What is the legal test for determining whether a defendant has been found guilty beyond a reasonable doubt?

Our review following a trial court's decision to instruct is therefore governed by familiar principles of substantial evidence review. (People v. Nelson (2016) 1 Cal.5th 513, 550 [recognizing it is essentially the same standard].) We review the whole record in the light most favorable to the judgment below to determine whether it discloses substantial evidence-that is, evidence which is reasonable, credible, and of solid value-such that a reasonable trier of fact could find the defendant guilty beyond a reasonable doubt.' [Citation.] In determining whether a reasonable trier of fact could have found [the defendant] guilty beyond a reasonable doubt, we presume in support of the judgment the existence of every fact the trier could reasonably deduce from the evidence.' (Ibid.)

Appellate inquiry into the sufficiency of the evidence does not require a court to ask itself whether it believes that the evidence at the trial established guilt beyond a reasonable doubt. [Citation.] Instead, the relevant question is whether, after viewing the evidence in the light most favorable to the prosecution, any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt.' [Citation.] In other words, it is the jury, not the appellate court which must be convinced of the defendant's guilt.' (People v. Nguyen (2015) 61 Cal.4th 1015, 1055-1056.)