What is the test for error in section 654 of the California Criminal Code?

Under section 654, subdivision (a), "An act or omission that is punishable in different ways by different provisions of law shall be punished under the provision that provides for the longest potential term of imprisonment, but in no case shall the act or omission be punished under more than one provision." " 'Errors in the applicability of section 654 are corrected on appeal regardless of whether the point was raised by objection in the trial court or assigned as error on appeal.' [Citation.] This is an exception to the general rule that only those claims properly raised and preserved by the parties are reviewable on appeal." (People v. Hester (2000) 22 Cal.4th 290, 295 (Hester).) It applies because "a court acts in excess of its jurisdiction and imposes an unauthorized sentence when it fails to stay execution of a sentence under section 654." (Ibid.)