Migrated tests to jest

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

test/findLastIndex/findLastIndex.js

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