public static BitSetCoder of() {
    return INSTANCE;
  }
@Test
  public void testRegisterByteSizeObserver() throws Exception {
    CoderProperties.testByteCount(
        ByteArrayCoder.of(), Coder.Context.OUTER, new byte[][] {{0xa, 0xb, 0xc}});

    CoderProperties.testByteCount(
        ByteArrayCoder.of(),
        Coder.Context.NESTED,
        new byte[][] {{0xa, 0xb, 0xc}, {}, {}, {0xd, 0xe}, {}});
  }