Testing asynchronous processes is always hard. After editing the messaging queue content, you can make sure that changes are up and running by testing the Pipeline itself.
To test your Pipeline, simply go with the following steps:
Add a queue item. Make sure that:
Messaging Queue start date is in the past and end date is in the future or empty
Queue item send time is in the past
You should be able to see the item in your Queue with status Pending
Wait up to 5 minutes to receive your message