Auto load site configuration

Hi,

I am new to simpletest and I am trying to see if it would be a good tool for us or not. One important thing to know is stated in the documentation as:

It's terribly important to realize that each test runs in a completely new Drupal instance, which is created from scratch for the test. In other words, none of your configuration and none of your users exists! None of your modules are enabled beyond the default Drupal core modules.

So, we have to put all configuration steps in the setUp function. What if our final site we want to test is quite complex to setup (lots of modules, lots of configuration to do, etc). Do we have to recode all this in the setUp function or is there any possibilities to catch the entire configuration of a site and tell simpletest to rebuild this site exactly?

If no, then why using SimpleTest over Selenium for example?

Regards.