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I am working on a project that makes some brain-twisting changes to a database. It is the first database work I have done in a while, the changes are a bit tricky, and the consequences of failure grim (breaking large production databases in use by many thousands of customers daily), so I am writing unit tests for everything using DbUnit.
DbUnit has one feature that I really like - the setUp() method of a test case can initialize the database to a known state. This feature alone is enough to adopt DbUnit.
What really stands out is how slowly I am making progress. There are many reasons for this - I am learning the problem domain as I go along, the problem has a number of wrinkles to it. But part it is that writing the unit tests is just plain hard.
Often unit testing is pretty simple - pass a few parameters to a function, check the result. Repeat for a few different sets of parameters. Sometimes there is a structure to be set up or checked. It's easy to work in small bites.
For this project, each test case requires the database to be set up. With DbUnit, this means creating an XML file that reflects the desired state of the database tables. These files are hard to read and hard to create when the table has foreign keys to another table. In my case, one of the tables represents a tree structure so it is essentially a list of parent-child relationships.
So first I have to figure out what will make a good test case. Then I create the XML file, either by hand editing or by somehow getting the database into the desired state and dumping it to XML. Finally I can write the actual test. This usually involves writing some queries to figure out if the database is in the correct state.
Then I can actually write the code to make the test pass. No wonder it is going slowly!
By the way I am writing the project in Jython. DbUnit works well with Jython because you don't have to subclass a DbUnit test case class - you can use DbUnit using independent objects and static assertions. I am writing the test cases with Python's unittest module and calling DbUnit as a library.
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