in reply to Interesting testing idea ...

I think to do this you'd either need a source filter (gah!) or Devel::Declare.

As for whether it's a good idea. I don't know. I'm not a big fan of subroutine attributes, and your attribute seems redundant anyway. I think I'd prefer something more like this:

sub foo { ... } is tested(2) { ... }

That looks fairly 6-ish.