In most real systems, deletes of core business objects like 'product' are really only soft deletes; there are caching layers; deleting things has knock-on consequences for other things (if you delete a product when an instance of it is in a customer's shopping basket, what happens?) - it doesn't seem illogical to want to test that when you 'delete' a product, it disappears from the product catalog... but then you'd want to do other tests to verify it remains in a shopping basket, and is still visible in purchase history, and so on.

Fair enough - but in that case we're really not talking about the kind of test the grandparent described, the one that looks like

    p = productDao.create("My New Product")
    assert true p.delete()

The grandparent was pointing out that a unit test like that doesn't give you any confidence in your system precisely because it fails to exercise the broader context - so while it tells you that 'yup, you deleted it', it doesn't tell you that 'other code is now treating it as deleted'. GP was arguing that a unit test was not useful but a functional test was.

You, on the other hand, argued that simple deletion didn't need ANY tests, unit or functional - I was responding with examples that demonstrated that functional integration tests for deletion are perfectly valid.

You need to compare apples to apples. An integration test that tests some logic is better than a unit test that doesn't test any logic, duh. But if you're not testing any logic then the test is useless either way. And if you are testing something like cache invalidation, then you can do that just as well, probably better, at the unit level.

Actually yes! The gist of the story was deleting a product was not removing it from the product list because of query caching. It was something you would only have found when running against the site itself as query caching doesn't exist at unit or integration testing time. That was an interesting one. Our rest layer tests found it, although even still it took awhile to figure out (how the #@!$ is it still in the list?)

I can imagine deleting products may be failing due to some UI change. Maybe a button isn't visible in certain IE versions. Maybe the JS code executing the backend request is failing in some browsers. That's where e2e tests are useful.

Those are purely failures in the UI layer. To the extent that "unit testing" a web frontend is possible, you could catch those problems with a pure unit test that mocked out the backend, it wouldn't have to be an end-to-end test.