As of March 24, 2015 that the 'windows-guest-support' branch of test-kitchen has been merged to master, but not the equivalent kitchen-vagrant branch.
Using the Windows cookbook, Gemfile like so:
source "https://rubygems.org"
group :development do
gem "test-kitchen", :git => 'https://github.com/test-kitchen/test-kitchen.git'
gem 'kitchen-vagrant', git: 'https://github.com/test-kitchen/kitchen-vagrant.git', :branch => 'windows-guest-support'
gem "berkshelf"