A good place to start:
http://www.hirensbootcd.org/download/
A lot of diagnostic tools on the CD - easy download.
The best diagnostics are always supplied by the manufacturer of the drive, sometimes specific to the model of the drive. To test, you would need to visit each manufacturer's website, put in your model number and see what diagnostic software they have.
Depending upon the age of the drive, and the size of the drive, they could be paper weights. I have had hard drives that lasted many years, others that died quickly. After 5 years of usage, my personal preference is that they aren't not used for anything that is critical to my experience. I use them for temporary drives - often have a basic load on them - such as Ubuntu, Windows 7, Windows XP for diagnostic purposes - I put a label on them to identify what is on them...