Marcus there is a pattern that is happening over and over. People want another state in the workflow that indicates the code needs to be tested: https://bitbucket.org/site/master/issue/5179/add-a-status-of-closed-to-issues I think most people just need one more state in the workflow. I mean really the "invalid" and "wontfix" state are superfluous. If you could kill one of those and replace it with "testing" or something I would and I'm sure many others would be happy. No need for custom workflows or complicated the notification just replace or add a state in the workflow.
Issue #14852 open