What is the test for determining whether a trial judge's conduct deprived a defendant of a fair trial?

"In determining whether a trial judge's conduct deprived a defendant of a fair trial, we must examine the entire record to determine if jurors have been impressed with the trial judge's partiality to one side to the point that this became a factor in the[ir] determination. The district judge may actively participate and give his own impression, as long as he does not become an advocate for the government. Where the court assumes the role of prosecutor and displays bias, reversal is required. The judge should ask only those questions necessary to clarify ambiguities, correct misstatements, or obtain information necessary to make rulings. If a judge's actions create an impression of partisanship, curative instructions will generally not save the day." United States v. Leslie, 103 F.3d 1093, 1104 (2d Cir.) (citations and internal quotation marks omitted), cert. denied, --- U.S. ----, 117 S.Ct. 1713, 137 L.Ed.2d 837 (1997).