What is the test for retaining jurisdiction over state law claims in a civil action?

In any civil action of which the district courts have original jurisdiction, the district courts shall have supplemental jurisdiction over all other claims that are so related to claims in the action within such original jurisdiction that they form part of the same case or controversy under Article III of the United States Constitution. 28 U.S.C. 1367(a). However, once judicial power exists under 1367(a), retention of supplemental jurisdiction over state law claims under 1367(c) is discretionary. Acri v. Varian Assoc., Inc., 114 F.3d 999, 1000 (9th Cir. 1997).