What is the test for a claim of ineffective assistance against counsel who failed to object at trial?

As we explained recently in People v. Mitchell (2008) 164 Cal.App.4th 442, at page 467: "`[T]he mere failure to object rarely rises to a level implicating one's constitutional right to effective legal counsel.' [Citation.] If, as here, the record fails to show why counsel failed to object, the claim of ineffective assistance must be rejected on appeal unless counsel was asked for an explanation and failed to provide one or there can be no satisfactory explanation. [Citation.] `A reviewing court will not second-guess trial counsel's reasonable tactical decisions.' [Citation.]"