20 ms·

The trouble with TDD is that quite often we don't really know how our programs are going to work when we start writing them, and often make design choices itera

• SomeCallMeTim 4y ago
  That's one issue with TDD. I agree 100% in that respect. Another partly orthogonal issue is that design is important for some problems, and you don't usually reach a good design by chipping away at a problem in tiny pieces. TDD fanatics insist that it works for everything. Do I believe them that it improved the quality of their code? Absolutely; I've seen tons of crap code that would have benefited from any improvement to the design, and forcing it to be testable is one way to coerce better design decisions. But it really only forces the first-order design at the lowest level to be decent. It doesn't help at all, or at least not much, with the data architecture or the overall data flow through the application. And sometimes the only sane way to achieve a solid result is to sit down and design a clean architecture for the problem you're trying to solve. I'm thinking of one solution I came up with for a problem that really wasn't amenable to the "write one test and get a positive result" approach of TDD. I built up a full tree data structure that was linked horizontally to "past" trees in the same hierarchy (each node was linked to its historical equivalent node). This data structure was really, really needed to handle the complex data constraints the client was requesting. As yes, we pushed the client to try to simplify those constraints, but they insisted. The absolute spaghetti mess that would have resulted from TDD wouldn't have been possible to refactor into what I came up with. There's just no evolutionary path between points A and B. And after it was implemented and it functioned correctly--they changed the constraints. About a hundred times. I'm not even exaggerating. Each new constraint required about 15 minutes of tweaking to the structure I'd created. And yes, I piled on tests to ensure it was working correctly--but the tests were all after the fact, and they weren't micro-unit tests but more of a broad system test that covered far more functionality than you'd normally put in a unit test. Some of the tests even needed to be serialized so that earlier tests could set up complex data and states for the later tests to exercise, which I understand is also a huge No No in TDD, but short of creating 10x as much testing code, much of it being completely redundant, I didn't really have a choice. So your point about the design changing as you go is important, but sometimes even the initial design is complex enough that you don't want to just sit down and start coding without thinking about how the whole design should work. And no methodology will magically grant good design sense; that's just something that needs to be learned. There Is No Silver Bullet, after all.
  • ivan_gammel 4y ago
    > Another partly orthogonal issue is that design is important for some problems, and you don't usually reach a good design by chipping away at a problem in tiny pieces. True, but… you can still design the architecture, outlining the solution for the entire problem, and then apply TDD. In this case your architectural solution will be an input for low level design created in TDD.
    • SomeCallMeTim 4y ago
      You can't always, though. I described a situation where TDD really, really, really wouldn't have worked. The whole structure needed to be developed, or at least 80% of it, before it would have made sense to write any tests--and the actual TDD philosophy would be to write "one small test" and only write exactly as much code as required to satisfy the test. The sane approach was to create the entire structure based on the design, and then test it after it was complete as an entire system. Some of the micro-functionality that TDD would have had you test would have become technical debt as a change-detector later when the client changed their specific requirements. As I said above, there is no evolutionary path from tiny pieces to the full structure, and TDD requires that you follow such an evolutionary path. If you're writing a bunch of tests and then creating a nontrivial amount of code, then you're following test-first, but not really following TDD. And I question even how valuable that is when you don't necessarily understand what would need to be tested before you've finished implementing the system.
      • ivan_gammel 4y ago
        I disagree with you here. TDD does require evolutionary path for the entire system, but the minimum unit is a feature that is expected to be fully specified and implemented to pass the first test. You cannot evolve a data structure or an algorithm with TDD, because TDD by original definition allows only refactoring, not re-engineering (I.e. if your feature is addition, writing „return 4“ to pass test2plus2 isn’t meaningful TDD). So in your case properly applied TDD would require fully implemented structure or at least an atomic part of it within the known design to pass the first test (e.g. testing Feistel round function in an encryption algorithm is ok, but you will know the design of the entire algorithm from the start).
• Alex3917 4y ago
  > The trouble with TDD is that quite often we don't really know how our programs are going to work when we start writing them Even if you know exactly how the software is going to work, how would you know if your test cases are written correctly without having the software to run them against? For that reason alone, the whole idea of TDD doesn't even make sense to me.
  • Byamarro 4y ago
    Most tests shouldn't be hard to read and reason about so it shouldn't be a problem. In case of more complex tests, you can do it like you would do it during iterative development - debug tests and code to figure out what's wrong - nothing changes here.
