What is the test for admitting expert testimony at trial?

"A trial court's decision to admit expert testimony is reviewed for abuse of discretion. [Citation.]" (People v. Lindberg (2008) 45 Cal.4th 1, 45.) "[A]lthough expert testimony is generally inadmissible on topics 'so common' that jurors of ordinary knowledge and education could reach a conclusion as intelligently as the expert, an expert may testify on a subject about which jurors are not completely ignorant. [Citations.] In determining the admissibility of expert testimony, 'the pertinent question is whether, even if jurors have some knowledge of the subject matter, expert opinion testimony would assist the jury.' [Citations.]" (Ibid.)