public void TestCallbacks()
        {
            List<string> messages = new List<string>();

            StateMachine<TestNum> machine = new StateMachine<TestNum>();
            machine.AddState(TestNum.Red);
            machine.SubscribeToEntry(TestNum.Red, (TestNum oldState, TestNum newState) =>
            {
                messages.Add("Enter the red!");
            });
            machine.SubscribeToExit(TestNum.Red, (TestNum oldState, TestNum newState) =>
            {
                messages.Add("Exit the red!");
            });

            machine.AddState(TestNum.White);
            machine.SubscribeToEntry(TestNum.White, (TestNum oldState, TestNum newState) =>
            {
                messages.Add("Enter the white!");
            });
            machine.SubscribeToExit(TestNum.White, (TestNum oldState, TestNum newState) =>
            {
                messages.Add("Exit the white!");
            });
            machine.SubscribeToExit(TestNum.White, (TestNum oldState, TestNum newState) =>
            {
                messages.Add("Sneaky Second Message!");
            });

            machine.ChangeState(TestNum.Red);
            machine.ChangeState(TestNum.White);
            machine.ChangeState(TestNum.Red);

            Assert.AreEqual(6, messages.Count);
            Assert.AreEqual("Enter the red!", messages[0]);

            Assert.AreEqual("Exit the red!", messages[1]);
            Assert.AreEqual("Enter the white!", messages[2]);

            Assert.AreEqual("Exit the white!", messages[3]);
            Assert.AreEqual("Sneaky Second Message!", messages[4]);
            Assert.AreEqual("Enter the red!", messages[5]);
        }