@Override
            public String call(TestRpcServiceProtos.TestProtobufRpcProto instance)
              throws IOException {
              CoprocessorRpcUtils.BlockingRpcCallback<TestProtos.EchoResponseProto> callback =
                new CoprocessorRpcUtils.BlockingRpcCallback<>();
              instance.echo(controller, request, callback);
              TestProtos.EchoResponseProto response = callback.get();
              LOG.debug("Batch.Call got result " + response);
              return null;
            }
TestEndpoint: test cases to verify coprocessor Endpoint
hbase-endpoint/src/test/java/org/apache/hadoop/hbase/coprocessor/TestCoprocessorEndpoint.java