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