private static void AssertShouldBe(int[] queue, int tills, int expect)
        {
            //act
            int actual = new CheckoutTills().CaculateRequestTime(queue, tills);

            //assert
            Assert.AreEqual(expect, actual);
        }
        public void InputQueueIs_1_2_3_4_andOneTill()
        {
            //arrange
            var queue  = new[] { 1, 2, 3, 4 };
            var tills  = 1;
            var expect = 10;
            //act
            int actual = new CheckoutTills().CaculateRequestTime(queue, tills);

            //assert
            Assert.AreEqual(expect, actual);
        }