message: [accumulator] add common ancestor test
diff: @@ -501,5 +501,11 @@ mod tests {
  .unwrap();
  let desert_vec = vec![block_header3.clone().id(), block_id];
  assert_eq!(hashes, desert_vec);
  + let comm_hash = storage
  + .block_store
  + .get_common_ancestor(block_header1.id(), block_header2.id())
  + .unwrap()
  + .unwrap();
  + assert_eq!(comm_hash, parent_hash);
  }
  }
  