public override object Create(MaterializationContext context, out TestSubscriber.Probe <ByteString> materializer)
{
var promise = _properties.Probes[_properties.ProbesWriterTop];
var probe = TestSubscriber.CreateSubscriberProbe <ByteString>(_properties.Kit);
promise.SetResult(probe);
_properties.ProbesWriterTop++;
materializer = probe;
return(probe);
}