[TestFixture]
public class MyProcessStateMachineTests
{
    InMemoryTestHarness _Harness;
    MyProcessStateMachine _Machine;
    StateMachineSagaTestHarness<MyProcess, MyProcessStateMachine> _Saga;

    [OneTimeSetUp]
    public void ConfigureMessages()
    {
        MessageCorrelation.UseCorrelationId<RequestMyDetails>(x => x.CorrelationId);
        MessageCorrelation.UseCorrelationId<FileAttached>(x => x.CorrelationId);
        MessageCorrelation.UseCorrelationId<PDFGenerated>(x => x.CorrelationId);
        MessageCorrelation.UseCorrelationId<CustomerAttachFile>(x => x.CorrelationId);
        MessageCorrelation.UseCorrelationId<AddCustomerNote>(x => x.CorrelationId);
        MessageCorrelation.UseCorrelationId<EmailPublished>(x => x.CorrelationId);
    }


    [SetUp]
    public void InitializeTestHarness()
    {
        _Harness = new InMemoryTestHarness();
        _Machine = new MyProcessStateMachine( /* snip */ );
        _Saga = _Harness.StateMachineSaga<MyProcess, MyProcessStateMachine>(_Machine);

        _Harness.Start().Wait();
    }

    [TearDown]
    public void StopTestHarness()
    {
        _Harness.Stop();
    }


    [Test]
    public async Task ShouldAttachToCustomer()
    {
        var sagaId = Guid.NewGuid();
        var custId = Guid.NewGuid();
        var fileAttached = BuildFileAttachedMessage(sagaId);

        await _Harness.InputQueueSendEndpoint.Send(BuildStartMessage(sagaId));
        await _Harness.InputQueueSendEndpoint.Send(BuildDetailsReceivedMessage(sagaId));
        await _Harness.InputQueueSendEndpoint.Send(BuildPdfGeneratedMessage(sagaId));
        await _Harness.InputQueueSendEndpoint.Send(fileAttached);

        // Next line is based on [the answer here][1]
        // Once the above messages are all consumed and processed,
        // the state machine should be in AwaitingEmail state
        await _Saga.Match(x =>
            x.CorrelationId == sagaId
                && x.CurrentState == _Machine.AwaitingEmail.Name,
            new TimeSpan(0, 0, 30));

        // Grab the instance and Assert stuff...
    }

    // Snip...
}

var inst = _Saga.Sagas.FirstOrDefault(x => x.Saga.CorrelationId == sagaId);

var test = _Harness.Published
    .FirstOrDefault(x => x.MessageType == typeof(IAttachFile) && x.Context.CorrelationId == sagaId);