Think that you must remember that in an environment where there are many dependencies, you must have all the dependencies mapped and all paths should be tested.
Using services, they should be used with a large number of clients, so each client should follow the test cases.
Using services, you also need to pay attention to network problems. Do traditional tests, putting a lot of traffic on the network and turn it off to see how it works.
In addition, the provision of services does not require a different approach. Just control all inputs and outputs.