### Question:
RocksdbObjectDatabase extends RocksdbObjectStore implements ObjectDatabase { public @Override synchronized void open() { if (isOpen()) { return; } super.open(); try { File blobsDir = new File(super.dbDirectory, "blobs"); File graphDir = new File(super.dbDirectory.getParentFile(), "graph.rocksdb"); blobsDir.mkdir(); graphDir.mkdir(); this.blobs = new RocksdbBlobStore(blobsDir, isReadOnly()); this.graph = new RocksdbGraphDatabase(graphDir, isReadOnly()); this.graph.open(); } catch (RuntimeException e) { close(); throw e; } } RocksdbObjectDatabase(@NonNull File dbdir, boolean readOnly); @Override RocksdbBlobStore getBlobStore(); @Override GraphDatabase getGraphDatabase(); @Override synchronized void open(); @Override synchronized void close(); @Override boolean put(final RevObject object);  }### Answer:
@Test public void testOpenTwice() { assertTrue(db.isOpen()); db.open(); assertTrue(db.isOpen()); }