What is the test for determining whether a party has a burden of proof?

Appellant recognizes the rule that a verdict may be directed in favor of a party having the burden of proof only in the exceptional case in which there is no dispute in the evidence and there is but one inference which may be drawn from the evidence. In a jury trial the trial court can decide a factual matter as a matter of law only when the facts are uncontroverted and where reasonable minds can draw but one legitimate inference therefrom. (Ferner v. Casalegno, 141 Cal.App.2d 467, 297 P.2d 91.)