On the last I\O Hangout Google introduced us a new tool for webmasters that have a international multi regional site.
Its the "International Targeting Section" in GWT(Still not public though).
The new tool show us info about error with href lang.
More detailed info and screenshots can be found over here: 22:20
I almost sure that +John Mueller
looked for testers on his G+ profile few days ago over herehttps://plus.google.com/u/0/+JohnMueller/posts/bz9MbE1nX2b