There are two general categories to GIS work. Much of GIS activity is performed be people who are an expert in a field other than GIS and who apply spatial technologies to their work. These people might be in Civil Service titles related to environmental, transportation, public safety, land management or scientific disciplines to name a few. In those cases, the GIS skills should be part the Civil Service requirements and testing along with lots of other skills needed in those fields.
For those people who focus on GIS as a discipline, the Information Technology Civil Service title series is most often used. The most common entry into the IT series for GIS work is through the Information Technology Specialist 2 (ITS2) title. To get on the ITS2 list, applicants do not need to sit for a traditional written exam, but rather apply on-line and fill out the education and skills inventory. Applications are accepted continuously. https://www.cs.ny.gov/pstit/announ.cfm.
In filling out the ITS2 be sure to apply for both the standard ITS2 and the ITS2 (Programming).