private void collectAssignmentManagerMetrics() {
    mergeSubmittedCount = mergeProcMetrics.getSubmittedCounter().getCount();
    mergeFailedCount = mergeProcMetrics.getFailedCounter().getCount();

    assignSubmittedCount = assignProcMetrics.getSubmittedCounter().getCount();
    assignFailedCount = assignProcMetrics.getFailedCounter().getCount();
    unassignSubmittedCount = unassignProcMetrics.getSubmittedCounter().getCount();
    unassignFailedCount = unassignProcMetrics.getFailedCounter().getCount();
  }
This tests two concurrent region merges
hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/TestMergeTableRegionsProcedure.java