  • rcxdude 4y ago
    One reason why TDD can be a good idea is the cycle involves actually testing the test cases: if you write the test, run it and see that it fails, then write the code, then run the test again and see that it succeeds, you can have some confidence the test is actually testing something (not necessarily the right thing, but at least something). Wheras if you're writing the test after writing the code and expect that it will succeed the first time you run it, it's quite possible to write a test which doesn't actually test anything and will always succeed. (There are other techniques like mutation testing which may get you a more robust indication that your tests actually depend on the state of your software, but I've rarely seem them used in practice).
    • pmarreck 4y ago
      This is a great point. You're literally testing the test validity as you go.
    • dgunay 4y ago
      Good point. Sometimes I cheat and implement before I test, but often when I do that I'll comment & uncomment the code that actually does the thing so I can see the tests go from red to green. Have been meaning to try mutation testing as a way of sussing out tests that cover lines but don't actually test behavior.
• deleted 4y ago
  [deleted]
• larschdk 4y ago
  I think we should try and separate exploration from implementation. Some of the ugliest untestable code bases I have worked with have been the result of some one using exploratory research code for production. It's OK to use code to figure out what you need to build, but you should discard it and create the testable implementation that you need. If you do this, you won't be writing tests up front when exploring the solution space, but you will be when doing the final implementation.
  • gabereiser 4y ago
    I think this is the reasonable approach I take. It's ok to explore and figure out the what. Once you know (or the business knows) then it's time to write a final spec and test coverage. In the end, the mantra should be "it's just code".
  • happytoexplain 4y ago
    This makes sense, but I think many (most?) pipelines don't allow for much playtime because they are too rigid and top-down. At best you will convince somebody that a "research task" is needed, but even that is just another thing you have to get done in the same given time frame. Of course this is the fault of management, not of TDD.
  • codereviewed 4y ago
    Have you ever had to convince a non-technical boss or client that the exploratory MVP you wrote and showed to them working must be completely rewritten before going into production? I tried that once when I attempted to take us down the TDD route and let me tell you, that did not go over well. People blame engineers for not writing tests or doing TDD when, if they did, they would likely be replaced with someone who can churn out code faster. It is rare, IME, to have culture where the measured and slow progress of TDD is an acceptable trade off.
    • lanstin 4y ago
      Places where software is carrying a great deal of value tend to be more like that. That is, if mistakes can cost $20,000 / hour or so, then even the business will back down on the push now vs. be sure it works debate. As always, the job of a paid software person is to merge what the product people want with what good software quality requires (and what power a future version will unleash). Implement valuable things in software in a way that makes the future of that software better and more powerful.
• fsdghrth3 4y ago
  > This ultimately means, what most programmers intuitively know, that it's impossible to write adequate test coverage up front Nobody out there is writing all their tests up front. TDD is an iterative process, RED GREEN REFACTOR. - You write one test. - Write JUST enough code to make it pass. - Refactor while maintaining green. - Write a new test. - Repeat. I don't want this to come off the wrong way but what you're describing shows you are severely misinformed about what TDD actually is or you're just making assumptions about something based on its name and nothing else.
  • Supermancho 4y ago
    Writing N or 1 tests N times, depending on how many times I have to rewrite the "unit" for some soft idea of completeness. After the red/green 1 case, it necessarily has to expand to N cases as the unit is rewritten to handle the additional cases imagined (boundary, incorrect inputs, exceptions, etc). Now I see that I could have created optimizations in the method and rewrite it again and leverage the existing red/green. Everyone understands the idea, it's just a massive time sink for no more benefit than a test-after methodology provides.
    • fsdghrth3 4y ago
      See my other comment below. I don't recommend doing it all the time specifically because with experience you can often skip a lot of the rgr loop. > Everyone understands the idea, it's just a massive time sink for no more benefit than a test-after methodology provides. This is not something I agree with. In my experience, when TDD is used you come up with solutions to problems that are better than what you'd come up with otherwise and it generally takes much less time overall. Writing tests after ensures your code is testable. Writing your tests first ensures you only have to write your code once to get it under test. Again, you don't always need TDD and applying it when you don't need it will likely be a net time sink with little benefit.
  • DoubleGlazing 4y ago
    In my experience the write a new test bit is where it all falls down. It's too easy to skimp out on that when there are deadlines to hit or you are short staffed. I've seen loads of examples where the tests haven't been updated in years to take account of new functionality. When that happens you aren't really doing TDD anymore.
