adding spamassassin tests -- howto?

[Will Trillich <will@serensoft.com>]

we're looking for the approved "how-to-add-a-custom-test to
spamassassin" method...

okay, we've got spamassassin running, and Mail::SpamAssassin
perl paraphernalia is available as well.

	# /etc/apt/sources.list -- running woody, with backports:
	deb http://non-us.debian.org/debian-non-US stable/non-US main contrib non-free
	deb http://security.debian.org/ stable/updates main contrib non-free
	deb http://ftp.us.debian.org/debian/ stable main non-free contrib
	deb http://people.debian.org/~aurel32/BACKPORTS woody-spamassassin main
	deb http://people.debian.org/~aurel32/BACKPORTS woody-clamav main


since spamassassin seems to be an instance of Mail::SpamAssassin
that's invoked to scan email as it arrives, what's the procedure
for customizing the spam-recognition routines? not sure what to
google for in this instance -- we get hits on spamassassin's
features and the manpages for Mail::SpamAssassin, but not how to
customize the filters themselves.

we'd like to create our own tests (which look to belong in the
EvalTests arena) such as

	# ratio of non-alpha to alpha in the subject: field
	sub alpha_ratio_subject
		{
		my $self = shift;
		my $subj = $self->get('Subject');
		$subj =~ s/\s+//;
		my @alpha = ($subj =~ s/(\w)//g);
		my $alpha = scalar @alpha;
		my $punc  = length($subj);
		return 0
			unless $punc;
		return $punc / $alpha
			if $alpha;
		return 2**31;
		}

this test is probably not very international-friendly but being
in the torso of the american midwest, we don't have that issue.
:(

what's the approved approach for this kind of customization?

-- 
I use Debian/GNU Linux version 3.0;
Linux boss 2.4.18-bf2.4 #1 Son Apr 14 09:53:28 CEST 2002 i586 unknown
 
DEBIAN NEWBIE TIP #83 from Kieren Diment <kieren@mailandnews.com>
and USM Bish <bish@nde.vsnl.net.in>
:
GOT GIBBERISH?  And wondering what to do next, to clear the
mess? Clear your command-line buffer with control-C (in case
you'd entered something that might be harmful), and then enter
	reset
which is a symlink to /usr/bin/tset which is a portion of
"ncurses-bin" package. ("apt-get install ncurses-bin")
Also see "man tset" for more info.

Also see http://newbieDoc.sourceForge.net/ ...