What is the test for a motion to exclude a prospective juror from a jury?

motion is not whether there is a pattern of systematic exclusion; rather, the issue is whether a particular prospective juror has been challenged because of group bias. [Citation.] But in drawing an inference of discrimination from the fact one party has excused most or all members of a cognizable group [citation], a court finding a prima facie case is necessarily relying on an apparent pattern in the party's challenges. Although circumstances may be imagined in which a prima facie case could be shown on the basis of a single excusal, in the ordinary case, including this one, to make a prima facie case after the excusal of only one or two members of a group is very difficult. (People v. Bell (2007) 40 Cal.4th 582, 598, fn. 3, 54 Cal.Rptr.3d 453, 151 P.3d 292.)