I gave to Google Guice the responsibility of wiring my objects. But, how can I test if the bindings are working well?
For example, suppose we have a class A
A
IMHO, you should not be testing that. The Google Guice guys have the unit tests to assert that the injections work as expected - after all, that's what Guice is designed to do. You should only be writing tests for your own code (A and B).