//                                                                           =========
    private static final DuplicateHostDbm _instance = new DuplicateHostDbm();

    private DuplicateHostDbm() {
    }

    public static DuplicateHostDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    List<Future<String>> results;

    results = service.invokeAll(callables);
    assertThat(getOnlyElement(results)).isInstanceOf(TrustedListenableFutureTask.class);

    results = service.invokeAll(callables, 1, SECONDS);
    assertThat(getOnlyElement(results)).isInstanceOf(TrustedListenableFutureTask.class);

    /*
     * TODO(cpovirk): move ForwardingTestCase somewhere common, and use it to

    //                                                                           =========
    private static final AccessTokenDbm _instance = new AccessTokenDbm();

    private AccessTokenDbm() {
    }

    public static AccessTokenDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final FavoriteLogDbm _instance = new FavoriteLogDbm();

    private FavoriteLogDbm() {
    }

    public static FavoriteLogDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final GroupDbm _instance = new GroupDbm();

    private GroupDbm() {
    }

    public static GroupDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final LabelTypeDbm _instance = new LabelTypeDbm();

    private LabelTypeDbm() {
    }

    public static LabelTypeDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final BadWordDbm _instance = new BadWordDbm();

    private BadWordDbm() {
    }

    public static BadWordDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final FailureUrlDbm _instance = new FailureUrlDbm();

    private FailureUrlDbm() {
    }

    public static FailureUrlDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final CrawlingInfoParamDbm _instance = new CrawlingInfoParamDbm();

    private CrawlingInfoParamDbm() {
    }

    public static CrawlingInfoParamDbm getInstance() {
        return _instance;
    }

    // ===================================================================================

    //                                                                           =========
    private static final WebAuthenticationDbm _instance = new WebAuthenticationDbm();

    private WebAuthenticationDbm() {
    }

    public static WebAuthenticationDbm getInstance() {
        return _instance;
    }

    // ===================================================================================