модуль ActiveSupport::Testing::Isolation::Subprocess

# File activesupport/lib/active_support/testing/isolation.rb, line 76
def run_in_isolation(&blk)
  require "tempfile"

  if ENV["ISOLATION_TEST"]
    yield
    File.open(ENV["ISOLATION_OUTPUT"], "w") do |file|
      file.puts [Marshal.dump(self.dup)].pack("m")
    end
    exit!
  else
    Tempfile.open("isolation") do |tmpfile|
      env = {
        'ISOLATION_TEST' => self.class.name,
        'ISOLATION_OUTPUT' => tmpfile.path
      }

      load_paths = $-I.map {|p| "-I\"#{File.expand_path(p)}\"" }.join(" ")
      orig_args = ORIG_ARGV.join(" ")
      test_opts = "-n#{self.class.name}##{self.name}"
      command = "#{Gem.ruby} #{load_paths} #{$0} '#{orig_args}' #{test_opts}"

      # IO.popen lets us pass env in a cross-platform way
      child = IO.popen(env, command)

      begin
        Process.wait(child.pid)
      rescue Errno::ECHILD # The child process may exit before we wait
        nil
      end

      return tmpfile.read.unpack("m")[0]
    end
  end
end