@Override
  public Coder<SqsCheckpointMark> getCheckpointMarkCoder() {
    return SerializableCoder.of(SqsCheckpointMark.class);
  }
@Test
  public void testCheckpointCoderIsSane() {
    SqsUnboundedSource source = new SqsUnboundedSource(mock(SqsIO.Read.class));
    CoderProperties.coderSerializable(source.getCheckpointMarkCoder());
  }