Having used it on my current project for the last few months and improved the unit test coverage, I've released version 1.0.0 of the Handoff gem. You can get the gem file at RubyForge or just a wait a while and do
sudo gem install handoff -v 1.0.0
My first priority for future development is to improve the output when specifying delegation that hasn't been implemented yet. (Currently you just get one NoMethodError.) After that I may work on a couple of features requested by Ali, but it's a real hassle TDD'ing a library for making test assertions, so the going will likely be slow.
For those of you who don't work with me, Handoff is a tiny little gem providing a fluent interface for asserting on simple delegation. It aims to make asserting the behavior as simple as implementing it (with Forwardable). See the rdocs for examples.