> long term i think it would make sense to have specific tests for each rewriter, and common tests on the doctest execution function

This sounds like the right approach to me, too.

I'd like to pull in these changes, but first I'd like to handle the test failure one way or another. If you're keen to spend the time to split the test suite into JavaScript rewriter + CoffeeScript rewriter + doctest evaluator, great! If you'd rather add a dummy test to test.coffee for now, go for it. :)