You may also use Dagger instead of Guice for dependency injection. Dagger is also a recommended framework from AWS for lightweight dependency injection. You can technically use Spring for dependency injection, but it is not recommended because of its bigger size.

You may use TestNG instead of JUnit for unit testing. TestNG provides additional features such as DataProviders. DataProviders allow you to supply an array with all possible inputs and their expected values for a single test method. With JUnit, you will have to write a test method per input combination. You may also use Hamcrest to create more flexible expressions in tests.