight)

    # check that _parallel_fit_estimator will raise the right error
    # it should raise the original error if this is not linked to sample_weight
    class ClassifierErrorFit(ClassifierMixin, BaseEstimator):
        def fit(self, X, y, sample_weight):
            raise TypeError('Error unrelated to sample_weight.')
    clf = ClassifierErrorFit()
    with pytest.raises(TypeError, match='Error unrelated to sample_weight'):
        clf.fit(X, y, sample_weight=sample_weight)


def test_sample_weight_kwargs():
    """Check that VotingClassifier passes sample_weight as kwargs"""
    class MockClassifier(ClassifierMixin, BaseEstimator):
        """Mock Classifier to check that sample_weight is received as kwargs"""
        def fit(self, X, y, *args, **sample_weight):
            assert 'sample_weight' in sample_weight

    clf = MockClassifier()
    eclf = VotingClassifier(estimators=[('mock', clf)], voting='soft')

    # Should not raise an error.
    eclf.fit(X, y, sample_weight=np.ones((len(y),)))


def test_set_params():
    """set_params should be able to set estimators"""
    clf1 = LogisticRegression(random_state=123, C=1.0)
    clf2 = RandomForestClassifier(random_state=123, max_depth=None)
    clf3 = GaussianNB()
    eclf1 = VotingClassifier([('lr', clf1), ('rf', clf2)], voting='soft',
                             weights=[1, 2])
    assert 'lr' in eclf1.named_estimators
    assert eclf1.named_estimators.lr is eclf1.estimators[0][1]
    assert eclf1.named_estimators.lr is eclf1.named_estimators['lr']
    eclf1.fit(X, y)
    assert 'lr' in eclf1.named_estimators_
    assert eclf1.named_estimators_.lr is eclf1.estimators_[0]
    assert eclf1.named_estimators_.lr is eclf1.named_estimators_['lr']

    eclf2 = VotingClassifier([('lr', clf1), ('nb', clf3)], voting='soft',
                             weights=[1, 2])
    eclf2.set_params(nb=clf2).fit(X, y)
    assert not hasattr(eclf2, 'nb')

    assert_array_equal(eclf1.predict(X), eclf2.predict(X))
    assert_array_almost_equal(eclf1.predict_proba(X), eclf2.predict_proba(X))
    assert eclf2.estimators[0][1].get_params() == clf1.get_params()
    assert eclf2.estimators[1][1].get_params() == clf2.get_params()

    eclf1.set_params(lr__C=10.0)
    eclf2.set_params(nb__max_depth=5)

    assert eclf1.estimators[0][1].get_params()['C'] == 10.0
    assert eclf2.estimators[1][1].get_params()['max_depth'] == 5
    assert (eclf1.get_params()["lr__C"] ==
                 eclf1.get_params()["lr"].get_params()['C'])


# TODO: Remove parametrization in 0.24 when None is removed in Voting*
@pytest.mark.parametrize("drop", [None, 'drop'])
def test_set_estimator_none(drop):
    """VotingClassifier set_params should be able to set estimators as None or
    drop"""
    # Test predict
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(n_estimators=10, random_state=123)
    clf3 = GaussianNB()
    eclf1 = VotingClassifier(estimators=[('lr', clf1), ('rf', clf2),
                                         ('nb', clf3)],
                             voting='hard', weights=[1, 0, 0.5]).fit(X, y)

    eclf2 = VotingClassifier(estimators=[('lr', clf1), ('rf', clf2),
                                         ('nb', clf3)],
                             voting='hard', weights=[1, 1, 0.5])
    with pytest.warns(None) as record:
        eclf2.set_params(rf=drop).fit(X, y)
    assert record if drop is None else not record
    assert_array_equal(eclf1.predict(X), eclf2.predict(X))

    assert dict(eclf2.estimators)["rf"] is drop
    assert len(eclf2.estimators_) == 2
    assert all(isinstance(est, (LogisticRegression, GaussianNB))
               for est in eclf2.estimators_)
    assert eclf2.get_params()["rf"] is drop

    eclf1.set_params(voting='soft').fit(X, y)
    with pytest.warns(None) as record:
        eclf2.set_params(voting='soft').fit(X, y)
    assert record if drop is None else not record
    assert_array_equal(eclf1.predict(X), eclf2.predict(X))
    assert_array_almost_equal(eclf1.predict_proba(X), eclf2.predict_proba(X))
    msg = 'All estimators are dropped. At least one is required'
    with pytest.warns(None) as record:
        with pytest.raises(ValueError, match=msg):
            eclf2.set_params(lr=drop, rf=drop, nb=drop).fit(X, y)
    assert record if drop is None else not record

