How can I test my computer's security?

Hi all @ TS,
Today has been one of those days when I do some PC housekeeping by clearing internet history,defragging,junking old files etc and running full scans using the free application tools provided:
For instance,I have these 3 on my PC;
Avast! boot time scan followed by Avast! full scan
MBAM full scan
SUPERAntiSpyWare full scan.
I am happy to report all results showed NO threats in any shape or form after a recent problem I had with a Trojan agent called Gen-Nullo.
This got me wondering,is there a program/ application or a tool that deliberately infects your system so you,as the end user and diligent up-dater of all things Security related,can actually TEST your Security suite?
Any thoughts or ideas?
Thanks,
Drumma.

I wouldn't recommend that, at all. Antivirus isn't 100%.

Gen-Nullo.. Possible. There are hundreds of online scanners that show fake warning to lure users into installation. Use trusted programs like AVG and AVAST. If AVAST hasnt shown any threats, you probably need to stop worrying about your computer security.