Questions for my proyect about JUnitRunner and Espresso (Tests)

I have a couple of questions, to see if anyone can solve me.

I have an android app, which receives data from the server. Also I have a login screen, with buttons Sign In and Sign Up.

I want to make some tests on the SignUp and the SignIn to prove that receives the correct data when a user is logged correctly. I also want to check through tests if the server does not respond and the user can not be registered correctly, etc.

I want to use AndroidJUnitRunner (to check classes), and Espresso to check the steps of the GUI.

I you recommend?

Thank you very much.