On the trial of any issue joined, or in any matter, suit or proceeding, in any court, or on any inquiry arising in any suit or proceeding in any court, or before any officer or person having by law, or by consent of parties, authority to hear, receive, and examine evidence, the parties to any such suit or proceeding named in the record, and persons for whose benefit such suit or proceeding is prosecuted, or defended, may be witnesses therein in their own behalf or otherwise, in the same manner as other witnesses, except as hereinafter otherwise provided; and the deposition of any such party or person may be taken and used in evidence under the rules and statutes governing depositions, and any such party or person may be proceeded against and compelled to attend and testify, as is provided by law for other witnesses. No person shall be disqualified as a witness in any civil or criminal case or proceeding by reason of his interest in the event of the same as a party or otherwise or by reason of his having been convicted of any crime; but such interest or conviction may be shown for the purpose of affecting his credibility. A defendant in any criminal case or proceeding shall only at his own request be deemed a competent witness, and his neglect to testify shall not create any presumption against him, nor shall the court permit any reference or comment to be made to or upon such neglect.