### Question:
BlockDirectoryCache implements Cache { @Override public void renameCacheFile(String source, String dest) { Integer file = _names.remove(source); if (file != null) { _names.put(dest, file); } } BlockDirectoryCache(BlockCache blockCache); @Override void delete(String name); @Override void update(String name, long blockId, int blockOffset, byte[] buffer, int offset, int length); @Override boolean fetch(String name, long blockId, int blockOffset, byte[] b, int off, int lengthToReadInBlock); @Override long size(); @Override void renameCacheFile(String source, String dest);  }### Answer:
@Test public void validateEmptyOutputFile() { blockDirectoryCache.renameCacheFile("foo", "bar"); }