Migrated tests to jest

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

test/stableSort/stableSort.js

@@ -1,6 +0,0 @@
-const stableSort = (arr, compare) =>
-arr
-.map((item, index) => ({ item, index }))
-.sort((a, b) => compare(a.item, b.item) || a.index - b.index)
-.map(({ item }) => item);
-module.exports = stableSort;