This application is built using the Spring Boot framework and the Model-View-Controller (MVC) pattern. It allows for car rental operations to be performed through the CarService class, which acts as the controller.

The application does not have a database and instead uses storage classes (CarStorage and RentalStorage) to store the necessary information in a List data structure. The CarService class contains all the logic for performing car rental operations.

The CarService class has been tested using two types of tests:

• Unit tests (with mocking and without mocking)
• Integration test

Both types of tests ensure that the CarService class is functioning correctly and that all logic is working as intended.

To run the application, you will need to have the Spring Boot framework and a Java development environment set up on your machine. Once those are in place, you can run the application by executing the main method in the CarRentalApplication class.