Unnecessary unit test?
In my opinion No. There is hardly any behaviour at all. As soon you say "I have this method in my service layer" it make it much more obvious. Service layer provide communication and pretty much should orchestrate things. That's it. 

Note that Unit tests are good but have it unnecessary written they become a maintenance issue. 

Test your code which has behaviour from the customer's requirements point of view.

Typically you would have an acceptance type test or an integration test to cover service layer and other layers as well.