@Override
  protected InputStream openObject(String key, OpenOptions options, RetryPolicy retryPolicy) {
    return new GCSInputStream(mBucketName, key, mClient, options.getOffset(), retryPolicy);
  }
@Test
  public void testOpenObject() throws IOException, ServiceException {
    // test successful open object
    Mockito.when(mClient.getObject(ArgumentMatchers.anyString(), ArgumentMatchers.anyString()))
        .thenReturn(new GSObject());
    OpenOptions options = OpenOptions.defaults();
    RetryPolicy retryPolicy = new CountingRetry(1);
    InputStream result = mGCSUnderFileSystem.openObject(KEY, options, retryPolicy);
    Assert.assertTrue(result instanceof GCSInputStream);
  }