private void verifyCoordinator(String operationName, ProcedureCoordinator coordinator,
    List<String> expected) {
    // verify that we got all the expected nodes
    for (String node : expected) {
      verify(coordinator, once).memberAcquiredBarrier(operationName, node);
      verify(coordinator, once).memberFinishedBarrier(operationName, node, memberData);
    }
  }
Verify that the coordinator only got called once for each expected node
hbase-server/src/test/java/org/apache/hadoop/hbase/procedure/TestZKProcedureControllers.java