What is the test for dismissing an action under section 1385 of the Penal Code?

Penal Code section 1385, subdivision (a), provides that "[t]he judge or magistrate may, either of his or her own motion or upon the application of the prosecuting attorney, and in furtherance of justice, order an action to be dismissed. The reasons for the dismissal must be set forth in an order entered upon the minutes." "[A] dismissal without a written statement of reasons is invalid and of no effect regardless of the reviewing court's belief that the reasons for the dismissal can be discerned from other portions of the record." (People v. Bonnetta (2009) 46 Cal.4th 143, 149.) If a "trial court's order of dismissal is ineffective, the matter must be remanded at least for the purpose of allowing the trial court to correct the defect by setting forth its reasons in a written order entered upon the minutes. Alternatively, on remand the trial court may, but need not, revisit its earlier decision, as on reflection it might determine its reasoning was flawed or incomplete. Judicial economy is furthered by allowing the trial court to correct what, upon reconsideration and reflection, it perceives to have been an unwarranted dismissal, or to consider if a dismissal should be ordered for some new or different reason. In such cases, the court must also have the power to take action such as reconvening the sentencing hearing or allowing a defendant to withdraw a plea entered on the understanding a count or an enhancement would be dismissed." (Id., at p. 153.)