@Test
    void test() {
        CountDownLatch cdl = new CountDownLatch(1);
        SimpleMeterRegistry smr = new SimpleMeterRegistry();
        ExecutorService executorService =
            new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS,
                new SynchronousQueue<>()
            );

        Scheduler originalScheduler = Schedulers.fromExecutorService(executorService); // 1 thread - SynchronousQueue
        Scheduler timedScheduler = Micrometer.timedScheduler(originalScheduler, smr, "timed_scheduler");
        var meterIdStr = "timed_scheduler.scheduler.tasks.pending";
        RequiredSearch requiredSearch = smr.get(meterIdStr);
        LongTaskTimer longTaskTimer = requiredSearch.longTaskTimer();

        Runnable supp = () -> {
            try {
                cdl.await();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        };

        // 1 - Runnable is successfully submitted, but will be blocked by CDL
        Assertions.assertDoesNotThrow(() -> timedScheduler.schedule(supp));

        // 2nd is rejected because scheduler has only 1 thread and is currently busy with exec 1
        Assertions.assertThrows(RejectedExecutionException.class, () -> timedScheduler.schedule(supp));
        cdl.countDown(); // release 1st

        assertEquals(0, longTaskTimer.activeTasks(), "Expected no active task since 2nd submission has been rejected");
    }