What is the test for a successful party to claim attorney fees in a personal injury action?

"An important exception to the American rule that litigants are to bear their own attorney fees is found in [Code of Civil Procedure] section 1021.5" (Graham v. DaimlerChrysler Corp. (2004) 34 Cal.4th 553, 565, fn. omitted.) Code of Civil Procedure section 1021.5 provides in part: "Upon motion, a court may award attorneys' fees to a successful party against one or more opposing parties in any action which has resulted in the enforcement of an important right affecting the public interest if: (a) a significant benefit, whether pecuniary or nonpecuniary, has been conferred on the general public or a large class of persons, (b) the necessity and financial burden of private enforcement . . . are such as to make the award appropriate, and (c) such fees should not in the interest of justice be paid out of the recovery, if any."