Hey @steve.robey
Welcome to the community! 
So the message isn’t an error, it’s just informing you that, those particular requests, don’t have any Tests associated with them in the Tests tab in the Request Builder. It doesn’t impact the Collection run in any way.
The issue that I can see here is that the request is returning a 404 Not Found, as you are using variables {{url}}/api/v1/users/{{username}} it might be that those are not resolving during runtime.