Rails - Dec 2005 - Question about testing (chapter 12)

Hey,

i have created my website, and i saw in the book about testing and stuff,
started reading that, but a lot is over data, like the correct types and
validation.

In my website i have model validation and that works fine, i was wondering if
with that testing my site would benefit more?? I know you should test first
and then create the website, but i did that any way.

Thanks
Nick