• happytoexplain 4y ago
  >Unfortunately most software is just not well defined up front. This is exactly how I feel about TDD, but it always feels like you're not supposed to say it. Even in environments where features are described, planned, designed, refined, written as ACs, and then developed, there are still almost always pivots made or holes filled in mid-implementation. I feel like TDD is not for the vast majority of software in practice - it seems more like something useful for highly specialist contexts with extremely well defined objective requirements that are made by, for, and under engineers, not business partners or consumers.
  • ethbr0 4y ago
    I forget which famous Unix personality the quote / story comes from, but it amounts to "The perfect program is the one you write after you finish the first version, throw it in the garbage, and then handle in the rewrite all the things you didn't know that you didn't know." That rings true to my experience, and TDD doesn't add much to that process.
    • dgb23 4y ago
      Well except for the second step where you aim precisely.
    • sdevonoes 4y ago
      Exactly. I write my programs/systems a few times. Each time I discard the previous version and start from scratch. I end up writing code that's easy to test and easy to swap parts if needed. I also know what TDD brings to the table. On top of that I have over 15 years of professional experience... so I usually know how to write software that complies with what we usually call "good code", so TDD offers me zero help. For more junior engineers, I think TDD can help, but once you "master" TDD, you can throw it out of the window: "clean code" will come out naturally without having to write tests first.
      • dfinninger 4y ago
        I was taken by TDD for about six months, years ago. I always felt that I was never good at it because edge cases I hadn’t thought of came up or the interface wasn’t actually the best/cleanest/most maintainable way to write that code. But it got me thinking about testing while writing the class instead of shoehorning a class into a test just before the PR went up. That’s what I think my takeaway was. To this day I think about not just how clean/maintainable the code is, but also how testable the code is while I am writing it. It really helps keep monkeypatching and mocking down.
• generalk 4y ago
  +1 on "well defined spec" -- a lot of Healthcare integrations are specified as "here's the requests, ensure your system responds like this" and being able to put those in a test suite and know where you're at is invaluable! But TDD is fantastic for growing software as well! I managed to save an otherwise doomed project by rigorously sticking to TDD (and its close cousin Behavior Driven Development.) It sounds like you're expecting that the entire test suite ought to be written up front? The way I've had success is to write a single test, watch it fail, fix the failure as quickly as possible, repeat, and then once the test passes fix up whatever junk I wrote so I don't hate it in a month. Red, Green, Refactor. If you combine that with frequent stakeholder review, you're golden. This way you're never sitting on a huge pile of unimplemented tests; nor are you writing tests for parts of the software you don't need. For example from that project: week one was the core business logic setup. Normally I'd have dove into users/permissions, soft deletes, auditing, all that as part of basic setup. But this way, I started with basic tests: "If I go to this page I should see these details;" "If I click this button the status should update to Complete." Nowhere do those tests ask about users, so we don't have them. Focus remains on what we told people we'd have done. I know not everyone works that way, but damn if the results didn't make me a firm believer.
  • andix 4y ago
    TDD usually means that you write the tests before writing the code. Writing tests as you write the code is just regular and proper software development.
    • Spivak 4y ago
      Odd, I was taught TDD as 1. Write test, see that it fails the way you expect. 2. Write code that makes the test pass. 3. Write test... and be secure that you can fearlessly refactor and not backslide while you play with different ideas so long as all your tests stay green. I would get overwhelmed so fast if I just had 50 failing tests and no implementation.
      • imran-iq 4y ago
        That's the right way to do TDD, see this talk: https://www.youtube.com/watch?v=EZ05e7EMOLM https://www.youtube.com/watch?v=EZ05e7EMOLM One of the above comments mentions BDD as a close cousin to TDD, but that is wrong as TDD is actually BDD as you should only be testing behaviours, which allow you to "fearlessly refactor"
• bitwize 4y ago
  And this is why you use spike solutions, to explore the problem space without the constraints of TDD. But spikes are written to be thrown away. You never put them into production. Production code is always written against some preexisting test, otherwise it is by definition broken.
• waynesonfire 4y ago
  jeez, well defined spec? what a weird concept. Instead, we took a complete 180 and all we get are weekly sprints. just start coding, don't spend time understanding your problem. what a terrible concept.
• AnimalMuppet 4y ago
  > In theory TDD should work as part of that iterative design, but in practice it means a growing collection of broken tests and tests for parts of the program that end up being completely irrelevant. If you have "a growing collection of broken tests", that's not TDD. That's "they told us we have to have tests, so we wrote some, but we don't actually want them enough to maintain them, so instead we ignore them". Tests help massively with iterating a design on a partly-implemented code base. I start with the existing tests running. I iterate by changing some parts. Did that break anything else? How do I know? Well, I run the tests. Oh, those four tests broke. That one is no longer relevant; I delete it. That other one is testing behavior that changed; I fix it for the new reality. Those other two... why are they breaking? Those are showing me unintended consequences of my change. I think very carefully about what they're showing me, and decide if I want the code to do that. If yes, I fix the test; if not, I fix the code. At the end, I've got working tests again, and I've got a solid basis for believing that the code does what I think it does.
