How to use Capybara in pure Ruby (without Rails)?

Here’s something that seems to work for me:

require 'rubygems'
require 'capybara'
require 'capybara/dsl'

Capybara.run_server = false
Capybara.current_driver = :selenium
Capybara.app_host="http://www.google.com"

module MyCapybaraTest
  class Test
    include Capybara::DSL
    def test_google
      visit("https://stackoverflow.com/")
    end
  end
end

t = MyCapybaraTest::Test.new
t.test_google