Matthias Noback: Test-driving repository classes - Part 2: Storing and retrieving entities
Matthias Noback has continued his series of tutorials covering various uses of the Repository design pattern. This is the second part of the series and picks up where part one left of, showing the handling of entities in the repository, performing the usual CRUD operations.
In part 1 of this short series (it's going to end with this article) we covered how you can test-drive the queries in a repository class. Returning query results is only part of the job of a repository though. The other part is to store objects (entities), retrieve them using something like a save() and a getById() method, and possibly delete them. Some people will implement these two jobs in one repository class, some like to use two or even many repositories for this. When you have a separate write and read model (CQRS), the read model repositories will have the querying functionality (e.g. find me all the active products), the write model repositories will have the store/retrieve/delete functionality.
In particular if you write your own mapping code (like I've been doing a lot recently), you need to write some extra tests to verify that the persistence-related activities of your repository function correctly.
He starts with the test cases for the functionality (following the test-drive design mentality) and talks about the expected behavior of the various entity and repository methods. He includes the code for these tests covering state changes, handling child entities, deleting entities, and working with ports/adapters.