@VisibleForTesting
    public List<ResourceGroupSelector> getSelectors()
    {
        checkMaxRefreshInterval();

        if (selectors.get().isEmpty()) {
            throw new PrestoException(CONFIGURATION_INVALID, "No selectors are configured");
        }
        return selectors.get();
    }
@Test(expectedExceptions = PrestoException.class, expectedExceptionsMessageRegExp = "No selectors are configured")
    public void testInvalidConfiguration()
    {
        H2DaoProvider daoProvider = setup("selectors");
        H2ResourceGroupsDao dao = daoProvider.get();
        dao.createResourceGroupsTable();
        dao.createSelectorsTable();
        dao.insertResourceGroup(1, "global", "100%", 100, 100, 100, null, null, null, null, null, null, null, null, 0, null, ENVIRONMENT);

        DbManagerSpecProvider dbManagerSpecProvider = new DbManagerSpecProvider(daoProvider.get(), ENVIRONMENT, new ReloadingResourceGroupConfig());
        ReloadingResourceGroupConfigurationManager manager = new ReloadingResourceGroupConfigurationManager(
                (poolId, listener) -> {},
                new ReloadingResourceGroupConfig().setMaxRefreshInterval(Duration.valueOf("1ms")),
                dbManagerSpecProvider);

        manager.getSelectors();
    }