What is the test for determining whether a policy has been a violation of the constitutional right to exercise power?

right; and (4) that the policy is the 'moving force behind the constitutional violation.'" Oviatt By & Through Waugh v. Pearce, 954 F.2d 1470, 1474 (9th Cir.1992) (quoting City of Canton v. Harris, 489 U.S. 378, 389-91 (1989)). A policy is "a deliberate choice to follow a course of action . . . made from among various alternatives by the official or officials responsible for establishing final policy with respect to the subject matter in question." Id. at 1477 (quoting Pembaur v. City of Cincinnati, 475 U.S. 469, 481 (1986) (plurality opinion)).