My initial problem:
How to tell Moose that an attribute was an instance of My::Class OR My::Test::Class.
Whaddaya know, there is more than one way to do it
Seeing as how I got a lot of help from #moose on irc.perl.org I thought I'd write up my findings
. (There is a way to do it without creating a sub-type, but the sub-typing seemed a lot more interesting and general purpose that the specific solution to the original problem)