Is there a script that can figure out the settings of the current drupal install?
The short answer is no.
Essentially simpletest should be used as a unit test framework. Where all of the data that is needed is set up at the beginning of the test and it is not reliant on system setting or a particular user having a permission. It does this quite well, and can test core functionality and individual modules easily. If you are testing an indavidual module you have written using simpletest is, well, simple.
Unfortunately most websites use a number of modules and are configured to work together in a very specific way. Simpletest doesn't cope with this very well.
There are ways to get around this:
One option is to write a setup script in php which will work as a big setup script for your test. This can create users, set settings and permissions. This can be dificult to write and maintain and can cause the tests to take a long time to run.
Another option is for the site testing (which is different from unit testing) to be done in a tool other than simpletest. I have had some success with selenium. The downside to this is that you need to find a way have clean data. Which can be tricky, copying a database works but doesn't scale.