@Override
  public Optional<String> getContentHash() {
    return Optional.ofNullable(mContentHash);
  }
@Test
  public void close() throws Exception {
    mStream.close();
    Mockito.verify(mMockS3Client, never())
        .initiateMultipartUpload(any(InitiateMultipartUploadRequest.class));
    Mockito.verify(mMockS3Client, never())
        .completeMultipartUpload(any(CompleteMultipartUploadRequest.class));
    assertTrue(mStream.getContentHash().isPresent());
    assertEquals("putTag", mStream.getContentHash().get());
  }