Unit tests would be good to ensure that updates don't break the library. Being a networking library however, this is rather difficult. Even mocking connections can't really test the library fully as the most basic functionality of the library is to establish a real connection over the web. Unit tests rely on code always working - they don't factor in dodgy internet connections, the lag of the real world, or what happens to servers under pressure.
I'll have to do some more reading on this. Let me know if you have any input.