@Override
    public Checkpoint read(String fileName) throws IOException {
        return read(
            ByteBuffer.wrap(Files.readAllBytes(dirPath.resolve(fileName)))
        );
    }
@Test
    public void read() throws Exception {
        URL url = this.getClass().getResource("checkpoint.head");
        io = new FileCheckpointIO(Paths.get(url.toURI()).getParent());
        Checkpoint chk = io.read("checkpoint.head");
        assertThat(chk.getMinSeqNum(), is(8L));
    }