Website, DB, & Software Developers

I'm using .Net on the server side. Mainly though I'm going straight to JavaScript/HTML/CSS. This Unit Testing concept... how does it work? Does it actually figure out what happens when users press buttons on the site? That would be amazing.

In this particular situation, I have a simple site that allows users to upload multiple files along with their orders. The file upload code is often the problem. I need to use plugins like Silverlight or Flash, for older browsers to bring up a multiple file select box. Newer browsers can use HTML5. I was using only Silverlight, but today, I just switched to PLUpload which amazingly figures out the best upload engine to use. So anyway, in a perfect world we would stress test the site with every possible computer/browser configuration, which I would suspect a testing firm would have. Really it's an academic question at this point because my boss would never invest in anything like that.