Testing for exceptions in JUnit is something we have to deal with! We want to test if an exception occurs in a particular situation, or even if the exception contains a particular message. The question is: How to test for an exception in Junit? What we see very often is this:

import org.junit.Test;

public class JDrivenServiceTest {

    JDrivenService service = new JDrivenService();

    @Test(expected = ArticleNotFoundException.class)
    public void testPublishArticle_WithException() throws Exception {
        service.publishArticle(null);
    }
}

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Mockito is a mock framework which you can use to write simple and clean tests. One of it’s nice features is the ArgumentMatcher. With the ArgumentMatcher you can determine the outcome of your mocked service or repository based on any condition you want. Imagine we have a CandyService which can get a list of candies which are liked by a specific customer. This service uses the external ChocalateService which specifically checks if the customer likes chocolate. The CandyServiceTest class looks like this:

@RunWith(MockitoJUnitRunner.class) // will initiate and inject the mocks

public class CandyServiceTest {

    @Mock
    private ChocolateService chocolateService;

    @InjectMocks
    private CandyService candyService = new CandyServiceImpl();

    @Test
    public void testCustomerLikesChocolate() throws ParseException {
        Customer customer = new Customer();
        customer.setFirstName("Albert");
        List candiesLikedByCustomer = candyService.getCandiesLikeByCustomer(customer);
        assertTrue(candiesLikedByCustomer.contains(Candy.CHOCOLATE), "Expected customer to like chocolate");

    }

    @Test
    public void testCustomerWhoNotLikesChocolate() throws ParseException {
        Customer customer = new Customer();
        customer.setFirstName("Any other firstname");
        List candiesLikedByCustomer = candyService.getCandiesLikedByCustomer(customer);
        assertFalse(candiesLikedByCustomer.contains(Candy.CHOCOLATE), "Expected customer not to like chocolate");

    }
}

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