There's also Swiftest[1], a Swift BDD framework for both Mac and Linux, created and actively maintained by old colleague Brian, who's very passionate about Swift and knows it inside and out. It only works on the open source Swift version, so if that's what you're using, it's worth checking out.
I think the largest challenge with Swift testing at the moment is the lack of easy mocking. You can define inline classes, but it's far inferior to the functionality that something like Kiwi provided for Objective-C.
[(inc 0)]: https://github.com/bppr/Swiftest