Testing an EJB with JUnit

Question

How should I test an EJB 3.1 which gets an instance of EntityManager injected?

A possible EJB:

@Stateless
@LocalBean
public class CommentService {

    @PersistenceContext
    private EntityManager em;

    public List<Comment> findAll() {
        TypedQuery<Comment> query = em.createNamedQuery(
            Comment.FIND_ALL, Comment.class
        );
        return query.getResultList();
    }

}

A possible test:

@Test
public void testFindAll() {
    List<Comment> all = service.findAll();
    Assert.assertEquals(8, all.size());
}

I am only using GlassFish 3.1 and Eclipse Indigo for Java EE Developers. I already tried things like that:

@Before
public void setUp() throws Exception {
    ejbContainer = EJBContainer.createEJBContainer();
    service = (CommentService) ejbContainer.getContext()
        .lookup("java:global/classes/CommentService");
}

But all I got was:

javax.ejb.EJBException:
No EJBContainer provider available: no provider names had been found.

Answer 1

First of all, make sure you distinguish between unit tests and integration tests. JUnit is just a framework that helps you organize and run the tests, but you have to determine the scope of your tests.

I assume you're interested in defining a unit test of CommentService.findAll(). What does that mean? That means I'll verify that calling the findAll() method results in CommentService invoking the named query named by the FIND_ALL string constant.

Thanks to dependency injection and stubbing, you can easily achieve that using e.g. Mockito to stub out the EntityManager. For the unit test, we're only focusing on the business logic in findAll(), so I won't bother testing lookup of the Comment service either--testing that the Comment service can be looked up and is wired to a proper entity manager instance is in the scope of an integration test, not a unit test.

public class MyCommentServiceUnitTest {
    CommentService commentService;
    EntityManager entityManager;

    @Before
    public void setUp() {
        commentService = new CommentService();

        entityManager = mock(EntityManager.class);
        commentService.setEm(entityManager); // inject our stubbed entity manager
    }

    @Test
    public void testFindAll() {
        // stub the entity manager to return a meaningful result when somebody asks
        // for the FIND_ALL named query
        Query query = mock(Query.class);
        when(entityManager.createNamedQuery(Comment.FIND_ALL, Comment.class)).thenReturn(query);
        // stub the query returned above to return a meaningful result when somebody
        // asks for the result list
        List<Comment> dummyResult = new LinkedList<Comment>();
        when(query.getResultList()).thenReturn(dummyResult);

        // let's call findAll() and see what it does
        List<Comment> result = commentService.findAll();

        // did it request the named query?
        verify(entityManager).createNamedQuery(Comment.FIND_ALL, Comment.class);
        // did it ask for the result list of the named query?
        verify(query).getResultList();
        // did it return the result list of the named query?
        assertSame(dummyResult, result);

        // success, it did all of the above!
    }
}

With the unit test above, I tested the behavior of the findAll() implementation. The unit test verified that the correct named query is obtained and that the result returned by the named query was returned to the callee.

What's more, the unit test above verifies that the implementation of findAll() is correct independently of the underlying JPA provider and the underlying data. I don't want to test JPA and the JPA provider unless I suspect there are bugs in the 3rd party code, so stubbing out these dependencies lets me focus the test entirely on the business logic of the Comment service.

It can take a little while to adjust to the mindset of testing behavior using stubs, but it is a very powerful technique for testing the business logic of your EJB 3.1 beans because it lets you isolate and narrow the scope of each test to exclude external dependencies.