What is the test for res judicata?

The doctrine of res judicata rests upon the ground that the party to be affected ... has litigated, or had an opportunity to litigate the same matter in a former action in a court of competent jurisdiction, and should not be permitted to litigate it again to the harassment and vexation of his opponent. Public policy and the interest of the litigants alike require that there be an end to litigation. (Fairchild v. Bank of America (1958) 165 Cal.App.2d 477, 482, 332 P.2d 101, italics added.)