public void Factorial8()
        {
            int number = 8;
            int expect = 40320;

            int res = FactorialSolver.FactorialRecursion(number);

            Assert.Equal(expect, res);
        }
        public void Factorial9()
        {
            int number = 9;
            int expect = 362880;

            int res = FactorialSolver.FactorialRecursion(number);

            Assert.Equal(expect, res);
        }
        public void Factorial3()
        {
            int number = 3;
            int expect = 6;

            int res = FactorialSolver.FactorialRecursion(number);

            Assert.Equal(expect, res);
        }