How to share serverspec tests among hosts

Rakefile

require 'rake'
require 'rspec/core/rake_task'

hosts = [
  {
    :name  => 'proxy001.example.jp',
    :roles => %w( base proxy ),
  },
  {
    :name  => 'proxy002.example.jp',
    :roles => %w( base proxy ),
  },
  {
    :name  => 'app001.example.jp',
    :roles => %w( base app ),
  },
  {
    :name  => 'app002.example.jp',
    :roles => %w( base app ),
  },
  {
    :name  => 'db001.example.jp',
    :roles => %w( base db ),
  },
  {
    :name  => 'db002.example.jp',
    :roles => %w( base db ),
  },
]

hosts = hosts.map do |host|
  {
    :name       => host[:name],
    :short_name => host[:name].split('.')[0],
    :roles      => host[:roles],
  }
end

desc "Run serverspec to all hosts"
task :serverspec => 'serverspec:all'

namespace :serverspec do
  task :all => hosts.map {|h| 'serverspec:' + h[:short_name] }
  hosts.each do |host|
    desc "Run serverspec to #{host[:name]}"
    RSpec::Core::RakeTask.new(host[:short_name].to_sym) do |t|
      ENV['TARGET_HOST'] = host[:name]
      t.pattern = 'spec/{' + host[:roles].join(',') + '}/*_spec.rb'
    end
  end
end

spec_helper.rb

require 'serverspec'
require 'net/ssh'

include Serverspec::Helper::Ssh
include Serverspec::Helper::DetectOS

RSpec.configure do |c|
  c.host  = ENV['TARGET_HOST']
  options = Net::SSH::Config.for(c.host)
  user    = options[:user] || Etc.getlogin
  c.ssh   = Net::SSH.start(c.host, user, options)
  c.os    = backend(Serverspec::Commands::Base).check_os
end