@Override
    public int sizeIdx2size(int sizeIdx) {
        return sizeClass.sizeIdx2size(sizeIdx);
    }
@Test
    public void testSizeIdx2size() {
        SizeClasses sc = new SizeClasses(PAGE_SIZE, PAGE_SHIFTS, CHUNK_SIZE, 0);
        PoolArena<ByteBuffer> arena = new PoolArena.DirectArena(null, sc);
        for (int i = 0; i < arena.sizeClass.nSizes; i++) {
            assertEquals(arena.sizeClass.sizeIdx2sizeCompute(i), arena.sizeClass.sizeIdx2size(i));
        }
    }