Allows sequencing of Moq'd objects to enforce specific call orders.

MockSequence.cs

using System;
using System.Collections.Generic;
using System.Linq;
using Moq.Language.Flow;

namespace Moq.Sequencing
{
    public static class CallSequenceExtensions
    {
        public static void InSequence<TMock>(this ISetup<TMock> setup, CallSequence callSequence) where TMock : class
        {
            callSequence.InSequence(setup);
        }
    }

    internal class MockSequenceException : ApplicationException
    {
        public MockSequenceException(string message) : base(message)
        {
        }
    }

    public class CallSequence
    {
        private int _sequenceNumber;
        private int _sequenceLength;
        private readonly IList<string> _steps = new List<string>();

        internal void InSequence<TMock>(ISetup<TMock> setup) where TMock : class
        {
            _steps.Add(setup.ToString());
            var expectedSequenceNumber = _sequenceLength++;
            setup.Callback(() => VerifySequence(expectedSequenceNumber));
        }

        private void VerifySequence(int expectedSequenceNumber)
        {
            if (_sequenceNumber == expectedSequenceNumber)
            {
                _sequenceNumber++;
            }
            else
            {
                var message =
                    string.Format(
                        "Expected call at step {0} but executed at step {1}. Expected sequence:{2}{3}",
                        expectedSequenceNumber + 1, _sequenceNumber + 1, Environment.NewLine,
                        string.Join(Environment.NewLine, _steps.Select((step, i) => string.Format("{0}) {1}", i + 1, step))));
                throw new MockSequenceException(message);
            }
        }
    }
}