Port of http://gmoeck.github.com/2011/10/26/stubbing-is-not-enough.html to C# Asserts on the behaviour of an object instead of the state.

TicketMachineTest.cs

using NUnit.Framework;
using Rhino.Mocks;

namespace ScratchPad
{
	[TestFixture]
	public class TicketMachineTest
	{
		[Test]
		public void ShouldReserveTheNumberofTicketsInputtedWhenTheUserSubmitsARequest()
		{
			TicketReserver reserver = MockRepository.GenerateMock<TicketReserver>();

			var machine = new TicketMachineInterface(reserver);
			machine.NumberPressed(5);
			machine.NumberPressed(5);
			machine.SubmitRequest();

			reserver.AssertWasCalled(t => t.Reserve(55));
		}

		[Test]
		public void ShouldRemoveExtraTicketIfDeleteIsPressed()
		{
			TicketReserver reserver = MockRepository.GenerateMock<TicketReserver>();

			var machine = new TicketMachineInterface(reserver);
			machine.NumberPressed(5);
			machine.NumberPressed(5);
			machine.DeletePressed();
			machine.SubmitRequest();

			reserver.AssertWasCalled(t => t.Reserve(5));
		}
	}

	public class TicketMachineInterface
	{
		private TicketReserver ticketReserver;
		private string currentDisplay;

		public TicketMachineInterface(TicketReserver ticketReserver)
		{
			this.ticketReserver = ticketReserver;
			currentDisplay = string.Empty;
		}

		public void NumberPressed(int number)
		{
			currentDisplay += number.ToString();
		}

		public void DeletePressed()
		{
			currentDisplay = currentDisplay.Remove(currentDisplay.Length - 1);
		}

		public void SubmitRequest()
		{
			ticketReserver.Reserve(int.Parse(currentDisplay));
		}
	}

	public class TicketReserver
	{
		public virtual void Reserve(int numberOfTickets)
		{
		}
	}
}