[akeefer]

I think this is a great explanation of a lot of the obvious pitfalls with "basic" TDD, and why so many people end up putting in a lot of effort with TDD without getting much return.

I personally have kind of moved away from TDD over the years, because of some of these reasons: namely, that if the tests match the structure of the code too closely, changes to the organization of that code are incredibly painful because of the work to be done in fixing the tests. I think the author's solution is a good one, though it still doesn't really solve the problem around what you do if you realize you got something wrong and need to refactor things.

Over the years I personally have moved to writing some of the integration tests first, basically defining the API and the contracts that I feel like are the least likely to change, then breaking things down into the pieces that I think are necessary, but only really filling in unit tests once I'm pretty confident that the structure is basically correct and won't require major refactorings in the near future (and often only for those pieces whose behavior is complicated enough that the integration tests are unlikely to catch all the potential bugs).

I think there sometimes needs to be a bit more honest discussion about things like: * When TDD isn't a good idea (say, when prototyping things, or when you don't yet know how you want to structure the system) * Which tests are the most valuable, and how to identify them * The different ways in which tests can provide value (in ensuring the system is designed for testability, in identifying bugs during early implementation, in providing a place to hang future regression tests, in enabling debugging of the system, in preventing regressions, etc.), what kinds of tests provide what value, and how to identify when they're no longer providing enough value to justify their continued maintenance * What to do when you have to do a major refactoring that kills hundreds of tests (i.e. how much is it worth it to rewrite those unit tests?) * That investment in testing is an ROI equation (as with everything), and how to evaluate the true value the tests are giving you against the true costs of writing and maintaining them * All the different failure modes of TDD (e.g. the unit tests work but the system as a whole is broken, mock hell, expensive refactorings, too many tiny pieces that make it hard to follow anything) and how to avoid them or minimize their cost

Sometimes it seems like the high level goals, i.e. shipping high-quality software that solves a user's problems, get lost in the dogma around how to meet those goals.

[vinceguidry]

> I think this is a great explanation of a lot of the obvious pitfalls with "basic" TDD, and why so many people end up putting in a lot of effort with TDD without getting much return.

If you have the cash, spring for Gary Bernhardt's Destroy All Software screencasts. That $240 was the best money my employer ever spent on me. Trying to learn TDD on your own is asking for a lot of pain, and all you'll end up doing is reinventing the wheel.

There are a lot of subtle concepts Gary taught me that I'm still learning to master. You learn what to test, how to test it, at what level to test it, how to structure your workflow to accommodate it.

[searls]

+1 for DAS. Gary's great and I think we agree pretty closely on these issues.

[taude]

Were there any particular seasons your found useful in Destroy All? It seams like it's mixed where there's just snipped of TDD spread around at will, whenever the need hit.

(I ask because there's no way I'm going to have time to watch/absorb all those things).

[vinceguidry]

There was one 4-episode series on testing untested code that I thought was great. Especially because I have a ginormous untested codebase that I have to work with. It's in season 3. Also the one before that series about Test Isolation, that's a great topic.

[ArbitraryLimits]

> When TDD isn't a good idea (say, when ... you don't yet know how you want to structure the system)

(Apologies in advance as I can't figure out how not to sound snarky here.)

Isn't that called "the design? And is there any meaningful way in which, if "test-driven design" fails if you don't already have the design, it's worth anything at all?

[akeefer]

Sure, you can call that structure the design, or the architecture, or whatever you like. Either way, it's a fair question.

As a point of semantics: TDD generally stands for "test-driven development," not "test-driven design," though the article here does make the claim that TDD helps with design.

To reduce my personal philosophy to a near tautology: if you don't design the system to be testable, it's not going to be testable. TDD, to me, is really about designing for testability. Doing that, however, isn't easy: knowing what's testable and what's not requires a lot of practical experience which tends to be gained by writing a bunch of tests for things. In addition, the longer you wait to validate how testable your design actually is, the more likely it is that you got things wrong and will find it very painful to fix them. So when I talk about TDD myself, I'm really talking about "design for testability and validate testability early and often." If you don't have a clue how you want to build things, TDD isn't going to help.

If you take TDD to mean strictly test-first development . . . well, I only find that useful when I'm fixing bugs, where step 1 is always to write a regression test (if possible). Otherwise it just makes me miserable.

