Assuming you are looking for how to unit test a class which uses Google Guice Dependency Injection, here are a few things you can do:
First, you will want to create a test module which binds all of the dependencies that your class under test will need. You can do this by creating a module which extends com.google.inject.AbstractModule and overriding the configure() method. In this method, you will want to bind all of the dependencies that your class under test needs.
Next, you will want to create a test injector. To do this, you will need to create a com.google.inject.Injector and passing in your test module to the injector's createInjector() method.
Once you have your test injector, you can then use it to inject dependencies into your class under test. To do this, you will need to get the instance of your class under test from the injector, and then call the injector's injectMembers() method passing in your class under test.
You can then proceed to write your unit tests as normal.
For more information, please see the following links: