@Override
  protected OutputStream createObject(String key) throws IOException {
    return new GCSOutputStream(mBucketName, key, mClient,
        mUfsConf.getList(PropertyKey.TMP_DIRS));
  }
@Test
  public void testCreateObject() throws IOException, ServiceException {
    // test successful create object
    Mockito.when(mClient.putObject(ArgumentMatchers.anyString(),
        ArgumentMatchers.any(GSObject.class))).thenReturn(null);
    OutputStream result = mGCSUnderFileSystem.createObject(KEY);
    Assert.assertTrue(result instanceof GCSOutputStream);
  }