The reason why you are receiving messages with “Test” word in the subject line to your Sent Messages page is because you might have pushed the Save & Send Test button after the message was updated. They will be visible only on the Sent Messages page under Communications in your left navigation, NOT to your customers.

You can confirm these messages are not sent to your customers by viewing the "Sent" page in your Amazon Seller Central account.  To do this, login to your Amazon Seller Central account, navigate to the "Messages" page (link in top left), then click on the "Sent" tab.  From this page, you can confirm that your Test messages are not sending to your customers.

When you click on “Save & Send Test”, the Communication Center does not have a real customer order from which to pull in details. When sending the test message, we populate the order details with fictitious content, including a fake Order Id, product, etc. So do not be alarmed when your email variables populate with words like “Test” or links containing “ORDER-ID”, etc. (Click here to read more about links in test messages.)
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As soon as you are sure your message is ready to go, you can change the status to "Active". From the Automated Messages page, under Communications in your left navigation, find the message you want to activate. Where you see the name of that message, navigate to the far right side of that row under "Status". To set your message to "Active", click on the dropdown and select "Active". You should see messages begin sending within 24 hours.