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GitHub User: crslade
I didn't get it working with just Capistrano 3, because Capistrano doesn't want to use the sudo command a lot, and now recommends passwordless sudo. However, I made it work by provisioning with Sunzi. I made a how to video you can follow.
I have simple project, updated to Rails 4, and the current version of all the testing gems he used. (It also includes spork.) The readme includes some vague instructions that will make more sense if you follow along to this railscast. With the railscast and my code, you should be able to get testing working.