    @Test
    public void checkExecutors() {

        ExecutionSource executions = Mockito.mock(ExecutionSource.class);
        ExecutorEventListener eventListener = null;
        Configuration configuration = Mockito.mock(Configuration.class);
        Mockito.when(configuration.getExecutorUri()).thenReturn("iri");
        ExecutorRestClient restClient = null;
        CheckExecutor checker = Mockito.mock(CheckExecutor.class);
        ExecutorService service = new ExecutorService(
                executions, eventListener, configuration, restClient, checker);
        service.onInit();
        //
        Mockito.verify(checker, Mockito.times(1)).check(Mockito.any());
        service.checkExecutors();
        Mockito.verify(checker, Mockito.times(2)).check(Mockito.any());
    }