Unit testing an endpoint that publishes an event

Endpoint.cs

[HttpGet("publish"), AllowAnonymous]
sealed class MyEndpoint : EndpointWithoutRequest
{
    public override async Task HandleAsync(CancellationToken c)
    {
        var evnt = new MyEvent { Message = "hello!" };
        await PublishAsync(evnt);
        await SendAsync("all good!");
    }
}

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

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

UnitTests.cs

public class EndpointTests
{
    [Fact]
    public async Task Endpoint_Returns_Correct_Response()
    {
        // it's not necessary to register any fake event handlers (subscribers)
        var ep = Factory.Create<MyEndpoint>();
        await ep.HandleAsync(default);
        ep.Response.Should().Be("all good!");
    }

    [Fact]
    public async Task Fake_Event_Handler_Executed()
    {
        //a fake event handler can be substituted during testing
        //in order to assert that an event handler was correctly executed
        var fakeEventHandler = new FakeEventHandler();
        var ep = Factory.Create<MyEndpoint>(
            ctx =>
            {
                ctx.AddTestServices(
                    s =>
                    {
                        s.AddSingleton<IEventHandler<MyEvent>>(fakeEventHandler);
                    });
            });

        await ep.HandleAsync(default);
        fakeEventHandler.Message.Should().Be("hello!");
    }

    sealed class FakeEventHandler : IEventHandler<MyEvent>
    {
        public string? Message { get; set; }

        public Task HandleAsync(MyEvent e, CancellationToken c)
        {
            Message = e.Message;

            return Task.CompletedTask;
        }
    }
}