public Promise<Void> gracefullyShutdownClientChannels() {
        return gracefullyShutdownClientChannels(ShutdownType.SHUTDOWN);
    }
@Test
    void connectionsNotForceClosed() throws Exception {
        String configName = "server.outofservice.close.timeout";
        AbstractConfiguration configuration = ConfigurationManager.getConfigInstance();

        DefaultEventLoop eventLoop = spy(EVENT_LOOP);
        shutdown = new ClientConnectionsShutdown(channels, eventLoop, null);

        try {
            configuration.setProperty(configName, "0");
            createChannels(10);
            Promise<Void> promise = shutdown.gracefullyShutdownClientChannels(ShutdownType.OUT_OF_SERVICE);
            verify(eventLoop, never()).schedule(isA(Runnable.class), anyLong(), isA(TimeUnit.class));
            channels.forEach(Channel::close);

            promise.await(10, TimeUnit.SECONDS);
            assertTrue(channels.isEmpty(), "All channels in group should have been closed");
        } finally {
            configuration.setProperty(configName, "30");
        }
    }