title: Jacoco doesn't detect interfaces
body: <p>I have configured Jacoco so that it generates a coverage reports when unit tests run.</p>
  
  <pre><code>&lt;plugin&gt;
              &lt;groupId&gt;org.jacoco&lt;/groupId&gt;
              &lt;artifactId&gt;jacoco-maven-plugin&lt;/artifactId&gt;
              &lt;version&gt;0.8.2&lt;/version&gt;
              &lt;executions&gt;
                  &lt;execution&gt;
                      &lt;id&gt;unit-test-prepare-agent&lt;/id&gt;
                      &lt;goals&gt;
                          &lt;goal&gt;prepare-agent&lt;/goal&gt;
                      &lt;/goals&gt;
                      &lt;configuration&gt;
                          &lt;propertyName&gt;surefireArgLine&lt;/propertyName&gt;
                          &lt;destFile&gt;${jacoco.report.directory}/jacoco-ut.exec&lt;/destFile&gt;
                      &lt;/configuration&gt;
                  &lt;/execution&gt;
                  &lt;execution&gt;
                      &lt;id&gt;unit-test-report&lt;/id&gt;
                      &lt;phase&gt;test&lt;/phase&gt;
                      &lt;goals&gt;
                          &lt;goal&gt;report&lt;/goal&gt;
                      &lt;/goals&gt;
                      &lt;configuration&gt;
                          &lt;dataFile&gt;${jacoco.report.directory}/jacoco-ut.exec&lt;/dataFile&gt;
                          &lt;outputDirectory&gt;${jacoco.report.directory}/jacoco-ut&lt;/outputDirectory&gt;
                      &lt;/configuration&gt;
                  &lt;/execution&gt;
      &lt;/executions&gt;
  &lt;/plugin&gt;
  </code></pre>
  
  <p>But for some reason it skips the dao package of the project, which contains the <code>Spring Data Jpa</code> repositories interfaces.</p>
  
  <p>For example, the following interface:</p>
  
  <pre><code>import com.shaunyl.website.dao;
  
  public interface ProductRepository extends JpaRepository&lt;Product, Long&gt;, JpaSpecificationExecutor&lt;Product&gt; {
  
      @Query(value = "SELECT p FROM Product p",
              countQuery = "SELECT COUNT(p) FROM Product p")
      Page&lt;Product&gt; findAll(Pageable pageable);
  }
  </code></pre>
  
  <p>has the following test:</p>
  
  <pre><code>@RunWith(SpringRunner.class)
  @DataJpaTest
  public class ProductRepositoryTests {
  
      private static final int INVENTORY_SIZE = 5;
  
      @Autowired
      ProductRepository productRepository;
  
      private Category[] categories;
  
      private List&lt;Product&gt; inventory;
  
      @Before
      public void setUp() {
          inventory = productRepository.saveAll(products(INVENTORY_SIZE));
          categories = inventory.stream().map(Product::getCategory).toArray(Category[]::new);
      }
  
  @Test
  public void shouldRetrieveOnePageOfProducts() {
      // given
      int PAGE = 0;
      int SIZE = 20;
      Pageable pageable = newUnsortedPage(PAGE, SIZE);
  
      // when
      Page&lt;Product&gt; products = productRepository.findAll(pageable);
  
      // then
      assertThat(products.getNumber()).isEqualTo(PAGE);
      assertThat(products.getNumberOfElements()).isEqualTo(INVENTORY_SIZE);
      assertThat(products)
              .as("categories are eagerly fetched")
              .extracting(Product::getCategory)
              .containsExactlyInAnyOrder(categories);
   }
  }
  </code></pre>
  
  <p>But in the Jacoco report, the dao package is skipped.
  I believe it's because the target class is instead an interface but I am not sure.</p>
  
  <p>Do you know what could be the problem, and how to fix it?</p>