Tosh said: "When we took this on we knew we'd be without important players.
"But this was the only time we could go, and while we know the senior players well this gives us a great chance to find out about the under-21s.
"We haven't come here to run people silly but to get to know each other. Wales are in a transitional phase."
Tosh has made clear to those players that failed to attend that their place with Wales could now be in jeopardy and go to those players who commited themselves to their country and flew out to Spain on Tuesday.