What is the test for appeal from a judgment that disposes fewer than all causes of action between the parties?

"[Code of Civil Procedure s]ection 904.1, subdivision (a) allows appeal '[f]rom a judgment, except . . . an interlocutory judgment . . . .' "² (Kurwa v. Kislinger (2013) 57 Cal.4th 1097, 1101 (Kurwa).)³ This rule, which is known as the one final judgment rule, precludes an appeal from a judgment disposing of fewer than all causes of action extant between the parties, even if the remaining causes of action have been severed for trial from those decided by the judgment. A judgment that disposes of fewer than all causes of action asserted by two parties against each other is necessarily " ' "interlocutory" ' " and, thus, not final if any cause of action remains pending between them. (Ibid.) The theory underlying the requirement of finality is that piecemeal dispositions and multiple appeals in a single action would be oppressive and costly and that a review of the superior court's intermediate rulings should await the final disposition of the case. (Id. at p. 1102.)

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