public OutputStreamSinkSpec(ITestOutputHelper helper) : base(Utils.UnboundedMailboxConfig, helper)
{
Sys.Settings.InjectTopLevelFallback(ActorMaterializer.DefaultConfig());
var settings = ActorMaterializerSettings.Create(Sys).WithDispatcher("akka.actor.default-dispatcher");
_materializer = Sys.Materializer(settings);
}