public void SmallestPositiveInteger1()
        {
            int[]     input    = { 1, 3, 6, 4, 1, 2 };
            const int expected = 5;

            Assert.AreEqual(expected, SmallestPositiveInteger.Solution(input));
        }
        public void SmallestPositiveInteger3()
        {
            int[]     input    = { -1, -3 };
            const int expected = 1;

            Assert.AreEqual(expected, SmallestPositiveInteger.Solution(input));
        }