code: function checkExec (mode, callback) {
    if (!exercise.passed)
      return callback(null, true) // shortcut if we've already had a failure
  
    childProcess.exec(
          '"'
        + process.execPath
        + '" "'
        + copyTempDir
        + '" "'
        + expected
        + '"'
      , function (err, stdout, stderr) {
          if (err) {
            process.stderr.write(stderr)
            process.stdout.write(stdout)
            return callback(err)
          }
  
          var pass = stdout.toString().replace('\r', '') == expected + '\n'
            , seminl = !pass && stdout.toString() == expected
  
          if (!seminl && !pass) {
            process.stderr.write(stderr)
            process.stdout.write(stdout)
          }
  
          if (seminl)
            exercise.emit('fail', 'Addon prints out expected string (missing newline)')
          else
            exercise.emit(pass ? 'pass' : 'fail', 'Addon prints out expected string')
  
          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