Test migration to jest by hand

Apparently using regular expressions is way easier.

test/sortedIndexBy/sortedIndexBy.js

@@ -0,0 +1,7 @@
+const sortedIndexBy = (arr, n, fn) => {
+const isDescending = fn(arr[0]) > fn(arr[arr.length - 1]);
+const val = fn(n);
+const index = arr.findIndex(el => (isDescending ? val >= fn(el) : val <= fn(el)));
+return index === -1 ? arr.length : index;
+};
+module.exports = sortedIndexBy;