DAO Unit testing
I have been looking at EasyMock and tutorials/examples around using it for Unit Testing DAO classes, for an "outside container" test. However, I think most of them talk about testing the Service Layer instead, mocking the DAO class. I am a bit confused, is it really how you Unit Test the DAO layer?
Some would say that the tests interacting with DB & EJBs are actually Integration tests and not Unit tests but then how would you know if your SQL is correct (assuming no ORM) and your DAO inserts/queries the right data from your real (read, local database which is similar to that in production) database?
I read that DBUnit is a solution for such a situation. But my question is about using a framework like DBUnit "outside container". What if the DAO depends on some EJBs, how do we handle the transactions, what happens if there are triggers that update other tables on your inserts?
What is the best way to Unit Test only the DAOs with such dependencies?
Answer
Personally, I unit test DAOs by hitting some sort of test database, preferable the same type of database (not the SAME database, obviously) that your app uses in production.
I think if you do that, the test is more of an integration test, because it has a dependency on a running database. This approach has the benefit in that it is as close as possible to your running production environment. It has the downsides that you need test configuration, you need a running test database (either local to your machine or somewhere in your environment) and the tests can take longer to run. You also need to be sure to rollback the test data after tests execute.
Once DAOs are tested, definitely mock them to unit test your services.