• mcv 4y ago
  Exactly. I use TDD in situations where it fits. And when it does, it's absolutely great. But there are many situations where it doesn't fit. TDD is not a silver bullet, it's one tool among many.
  • majikandy 4y ago
    I find it as close as I have ever found to a silver bullet.
• marcosdumay 4y ago
  At this point I doubt the existence of well defined specs. Regulations are always ambiguous, standards are never followed, and widely implemented standards are never implemented the way the document tells. You will probably still gain productivity by following TDD for those, but your process must not penalize too much changes in spec, because it doesn't matter if it's written in Law, what you read is not exactly what you will create.
• lupire 4y ago
  It's Test Driven Development, not Test Driven Research. Very few critics notice this.
  • anonymoushn 4y ago
    Maybe you disagree with GP about whether one should always do all their research without actually learning about the problem by running code?
• f1shy 4y ago
  This is exactly my problem with TDD. Note this problem is not only in SW. For any development you do, you could start with designing tests. You can do for some HW for sure. If you want to apply TDD to any other development, you see pretty fast, what the problem is: you are going to design lots of tests, that a at the end will not be used. A total waste. Also with TDD often it will be centered in quantity of tests and not so much quality. What I find is much much better approach is what I call "detached test development" (DTD). The idea is: 2 separate teams get the requirements; one team writes code, the other write tests. They do not talk to each other! Fist when a test is not passed, they have to discuss: is the requirement not clear enough? What is the part that A thought about, but not B? Assignment of tests and code can be mixed, so a team makes code for requirements 1 through 100, and tests for 101 to 200, or something like that. I had very very good results with such approach.
  • ivan_gammel 4y ago
    What you described is a quite common role of QA automation team, but it does not really replace TDD. Separate team working on a test can do it only relying on a remote contract (e.g. API, UI or database schema), they cannot test local contracts like a public interface of a class, because that would require the that code already to be written. In TDD you often write the code AND the test at the same time, integrating the test and the code in compile time.
  • EddySchauHai 4y ago
    > Also with TDD often it will be centered in quantity of tests and not so much quality. 100%. Metrics of quality are really really hard to define in a way that are both productive and not gamified by engineers. > What I find is much much better approach is what I call "detached test development" (DTD) I'm a test engineer and some companies do 'embed' an SDET like the way you mention within a team - it's not quite that clear cut, they can discuss, but it's still one person implementing and another testing. I'm always happy to see people with thoughts on testing as a core part of good engineering rather than an afterthought/annoyance :)
  • switchbak 4y ago
    Who starts with designing just the tests? I have no idea how this is an association with TDD. TDD is a feedback cycle, you write small increments of tests before writing a small bit of a code. You don't write a bunch of tests upfront, that'd be silly. The whole point is to integrate small amounts of learning as you go, which help guide the follow-on tests, as well as the actual implementation, not to mention questions to need to ask the broader business. Your DTD idea has been tried a lot in prior decades. In fact, as a student I was on one of those testing teams. It's a terrible idea, throwing code over a wall like that is a great way to radically increase the latency of communication, and to have a raft of things get missed. I have no idea why there's such common misconceptions of what TDD is. Maybe folks are being taught some really bad ideas here?
• AtlasBarfed 4y ago
  Yeah, TDD has way too much "blame the dev" for the usual cavalcade of organizational software process failures.
• BurningFrog 4y ago
  Agile, as the name hints, was developed precisely to deal with ever changing requirements. In opposition to various versions of "first define the problem precisely, then implement that in code, and then you're done forever". So the TDD OP describes here is not an Agile TDD. The normal TDD process is: 1. add one test 2. make it (and all others) pass 3. maybe refactor so code is sane 4. back to 1, unless you're done. When requirements change, you go to 1 and start adding or changing tests, iterate until you're done.
  • pjmlp 4y ago
    Add one test for GUI code.....
  • tra3 4y ago
    Exactly. Nobody's on board with paying at least twice as much for software though. But that's what you get when things change and you have to refactor BOTH your code AND your tests.
    • 0x457 4y ago
      To be fair, you have to refactor your code and tests when things change anyway, regardless of the order they were written.
