When I send a test email, a green notice shows up above the recipients list on your site for about 5 seconds saying that my test has been sent. But it disappears quickly. So if I miss the notice, I don't know if it actually was sent. Can you leave that notice up longer, please?
Perhaps it could even say something like "Test sent at 11:43 am" or something like that . . . until you send the next test.