How can I write Unit Test for persist and flush exceptions

Question

I have the following code:

try {
  em.persist(myObject);
  em.flush();
}
catch (Exception e) {
  System.out.println("An Exception occur when trying to persist and flush");
}

In test I have mock my EntityManager with Mockito:

    @Mock
EntityManager mockEm;

but as persist and flush are void methods, I'm not able able to write something like:

when(mockEm.persist(anObject).then(doSomeThing);

How can I write unit testing (with JUnit)to mock em.persist and em.flush in order to test both cases with and without exception? Thanks.

Answer 1

I guess we need more details. For now, you can do something like this: (it's kind of pseudo-code).

@Test // it passess when there's one object in repository (I assume u have clean memory db)
public void shouldPersistMyObject() throws Exception {
    em.persist(myObject);
    em.flush();
    Assert.assertThat(dao.findAll(), Matchers.equalTo(1));
}

@Test(expected = <YourDesiredException>.class) // if <YourDesiredException> is thrown, your test passes
public void shouldThrowExceptionWhenSavingCorruptedData() {
    //set NULL on some @NotNull value, then save, like:
    myObject.setUserId(null);
    em.save(myObject); //exception is thrown
}