Our project looks cool, but it's too simple and it is far from being a real project. It still doesn't use external resources. A database is required by Java projects so we'll try to introduce it, as well.

What is the common way to test code that uses external resources or third-party libraries? Mocks are the answer. A mock object, or simply a mock, is a simulated object that can be used to replace real ones. They are very useful when objects that depend on external resources are deprived of them.

In fact, you don't need a database at all while you are developing the application. Instead, you can use mocks to speed up development and testing and use a real database connection only at runtime. Instead of spending time setting up a database and preparing test data, we can focus on writing classes and think about them later on during integration time.

For demonstration purposes, we'll introduce two new classes. The Person class and the FriendCollection class that are designed...