let oldIterResult = {
  done: false,
  value: 123,
};

let testIterator = {
  next() {
    return oldIterResult;
  }
};

let iterable = {
  [Symbol.iterator]() {
    return testIterator;
  }
};

let iterator = Iterator.concat(iterable);

let iterResult = iterator.next();

assert.sameValue(iterResult.done, false);
assert.sameValue(iterResult.value, 123);

assert.notSameValue(iterResult, oldIterResult);