What is the test for expert testimony in a criminal action where a defendant claims she killed her abuser in self-defense?

"In a criminal action, expert testimony is admissible by either the prosecution or the defense regarding intimate partner battering and its effects, including the nature and effect of physical, emotional, or mental abuse on the beliefs, perceptions, or behavior of victims of domestic violence . . . ." (Evid. Code, 1107, subd. (a).) This statute is "intended as a rule of evidence only and no substantive change affecting the Penal Code is intended." (Id. at subd. (d).) When a defendant claims she killed her abuser in self-defense, the defense has the option to use expert testimony about battering syndrome and its effects on abused persons, to enable the jury to overcome stereotyped impressions about women who remain in abusive relationships. (People v. Humphrey (1996) 13 Cal.4th 1073, 1086.)

However, although an attorney may present expert testimony to assist the jury, there is no support for the claim that expert testimony must be presented by a defense attorney in every case. (People v. Datt (2010) 185 Cal.App.4th 942, 952.)

The decision whether to call a particular witness is a matter of trial tactics and strategy which a reviewing court generally may not second-guess, unless defendant shows an unreasonable failure to investigate. (People v. Bolin (1998) 18 Cal.4th 297,

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