@Override
      public void call() throws IOException {
        RowMutations mutation = new RowMutations(ROW);
        mutation.add(new Put(ROW).addColumn(FAMILY, QUALIFIER, VALUE));
        TABLE.checkAndMutate(
          CheckAndMutate.newBuilder(ROW).ifNotExists(FAMILY, QUALIFIER).build(mutation));
      }
Tests that one can implement their own RpcControllerFactory and expect it to successfully pass
custom priority values to the server for all HTable calls.
hbase-server/src/test/java/org/apache/hadoop/hbase/TestCustomPriorityRpcControllerFactory.java