async void

gistfile1.txt

 public abstract class TestBase
    {
        protected abstract Task Impl();
        protected abstract void Impl2();
    }

    public class Test : TestBase
    {
        protected override Task Impl()
        {
            Task.Run(() =>
            {
                //fire and forget
            });
            return Task.CompletedTask;
        }

        protected override void Impl2()
        {
            Task.Run(() =>
            {
                //fire and forget
            });
        }
    }
    
    public class Test2 : TestBase
    {
        protected override async Task Impl()
        {
            await Task.Run(() =>
            {
                
            });
        }

        protected override async void Impl2()
        {
            await Task.Run(() =>
            {
                
            });
        }
    }