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copied!<p>First of all, make sure you distinguish between <em>unit tests</em> and <em>integration tests</em>. JUnit is just a framework that helps you organize and run the tests, but you have to determine the scope of your tests.</p> <p>I assume you're interested in defining a <strong>unit</strong> test of <code>CommentService.findAll()</code>. What does that mean? That means I'll verify that calling the <code>findAll()</code> method results in CommentService invoking the named query named by the <code>FIND_ALL</code> string constant.</p> <p>Thanks to dependency injection and stubbing, you can easily achieve that using e.g. <a href="http://mockito.org/" rel="noreferrer">Mockito</a> to stub out the <code>EntityManager</code>. For the unit test, we're only focusing on the business logic in <code>findAll()</code>, 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.</p> <pre><code>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! } } </code></pre> <p>With the unit test above, I tested the <strong>behavior</strong> of the <code>findAll()</code> 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.</p> <p>What's more, the unit test above verifies that the implementation of <code>findAll()</code> 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.</p> <p>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.</p>

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