I am currently doing a lot of regression testing at my job. And like I want to look at some of the best code in the world for regression testing (i.e. Open source). So basically list open source projects that you think show good examples of regression testing.
P.S True regression testing is black box by the way. However the examples so far are a good read for testing
jQuery does a lot of regression testing, because it's supporting quite a few browsers and a lot of intricate tests (in particular, supporting css). I'm not sure if it's the best example or not for general regression, but for web development, it's a great case because it handles a VERY difficult task, regression testing against many browsers which are constantly changing, even within versions. Though it is hard to come up with a more pure case where changes in the external world can cause your code to regress :(.
Here is the documentation of KDE4's unit testing development: http://techbase.kde.org/Development/Tutorials/Unittests
In this blog you can see that QtSoftware/Nokia has opened all the regression testing applications to the world: http://ariya.blogspot.com/2009/06/all-blessings-in-may.html or direct link to the unit tests+benchmarks:
This blog is linked from the previous one: http://benjamin-meyer.blogspot.com/2009/05/open-qt-repository-and-hidden-gems.html read it as well :)
Would you like to see where the WebKit regression tests are saved? Or you want to google for it?