Causes open sources Buffet, a Ruby testing framework.

I don't think so. I mean, RSpec is pretty fast as is, at least for running only hundreds of tests. The problem we were encountering is that if you want to get full coverage, some tests will have to hit the database or do other (mildly) time consuming tasks, and if you have a large enough test suite doing these things all over the place, they tend to add up into ridiculously long test runs.

It speeds up about linearly; 5 more machines will make it run about 5 times as fast, etc. For incredibly fast suites, it isn't very helpful, because the startup and sync times across machines outweigh the benefits.

At causes, our tests run in about 20 minutes on 1 machine, and 4 minutes with buffet and 5.

This is a good question, because we actually were using Hydra for a while. We ran into a lot of problems where hydra workers would just hang once they finished their test (used strace to see what they were doing, and it looked like they were stuck in some sort of infinite loop). Hydra caused enough headaches that we just stopped using it; out of that frustration, Buffet was born. We tried pretty hard to make Buffet 'just work' and stable.

As far as I know Hydra can't run on 1.9 ( https://github.com/ngauthier/hydra/issues/29 )

Alternatively, you have parallel_tests ( https://github.com/grosser/parallel_tests ) which can run on multiple cores. That's great if you use a mac pro, or some behemoth machine.

Little known there's testbot ( https://github.com/joakimk/testbot ) which can run tests across machines & cores. They've even worked in a bootstrapping process https://github.com/joakimk/testbot_cloud

From ( https://github.com/joakimk/testbot/wiki/How-testbot-is-used ) "... 60 minutes of tests to run in 10 minutes using 16 medium EC2 instances (32 cores), read the blog post." reports thoughtbot!

Code softly hackers.

Ah, didn't realize that was ambiguous. I edited the opening - does that make it more clear?