Implementation of examples contained within S. Freeman's and N. Pryce's book, "Growing Object-Oriented Software, Guided by Tests"  http://www.amazon.co.uk/Growing-Object-Oriented-Software-Guided-Signature/dp/0321503627/ref=sr_1_1?ie=UTF8&qid=1413191116&sr=8-1&keywords=growing+object-oriented+software+guided+by+tests