Don't trust any random strong password test. I would make sure it's an https connection, and even then, try switching out a few letters and numbers just to make sure. I know Microsoft has a really simple one.

edit - or you could download software from a page like this http://www.passwordmeter.com/
if you really want to be extra cautious you can disconnect your Internet while using it.

Edit 2 - this one's cool. I'd make sure it's at least a few thousand years because the website looks pretty dated. http://lastbit.com/pswcalc.asp