public TestNullClass TestClassNull(TestNullClass arg)
        {
            if (arg != null)
            {
                Assert.Fail("Test Class Func(Class) -> Func(Unknown): argument value is different from null.");
            }

            return(arg);
        }
        public TestNullClass TestClass(TestNullClass arg)
        {
            if (arg.GetType() != typeof(TestNullClass))
            {
                Assert.Fail("Test Class Func(Class) -> Func(Class): argument type is different from Class.");
            }

            return(arg);
        }