Test migration to jest by hand

Apparently using regular expressions is way easier.

test/takeWhile/takeWhile.js

@@ -0,0 +1,5 @@
+const takeWhile = (arr, func) => {
+for (const [i, val] of arr.entries()) if (func(val)) return arr.slice(0, i);
+return arr;
+};
+module.exports = takeWhile;