// generate a random content key
String contentKey = NetworkTestUtil.randomString();
// create a message with target node B
TestMessageWithReply message = new TestMessageWithReply(nodeB.getNodeId(), contentKey);
// create and add a callback handler
TestCallBackHandler callBackHandler = message.new TestCallBackHandler(nodeA);
message.setCallBackHandler(callBackHandler);
// send message
assertTrue(nodeA.getMessageManager().send(message, getPublicKey(nodeB)));