[Dovecot] How do I test if the anti spam plugin is working?

I've configured the dspam anti spam plugin, but it doesn't appear to be doing anything when I move mail between mailboxes. Can anyone help me determine what's going on?

The plugin appears to be loading; at least if I don't define all the required configuration options I get a complaint in the log file. But beyond that I don't see any activity.

Here's the config:

babel# dovecot --version
2.1.3

The dovecot anti spam plugin config is:

protocol imap {
	  mail_plugins = $mail_plugins antispam
}

and

plugin {
    antispam_debug_target = syslog
    antispam_verbose_debug = 1

    antispam_backend = dspam
    antispam_signature = X-DSPAM-Signature

    antispam_signature_missing = error

    antispam_trash_pattern_ignorecase = trash;Deleted *
    antispam_spam_pattern = SPAM

    antispam_dspam_binary = /usr/local/bin/dspam

    antispam_dspam_args = --deliver=;--user;%n@_%d
}

I don't even appear to be seeing any log entries from the plugin.

I've moving an email from my main mailbox into a mailbox called 'SPAM', which is how I thought that it was supposed to be triggered.

Cheers, Joe