What is the test for reducing a felony to a misdemeanor?

"punishable either by a term in state prison or by imprisonment in county jail and/or by a fine." (Park, supra, 56 Cal.4th at p. 789.) The trial court has discretion to "reduce a wobbler to a misdemeanor either by declaring the crime a misdemeanor at the time probation is granted or at a later timefor example, when the defendant has successfully completed probation." (Id. at p. 793.) The decision to reduce a felony to a misdemeanor is a sentencing decision made by the trial court. In the absence of a showing that a criminal sentencing decision was irrational or arbitrary, the trial court is presumed to have acted to achieve the legitimate sentencing objectives, and its discretionary determination to impose a particular sentence will not be set aside on appellate review. (People v. Carmony (2004) 33 Cal.4th 367, 375.)