>, if bad programmers write bad code that needs unit tests, they're also going to write bad unit tests that don't test the code correctly. So what's the point?

I don't think one necessarily follows the other. Consider the examples of test pseudo-code:

  EXPECT[image_to_text("photo1.jpg") == "cat"]
  EXPECT[image_to_text("photo2.jpg") == "dog"]
  EXPECT[image_to_text("photo3.jpg") == "apple"]
  EXPECT[image_to_text("photo4.jpg") == "Barack Obama"]

A novice bootcamp graduate could write that test harness code. However, it requires an experienced programmer with a PhD in Machine Learning to write the actual neural net code for image_to_text(). (Relevant XKCD[1])

(Yes, there's also variability of skill in writing test code. An experienced programmer will think of extra edge cases that a novice will not and therefore, write more comprehensive tests.)

That still doesn't change the fact that writing code that tests to check for correct results is often easier than writing the algorithm itself.

It also contradicts the notion that refactoring code requires that the test code be refactored. That's not always true. Since the jpg file format came out in 1992, that test code could have been written in that same year and it would still be valid today, 25 years later. We still want to ensure the image_to_text() function will return "cat" for "photo1.jpg" even if we refactor the low-level code to use the latest A.I. algorithms.

Another example of a regression test to test performance:

  TIMING[EXPECT[image_to_text("photo1.jpg") == "cat"] < 500 milleseconds]

Again, it's easy for a novice programmer to write a "performance timing specification executes in less than 500ms". It's much harder to refactor the code from slow code O(n^2) to faster code O(n log n).

To do a meta-analysis of the debate with Coplien: a big reason we're arguing his conclusion is that he complains about this abstract thing he called "unit tests". If he had copy-pasted concrete examples of the bad unit testing code into his pdf, maybe more of us would agree with him? In other words, I'd like to see and judge for myself if Coplien's "unit tests" look like the regression tests that SQLite and NASA use to improve quality -- or -- if they are frivolous tests that truly wastes developers' time. Since he didn't do that, we're all in the dark as to the "test code waste" he's actually complaining about.

[1] https://xkcd.com/1425/