Test migration to jest by hand

Apparently using regular expressions is way easier.

test/nest/nest.js

@@ -0,0 +1,5 @@
+const nest = (items, id = null, link = 'parent_id') =>
+items
+.filter(item => item[link] === id)
+.map(item => ({ ...item, children: nest(items, item.id) }));
+module.exports = nest;