public void init() {
        if (isInitiated.compareAndSet(false, true)) {
            Assert.notNull(applicationContext, () -> "Application must not be null");
            Map<String, ReadinessCheckCallback> beansOfType = applicationContext
                    .getBeansOfType(ReadinessCheckCallback.class);
            readinessCheckCallbacks = HealthCheckComparatorSupport.sortMapAccordingToValue(beansOfType,
                    HealthCheckComparatorSupport.getComparatorToUse(applicationContext.getAutowireCapableBeanFactory()));

            String applicationCallbackInfo = "Found " + readinessCheckCallbacks.size() + " ReadinessCheckCallback implementation: " + String.join(",", beansOfType.keySet());
            logger.info(applicationCallbackInfo);
        }
    }
@Test
    public void applicationContextNull() {
        assertThatThrownBy(() -> new ReadinessCheckCallbackProcessor().init()).hasMessage("Application must not be null");
    }