What is the test for determining credibility of a witness in a medical malpractice case?

"We presume in support of the judgment the existence of every fact the trier of fact reasonably could infer from the evidence. [Citation.] If the circumstances reasonably justify the trier of fact's findings, reversal of the judgment is not warranted simply because the circumstances might also reasonably be reconciled with a contrary finding. [Citation.] A reviewing court neither reweighs evidence nor reevaluates a witness's credibility." (People v. Lindberg (2008) 45 Cal.4th 1, 27.)