Function enumerable

tests/js/quint.js:54–58

(obj, propertyName)

    if (!fn.toString().includes('[native code]')) throw new Error(`'${fn}' does not look native`);
  },
  enumerable(obj, propertyName)
  {
    const descriptor = Object.getOwnPropertyDescriptor(obj, propertyName);
    if (!descriptor.enumerable) throw new Error(`'${obj[Symbol.toStringTag]}.${propertyName}' is not enumerable`);
  },
};

const QUnit = {