Function callbackOnce

test/test-helper.js:1440–1446

(err)

  let timeout;

  const callbackOnce = (err) => {
    if (timeout) {
      clearTimeout(timeout);
    }
    cb(err);
    cb = utils.noop;
  };

  // If process hasn't completed in 10 seconds.
  timeout = setTimeout(function() {