@Override
    public void shutdown() {
        scheduledExecutorService.shutdown();
        try {
            web3jService.close();
        } catch (IOException e) {
            throw new RuntimeException("Failed to close web3j service", e);
        }
    }
@Test
    public void testStopExecutorOnShutdown() throws Exception {
        web3j.shutdown();

        verify(scheduledExecutorService).shutdown();
        verify(service).close();
    }