Subaru 2002 Legacy Outback overheating city & highway

Recently my 2002 Outback has been overheating while in city traffic. When this happens - I turn on my fans to cool down the engine. On the highways the car seems okay - but while making appointments yesterday - it was acting up on the highway as well. From what I have gathered off other discussion links is that it could be a head gasket issue or something with the radiator fans not cooling the engine. I am taking it to the dealer tomorrow for them to have a look at it. I have the car under warranty - how do I make sure dealership runs proper tests to diagnose my issue?

Let them make the diagnosis/correction and report back. It will get documented and they are on the hook. Try to avoid driving it in this condition and do not share the information you have been. You are causing more severe damage by letting it overheat in a continuous manner. Good luck