verify(mockClient).prepareSearch("test-index");
    }

    /**
     * Test: Verify that OnConnectListener is properly invoked
     */
    @Test
    public void testOnConnectListenerInvoked() {
        final AtomicBoolean listenerCalled = new AtomicBoolean(false);
        final OnConnectListener listener = () -> listenerCalled.set(true);

        fesenClient.addOnConnectListener(listener);

    /**
     * The address of the OpenSearch instance.
     */
    protected String address;

    /**
     * List of listeners for connection events.
     */
    protected List<OnConnectListener> onConnectListenerList = new CopyOnWriteArrayList<>();

    /**
     * Flag indicating whether the client is connected.
     */
    private volatile boolean connected;

    /**