### Question:
DiffScriptBackupWriter implements BackupWriter { @Override public void flush() throws IOException { mWriter.flush(); } @VisibleForTesting  DiffScriptBackupWriter(SingleStreamDiffScriptWriter writer); static DiffScriptBackupWriter newInstance(OutputStream outputStream); @Override void writeBytes(byte[] bytes); @Override void writeChunk(long start, int length); @Override long getBytesWritten(); @Override void flush();  }### Answer:
@Test public void flush_flushesWriter() throws IOException { mBackupWriter.flush(); verify(mDiffScriptWriter).flush(); }