Integration testing an endpoint that publishes an event

1-Event.cs

sealed class MyEvent : IEvent
{
    public string? Message { get; set; }
}

sealed class MyEventHandler : IEventHandler<MyEvent>
{
    public Task HandleAsync(MyEvent e, CancellationToken c)
        => Task.CompletedTask;
}

2-Endpoint.cs

[HttpGet("publish"), AllowAnonymous]
sealed class MyEndpoint : EndpointWithoutRequest
{
    public override async Task HandleAsync(CancellationToken c)
    {
        var evnt = new MyEvent
        {
            Message = "hello!"
        };
        await evnt.PublishAsync(); // "test event receiver" is used to determine if event was published.
        await SendAsync("all good!");
    }
}

3-AppFixture.cs

public class Sut : AppFixture<Program>
{
    protected override void ConfigureServices(IServiceCollection s)
    {
        s.RegisterTestEventReceivers(); // register the test event receiver service
    }
}

4-EndpointTests.cs

public class MyTests(Sut App) : TestBase<Sut>
{
    [Fact]
    public async Task Endpoint_Publishes_Correct_Event()
    {
        //obtain a "test event receiver" for you event type
        var receiver = App.Services.GetTestEventReceiver<MyEvent>();

        //call the endpoint
        var (rsp, _) = await App.Client.GETAsync<MyEndpoint, string>();
        rsp.IsSuccessStatusCode.ShouldBeTrue();

        //check if "test event receiver" received the event that's supposed to be published by the endpoint.
        var received = await receiver.WaitForMatchAsync(e => e.Message == "hello!", timeoutSeconds: 3, ct: Cancellation);
        received.Any().ShouldBeTrue();
    }
}