The the three prong test to determine whether a duty is mandatory under Gov. Code 815.6

Tirpak v. Los Angeles Unified School Dist., 187 Cal. App. 3d 639 (1986)

There is a three-prong test for ascertaining if liability may be imposed on a public entity under this statute. These three prongs are: '(1) an enactment must impose a mandatory, not discretionary, duty [citation]; (2) the enactment must intend to protect against the kind of risk of injury suffered 643 by the party asserting section 815.6 as a basis for liability [citations]; and (3) breach of the mandatory duty must be a proximate cause of the injury suffered.' (State of California v. Superior Court (1984) 150 Cal. App.3d 848, 854 [197 Cal. Rptr. 914].)"