Pub. Util. Code, § 2103

Upon the filing of a petition pursuant to Section 2102, the court shall specify a time, not exceeding 20 days after the service of the copy of the petition, within which the public utility complained of shall answer the petition, and in the meantime the public utility may be restrained. In case of default in answer, or after answer, the court shall immediately inquire into the facts and circumstances of the case. Such corporations or persons as the court deems necessary or proper to be joined as parties, in order to make its judgment, order or writ effective, may be joined as parties. The final judgment in any such action or proceeding shall either dismiss the action or proceeding or direct that the writ of mandamus or injunction issue or be made permanent as prayed for in the petition, or in such modified or other form as will afford appropriate relief. An appeal may be taken to the Supreme Court from such final judgment in the same manner and with the same effect, subject to the provisions of this part, as appeals are taken from judgments of the superior court in other actions for mandamus or injunction.