Somewhere between Ruby on Rails versions 2.3.0 (RC1) and 2.3.2 (final) a change was made to the arguments required for one of the methods the theme_support plugin requires. I must confess I hadn’t spotted it, but github user knapo kindly sent me a message with a patch. That patch is now applied in the main repository, as are a few tweaks to the ActionMailer integration to better handle multipart emails. You can get the new version from github.
Perhaps more significant than those small patches is that I’ve now pushed up a new rails app for use in testing theme_support. The tests are a series of cucumber stories, and the app is very barebones designed entirely to test the various features. I could do with tightening up the way the test app and the main plugin repository are connected, but it’s a start and has been very helpful with the aforementioned patches. Any improvements to the test suite would be much appreciated. You can, of course, find it on github.