Month: November 2022

Getting rid of the slow Masstransit test harness

I wrote a blog about replacing the timeout based test harness with a semaphore driven one here. This made things much more robust when you want blackbox type testing, fire a number of events and wait until all have been digested and their spawned child events are digested.

This worked well and robust. But it still used the Masstransit harness for hosting. This made the InMemory bus more than twice as slow as hosting Masstransit in a service, including database I/O so probably a lot slower when only looking at bus performance.

But it’s pretty easy hosting Masstransit from a none service project like a test project. Instead of configuring with AddMassTransitTestHarness use the standard AddMasstransit extension method. Now events will not be consumed when you publish them, this is because the IHostedService haven’t been started. So that’s an easy fix. If we base the code on the IHarness from my previous blog post.

public Harness(IEnumerable<IHostedService> services)
    _services = services;

public async Task Start()
    var source = new CancellationTokenSource();

    foreach (var service in _services)
        await service.StartAsync(source.Token);

public async Task Stop()
    var source = new CancellationTokenSource();

    foreach (var service in _services)
        await service.StopAsync(source.Token);

Call Start from your test setup and stop from your test teardown. This will start the background workers for Masstransit and make sure it listens and consumes events. The service will not work unless you add logging to your IoC config.

new ServiceCollection()

Coupled with the harness-code from previous blog post you now have a very robust and fast test harness. Full code below


Test .NET 6 (Or any Core version) from legacy .NET Framework

I’m currently working on moving a large legacy system from .NET Framework 4.8 to .NET 6. Since this is a large system the move will take years and we need to work iteratively meaning both systems will co-exist over a few years.

This means that integration tests we already have for the legacy system now needs to execute code over two application domains running two completely different CLRs. I ended up making a little service that the legacy code can call to execute code in the new system.

First we create a new web API project with a single controller.

public class TestController : ControllerBase
    private static readonly Dictionary<Guid, IServiceProvider> ServiceProviders = new();

    public bool Get()
        return true;

    public async Task SetupTest(Guid testId, string connectionString)

        var collection = new ServiceCollection();

        var provider = collection
            .AddCqs(configure => collection.AddMassTransitTestHarness(cfg =>
                cfg.UsingInMemory((ctx, mem) =>
            .AddDbContext<PcDbContext>(b =>

        var harness = provider.GetRequiredService<IHarness>();
        await harness.Start();

        ServiceProviders.Add(testId, provider);

    public void TeardownTest(Guid testId)

    private static readonly JsonSerializerOptions Options = new() { PropertyNameCaseInsensitive = true };

    public async Task ExecuteCommand(Guid testId, string cmdType)
        var provider = ServiceProviders[testId];

        var cmd = (await JsonSerializer.DeserializeAsync(HttpContext.Request.Body, Type.GetType(cmdType)!, Options))!;
        await provider.GetRequiredService<IBus>().Publish(cmd);
        await provider.GetRequiredService<IHarness>().WaitForBus();