message: Add reminder to add tests
diff: @@ -120,6 +120,8 @@ impl PacketNumberDecoder {
  PacketNumberDecoder { expected: largest_acknowledged + 1 }
  }
  + // TODO(mt) test this. It's a strict implementation of the spec,
  + // but that doesn't mean we shouldn't test it.
  fn decode_pn(&self, pn: u64, w: usize) -> PacketNumber {
  let window = 1u64 << (w * 8);
  let candidate = (self.expected & !(window - 1)) | pn;
  