In City of Moorpark v. Superior Court (1998) 18 Cal. 4th 1143, 959 P.2d 752, our Supreme Court reviewed the evolution of the "public policy" tort discussed in Rojo v. Kliger (1990) 52 Cal. 3d 65, 276 Cal. Rptr. 130, 801 P.2d 373, Gantt v. Sentry Insurance (1992) 1 Cal. 4th 1083, 824 P.2d 680, Jennings v. Marralle (1994) 8 Cal. 4th 121, 876 P.2d 1074, and Stevenson v. Superior Court (1997) 16 Cal. 4th 880, 941 P.2d 1157, as follows: "In Stevenson, the Court articulated a four-part test for determining whether a particular policy can support a common law wrongful discharge claim. the policy must be: (1) delineated in either constitutional or statutory provisions; (2) public in the sense that it inures to the benefit of the public rather than serving merely the interests of the individual; (3) well established at the time of the discharge; and (4) substantial and fundamental. ( Stevenson, supra, 16 Cal. 4th at p. 894; see also Jennings v. Marralle, supra, 8 Cal. 4th at p. 130; Gantt, supra, 1 Cal. 4th at pp. 1090, 1095; Rojo, supra, 52 Cal. 3d at pp. 89-90.) Public policy as a concept is notoriously resistant to precise definition, and . . . courts should venture into this area, if at all, with great care . . . . ( Gantt, supra, 1 Cal. 4th at p. 1095.)