What is the test for determining whether a plaintiff is a party to an arbitration agreement?

Bouton v. USAA Casualty Ins. Co. (2008),167 Cal.App.4th 412 [under Code Civ. Proc., 1281.2, subd. (a), "the trial court makes the preliminary determination whether the petitioner is a party to, or can otherwise enforce, an arbitration agreement"].) The statute contains this relevant exception: "If the court determines that there are other issues between the petitioner and the respondent which are not subject to arbitration and which are the subject of a pending action or special proceeding between the petitioner and the respondent and that a determination of such issues may make the arbitration unnecessary, the court may delay its order to arbitrate until the determination of such other issues or until such earlier time as the court specifies." (Code Civ. Proc., 1281.2, subd. (c), par. 3.)