Normally you would do this to install test-kitchen:

sudo gem install test-kitchen

To get the latest stable dev version from github, do it rather this way:

cd /tmp
git clone
cd test-kitchen/
sudo gem build test-kitchen.gemspec
sudo gem install

You eventuelly need to replace with the version that is shown after the build command – if it differs.
Omit "sudo" if you're already root.