A captcha only shows up if mollom is unsure if it s spam or not! If it is sure (=to be known) spam your message will be rejected immediately.

If it is no spam, no captcha will appear and the message goes through. If the quality of your submitted data is too poor (actually set: quality below 15%), it will also be rejected immediately (w/o captcha). So do not post too short messages cause it raises the chance to be poor content. Be aware of that!

And please, use REAL spam data, the system is quite intelligent and recognizes if its not real spam - you should not let it "know" that this is a test ;-)

E.g. if you just add "Viagra" but no suspicious url why should the system think it is spam?

So again: No captcha will appear if it is detected as "quite sure to be no spam"!