def test_mul(self) -> None:
        x = Vector([1, 2, 3])
        a = Vector([2, -1, 4])  # for test of dot product
        b = Vector([1, -2, -1])
        self.assertEqual(str(x * 3.0), "(3.0,6.0,9.0)")
        self.assertEqual((a * b), 0)