    # Test soft voting transform
    X1 = np.array([[1], [2]])
    y1 = np.array([1, 2])
    eclf1 = VotingClassifier(estimators=[('rf', clf2), ('nb', clf3)],
                             voting='soft', weights=[0, 0.5],
                             flatten_transform=False).fit(X1, y1)

    eclf2 = VotingClassifier(estimators=[('rf', clf2), ('nb', clf3)],
                             voting='soft', weights=[1, 0.5],
                             flatten_transform=False)
    with pytest.warns(None) as record:
        eclf2.set_params(rf=drop).fit(X1, y1)
    assert record if drop is None else not record
    assert_array_almost_equal(eclf1.transform(X1),
                              np.array([[[0.7, 0.3], [0.3, 0.7]],
                                        [[1., 0.], [0., 1.]]]))
    assert_array_almost_equal(eclf2.transform(X1),
                              np.array([[[1., 0.],
                                         [0., 1.]]]))
    eclf1.set_params(voting='hard')
    eclf2.set_params(voting='hard')
    assert_array_equal(eclf1.transform(X1), np.array([[0, 0], [1, 1]]))
    assert_array_equal(eclf2.transform(X1), np.array([[0], [1]]))


def test_estimator_weights_format():
    # Test estimator weights inputs as list and array
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    eclf1 = VotingClassifier(estimators=[
                ('lr', clf1), ('rf', clf2)],
                weights=[1, 2],
                voting='soft')
    eclf2 = VotingClassifier(estimators=[
                ('lr', clf1), ('rf', clf2)],
                weights=np.array((1, 2)),
                voting='soft')
    eclf1.fit(X, y)
    eclf2.fit(X, y)
    assert_array_almost_equal(eclf1.predict_proba(X), eclf2.predict_proba(X))


def test_transform():
    """Check transform method of VotingClassifier on toy dataset."""
    clf1 = LogisticRegression(random_state=123)
    clf2 = RandomForestClassifier(random_state=123)
    clf3 = GaussianNB()
    X = np.array([[-1.1, -1.5], [-1.2, -1.4], [-3.4, -2.2], [1.1, 1.2]])
    y = np.array([1, 1, 2, 2])

    eclf1 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
        voting='soft').fit(X, y)
    eclf2 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
        voting='soft',
        flatten_transform=True).fit(X, y)
    eclf3 = VotingClassifier(estimators=[
        ('lr', clf1), ('rf', clf2), ('gnb', clf3)],
        voting='soft',
        flatten_transform=False).fit(X, y)

    assert_array_equal(eclf1.transform(X).shape, (4, 6))
    assert_array_equal(eclf2.transform(X).shape, (4, 6))
    assert_array_equal(eclf3.transform(X).shape, (3, 4, 2))
    assert_array_almost_equal(eclf1.transform(X),
                              eclf2.transform(X))
    assert_array_almost_equal(
            eclf3.transform(X).swapaxes(0, 1).reshape((4, 6)),
            eclf2.transform(X)
    )


# TODO: Remove drop=None in 0.24 when None is removed in Voting*
@pytest.mark.parametrize(
    "X, y, voter",
    [(X, y, VotingClassifier(
        [('lr', LogisticRegression()),
         ('rf', RandomForestClassifier(n_estimators=5))])),
     (X_r, y_r, VotingRegressor(
         [('lr', LinearRegression()),
          ('rf', RandomForestRegressor(n_estimators=5))]))]
)
@pytest.mark.parametrize("drop", [None, 'drop'])
def test_none_estimator_with_weights(X, y, voter, drop):
    # TODO: remove the parametrization on 'drop' when support for None is
    # removed.
    # check that an estimator can be set to 'drop' and passing some weight
    # regression test for
    # https://github.com/scikit-learn/scikit-learn/issues/13777
    voter = clone(voter)
    voter.fit(X, y, sample_weight=np.ones(y.shape))
    voter.set_params(lr=drop)
    with pytest.warns(None) as record:
        voter.fit(X, y, sample_weight=np.ones(y.shape))
    assert record if drop is None else not record
    y_pred = voter.predict(X)
    assert y_pred.shape == y.shape


@pytest.mark.parametrize(
    "estimator",
    [VotingRegressor(
        estimators=[('lr', LinearRegression()),
                    ('tree', DecisionTreeRegressor(random_state=0))]),
     VotingClassifier(
         estimators=[('lr', LogisticRegression(random_state=0)),
                     ('tree', DecisionTreeClassifier(random_state=0))])],
    ids=['VotingRegressor', 'VotingClassifier']
)
def test_check_estimators_voting_estimator(estimator):
    # FIXME: to be removed when meta-estimators can specified themselves
    # their testing parameters (for required parameters).
    check_estimator(estimator)
    check_no_attributes_set_in_init(estimator.__class__.__name__, estimator)


# TODO: Remove in 0.24 when None is removed in Voting*
@pytest.mark.parametrize(
    "Voter, BaseEstimator",
    [(VotingClassifier, DecisionTreeClassifier),
     (VotingRegressor, DecisionTreeRegressor)]
)
def test_deprecate_none_transformer(Voter, BaseEstimator):
    est = Voter(estimators=[('lr', None),
                            ('tree', BaseEstimator(random_state=0))])

    msg = ("Using 'None' to drop an estimator from the ensemble is "
           "deprecated in 0.22 and support will be dropped in 0.24. "
           "Use the string 'drop' instead.")
    with pytest.warns(DeprecationWarning, match=msg):
        est.fit(X, y)


# TODO: Remove drop parametrize in 0.24 when None is removed in Voting*
@pytest.mark.parametrize(
    "Voter, BaseEstimator",
    [(VotingClassifier, DecisionTreeClassifier),
     (VotingRegressor, DecisionTreeRegressor)]
)
@pytest.mark.parametrize("drop", [None, 'drop'])
def test_correct_named_estimator_with_drop(Voter, BaseEstimator, drop):
    est = Voter(estimators=[('lr', drop),
                            ('tree', BaseEstimator(random_state=0))])

    with pytest.warns(None) as rec:
        est.fit(X, y)
    assert rec if drop is None else not rec

    assert est.named_estimators_['lr'] == drop
