Article VI. Witnesses
The judge or chancellor presiding at the trial may not testify in that trial. No objection need be made in order to preserve the point.
Advisory Commission Comments.
The rule would change Tennessee law. T.C.A. § 24-1-205 [repealed] permits trial testimony by a presiding judge. The commission thought it wiser to avoid this awkward practice. See also Canon 3 of the Code of Judicial Conduct.
Of course a judge could testify in a later collateral attack proceeding. The subsequent proceeding would not be "that trial."
The rule does not change a judge's power to notice facts or law under Rules 201 and 202.