@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();
    }
In HBASE-26029, we reimplement the claim queue operation with proc-v2 and make it a step in SCP,
this is a UT to make sure the {@link AssignReplicationQueuesProcedure} works correctly.
hbase-server/src/test/java/org/apache/hadoop/hbase/replication/TestClaimReplicationQueue.java