public static UnionCoder of(List<Coder<?>> elementCoders) {
    return new UnionCoder(elementCoders);
  }
@Test
  public void testCoderIsSerializable() {
    CoderProperties.coderSerializable(
        UnionCoder.of(ImmutableList.of(StringUtf8Coder.of(), DoubleCoder.of())));
  }