minitest/unit is a small and fast replacement for ruby's huge and slow test/unit. This is meant to be clean and easy to use both as a regular test writer and for language implementors that need a minimal set of methods to bootstrap a working unit test suite. mini/spec is a functionally complete spec engine. mini/mock, by Steven Baker, is a beautifully tiny mock object framework. (This package was called miniunit once upon a time) -- (this gem as maintained by Matt Lyon contains patches and extensions to minitest/spec that will apparently never make it upstream. Go Open Source!)