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Comment by akst | Hacker News Reader

ATM I feel like LLM writing tests can be a bit dangerous at times, there are cases where it's fine there are cases where it's not. I don't really think I could articulate a systemised basis for identifying either case, but I know it when I see it I guess.

Like the the other day, I gave it a bunch of use cases to write tests for, the use cases were correct the code was not, it saw one of the tests broken so it sought to rewrite the test. You risking suboptimal results when an agent is dictating its own success criteria.

At one point I did try and use seperate Claude instances to write tests, then I'd get the other instance to write the implementation unaware of the tests. But it's a bit to much setup.

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I work with individuals who attempt to use LLMs to write tests. More than once, it's added nonsensical, useless test cases. Admittedly, humans do this, too, to a lesser extent.

Additionally, if their code has broken existing tests, it "fixes" them by not fixing the code under test, but changing the tests... (assert status == 200 becomes 500 and deleting code.)

Tests "pass." PR is opened. Reviewers wade through slop...

The most annoying thing is that even after cleaning up all the nonsense, the tests still contain all sort of fanfare and it’s essentially impossible to get the submitter to trim them because it’s death by a thousand cuts (and you better not say "do it as if you didn’t use AI" in the current climate..)

That’s also another thing. Sometimes the output is just junk, like there wasn’t really any intention behind the test to prevent a certain likely scenario arising

Sometimes it just add tests that lock in specific quirks of the code that weren’t necessarily intentional

Yep. We've had to throw PRs away and ask them to start over with a smaller set of changes since it became impossible to manage. Reviews went on for weeks. The individual couldn't justify why things were done (and apparently their AI couldn't, either!)

Luckily those I work with are smart enough that I've not seen a PR thrown away yet, but sometimes I'm approving with more "meh, it's fine I guess" than "yeah, that makes sense".

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