What is the legal test for disqualifying a judge for bias?

particular case, there must exist '"the probability of actual bias on the part of the judge . . . [that] is too high to be constitutionally tolerable."'" (People v. Freeman (2010) 47 Cal.4th 993, 996.) Under this objective standard, "only the most 'extreme facts' would justify judicial disqualification based on the due process clause." (Ibid.) The due process clause does not require judicial disqualification based on the mere appearance of bias. (Id. at pp. 1000, 1006.)