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Comment by eranation | Hacker News Reader

If you write a library, or expose a public interface, I do expect a lot of unit tests. Unit tests can run offline, fast, during build time. I don’t mind integ-unit tests that perhaps simulate a database in memory to avoid mocking the entire storage layer. I rather have tests that are technically integration tests as they include more than, well, a unit, as long as they are idempotent, test mainly one thing, and can run fast and offline. Not sure if there is a term for it but I call these integunit tests... (probably the worst name possible)

But unit / unit++ tests are not just for you, they are for me, they give me confidence I can touch your code without inadvertently breaking something critical that you may have missed in your acceptance tests. It gives you peace of mind to be able to refactor. An acceptance test may tell you they something broke, but a good unit test will show you exactly where.

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> breaking something critical that you may have missed in your acceptance tests.

So you can miss things in your acceptance tests but can't miss them in your unit tests? Why do you feel more confident with unit tests than with acceptance tests? Maybe because unit tests break more often so they are providing you with a false sense of security? Do you know that when a test fails for a reason other than the specified assertion its a called a false negative and the failure is meaningless? Do you know if your tests fail and no functional or non-functional requirements of the program has changed the failure is also meaningless (you are testing implementation)? Ask yourself how often does your group give you time to do these hypothetical large refactoring that give merit to large unit test suites? How many times, even, do you do small refactorings and find all the test have to go away or significantly change anyway because they made some implementation assumption that is no longer true? How many times have you gone into a test suite and have seen that its been patched up so many times that you can swear its testing something but you just don't know what? I know that Uncle Bob tells us about test for refactoring and this and that, but I just don't buy it any more. The emperor is naked god dammit. Uncle Bob and the like are very famous because people swallow their anecdote without due scrutiny.

One thing I can't find much evidence of is Uncle Bob's experience in delivering commercial software. I get the feeling he works mainly on toy examples which might explain some of the things he advocates that, like you, don't match my experience at all.

If you write a library or expose a public interface, I expect functional tests that cover that interface. Unit testing would require going below that level, and test implementation details - which is exactly why those tests tend to be so brittle, and the overhead of maintaining them is so high.

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