Migrated tests to jest

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

test/intersectionBy/intersectionBy.js

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