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

node_modules/lodash/_baseSum.js

@@ -0,0 +1,24 @@
+/**
+ * The base implementation of `_.sum` and `_.sumBy` without support for
+ * iteratee shorthands.
+ *
+ * @private
+ * @param {Array} array The array to iterate over.
+ * @param {Function} iteratee The function invoked per iteration.
+ * @returns {number} Returns the sum.
+ */
+function baseSum(array, iteratee) {
+  var result,
+      index = -1,
+      length = array.length;
+
+  while (++index < length) {
+    var current = iteratee(array[index]);
+    if (current !== undefined) {
+      result = result === undefined ? current : (result + current);
+    }
+  }
+  return result;
+}
+
+module.exports = baseSum;