What is the test for retrial after a jury deadlock?

"The federal and state Constitutions protect persons against being twice placed in jeopardy for the same offense. [Citations.] Retrial after discharge of a jury without "manifest" (in federal terminology) or "legal" necessity violates the protections afforded under both charters. Jury deadlock constitutes necessity for declaration of a mistrial and permits retrial of the defendant. [Citations.] This principle is codified in section 1140, which prohibits discharge of the jury after the case is submitted to it until it has rendered a verdict, unless by consent of both parties or it appears there is no reasonable probability the jury can agree, and section 1141, which permits retrial under such circumstances. [Citations.] The determination whether there is a reasonable probability of agreement rests in the sound discretion of the trial court, based on consideration of all the factors before it. [Citation.]" (People v. Halvorsen (2007) 42 Cal.4th 379, 425-426.)