I see this get mentioned a lot but I still am skeptical that AI can generate tests we can trust more than any other code we know we cannot trust.

Yes tests are conceptually isolated and that helps, but I've personally seen unit tests get generated that are semantically incorrect - that is, they test the structure of the code (e.g. they can check function output types and values), but they can't know _why_ the unit tests need to be there, so the really really helpful tests never get generated. Not to mention the obvious issues with generated tests only testing is x = x, or needless redundant tests for the same thing, or them essentially testing basic features of the language.

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jaggederest 2 hours ago | parent | next [-]

You have to iterate on the tests, review and validate them, just like any other code, and if you generate a whole project's tests all at once the quality is abysmal, of course. I've been using a lot of old school data-driven testing techniques, where the harness is just code I review, and the data itself is e.g. json files and drives the system.

I actually have a public (AGPL) example here: https://github.com/pgdogdev/pgdog/tree/main/integration/sql - pgdog is particularly testable since it is trying for complete transparency, so you have a perfect oracle in hand via base postgresql, but it demonstrates the concept at least.

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fzeroracer 16 minutes ago | parent [-]

Then this falls into the exact same pit the OP mentioned, either you need to blindly trust that the LLM is generating tests that actually work, or you need extensive test coverage for your tests to ensure that your tests are actually testing.

	▲	jaggederest 13 minutes ago \| parent [-]
		It turns out that you don't actually need tests for your tests, because the code provides a baseline truth for the tests. You do, at some point, have to be epistemically sound enough to actually look for correctness in either the code, behavior, or tests. We unfortunately haven't fully unlocked completely solipsistic value generation yet. This is also part of why I like end to end tests that use actual UI flow, so I can watch it go by in slow mode before letting it loose fully automated.

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nzeid 2 hours ago | parent | prev | next [-]

Which is why test generation has to be carefully guided as well, and this is something at which I've incidentally been fast. Ultimately it's a constant battle between LLM handholding and doing things yourself.

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skydhash 2 hours ago | parent | prev [-]

I don't even care about tests being correct as you can still verify them even when tedious. What I care is that, more often than not, the shape of the solution is not fixed. Having unit tests for those can be extremely costly as when the changes happens, you have to change all the tests.

I've been burned by this in my honeymoon period with unit testing (pretty much the reason it ended). These days, I prefer broader scope of testing, especially user-facing part. The users may be other developers or end users. I only do unit testing for tricky algorithms or math formulae.

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jaggederest an hour ago | parent [-]

I want all the layers of the pyramid, eventually, but the top layers matter the most. I can't count the number of times my paranoid "make sure that customers can successfully pay us" end to end test suite has prevented the money faucet from being shut off. I install one perennially at any company I work at and they always pay for themselves surprisingly quickly.

	▲	skydhash 25 minutes ago \| parent [-]
		I’ve been involved in B2B (so no payment flow). But it’s basically the same with an handful of integration tests for common workflows. They run fast and mostly serve a canary to ensure that we are not crippling some use cases. When a bug hits us, a test case is added/modified for it. They’re mostly a reflection of the current requirement of the project.