Test via JUnit DAO class

Question

I have a DAO class in which I need to test method called getItemById() which returns Item object from DB's table.

As long as I understand I have to make an Item object in that test and check if it equals to returned from method? Or I have to just check if it returns an Item object?

What if table is empty or no row with that id at all?

Sorry, this is a quite newbie question, but I can't make it clear in my head. Please help!

Answer 1

Running tests against a database where you can't predict what's in it is not effective; any test that is resilient enough to accommodate changing data is going to be worthless for the purpose of confirming whether the code under test actually does the right thing. I would make the test use its own database instance, so that there's no question of interference from other users mucking up my test, or my test changing data out from under somebody else. The ideal choice would be an in-memory database like H2 , that the test can instantiate and throw away when it's done with it. That way the test can run anywhere (for instance on a CI server), with the same results.

The test needs to run the ddl to create the schema and populate the database before executing. There are different tools you can use for this. DbUnit is popular, there is also an alternative called DBSetup which is supposed to be less complicated. You can have separate test data for different scenarios. DbUnit has tools to extract data from a database to make it easier to create your test data.

Since the database is under your control and you can populate it as you wish, you should verify that the returned object's fields are what you expect based on the populated data. Make the test as specific as possible.

For testing the SQL and how the object is mapped to the resultset it makes sense to use a database. For some parts of this it would make sense to use a unit test that doesn't touch the database and uses mocks. For instance, it would be good to confirm that the connection gets closed in all cases, it's easier to use mocks than it is to cause a SQLException in your code.

Testing using mocks would be easier if the DBConnection class was injected instead of being instantiated within the method. If you changed the code to inject the DBConnection then you could write a unit test (one using mocks that doesn't use a database) that checks whether the connection gets closed.

Answer 2

To perform unit test you should walk by three steps:

1. Prepare test environement (eg. populate db with known test data)- so you wont ask is the table empty or not etc.
2. Perform test and assert result
3. Do cleanup - so test wont have influence on other tests

Besides, you should test all scenarios cuz you sholuld handle all of them