Would it be possible to have a DataSourceGeneratorAttribute that generates IAsyncInitializers?

[TheRumle]

I implement many services which has a shared interface, and I want to test they all have the same behaviour. For instance, I want to test all implementations of the interface public interface IMyService<T> : IMyService - in particular, the behaviour defined in IMyService.

Many of the services require some server or hosted service before they can be integration tested. So I create an
ApplicationFixture<T> which implements IAsyncInitializer to start the different services. The fixture wires up a ServiceCollection and waits for a server to start etc., and provides a means to get the T.

I do not want to create a test for each of my IMyService, but rather find the implementors on runtime through a ServiceCollection, and then generate the tests. Aha! This functionality is already provided - I implement a DataSourceGenerator:

public sealed class ApplicationFixtureGeneratorAttribute<T> : DataSourceGeneratorAttribute<ApplicationFixture<T>> where T : notnull
{
    /// <inheritdoc />
    public override IEnumerable<Func<ApplicationFixture<T>>> GenerateDataSources(DataGeneratorMetadata dataGeneratorMetadata)
    {
        ...
        foreach (var service in wantedServices)
        {
            var f = new ApplicationFixture<T>(...);
            f.InitializeAsync().Wait();
            yield return () => f;
        }
    }
}

But ALAS! My test time goes up substantially!
This approach to finding the services is elegant, but obviously suffers from not being able to initialize the Fixture in a performant way. Would it be possible to circumvent this with existing functionality in TUnit?

[thomhurst]

Try this:

public override IEnumerable<Func<ApplicationFixture<T>>> GenerateDataSources(DataGeneratorMetadata dataGeneratorMetadata)
    {
        ...
        foreach (var service in wantedServices)
        {
            var f = new ApplicationFixture<T>(...);

            dataGeneratorMetadata.TestBuilderContext.Current.Events.OnInitialize += async (_,_) =>
            {
                await f.InitializeAsync();
            }

            yield return () => f;
        }
    }

[TheRumle]

Amazing. Seems to work perfectly. Maybe it would be a really neat thing to have in the docs as well? Where can I read about the process to contribute? That is, if this is not subject to change in the future @thomhurst.

[thomhurst]

Glad that worked!

I haven't written any formal develop docs yet. But docs are here if you wanna write something up:

\docs\docs\tutorial-advanced