The other thing worth pointing out is that design for testability isn't always 100% aligned with other design concerns like performance, readability, or flexibility: you often have to make a tradeoff, and testability isn't always the right answer. I personally get really irked by the arguments some people make that "TDD always leads to good design; if you did TDD and the result isn't good, you're doing TDD wrong." Sure, plenty of people have no clue what they're doing and make a mess of things in the name of testability. (To be clear, I don't think the author here makes the mistake of begging the question: I liked the article because I think it honestly points out many of the types of mistakes people make and provides a reasonable approach to avoiding them.)

[couchand]

I think you're spot on here - TDD is great as long as you're not too obstinate about it. It's a trade off, just like every interesting problem.

One point I'd like to draw out. If you don't have a clue how you want to build things, TDD isn't going to help.

This is exactly right. If you find yourself completely unable to articulate a test for something, you probably don't really know what it is you're trying to build. I think that's the greatest benefit to TDD: it forces you to stop typing and think.

[bphogan]

Exactly. This is the whole purpose behind the "spike" - make a branch, write a crap implementation of some code to help understand the problem, put it aside. Then go write the production version TDD style. Once you understand the problem, you can use TDD to create a good design to solve that problem.

Sounds crazy, but this is how I do everything I don't understand. And my second implementation is usually better than my first.

[couchand]

Or, in the words of Fred Brooks, build one to throw away. I'm always amazed at how prescient he was.

Unfortunately I find all too often that spike project finds its way into production for one reason or another. Now I only spike in Befunge.

[Chris_Newton]

If you find yourself completely unable to articulate a test for something, you probably don't really know what it is you're trying to build.

I don’t buy this argument. How would you write tests to drive the development of a graphics demo, say rendering a Mandelbrot set? Or a tool to convert audio data from one format to another? Or any other kind of software where the output doesn’t consist of readily verifiable, discrete data points?

[couchand]

Are you asking about unit tests or acceptance tests?

The problems you describe are very high level, but we could design an acceptance testing scheme for them. For the Mandelbrot set it might involve comparison to a reference rendering, for the audio tool a reference recording. In both cases you'd allow a delta relevant to the application, and probably also benchmark for acceptable performance.

But my point was more aimed at unit testing. When you set out to write a function you should know something about that function before starting. If you know enough to write the function signature, you can first write a failing test. If you can write a bit of code in that function, you can write a bit expecting the behavior of that code.

[Chris_Newton]

Are you asking about unit tests or acceptance tests?

I suppose what I’m really asking is how you would go from not having software to having software that does those things, using TDD. I think in practice its fail-pass-refactor cycle is normally applied at the level of unit tests, but in any case, how would using TDD help to drive a good design, to ensure testability, or otherwise, in that kind of situation?

(I’m asking this rhetorically. I don’t think TDD is a very helpful process in this context. I’m just trying to demonstrate this with practical examples rather than bluntly stating it without any supporting argument.)

[twic]

"Test-driven design", as it is commonly understood, does seem to be a mythical beast. I've hunted it with both logic and experience and come up empty-handed.

That said, i do still find that while test-driven development doesn't itself create good design, it is a useful tool to help me create good design. I have a bite-size piece of functionality to write; i think about what the class should look like; i write tests to describe the class; i write the class. The key thing is that the tests are a description of the class. The act of writing down a description of something has an amazing power to force the mind to really understand it; to see what's missing, what's contradictory, what's unnecessary, and what's really important. I experience this when i write presentations, when i write documentation, and when i write tests. The tests don't do the thinking for me, but they are a very useful tool for my thinking.

[dboat]

It's very common in software development to receive incomplete requirements. My world would be a very different place if I always receive feature complete design documents (and in same cases, any documents at all). Had I insisted on any kind of TDD, it would greatly increase my workload by reducing my ability to alter the design to accommodate new feature requests and changes while internal clients test the code.

I do gather some places do things differently though. Must be nice.

[searls]

I think I'd have to offer that my experience differs. TDD is not at all big-design-up-front, even with this reductive exercise. In fact, most features start very minimally and the tree of dependencies grows over time, just like any system becomes incrementally more complex. TDD is just one tool (of many) to help manage that complexity. Both by offering some regression value (at least of the logical bits) and also by encouraging small, bite-sized units that are easy to make sense of (and therefore change or replace)