What is the test for determining who is the "prevailing party" under section 1717 of the California Civil Code?

"In cases where Civil Code section 1717's definition of 'prevailing party' applies, the identification of the party entitled to a fee award must be determined by the final result of the litigation, i.e., after conclusion of the appeal if an appeal is taken. [Citations.] [] Thus, for example, if a litigant successfully obtains reversal on appeal of an unfavorable summary judgment on a contract cause of action, he or she cannot collect an award of attorney fees under [Civil Code] section 1717 until the case has been remanded, tried on the merits and reviewed on appeal, if an appeal is taken, because the party ultimately prevailing on the cause of action cannot be known with certainty until the case is at an end. If the successful appellant loses on the merits after trial, he or she will not be entitled to [Civil Code] section 1717 attorney fees for the appeal because he or she ultimately was not the prevailing party with respect to the contract cause of action." (Butler-Rupp v. Lourdeaux (2007) 154 Cal.App.4th 918, 928.)