added unit testing, and started implementing unit tests...phew

node_modules/async/concatLimit.js

@@ -0,0 +1,65 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+
+exports.default = function (coll, limit, iteratee, callback) {
+    callback = callback || _noop2.default;
+    var _iteratee = (0, _wrapAsync2.default)(iteratee);
+    (0, _mapLimit2.default)(coll, limit, function (val, callback) {
+        _iteratee(val, function (err /*, ...args*/) {
+            if (err) return callback(err);
+            return callback(null, (0, _slice2.default)(arguments, 1));
+        });
+    }, function (err, mapResults) {
+        var result = [];
+        for (var i = 0; i < mapResults.length; i++) {
+            if (mapResults[i]) {
+                result = _concat.apply(result, mapResults[i]);
+            }
+        }
+
+        return callback(err, result);
+    });
+};
+
+var _noop = require('lodash/noop');
+
+var _noop2 = _interopRequireDefault(_noop);
+
+var _wrapAsync = require('./internal/wrapAsync');
+
+var _wrapAsync2 = _interopRequireDefault(_wrapAsync);
+
+var _slice = require('./internal/slice');
+
+var _slice2 = _interopRequireDefault(_slice);
+
+var _mapLimit = require('./mapLimit');
+
+var _mapLimit2 = _interopRequireDefault(_mapLimit);
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+var _concat = Array.prototype.concat;
+
+/**
+ * The same as [`concat`]{@link module:Collections.concat} but runs a maximum of `limit` async operations at a time.
+ *
+ * @name concatLimit
+ * @static
+ * @memberOf module:Collections
+ * @method
+ * @see [async.concat]{@link module:Collections.concat}
+ * @category Collection
+ * @param {Array|Iterable|Object} coll - A collection to iterate over.
+ * @param {number} limit - The maximum number of async operations at a time.
+ * @param {AsyncFunction} iteratee - A function to apply to each item in `coll`,
+ * which should use an array as its result. Invoked with (item, callback).
+ * @param {Function} [callback] - A callback which is called after all the
+ * `iteratee` functions have finished, or an error occurs. Results is an array
+ * containing the concatenated results of the `iteratee` function. Invoked with
+ * (err, results).
+ */
+module.exports = exports['default'];