@Override
    public List<ServerName> getOnlineServersList() {
      // return no region server to make the procedure hang
      if (EMPTY) {
        for (StackTraceElement e : Thread.currentThread().getStackTrace()) {
          if (e.getClassName().equals(AssignReplicationQueuesProcedure.class.getName())) {
            return Collections.emptyList();
          }
        }
      }
      return super.getOnlineServersList();
    }
Make sure we will wait until all the SCPs finished in RemovePeerProcedure.
<p/>
See HBASE-27109 for more details.
hbase-server/src/test/java/org/apache/hadoop/hbase/replication/TestRemovePeerProcedureWaitForSCP.java