public function next(): Answer
    {
        if ($this->calledCount > $this->lastIndex) {
            $index = $this->lastIndex;
        } else {
            $index = $this->calledCount;
        }

        ++$this->calledCount;

        if (
            !isset($this->answers[$index]) ||
            !$this->answers[$index]->primaryRequest()
        ) {
            throw new UndefinedAnswerException();
        }

        return $this->answers[$index];
    }