Maintained by Paul Dietz, the test suite is roughly 85% done. Currently working on tests for: section 25 (Environment).
A mirror: ftp://gatekeeper.dec.com/pub/GNU/gcl/gcl-2.5.3.tar.gz (this version is not current)
The cvs tree: http://savannah.gnu.org/cgi-bin/viewcvs/gcl/gcl/ansi-tests/
The SVN tree: svn://common-lisp.net/project/ansi-test/svn/trunk/ansi-tests