What is the test for determining whether a public entity is liable for an injury caused by negligence?

Plaintiffs rely on Government Code section section 815.6 to establish the defendant's duty in this case. That section states, "Where a public entity is under a mandatory duty imposed by an enactment that is designed to protect against the risk of a particular kind of injury, the public entity is liable for an injury of that kind proximately caused by its failure to discharge the duty unless the public entity establishes that it exercised reasonable diligence to discharge the duty." The statute imposes liability on a public entity where an enactment imposes a mandatory rather than a discretionary duty which is intended to protect against the kind of risk suffered by the party seeking relief and breach of the mandatory duty was the proximate cause of the injury suffered. (State of California v. Superior Court (1984) 150 Cal.App.3d 848, 854, 197 Cal.Rptr. 914.)