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

^14. Section 815.6 of the Government Code provides: "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." This requires that the plaintiff must prove that the defendant public entity failed to perform an express mandatory obligation that is imposed by statute. (Eastburn v. Regional Fire Protection Authority (2003) 31 Cal.4th 1175, 1179-1180; Gray v. State of California (1989) 207 Cal.App.3d 151.)