While I agree with you that this blog post (and the "carrot disclosure" described in it) is ill-considered, the pull request is not really "new code", it adds quotes to HTML attributes that are missing them. I think it's entirely reasonable for a contributor to assume that a new test case would not be needed for this small change, and that the maintainer's response ("So a simple question: is this code covered under a test? If not, you will have to add one.") is more abrasive than necessary.

> Someone asking you to write a test for new code

per the response: "I'm not sure what kind of test would you like me to write for this change, as it's simply adding 4 quotes"

To hell with writing a test for you. That’s what you say to someone who gets paid by you. If the project doesn’t want the fix. That’s their issue, not the reporter’s.