Migrated tests to jest

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

test/sortedLastIndexBy/sortedLastIndexBy.js

@@ -1,10 +0,0 @@
-const sortedLastIndexBy = (arr, n, fn) => {
-const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
-const val = fn(n);
-const index = arr
-.map(fn)
-.reverse()
-.findIndex(el => (isDescending ? val <= el : val >= el));
-return index === -1 ? 0 : arr.length - index;
-};
-module.exports = sortedLastIndexBy;