What is the test for retaining jurisdiction over a state law claim?

Pursuant to 28 U.S.C. 1367(a), in any civil action in which the district court has original jurisdiction, the district court "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," except as provided in subsections (b) and (c). "[O]nce 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).