I haven't had too much cause to use that type of test myself, I tend to use "Use data from previous runs". I run it just once, then do that. Although, I can see from your image there are no previous runs.
It says: "Let Microsoft Flow trigger the test by using example data that it pulls from the connector. For example, if you use the When a new email arrives trigger, Microsoft Flow automatically gets the most recent email from your inbox and uses that to test your flow."
So, "Microsoft Flow automatically gets the most recent email from your inbox". Is it possible that the most recent Flow doesn't meet the requirements of the Flow and that's why it isn't running?
I am just trying to give you something to go on here ...
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