Class DoubleCheckTest

javatests/dagger/internal/DoubleCheckTest.java:40–170

import org.junit.runners.JUnit4;

@RunWith(JUnit4.class)
public class DoubleCheckTest {
  @Test
  public void provider_nullPointerException() {
    try {
      DoubleCheck.provider(null);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  @Test
  public void lazy_nullPointerException() {
    try {
      DoubleCheck.lazy(null);
      fail();
    } catch (NullPointerException expected) {
    }
  }

  private static final Provider<Object> DOUBLE_CHECK_OBJECT_PROVIDER =
      DoubleCheck.provider(Object::new);

  @Test
  public void doubleWrapping_provider() {
    assertThat(DoubleCheck.provider(DOUBLE_CHECK_OBJECT_PROVIDER))
        .isSameAs(DOUBLE_CHECK_OBJECT_PROVIDER);
  }

  @Test
  public void doubleWrapping_lazy() {
    assertThat(DoubleCheck.lazy(DOUBLE_CHECK_OBJECT_PROVIDER))
        .isSameAs(DOUBLE_CHECK_OBJECT_PROVIDER);
  }

  @Test
  public void get() throws Exception {
    int numThreads = 10;
    ExecutorService executor = Executors.newFixedThreadPool(numThreads);

    final CountDownLatch latch = new CountDownLatch(numThreads);
    LatchedProvider provider = new LatchedProvider(latch);
    final Lazy<Object> lazy = DoubleCheck.lazy(provider);

    List<Callable<Object>> tasks = Lists.newArrayListWithCapacity(numThreads);
    for (int i = 0; i < numThreads; i++) {
      tasks.add(
          () -> {
            latch.countDown();
            return lazy.get();
          });
    }

    List<Future<Object>> futures = executor.invokeAll(tasks);

    assertThat(provider.provisions.get()).isEqualTo(1);
    Set<Object> results = Sets.newIdentityHashSet();
    for (Future<Object> future : futures) {