What is the test for declaring a mistrial when the jurors believe they may be deadlocked?

A trial court is not required to declare a mistrial when the jurors believe they may be deadlocked. "Section 1140 allows a trial court to discharge a jury and declare a mistrial if the court determines that the proper period of time for deliberation has expired and 'there is no reasonable probability' that the jurors can agree on a verdict. The decision whether to declare a hung jury or to order further deliberations rests in the trial court's sound discretion. [Citations.] 'Although the court must take care to exercise its power without coercing the jury into abdicating its independent judgment in favor of considerations of compromise and expediency [citation], the court may direct further deliberations upon its reasonable conclusion that such direction would be perceived " 'as a means of enabling the jurors to enhance their understanding of the case rather than as mere pressure to reach a verdict on the basis of matters already discussed and considered.' " ' " (People v. Debose (2014) 59 Cal.4th 177, 209.)