Improve code quality and write tests

node_modules/lodash/_WeakMap.js

@@ -0,0 +1,7 @@
+var getNative = require('./_getNative'),
+    root = require('./_root');
+
+/* Built-in method references that are verified to be native. */
+var WeakMap = getNative(root, 'WeakMap');
+
+module.exports = WeakMap;