public CompletableFuture<Void> getAvailabilityFuture() {
        return currentFuture;
    }
@Test
    public void testUnavailableWhenEmpty() {
        final FutureCompletingBlockingQueue<Object> queue = new FutureCompletingBlockingQueue<>();
        assertThat(queue.getAvailabilityFuture().isDone()).isFalse();
    }