I have a weird scenario where I am creating an empty List as a class variable, then I have a scheduler that updates that list. In my tests, I want to be able to see whether or not that List was updated. But from my understanding this isn't possible.

public class Scheduler {

    private List<String> list = new ArrayList<>(); //want to track this variable in my test
    private final ListAccessor listAccessor;

    Scheduler(final ListAccessor listAccessor) {
        this.listAccessor = listAccessor

        scheduler.scheduleAtFixedRate(this::updateString, 1, TimeUnit.HOURS);
    }

    public void updateString() {
        try {
            list = listAccessor.getUpdatedList(someParam); //want to see the value in my test after it gets updated
            log.info("Successfully updated list");
        } catch (final Exception e) {
            log.error("Failed to get updated list", e);
        }
    }

}

    @Test
    public void testCheckForUpdate_listAccessorThrewError() {
        Mockito.when(listAccessor.getUpdatedList(someParam)).thenThrow(Exception.class);
        // assert that the list in my class wasn't updated
    }

Is something like this possible? I don't want to throw any errors when the list fails to update, so it seems the only way is to spy on the list somehow. Any help appreciated