I think it's prudent to make UI testing as much like unit testing as possible. Tools and tests that poke at the GUI from "outside" are notoriously fragile. I gave a talk at Mountain West RubyConf on using TDD for user interfaces (using RubyCocoa, but the idea is the same for MacRuby). <http://mwrc2009.confreaks.com/videos/13-mar-2009-17-00-test-driving-guis-wit...
This week, I'll be updating my tooling for MacRuby and starting to use it to reimplement the /Developer/Examples Objective-C samples. (Shameless plug: There's a more detailed description of the testing approach in my RubyCocoa book: <http://pragprog.com/titles/bmrc/rubycocoa
.)
----- Brian Marick, independent consultant Mostly on agile methods with a testing slant www.exampler.com, www.exampler.com/blog, www.twitter.com/marick