"use strict"; const Base = { }; const obj = { get test() { }, set() { return super.test = 3; }, }; Object.setPrototypeOf(obj, Base); expect(() => { // this requires helpers to be in file (not external), so they // are in "strict" mode code. obj.set(); }).toThrow(); expect(Base.test).toBeUndefined(); expect(obj.test).toBeUndefined();