@Override
    public Optional<Decision> onMemoryUsageChanged(
            int numTotalRequestedBuffers, int currentPoolSize) {
        return numTotalRequestedBuffers < currentPoolSize * releaseThreshold
                ? Optional.of(Decision.NO_ACTION)
                : Optional.empty();
    }
@Test
    void testOnUsedMemoryExceedThreshold() {
        final int poolSize = 10;
        final int threshold = (int) (poolSize * FULL_SPILL_RELEASE_THRESHOLD);
        Optional<Decision> memoryUsageChangedDecision =
                spillStrategy.onMemoryUsageChanged(threshold + 1, poolSize);
        assertThat(memoryUsageChangedDecision).isNotPresent();
    }