What is the test for a motion to amend or amend information in a criminal case?

Amendments to the information ordinarily involve the prosecutor seeking to add a charge. In that case, the authorities tell us that "[t]he focus of the trial court's exercise of discretion in ruling on a motion to amend should be directed primarily to determining whether, on the facts presented, the requested amendment would prejudice [the defendant's] substantial rights." (People v. Superior Court (Alvarado) (1989) 207 Cal.App.3d 464, 477.) But that does not mean that the court must allow an amendment in every case where it is not demonstrated that the defendant's substantial rights are prejudiced by the amendment. While refusal to allow an amendment omitting a charge is rare, and a trial court would appropriately do so with caution, such a refusal is within the trial court's discretion.

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