@Override
  public PositionReader openPositionRead(String path, long fileLength) {
    return new GCSPositionReader(mClient, mBucketName, stripPrefixIfPresent(path), fileLength);
  }
@Test
  public void testOpenPositionRead() {
    PositionReader result = mGCSUnderFileSystem.openPositionRead(KEY, 1L);
    Assert.assertTrue(result instanceof GCSPositionReader);
  }