Genny is a lua libraries for working with generators.
Lua defines iterators that can be used with for loops. Unfortunately, since they are defined as 3 separate values, it is very hard to manipulate these iterators. Genny defines so-called "generators", which nothing but lua iterators that don't take any arguments. Since this means a generator is a single (callable) value, it's much easier to pass them around, manipulate them, store them, etc.
For documentation see here.
The tests (in genny_spec.lua) can be run using busted.