Testing a Windows service, for an application with client-server architecture

I am a software test engineer and want to test a new windows service for my application which has a client server architecture. The service keeps running on the background and checks for the database updates. It is developed by Delphi. The developers have debugged and tested the service. My question is what should be the testing approach to test a windows service, or what kind of test should a tester have to perform on a windows service? And how can this test be executed?