What is the test for expert testimony in criminal law?

"Expert testimony is admissible to establish the existence, composition, culture, habits, and activities of street gangs; a defendant's membership in a gang; gang rivalries; the 'motivation for a particular crime, generally retaliation or intimidation'; and 'whether and how a crime was committed to benefit or promote a gang.' " (People v. Hill (2011) 191 Cal.App.4th 1104, 1120.) Until recently, experts could testify about out-of-court statements upon which they had relied in forming their opinions even if the statements

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