code: function checkExec (mode, callback) {
    if (!exercise.passed)
      return callback(null, true) // shortcut if we've already had a failure
  
    var start = Date.now()
    execWith(copyTempDir, 111, 'Done!\n', function (err, pass) {
      if (err)
        return callback(err)
  
      if (!pass) {
        exercise.emit('fail', 'JavaScript code loads addon, invokes `delay(x, cb)` method and sleeps for x milliseconds')
        return callback(null, false)
      }
  
      var delay = Date.now() - start
  
      if (delay < 100 || delay > 300) {
        exercise.emit('fail', 'Slept for the right amount of time (asked for 111ms, slept for ' + delay + ')')
        return callback(null, false)
      }
  
      start = Date.now()
      execWith(copyTempDir, 1111, 'Done!\n', function (err, pass) {
        if (err)
          return callback(err)
  
        delay = Date.now() - start
  
        if (delay < 1000 || delay > 1300) {
          exercise.emit('fail', 'Slept for the right amount of time (asked for 1111ms, slept for ' + delay + 'ms)')
          return callback(null, false)
        }
  
        exercise.emit(pass ? 'pass' : 'fail'
          , 'JavaScript code loads addon, invokes `delay(x, cb)` method and sleeps for x milliseconds')
        callback(null, pass)
      })
    })
  }
docs: run a full execution of their code & addon, uses a `require()` in a child process and check the stdout for expected