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.

[ApiController]
[Route("[controller]")]
public class TestController : ControllerBase
{
    private static readonly Dictionary<Guid, IServiceProvider> ServiceProviders = new();

    public bool Get()
    {
        return true;
    }

    [HttpPost("SetupTest")]
    public async Task SetupTest(Guid testId, string connectionString)
    {

        var collection = new ServiceCollection();

        var provider = collection
            .AddCqs(configure => collection.AddMassTransitTestHarness(cfg =>
            {
                cfg.UsingInMemory((ctx, mem) =>
                {
                    mem.ConfigureTestHarness(ctx);
                    mem.AddOutbox(ctx);
                    mem.ConfigureEndpoints(ctx);
                });
                configure(cfg);
            }))
            .AddDbContext<PcDbContext>(b =>
            {
                b.UseSqlServer(connectionString);
            })
            .AddBusinessCore()
            .AddRepositories()
            .AddDomain()
            .AddTestHarness()
            .AddTestGuidFileRepository()
            .BuildServiceProvider();


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

        ServiceProviders.Add(testId, provider);
    }

    [HttpPost("TeardownTest")]
    public void TeardownTest(Guid testId)
    {
        ServiceProviders.Remove(testId);
    }


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

    [HttpPost("ExecuteCommand")]
    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();
    }
}

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