IndexOutput out = directory.createOutput("packed-ints.bin", IOContext.DEFAULT);
mutable.save(out);
out.close();
IndexInput in = directory.openInput("packed-ints.bin", IOContext.DEFAULT);
PackedInts.Reader reader = PackedInts.getReader(in);
assertEquals(mutable.getBitsPerValue(), reader.getBitsPerValue());
assertEquals(valueCount, reader.size());
if (mutable instanceof Packed64SingleBlock) {
// make sure that we used the right format so that the reader has