Migrated tests to jest

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

test/intersection/intersection.js

@@ -1,5 +0,0 @@
-const intersection = (a, b) => {
-const s = new Set(b);
-return a.filter(x => s.has(x));
-};
-module.exports = intersection;