What is the test for a motion requiring a defendant to produce evidence in a civil case?

"After a party has completed his presentation of evidence in a trial by the court, the other party, without waiving his right to offer evidence in support of his defense or in rebuttal in the event the motion is not granted, may move for a judgment. . . ." (Code Civ. Proc., 631.8.) " ' "The purpose of Code of Civil Procedure section 631.8 is to enable a trial court which, after weighing the evidence at the close of the plaintiff's case, is persuaded that the plaintiff has failed to sustain his burden of proof, to dispense with the need for the defendant to produce evidence. [Citations.]" [Citation.]' " (Roth v. Parker (1997) 57 Cal.App.4th 542, 549.)