These scripts were the result of the "Faster Rails test runs...with Unix!" screencast at https://www.youtube.com/watch?v=RSehcT4MnRM.

tclient.rb

#!/usr/bin/env ruby

require 'socket'

test_file = ARGV[0]

socket = UNIXSocket.new('testing.sock')

socket.write(test_file)
socket.close_write

puts socket.read

tserver.rb

#!/usr/bin/env ruby

require 'benchmark'
require 'socket'
ENV['RAILS_ENV'] = 'test'

rails_boot = Benchmark.measure {
  require './config/application'
}

puts "Rails loaded after #{rails_boot}s..."

server = UNIXServer.new('testing.sock')

parent_process_id = Process.pid
at_exit {
  if Process.pid == parent_process_id
    File.unlink('testing.sock')
  end
}

trap('INT') { exit }

loop do
  client = server.accept
  test_file = client.read

  pid = fork do
    $stdout.reopen(client)
    require test_file
  end

  Process.wait(pid)
  client.close
end