@Override
    protected AssignmentManager createAssignmentManager(MasterServices master,
      MasterRegion masterRegion) {
      return new AssignmentManagerForTest(master, masterRegion);
    }
See HBASE-22060 and HBASE-22074 for more details.
hbase-server/src/test/java/org/apache/hadoop/hbase/master/assignment/TestOpenRegionProcedureHang.java