Chapter 17. Testing database access
Dependency is the key problem in software development at all scales.... Eliminating duplication in programs eliminates dependency.
Kent Beck, Test-Driven Development: By Example
This chapter covers
- Challenges of database testing
- Introduction to DbUnit
- Advanced DbUnit techniques
- DbUnit best practices
The persistence layer (or, roughly speaking, the database access code) is undoubtedly one of the most important parts of any enterprise project. Despite its importance, the persistence layer is hard to unit test, mainly because of the following issues:
- Unit tests must exercise code in isolation; the persistence layer requires interaction with an external entity, the database.
- Unit tests must be easy to write and run; code that accesses the database can be cumbersome.
- Unit tests must be fast to run; database access is relatively slow.
We call these issues the database unit testing impedance mismatch, in reference to the object-relational impedance mismatch (which describes the difficulties of using a relational database to persist data when an application is written using an object-oriented language).
The database-testing mismatch can be minimized using specialized tools, one of them being DbUnit. In this chapter, we show how DbUnit can be used to test database code, and we not only describe its basic concepts but also present techniques that make its usage more productive and the resulting code easier to maintain.