🚀 TDD, Where Did It All Go Wrong (Ian Cooper)

'Test Pyramid' considered harmful IMO. It discourages people from writing tests against the public interface of their system , and instead encourages testing against internals. This leads to a test pack that prevents refactoring, and can't be trusted to catch regression errors. This is partly down to the widely confused definition of a 'unit test' (which a lot of people interpret as 'one test per class'). If you haven't seen it, please watch Ian Cooper's "TDD, Where Did It All Go Wrong" [VIDEO] Also, I thought continuous testing was having your test pack run all the time while coding, but hey ho.

The best talk on this topic, IMO is Ian Cooper: "TDD, Where did it all go wrong?" [VIDEO] Couple of notes: - TDD, much like scrum, got corrupted by the "Agile Consulting Industry". Sticking to the original principles as laid out by Kent Beck results in fairly sane practices. - When people talk about "unit tests", a unit doesn't refer to the common pattern of "a single class". A unit is a piece of the software with a clear boundary. It might be a whole microservice, or a chunk of a monolith that is internally consistent. - What triggers writing a test is what matters. Overzealous testers test for each new public method in a class. This leads to testing on implementation details of the actual unit, because most classes are only consumed within a single unit. - Behavior driven testing makes most sense to decide what needs tests. If it's required behavior to the people across the boundary, it needs a test. Otherwise, tests may be extraneous or even harmful. - As such, a good trigger rule is "one test per desired external behavior of the unit, plus one test per bug fixed". The test for each bugfix comes from experience -- they delineate tricky parts of your unit and enforce workign code around them.

> Firstly if the dependency isn't doing any io, you can test your code as a whole along with its dependency. No need to mock. This the thing. People have a tendency to overuse mocks. The point of automated testing (whether it's unit tests or something else), is to enable refactoring. That's really the only reason. Code that you don't touch doesn't suddenly change its behaviour one day. In a previous jobs the developers started to go crazy with mocking and it reached a kind of singularity where essentially if a function called anything, that thing was mocked. It definitely tests each function in complete isolation, but what's the point? It makes refactoring impossible, which is the entire point of the tests in the first place! This excellent talk completely changed the way I approached testing. Every developer who writes tests needs to watch this now! [VIDEO]

Ian Cooper talked about this (and more) 5 years ago: [VIDEO] Well worth listening to this talk. It completely changed the way I did testing.

This the best talk I've ever seen about testing (Ian Cooper): [VIDEO] I see he's done a much more recent follow up, which I intend to watch: [LINK] Not sure if it contains new ideas. He says the unit is not "a class" but a module. It's up to you to decide what the module does (ie. what level of abstraction it's at). More importantly, he argues against mocking and essentially "unit testing" in most cases.

For those who want to know more about this approach: see Ian Cooper - TDD, Where Did It All Go Wrong [VIDEO] I post this all the time, it's like free upvotes :)

I find [VIDEO] describes my own experiences with automated testing quite well. tl;dr: - Focus on "automated testing", don't get obsessed with philosophising about "the true nature of a 'unit'", or other such dogma. - Be empirical: base your rules on what works; don't base your work on "the rules". - The goal of testing is to expose problems in our program: "test failure" is a success, because we've found a problem (even if that problem is with the test!). Anything else is secondary (e.g. isolating the location of failures, documenting our API, etc.). Avoiding this goal defeats the point (e.g. choosing to ignore edge cases). - Focus on functionality rather than implementation details, e.g. 'changing a user's email address' rather than 'the setEmail method of the User class'. This improves reliability and makes failures more useful/meaningful (i.e. "this feature broke" vs "this calling convention has changed"). - Mocking is a crutch: it works-around problems that can usually be avoided entirely during design; it can still be very useful when a design can't be changed (e.g. adding tests to a legacy system). - Testing a real thing is objectively better than testing a fake thing; we should only mock if testing the real thing is unacceptable. - If two components always exist together, pretending that they're independent is a waste of time and complexity. - Having some poor tests is better than having no tests. Tests can be added, removed and improved over time, just like anything e

I see this opinion a lot from people who haven't seen tests and code written by people experienced with TDD. The tests should not end up that coupled to the code. The implementation structure and the test structure end up somewhat different when refactoring every time the tests are green. When listening to the feedback from the tests & code. With the skills to spot the refactoring opportunities. Oftentimes people seem to equate unit testing with a 1:1 correspondence of test and implementation with high coupling between the two. These sort of tests resist refactoring, rather than enabling it. With good tests you can pivot the implementation and tests independently. Recommend [VIDEO] and [LINK] on TDD