def METHOD_NAME(self):
    pen = self.pen
    x = self.params
    p = np.array([pen.func(np.atleast_1d(xi)) for xi in x])
    assert_allclose(p, p[::-1], rtol=1e-10)
    # func(0) should be 0
    assert_allclose(pen.func(0 * np.atleast_1d(x[0])), 0, rtol=1e-10)