Unit testing after adding database with Hibernate

You could start the database transaction before each test:

@PersistenceContext
private EntityManager em; 

@Before
public void init() {
    em.getTransaction().begin();
}

@After
public void destroy() {
    em.getTransaction().rollback();
}

This way, each test has a transaction running before the test starts and this transaction is rolled back after the test finishes, so you always discard all changes the current test underwent.

I think we should be clear with the definition of Unit Test. Unit Test must only test a small unit (a public method) in the application.

Assuming you have a DAO layer which uses Hibernate to interact with Database. Now the Hibernate uses a SessionFactory that requires a dataSource. The data source of the Unit Test should not be same as the one for your production application.

The idea is to define a test datasource and use a in memory DB (hsqldb or any other). For each of the test case you can execute some queries on the in memory DB, using the test dataSource and clear that after the execution of the Unit Test. For each Unit Test you should execute the query so that the test data setup is done for that particular test.

For e.g.: If you want to test the following: 1) Create Account 2) Update Account 3) Delete Account

Then there are three test scenarios and there can bee multiple Unit Tests possible for each of the scenario.

Now before executing the Create Account Test, it is important that the DB doesn't have this account. and then you call the createAccount method in the DAO to test the same. No need to verify if the result is in DB or not. Just check the return of your method and if it is same as expected on a successful account creation then your test case should pass.

For Update Account, your setup method should insert one account through query and then you must call the updateAccount in DAO for this account id and so on.

Please stick to the definition of Unit Tests and do not use it for testing more than one functionality at a time.

Hope this helps.