def METHOD_NAME():
    X = pd.DataFrame([[i] for i in range(5)])
    undersampler = Undersampler()
    with pytest.raises(ValueError, match="y cannot be None"):
        undersampler.fit(X, None)
    with pytest.raises(ValueError, match="y cannot be None"):
        undersampler.fit_transform(X, None)
    undersampler.fit(X, pd.Series([0] * 4 + [1]))
    with pytest.raises(ValueError, match="y cannot be None"):
        undersampler.transform(X, None)