I've just uploaded the new Test::Aggregate. The only change is that it sets the $ENV{TEST_AGGREGATE} variable to true (for VMS users: and explicitly deletes it in an END block). This allows you to do this:
die "Cannot use $0 in aggregated tests"
if $ENV{TEST_AGGREGATE};
Blew a chunk of time yesterday trying to debug why the aggregated tests were failing. Now I can add that to some code to ensure that I'll know immediately next time.