Oftentimes, finagling with the REPL is merely about getting the syntax right ("did I use the right number of parens?") rather than formulating assumptions. In such cases, using this tool doesn't invalidate the TDD workflow, since your assumptions don't change.

The essential complexity of writing unit tests is in formulating your assumptions ahead of time. As you correctly point out, no tool can ever solve this. However, an accidental complexity is correctly expressing your assumptions in code. Tools such as a REPL and this library can definitely help with that.

It's for regression testing.

Title says unit tests. But to GP's point, it isn't really automatic, the developer still decides what to test. It is transforming REPL logs, not generating tests based directly on the code (which isn't useful in my experience).

To be honest, my development REPL logs have a lot of junk, so it would be extra work to write a clean one, and then make the right assertion (maybe I was looking for "even number" not "exactly 132"). Lisp-y REPLs are friendlier than some, but it would be cool to associate it with something like a notebook where it is easier to update imports/mocks/etc out of order. Cool idea though.

Unit test and regression test are not in conflict.

They are when you refer to regressions tests as unit tests.

Unit testing is "what" you test, it's your scope. And regression testing is "why" you're testing, you running tests to detect regressions.

Right, but if you're testing the 'why' and calling it a unit test... confusion ensues...

Is it that confusing that units of code are subject to change, hence subject to regressions, hence their tests are used to prevent regression?

1. Unit testing is a kind of functional testing. On a unit.

2. And regression testing is rerunning your existing functional tests after, say, refactoring, to see if they pass.

Complex? Confusing? Which part of this precisely is confusing?

Realisticly the problem here is;

The headline says they're generating unit tests automatically.

Which means I expect that I run a command, and it plops out unit test code. automatically. without my interaction.

The article is about recording repl interactions. that's not automatic.

and really, they look like implementation details? so bad examples? I don't know scheme, so shrug

Your problem appears to be your entire focus is pointlessly nitpicking the meaning of everyone’s words where enough context exists to trivially disambiguate it.

You gotta pick a better hobby.

You said a unit test is 'what' you test?

So if I say 'I wrote a unit test' what kind of test do you expect?

I expect test for a unit. Honestly don’t know what your problem is.

Makes sense, but it's always good to capture the intent of the test. If it is to prevent a regression, having data about the issue that was fixed is vital.

In general, I prefer to start writing tests, just enough the tests fail but call the functionality (this makes API design flaws obvious), then actually build the functionality and, finally, make the test conditions reflect what we need.

It is tough. On the one hand, I agree with you. On the other , writing tests seems both incredibly inefficient as well as missing the intended purpose. You cannot have a test suite which ‘proves’ the implementation is correct. A test suite is really like Swiss cheese - there are so many holes that implementation code can get through.

Now, bear in mind that I say this as a passionate tester and verification enthusiast. I don’t have a better alternative, so I keep writing tests. And yes, they do catch bugs. I’m not saying they have no value. I’m saying, they always let some bugs through, I.e, they are not complete.

And that makes the cost of them very depressing. Not only cost to write, cost to continuously run.

This is more, did I accidentally break something? The correctness of the tests is not known but you will know which tests have changed. Then you can go and review that code and see why it changed and whether the new behavior is correct. This gives you confidence in a change didn’t break anything but not that things weren’t broken from the start.

To me, testing in the REPL is also about validating my assumptions.

REPL-driven development is basically test-driven development with sorter feedback cycles during active development, but the downside is you need to make an extra effort to go back and preserve the important tests for posterity. This might well reduce some of that friction.

Ian Cooper agrees, in spades. "TDD, Where Did It All Go Wrong" https://www.youtube.com/watch?v=EZ05e7EMOLM