Migrated tests to jest

Used jest-codemods to migrate, will have to pass everything by hand before we can merge.

test2/findLastKey/findLastKey.js

@@ -0,0 +1,5 @@
+const findLastKey = (obj, fn) =>
+Object.keys(obj)
+.reverse()
+.find(key => fn(obj[key], key, obj));
+module.exports = findLastKey;