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How should I unit test methods which their intent is querying the database and return some data? For other situations I can just mock the objects but in this case which I want to test whether they return the correct data, how should I check it isolated from db? Should I use some kind of special db? But then how should I configure that new db to work like the other one with all those columns, etc?

Thanks.

Update: Thanks to everyone, their responses leaded me to the correct path. I finally used debry. I just added a new persistence.xml for that. No other significant changes and it seems to be working now.

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    What specifically are you trying to test? If you're doing an integration test with a database you can either run against a real database, use an in-memory one, etc. Either way, yes, if there's a DB, you've need data that confirms ti the actual schema, at least to the extent your tests operate against it. Commented Jul 16, 2012 at 17:00
  • Thanks, so for example if I want to test debry. Inside the mothods of the class which I am testing I have persist(model) commands. So without changing the class code, can I just configure the environment to use debry instead of mysql? Commented Jul 16, 2012 at 17:17

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One approach I've used with great success is to use:

  1. Maven to build your project
  2. Liquibase (or Flyway) to manage your database schema, and versioning it
  3. H2 as an in-memory database that is started along with your tests.

There's a fair bit to learn there if you haven't used any of the above, but in my experience it was well worth it. This worked really well with a Spring application; with other setups your mileage may vary.

Maven should start an instance of the H2 database in-memory before doing any tests. In a Spring application, you can just specify your datasource with an H2 JDBC URL and it'll start automagically.

You can use Liquibase to run a set of XML scripts to set up your database schema, and then a separate file to populate them with test data (either by specifying different files when running Liquibase, or by using the context attribute of each changeSet). This can be done with Maven, or in Spring using a specific Liquibase bean.

From there you can test your application exactly as if it was a normal app. No need for mocking, and you get much more useful tests as a result. You may need to change your schema or otherwise work around SQL differences between H2 and your native RDBMS.

As an aside, I'm greatly in favour of these sorts of tests. In my experience mocking everything doesn't really gain you any interesting insights, and should be a last resort for when intra-build integration tests aren't possible. There are many that disagree with me though!

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The question is what behavior do you need to unit test? If you mocked out the database then you've tested all the important logic. Your database adapter will either work or not work, which you can verify in integration/acceptance tests against a real database.

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I have a huge class. Which works like this: It has several methods for example, getAssets() inside this method it creates a Hibernate criteria and then based on that returns assets from Asset table. So I want to test this method. If I use mocked objects and tell it what to return then I haven't actually tested the functionality of this class. Have I?
Or maybe I haven't understood mocking very well!
Ideally, all your access to external resources are provided by thin (minimal logic) adapter classes. You mock these classes to do your unit testing by seeing if the methods they contain are being called correctly. The adapters themselves are stupid and do not need to be heavily unit tested. Now, it doesn't always work this nicely in practice, if you post some of the code you need to unit test maybe we could help you better.
Thanks for your time, I have mocked the Model(entity) objects. The problem is one of my classes does not use that data model layer object and explicitly queries the db using Hibernate criterias. I ll post more details later on today. Thanks.
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You can use DBUnit. It takes your current schema and you can easily mock your data.

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