How to simulate a DB for testing (Java)?

Question

I\'m programming in Java and my applications are making a lot of use of DB. Hence, it is important for me to be able to test my DB usage easily.
What DB tests are all ab

Answer 1

We're creating a database test environment at work right now. We feel we must use a real database management system with simulated data. One problem with a simulated DBMS is that SQL never really totally gelled as a standard, so an artificial testing environment would have to faithfully support our production database's dialect. Another problem is that we make extensive use of column value constraints, foreign key constraints, and unique constraints, and since an artificial tool probably wouldn't implement these, our unit tests could pass but our system tests would fail when they first hit the real constraints. If tests take too long, this indicates an implementation error and we would tune our queries (typically test data sets are miniscule compared to production).

We've installed a real DBMS on each developer machine and on our continuous integration and test server (we use Hudson). I don't know what your work policy restrictions are, but it's pretty easy to install and use PostgreSQL, MySQL, and Oracle XE. These are all free for development use (even Oracle XE), so there's no rational reason to prohibit their use.

The key issue is how do you guarantee that your tests always start out with the database in a consistent state? If the tests were all read-only, no problem. If you could engineer mutating tests to always run in transactions that never commit, no problem. But typically you need to worry about reversing updates. To do this you can export the initial state to a file, then importing it back post-test (Oracle's exp and imp shell commands do this). Or you can use a checkpoint/rollback. But a more elegant way is to use a tool like dbunit, which works well for us.

The key advantage to this is that we catch many more bugs up front where they're far easier to fix and our real system testing doesn't get blocked while developers feverishly try to debug problems. This means we produce better code faster and with less effort.