For example, spamhaus.org has such test. This isn't difficult to release, the price is losing one IP only. It will help to avoid many messages from users like "I have set the BL up, but it doesn't work!". Really if I still get a spam, what is a reason? The sender's relay was not listed at receiving time, or maybe something is wrong in my setup? Hard to diagnose.
It's very desirable to have a block list setup test. That is: - have a Web page to start test; - have a special permanently listed test IP; - at user's request try to send a mail to him from this IP; - send him another mail (from clean IP) with full SMTP session report from the previous attempt.