get the latest installed version of a gem without deprecation warnings

README.md

bundle exec rspec spec/rubygems/util_spec.rb 
Bundling your gems. This may take a few minutes on first run.
............................

Finished in 10.89 seconds
28 examples, 0 failures

Gemfile

source :rubygems
gem 'rspec'
gem 'aruba', :require => 'aruba/api'
gem 'test-construct', :require => 'construct'

util.rb

module Gem::Util

  def self.latest_installed_version(name)
    begin
      if Gem::Specification.respond_to?(:find_by_name)
        Gem::Specification.find_by_name(name).version.to_s
      else
        Gem::SourceIndex.from_installed_gems.find_name(name).last.version.to_s
      end
    rescue Gem::LoadError, NoMethodError
      nil
    end
  end

end

util_spec.rb

require "bundler/setup"
Bundler.require

# These versions seem to be missing from 
# http://production.cf.rubygems.org/rubygems/rubygems-#{rubygems_version}.tgz
#
# 1.8.0
# 1.8.1
# 1.8.2
# 1.8.3
# 1.8.4
%w{
  1.3.7
  1.4.0
  1.4.1
  1.4.2
  1.5.0
  1.5.1
  1.5.2
  1.6.0
  1.6.1
  1.6.2
  1.7.0
  1.7.1
  1.7.2
  1.8.5
}.each do |rubygems_version|
  describe "rubygems #{rubygems_version}" do
    include Construct::Helpers
    include Aruba::Api

    it "is installable" do
      run_simple "wget -q http://production.cf.rubygems.org/rubygems/rubygems-#{rubygems_version}.tgz -O rubygems-#{rubygems_version}.tgz"
      run_simple "tar zxvf rubygems-#{rubygems_version}.tgz"
      cd "rubygems-#{rubygems_version}"

      # need --disable-gems  if 1.9?
      run_simple "ruby setup.rb"
    end

    context "can lookup versions" do
      it "without deprecation warnings" do
        unset_bundler_env_vars
        run "ruby -rrubygems /home/rails/rubygems_version_spec/lib/rubygems/util.rb -e \"puts Gem::Util.latest_installed_version('rails')\""
        fail all_output if all_output.to_s =~ /deprecated/
      end
    end
  end
end