Garbage code is bad enough, but it's not like people have never had to walk juniors through mistakes before LLMs.
But this is actually so much worse for that same reason - the type of developer who'd submit Copilot output (I can call it that, as it's definitely not code) for a PR is unable to respond to any comment beyond asking Copilot again and wasting everyone's time with 6 more rounds of reviews. I've literally had to write test cases for someone else and told them "You can't ask for another code review until your code passes these."
Bit of a tangent, though related. It looks like you accidentally stumbled into a version of test driven development ;)
With the big difference obviously being that typically the developer who writes the test also will write the code.
In some situations, this actually makes sense to do with junior developers as part of their training. Where a senior developer sits down with them and write out the tests together, then with the tests as a guide they are thrown into the waters to develop the functionality.
Of course, I suspect that in this case, you were not dealing with a junior. Rather the sort of person who looks at your tests, still is confused and asks for a "quick call" to talk about the tests.
But this is actually so much worse for that same reason - the type of developer who'd submit Copilot output (I can call it that, as it's definitely not code) for a PR is unable to respond to any comment beyond asking Copilot again and wasting everyone's time with 6 more rounds of reviews. I've literally had to write test cases for someone else and told them "You can't ask for another code review until your code passes these."