CurrentChampionGetter can get the current champion somehow This is a declaration of intent. Whoever asks for this interface is going to ask for "som

Db does some IO with a database, mocked here for simplicity

GSLDataStore knows how to get GSL data

GSLDataStore knows how to get GSL data

Leaderboard knows how to interact with top users

Notifier sends notifications to the user Actual implementation doesn't matter here, we're just including this to have something other than a database

TopScoreNotifier notifies users they have a high score As above, focus on how this feels to read in terms of understanding the code in this package.

TopUserGetter gets top users from somewhere Notice that we're tying ourselves to the database package here, but we'll live with it. The important pa

User represents a user as it's stored in the database

UserDataStore can access and modify user data This is a little more broad and we're assuming the same type will have all these methods, but that's a

A simple mock that lets us specify who the current champion is, or even what error to return to test our error handling!

We mock our interface here; notice how simple and self-contained this can be when we don't have to worry about the full database functionality!