Ok, think I found the problem. ScriptContentTest already has a JUnit4 Assume.assumeThat call to prevent tests from being run when on Mac OS X.
Unfortunately - JUnit4 Assume calls don't work properly when you extend TestCase. Easy enough to fix for most tests, but in this case we extend HudsonTestCase, an abstract base class, for important reasons. And changing HudsonTestCase to a JUnit 4 style test is probably a much bigger deal, and it isn't part of email-ext. I'm not sure how I got this to build before!
