Transactional database in Minitest in 7 lines of code

transactional.rb

module TransactionalTests
  # See minitest doco - use_transactional_fixtures_but_in_ruby
  # to use include this into your test case
  def run(runner)
    test_result = nil
    ActiveRecord::Base.transaction { test_result = super; raise ActiveRecord::Rollback }
    test_result
  end
end

where do you put this and how do you include it?