How did he do?
I get the feeling that, and it's nothing against him, but if he plays well throughout preseason that Wenger and Arsenal might change their tune on adding another CB. Good and bad points can be had here, but I've still not seen anything to suggest where Holding stands in our squad? Apart from the low number (16, could mean nothing) he may well be considered first team at this point. I don't even think Wenger knows just yet.
Regardless, I'd like to see him improve more and more without worrying about such situations, Wenger gets paid millions to sort that part out!