How it works...

We added a lightweight dependency injection framework, Guice, and modified code to incorporate it. We also used JUnit and Mockito to do unit testing of the code. Going deep into the working of Guice, JUnit, or Mockito is outside the scope of this book. But, you may ask any questions on the open source repository for the project (given in the introduction in Chapter 1, Getting Started with Serverless Computing on AWS).