forked_specs.rb

module ForkedSpecs
  def forked_specs(*specs)
    ActiveRecord::Base.clear_all_connections!

    pids = []
    specs.each do |spec|
      pids << fork do
        ActiveRecord::Base.establish_connection
        spec.call
      end
    end

    pids.each do |pid|
      Process.wait(pid)
      $?.should be_success, 'expected forked spec to succeed'
    end
  ensure
    ActiveRecord::Base.establish_connection
  end
end

ipc_message.rb

require 'fileutils'
require 'timeout'

class IPCMessage
  class << self
    def clean
      FileUtils.rm_f(Dir.glob(file_name('*')))
    end

    def broadcast(message)
      FileUtils.touch(file_name(message))
    end

    def wait_for(message)
      Timeout.timeout(5) do
        sleep 0.001 until broadcasted?(message)
        FileUtils.rm_f(file_name(message))
      end
    rescue
      raise "timed out waiting for IPC message #{message}"
    end

    def broadcasted?(message)
      File.exists?(file_name(message))
    end

    def file_name(message)
      "#{Rails.root}/tmp/ipc_message_#{message}"
    end
  end
end

some_spec.rb

it 'handles stale records', forked: true do
  s1 = -> do
    IPCMessage.wait_for(:parallel_deposit)
    @ca.withdraw!(25)
    @ca.credit.should == 76
  end

  s2 = -> do
    @ca.deposit!(1).should be_true
    IPCMessage.broadcast(:parallel_deposit)
  end

  forked_specs(s1, s2)
end