How to use d3-queue

pathsToTest.forEach(pathToTest => {
  var messageValue = {
   message: 'Warning: the file you asked to watch does not exist...',
   value: pathToTest + hintStr
  };

  q.defer(validatePath(messageValue), pathToTest);
 });

q.awaitAll(function(err, results) {
  console.log('all done', err, results);
});

/* --------------------------------------------
  * Check that our taskFiles exist
  */
 watchGroup.events.forEach(evt => {
  if (evt.taskFiles) {
   let taskFiles = _.isArray(evt.taskFiles) ? evt.taskFiles : [evt.taskFiles];
   taskFiles.forEach(pathToTest => {
    var messageValue = {
     message: `Error: Task file for \`${watchGroup.serviceName}\` service's \`${evt.type}\` event does not exist.`,
     value: pathToTest
    };
    q.defer(validatePath(messageValue), pathToTest);
   });
  }
 });

function add (watchGroups, onDone, testsCb) {
 if (!_.isArray(watchGroups)) {
  watchGroups = [watchGroups];
 }
 onDone = onDone || identity;
 // Add this hook for testing
 testsCb = _.defaults({}, testsCb || {}, {
  onInit: identity,
  onEvent: identity,
  onCommandEvent: identity,
  onTaskFileEvent: identity
 });

 var q = queue();

 // Loop through each file directive
 watchGroups.forEach(function (watchGroup) {
  q.defer(processWatchGroup(testsCb), watchGroup);
 });
 q.awaitAll(function (err, onDones) {
  onDone(err, onDones);
 });
}

/* --------------------------------------------
  * General purpose error reporter
  * The first argument are failing errors
  * Second argument are warnings
  */
 q.awaitAll(function (nS, warnings) {
  /* istanbul ignore if */
  if (nS) {
   cb.fail(nS);
   return false;
  }
  // Send any warnings back out to report
  warnings.filter(nS => nS).forEach(nS => cb.warn(nS));
  // And then proceed
  cb.proceed();
 });