@TestOnly
  public static @NotNull <Key, Value> PersistentMapImpl<Key, Value> unwrap(@NotNull PersistentHashMap<Key, Value> map) {
    //NOTE: on production, it can be another implementation behind the PersistentHashMap
    try {
      Field field = PersistentHashMap.class.getDeclaredField("myImpl");
      field.setAccessible(true);
      //noinspection unchecked
      return (PersistentMapImpl<Key, Value>)field.get(map);
    }
    catch (Exception e) {
      throw new RuntimeException(e);
    }
  }
@TestOnly
  public static @NotNull <Key, Value> PersistentMapImpl<Key, Value> unwrap(@NotNull PersistentHashMap<Key, Value> map)