def test_length(self):
        self.assertEqualOnAllArrayTypes(length, [1, 2, 3, 4], 4)
        self.assertEqualOnAllArrayTypes(length, [1, 2, 3], 3)
        self.assertEqualOnAllArrayTypes(length, [1, 2], 2)
        self.assertEqualOnAllArrayTypes(length, [1, 2, 3, np.NaN], 4)
        self.assertEqualOnAllArrayTypes(length, [], 0)