def METHOD_NAME():
    """NA robustness"""
    model_formula = "(dd1(f))^^2"
    expected_data = pd.DataFrame(
        {
            "f": [np.NaN, 6, 4, 2, 0],
            "f_power2": [np.NaN, 36, 16, 4, 0],
            "f_derivative1": [np.NaN, np.NaN, -2, -2, -2],
            "f_derivative1_power2": [np.NaN, np.NaN, 4, 4, 4],
        }
    )
    exp_data = _expand_test(model_formula)
    assert set(exp_data.columns) == set(expected_data.columns)
    for col in expected_data.columns:
        pd.testing.assert_series_equal(
            expected_data[col], exp_data[col], check_dtype=False
        )