I'd be very happy to add tests, since those are absolutely trivial to write.

However, this is, down to the character, a standard implementation of a standard data structure. It was lifted directly from a page of the most standard textbook on algorithms I know (Cormen Rivest Leierson). I'm not sure scala-refactoring's test suite is the best place for those tests, and I'm pretty sure we do not need to run them on every one of refactoring's test runs.