California Code, Government Code - GOV § 19253

Subject to approval by the department, an appointing power with the concurrence or at the request of an employee may request the voluntary demotion of such employee to a vacant position.

If the class to which the demotion is proposed requires qualifications, knowledges, or abilities not measured by the examination for the class from which demotion is proposed, the department may examine the employee for the possession of those additional qualifications, knowledges, and abilities.