testing threaded code in ruby

Question

I'm writing a delayed_job clone for DataMapper. I've got what I think is working and tested code except for the thread in the worker process. I looked to delayed_job for how to test this but there are now tests for that portion of the code. Below is the code I need to test. ideas? (I'm using rspec BTW)

def start
  say "*** Starting job worker #{@name}"
  t = Thread.new do
    loop do
      delay = Update.work_off(self) #this method well tested
      break if $exit
      sleep delay
      break if $exit
    end
    clear_locks
  end

  trap('TERM') { terminate_with t }
  trap('INT')  { terminate_with t }

  trap('USR1') do
    say "Wakeup Signal Caught"
    t.run
  end

see also this thread

Answer 1

Its impossible to test threads completely. Best you can do is to use mocks.

(something like) object.should_recieve(:trap).with('TERM').and yield object.start

Answer 2

You could start the worker as a subprocess when testing, waiting for it to fully start, and then check the output / send signals to it.

I suspect you can pick up quite a few concrete testing ideas in this area from the Unicorn project.