c# List Sort排序

Test test1 = new Test();
            test1.sortIndex = 1;
            test1.name = "1";

            Test test2 = new Test();
            test2.sortIndex = 2;
            test2.name = "2";

            Test test3 = new Test();
            test3.sortIndex = 3;
            test3.name = "3";

            Test test4 = new Test();
            test4.sortIndex = 4;
            test4.name = "4";

            List<Test> list = new List<Test>();
            list.Add(test4);
            list.Add(test1);
            list.Add(test2);
            list.Add(test3);

            list.Sort((a, b) => {
                var o = a.sortIndex - b.sortIndex;
                return o;
            });