Felbook.Models.MessageService.FindById C# (CSharp) Method

        public Message FindById(int ID)
        {
            try
            {
                return db.MessageSet.Single(m => m.Id == ID);
            }
            catch (InvalidOperationException)
            {
                return null;
            }
        }

        public void FindByIdTest()
        {
            FelBookDBEntities DbEntities = new FelBookDBEntities();
            MessageService target = new MessageService(DbEntities);

            int ID = 0;
            Message expected = null;
            Message actual = target.FindById(ID);
            Assert.AreEqual(expected, actual);

            expected = new Message();
            User mockUser = User.CreateUser(0, "test", "test",
                DateTime.Now, "mail", "test user", "");

            expected.Recievers.Add(mockUser);
            expected.Sender = mockUser;
            expected.Text = "text";
            expected.Created = DateTime.Now;

            DbEntities.MessageSet.AddObject(expected);
            DbEntities.SaveChanges();
            ID = expected.Id;
            actual = target.FindById(ID);
            Assert.AreEqual(expected.Text, actual.Text);

            DbEntities.MessageSet.DeleteObject(expected);
            DbEntities.UserSet.DeleteObject(mockUser);
            DbEntities.SaveChanges();
        }