final FessMessages result = messages.addErrorsOperationAlreadyRunning("testProperty", "host1");
        assertNotNull(result);
        assertFalse(result.isEmpty());
        assertTrue(result.hasMessageOf("testProperty"));
    }

    @Test
    public void test_addErrorsOperationAlreadyRunning_withDifferentHosts() {
        final FessMessages messages1 = new FessMessages();