There are a number of mock object libraries out there (mockery, shmock, phpunit's mock syntax, etc). This just looks like another builder syntax for making mocks / stubs with some fanciness around class extension - what's the benefit?<p>Also, how often is it useful to define a class at test time that is initialized by production code (from the section I Still Have Serious Dependency Issues!). This seems like an unlikely use case.