What is the test for a disqualification motion for abuse of discretion?

^7."We review a trial court's ruling on a disqualification motion for abuse of discretion, and we accept as correct all express or implied findings that are supported by substantial evidence. [Citations.] 'However, the trial court's discretion is limited by the applicable legal principles. [Citation.] Thus, where there are no material disputed factual issues, the appellate court reviews the trial court's determination as a question of law. [Citation.] In any event, a disqualification motion involves concerns that justify careful review of the trial court's exercise of discretion. [Citation.]'" (Brand v. 20th Century Ins. Co./21st Century Ins. Co., supra, 124 Cal.App.4th at p. 601.)