Test migration to jest by hand

Apparently using regular expressions is way easier.

test/findLastIndex/findLastIndex.js

@@ -0,0 +1,6 @@
+const findLastIndex = (arr, fn) =>
+arr
+.map((val, i) => [i, val])
+.filter(([i, val]) => fn(val, i, arr))
+.pop()[0];
+module.exports = findLastIndex;