[hitchstory]

There isnt much consensus on the right kind of test to write with TDD, but when you get it right or wrong it makes or breaks TDD.

Recently Ive been writing mostly "end-to-end unit tests" - stateless, faking all external services (database, message queue, etc.) with TDD which works great.

There is a sweet spot on default test types - at a high a level as possible while being hermetic seems to be ideal.

The other un-talked about thing is that to be able to always write this kind of test you need test infrastructure which isnt cheap to build (all those fakes).

[devjab]

My biggest problem with TDD is that it doesn't actually protect you from the things you miss. This is great for the consultants who sell TDD courses, because they get to tell you that you did it wrong. They'll be right, but that fact is also useless. I don't have a problem with testing though, as I said I think it's hard to regret doing it, but I'm not sure why we wouldn't push something like runtime assertions instead if we were to do the whole "best practice" thing. With runtime assertions you'll get both the executable documentation and the ability to implement things like triple modular redundancy, so basically everything TDD does but much better.

Yet many developers don't even know what a runtime assertion is while everyone knows what TDD is. I guess it doesn't really matter if you're working on something which can crash and then everyone will be like "oh it's just IT, it does that".

[hitchstory]

It often protects me from things I miss. E.g. when I'm TDD'in a feature and I'm implementing the 5th-6th test I often find myself inadvertently breaking one of the earlier tests.

I do think there is such a thing as overtesting - i.e. regretted tests. TDD actually protects you from this to an extent by tying each test / modification of a test to a change in code.

Runtime assertions definitely give you more bang for the buck (they are ridiculously cheap) but they are complementary to tests, not a replacement. It attacks the same problem from the bottom up instead of top down.

I also find that when you combine the two, the tests become more useful - previously passing tests will fail when they trigger those assertions.