How do I unit test persistence?

Question

As a novice in practicing test-driven development, I often end up in a quandary as to how to unit test persistence to a database.

I know that technically this would

Answer 1

Look into DB Unit. It is a Java library, but there must be a C# equivalent. It lets you prepare the database with a set of data so that you know what is in the database, then you can interface with DB Unit to see what is in the database. It can run against many database systems, so you can use your actual database setup, or use something else, like HSQL in Java (a Java database implementation with an in memory option).

If you want to test that your code is using the database properly (which you most likely should be doing), then this is the way to go to isolate each test and ensure the database has expected data prepared.

Answer 2

The problem I experienced when unit testing persistence, especially without an ORM and thus mocking your database (connection), is that you don't really know if your queries succeed. It could be that you your queries are specifically designed for a particular database version and only succeed with that version. You'll never find that out if you mock your database. So in my opinion, unit testing persistence is only of limited use. You should always add tests running against the targeted database.

Answer 3

For JDBC based projects, my Acolyte framework can be used: http://acolyte.eu.org . It allows to mockup data access you want to tests, benefiting from JDBC abstraction, without having to manage a specific test DB.

Answer 4

I would also mock the database, and check that the queries are what you expected. There is the risk that the test checks the wrong sql, but this would be detected in the integration tests