Enumeration<Integer> enumer = enumerate();
    Iterator<Integer> iter = Iterators.forEnumeration(enumer);

    assertFalse(iter.hasNext());
    assertThrows(NoSuchElementException.class, () -> iter.next());
  }

  @SuppressWarnings("DoNotCall")
  public void testForEnumerationSingleton() {
    Enumeration<Integer> enumer = enumerate(1);

    Enumeration<Integer> enumer = enumerate();
    Iterator<Integer> iter = Iterators.forEnumeration(enumer);

    assertFalse(iter.hasNext());
    assertThrows(NoSuchElementException.class, () -> iter.next());
  }

  @SuppressWarnings("DoNotCall")
  public void testForEnumerationSingleton() {
    Enumeration<Integer> enumer = enumerate(1);

    val route = selection.next()
    assertRoute(route, address, proxyA, dns.lookup(PROXY_A_HOST, 0), PROXY_A_PORT)
    routeDatabase.failed(route)
    routeSelector = newRouteSelector(address)

    // Confirm we enumerate both proxies, giving preference to the route from ProxyB.
    val selection2 = routeSelector.next()
    dns.assertRequests(PROXY_A_HOST, PROXY_B_HOST)