What is the test for determining whether a judge's comments were prejudicial to a defendant at trial?

"'"[O]ur role . . . is not to determine whether the trial judge's conduct left something to be desired, or even whether some comments would have been better left unsaid. Rather, we must determine whether the judge's behavior was so prejudicial that it denied [the defendant] a fair, as opposed to a perfect, trial."' [Citation.] We make that determination on a case-by-case basis, examining the context of the court's comments and the circumstances under which they occurred. [Citation.] Thus, the propriety and prejudicial effect of a particular comment are judged by both its content and the circumstances surrounding it. [Citation.]" (People v. Abel (2012) 53 Cal.4th 891, 914.)