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.

Why?

Have you made this same request to the thousands of other BL maintainers around the world?

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.

I can honestly say I don't remember one person coming here with that complaint in the entire history of this message board, nor during a year before that on the newsgroups.

And if spamhaus has one setup, you simply use that one to configure the application and change the bl name. There really is no difference between bl's. They all work the saem way.

Wasn't AT&T blocking access to the SCBL servers at one point, causing AT&T customers who tried to use the SCBL to fail?

Your posted Announcement -> Problem using SCBL from AT&T Explained

Ah yes, over two years ago. Would any AT&T customers care to comment on whether or not AT&T has changed their tune yet? Thanks!

I was truthful, I did not remember that episode until you brought it up and I read it.

Don't worry about it. I didn't remember the details, either.