You can test your message flows using the Test Client.
Instead, you can send messages to the flow by using Enqueue and Dequeue; see Enqueue and Dequeue.
The test message is put to the selected input node. The Test Client monitors the output nodes in the message flow and events are generated as the message passes through the message flow. You might need to stop the test manually, depending on the nodes in the message flow and the settings that you have configured in the Test Client.
To test the message flow again, right-click Invoke Message Flow in the Message Flow Test Events pane and click Invoke to start a new test; or click Duplicate or Re-run to re-run the test using the same message.