message: Fix storage tests.
  Overwrites are not allowed.
diff: @@ -210,11 +210,11 @@ fn can_put_and_get_block() {
  let was_new = put_block(&mut harness, &mut storage, block.clone());
  assert!(was_new, "putting block should have returned `true`");
  - // Storing the same block again should work, but yield a result of `false`.
  + // Storing the same block again should work, but yield a result of `true`.
  let was_new_second_time = put_block(&mut harness, &mut storage, block.clone());
  assert!(
  - !was_new_second_time,
  - "storing block the second time should have returned `false`"
  + was_new_second_time,
  + "storing block the second time should have returned `true`"
  );
  let response = get_block(&mut harness, &mut storage, *block.hash());
  @@ -321,7 +321,7 @@ fn different_block_at_height_is_fatal() {
  assert!(was_new);
  let was_new = put_block(&mut harness, &mut storage, block_44_a);
  - assert!(!was_new);
  + assert!(was_new);
  // Putting a different block with the same height should now crash.
  put_block(&mut harness, &mut storage, block_44_b);
  