🤔 to me it's not the same
having tests against a real REST api, there are numerous reasons things can fail that are not related to your code, like you mentioned internet, server goes down, the API changes, etc
Firebase Test Lab will run your instrumented tests on emulators or real devices, but it's still running your test code. These could be espresso tests, activity/fragment scenarios, etc. So it's still your environment to control. However, yes it's possible that there's service interruption (it did happen to me before)