Hi all,
Last week, I released FileSystem 0.1.0, only to be told that there's already a FileSystem for Ruby. D'oh! I've now renamed this library to MockFS, and re-released it as 0.1.1. Please note that this is the exact same library as before, and the same precautions apply: I use this library in production code, but you will most likely discover cases I have not covered. Please submit bugs! I live for bugs. Yum.
http://rubyforge.org/projects/mockfs/
Francis Hwang
http://fhwang.net/