You can use any javascript testing framework with CoffeeScript. This will be testing the Javascript that CoffeeScript outputs which is necessary since CoffeeScript itself can’t be executed.
Writing your own testing framework for CoffeeScript is fun (I did) but entirely uneccessary.
UPDATE: Jasmine tests can be run on node.js in which case both the tests and the code under test can be CoffeeScript, without the need for any compilation step.