shutdown

# File activesupport/lib/active_support/testing/parallelization.rb, line 113
      def shutdown
        @queue_size.times { @queue << nil }
        @pool.each { |pid| Process.waitpid pid }

        if @queue.length > 0
          raise "Queue not empty, but all workers have finished. This probably means that a worker crashed and #{@queue.length} tests were missed."
        end
      end