message: remove the loop and simply use the modulo of the MAX_COIN
diff: @@ -21,17 +21,8 @@ impl Arbitrary for Wrapper<config::ProtocolMagic> {
  impl Arbitrary for Wrapper<coin::Coin> {
  fn arbitrary<G: Gen>(g: &mut G) -> Self {
  - let mut coin = coin::Coin::zero();
  - while {
  - let v = <u64 as Arbitrary>::arbitrary(g);
  - if let Ok(r) = coin::Coin::new(v) {
  - coin = r;
  - false
  - } else {
  - true
  - }
  - } {}
  - coin.into()
  + let value = u64::arbitrary(g) % coin::MAX_COIN;
  + coin::Coin::new(value).unwrap().into()
  }
  }
  