code: @VisibleForTesting
      @Synchronized
      public void pruneUnusedConnections() {
          for (List<Connection> connections : connectionMap.values()) {
              for (Iterator<Connection> iterator = connections.iterator(); iterator.hasNext();) {
                  Connection connection = iterator.next();
                  if (isUnused(connection)) {
                      connection.getFlowHandler().close();
                      iterator.remove();
                  }
              }
          }
      }
docs: Used only for testing.