What is the test for admitting or excluding expert testimony at trial?

The trial court has broad discretion in determining whether to admit or exclude expert testimony, and we do not interfere with the trial court's exercise of that discretion unless it was clearly abused. ( People v. Cornwell (2005) 37 Cal.4th 50, 81, 33 Cal.Rptr.3d 1, 117 P.3d 622.)