public void Method_on_base_class()
        {
            var person = new Person();

            var greeting = person.GreetMe();

            // TODO: fill in the expected value
            Assert.IsTrue(greeting == ReplaceMe);
        }
        public void On_interface()
        {
            IFriend friend = new Person();

            var greeting = friend.GreetMe();

            // TODO: fill in the expected value
            Assert.IsTrue(greeting == ReplaceMe);
        }