Migrated tests to jest

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

test3/intersection/intersection.js

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