Function throws

tests/js/quint.js:37–49

(fn, error)

    if (JSON.stringify(a) !== JSON.stringify(b)) throw new Error(`'${a}' does not equal to '${b}'`);
  },
  throws(fn, error)
  {
    try
    {
      fn();
    } 
    catch (err)
    {
      if (!err.toString().includes(error)) throw new Error(`'${fn}' throws '${err}' but expects '${error}'`);
      return;
    }
    throw new Error(`'${fn}' does not throw`);
  },
  looksNative(fn)
  {
    if (!fn.toString().includes('[native code]')) throw new Error(`'${fn}' does not look native`);