def test_mean_change(self):
        self.assertEqualOnAllArrayTypes(mean_change, [-2, 2, 5], 3.5)
        self.assertEqualOnAllArrayTypes(mean_change, [1, 2, -1], -1)
        self.assertEqualOnAllArrayTypes(mean_change, [10, 20], 10)
        self.assertIsNanOnAllArrayTypes(mean_change, [1])
        self.assertIsNanOnAllArrayTypes(mean_change, [])