regression-test

[bf]

I'd agree with Thierry.  Ideally, you wouldn't want to
even build a piece of software that didn't work right,
let alone install it.  But once you admit the
possibility that mistakes may have been made, and
recognize that tests are desirable, then
*conceptually*  you want to test a port in
circumstances as close as possible to those in which
it will be used -- i.e., after it's been installed. 
But pragmatically, it really comes down to the tests
that will be implemented.  If this regression-test
target is largely there to allow bundled testing
targets to be run from the port Makefile, and these
bundled tests are written with a port that is built,
but not installed in mind, then run them before
installation.  Otherwise, afterwards.  It's going to
be difficult to get people to rewrite test suites just
to fit someone's debatable notion of when tests should
be made -- we already have enough trouble keeping up
with other changes, and we have many unmaintained
ports.

b.