private void sendMessage(List<ExtendedCell> cells,
    TestRpcServiceProtos.TestProtobufRpcProto.BlockingInterface stub) throws Exception {
    HBaseRpcController pcrc =
      new HBaseRpcControllerImpl(PrivateCellUtil.createExtendedCellScanner(cells));
    String message = "hello";
    assertEquals(message,
      stub.echo(pcrc, TestProtos.EchoRequestProto.newBuilder().setMessage(message).build())
        .getMessage());
    int index = 0;
    CellScanner cellScanner = pcrc.cellScanner();
    assertNotNull(cellScanner);
    while (cellScanner.advance()) {
      assertEquals(CELL, cellScanner.current());
      index++;
    }
    assertEquals(cells.size(), index);
  }
Test that our fatal watermark is honored, which requires artificially causing some queueing so
that pendingOutboundBytes increases.
hbase-server/src/test/java/org/apache/hadoop/hbase/ipc/TestNettyChannelWritability.java