What is the test for discharging a juror who is biased against police testimony?

Section 1089 confers upon trial courts "broad discretion" to discharge a deliberating juror upon a showing of good cause that the juror is "unable to perform his or her duty . . . ." (People v. Boyette (2002) 29 Cal.4th 381, 462, fn. 19.) "A juror who is actually biased is unable to perform the duty to fairly deliberate and thus is subject to discharge. [Citations.] Specifically, a bias against law enforcement officers that renders a juror unable to fairly weigh police testimony is grounds for the juror's replacement." (People v. Barnwell (2007) 41 Cal.4th 1038, 1051 (Barnwell).)