You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: parallel.rb
    path of file: ./repos/truffleruby/lib/gems/gems/minitest-5.16.3/lib/minitest
    
    the code of the file until where you have to start completion: module Minitest
  module Parallel #:nodoc:

    ##
    # The engine used to run multiple tests in parallel.

    class Executor

      ##
      # The size of the pool of workers.

      attr_reader :size

      ##
      # Create a parallel test executor of with +size+ workers.

      def initialize size
    
      def << work; @queue << work; end

      ##
      # Shuts down the pool of workers by signalling them to quit and
      # waiting for them all to finish what they're currently working
      # on.

      def shutdown
        size.times { @queue << nil }
        @pool.each(&:join)
      end
    end

    module Test # :nodoc:
      def _synchronize; Minitest::Test.io_lock.synchronize { yield }; end # :nodoc:

      module ClassMethods # :nodoc:
        def run_one_method klass, method_name, reporter
          Minitest.parallel_executor << [klass, method_name, reporter]
        end

        def test_order
          :parallel
        end
      end
    end