message: add match on the sumtype
diff: @@ -366,6 +366,7 @@ mod tests {
  let b = cbor::decode_from_cbor(GET_BLOCK_HEADER_BYTES).unwrap();
  match b {
  BlockHeaderResponse::Ok(ll) => assert!(ll.len() == 1),
  + BlockHeaderResponse::Err(error) => panic!("test failed: {}", error)
  }
  }
  