A judge shall not testify as a character witness in a judicial, administrative, or other adjudicatory proceeding or otherwise vouch for the character of a person in a legal proceeding, except when duly subpoenaed.
Iowa. Code. Jud. Cond. 51:3.3
Comment
[1] A judge who, without being subpoenaed, testifies as a character witness abuses the prestige of judicial office to advance the interests of another. See rule 51:1.3. Except in unusual circumstances where the demands of justice require, a judge should discourage a party from requiring the judge to testify as a character witness.