The judge presiding at the trial may not testify in that trial as a witness. No objection need be made in order to preserve the point.
Wis. Stat. § 906.05
A judge who carefully considered the transcribed record and her recollection of a previous proceeding involving the defendant did not impermissibly testify. State v. Meeks, 2002 WI App 65, 251 Wis. 2d 361, 643 N.W.2d 526, 01-0263. Reversed on other grounds. 2003 WI 104, 263 Wis. 2d 794, 666 N.W.2d 859, 01-0263.