@Override
  public <K, T> UncommittedBundle<T> createKeyedBundle(
      StructuralKey<K> key, PCollection<T> output) {
    return UncommittedImmutableListBundle.create(output, key);
  }
@Test
  public void keyedWithVarIntKeyShouldCreateKeyedBundle() throws Exception {
    createKeyedBundle(VarIntCoder.of(), 1234);
  }