Migrated tests to jest

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

test/functions/functions.js

@@ -1,6 +0,0 @@
-const functions = (obj, inherited = false) =>
-(inherited
-? [...Object.keys(obj), ...Object.keys(Object.getPrototypeOf(obj))]
-: Object.keys(obj)
-).filter(key => typeof obj[key] === 'function');
-module.exports = functions;