What is the test for attorney fees under section 1021.5 of the California Code of Civil Procedure?

Cal. Civ. Pro. Code 1021.5. "The decision whether the claimant has met his burden of proving each of these prerequisites and is thus entitled to an award of attorney fees under [Code of Civil Procedure] section 1021.5 rests within the sound discretion of the trial court and that discretion shall not be disturbed on appeal absent a clear abuse." New West Charter Middle School, 187 Cal. App. 4th at 849; see also Graham v. DaimlerChrysler Corp., 34 Cal.4th 553, 575 (Cal. 2004) ("[T]he Legislature has assigned responsibility for awarding fees under section 1021.5 not to automatons unable to recognize extortionists, but to judges expected and instructed to exercise discretion.") (quotation omitted).