    • ivan_gammel 4y ago
      That can be an acceptable risk actually and it does quite often. There are two conceptually different phases in SDLC: verification that proves implementation is working according to spec and validation that proves that spec matches business expectations. Automated tests work on first phase, minimizing the risk that when reaching the next phase we will be validating the code that wasn’t implemented according to spec. If that risk is big enough, accepting the refactoring costs after validation may make a lot of sense.
    • BurningFrog 4y ago
      The only way to avoid that is to not have tests.
    • 4y ago
• shados 4y ago
  The big issue I see when people have trouble with TDD is really a cultural one and one around the definition of tests, especially unit tests. If you're thinking of unit tests as the thing that catches bugs before going to production and proves your code is correct, and want to write a suite of tests before writing code, that is far beyond the capabilities of most software engineers in most orgs, including my own. Some folks can do it, good for them. But if you think of unit tests as a way to make sure individual little bits of your code work as you're writing them (that is, you're testing "the screws" and "the legs" of the tables, not the whole table), then it's quite simple and really does save time, and you certainly do not need full specs or even know what you're doing. Write 2-3 simple tests, write a function, write a few more tests, write another function, realize the first function was wrong, replace the tests, write the next function. You need to test your code anyway and type systems only catch so much, so even if you're the most agile place ever and have no idea how the code will work, that approach will work fine. If you do it right, the tests are trivial to write and are very short and disposable (so you don't feel bad when you have to delete them in the next refactor). Do you have a useful test suite to do regression testing at the end? Absolutely not! In the analogy, if you have tests for a screw attaching the leg of a table, and you change the type of legs and the screws to hook them up, of course the tests won't work anymore. What you have is a set of disposable but useful specs for every piece of the code though. You'll still need to write tests to handle regressions and integration, but that's okay.
  • 0x457 4y ago
    Many people have a wrong perception of TDD. The main idea is to break a large, complicated thing into many small ones until there is nothing left, like you said. You're not supposed to write every single test upfront, you write a tiny test first. Then you add more and refactor your code, repeat until there is nothing left of that large complicated thing you were working on. There are also people who test stupid things and 3rd party code in their tests and either they get a fatigue from it and/or think their tests are well written.
    • pjmlp 4y ago
      How do you break those testes for a ray tracing algorithm on the GPU?
• eyelidlessness 4y ago
  > The trouble with TDD is that quite often we don't really know how our programs are going to work when we start writing them, and often make design choices iteratively as we start to realize how our software should behave. This is a trouble I often see expressed about static types. And it’s an intuition I shared before embracing both. Thing is, embracing both helped me overcome the trouble in most cases. - If I have a type interface, there I have the shape of the definition up front. It’s already beginning to help verify the approach that’ll form within that shape. - Each time I write a failing test, there I have begun to define the expected behavior. Combined with types, this also helps verify that the interface is appropriate, as the article discusses, though not in terms of types. My point is that it’s also verifying the initial definition. Combined, types and tests are (at least a substantial part of) the definition. Writing them up front is an act of defining the software up front. I’m not saying this works for everyone or for every use case. I find it works well for me in the majority of cases, and that the exception tends to be when integrating with systems I don’t fully understand and which subset of their APIs are appropriate for my solution. Even so writing tests (and even sometimes types for those systems, though this is mostly a thing in gradually typed languages) often helps lead me to that clarity. Again, it helps me define up front. All of this, for what it’s worth, is why I also find the semantics of BDD helpful: they’re explicit about tests being a spec.
• wodenokoto 4y ago
  This rings very true for me. I write tdd when doing advent of code. And it’s not that I set out to do it or to practice it or anything. It just comes very natural to small, well defined problems.
• grepLeigh 4y ago
  > Unfortunately most software is just not well defined up front. This is true, and I think that's why TDD is a valuable exercise to disambiguate requirements. You don't need to take an all/nothing approach. Even if you clarify 15-20% of the requirements enough to write tests before code, that's a great place to begin iterating on the murky 80%.
• randomdata 4y ago
  TDD isn't concerned with how your program works. In fact, implementation details leaking into your tests can become quite problematic, including introducing the problems you speak of. TDD is concerned with describing what your program should accomplish. If you don't know what you want to accomplish, what are you writing code for?
  • giantrobot 4y ago
    The issue is what you want to accomplish is often tightly coupled with how it is accomplished. In order to have a test for what it needs to contain the context of how. As a made up example. The "what" of the program is to take in a bunch of transactions and emit daily summaries. That's a straight forward "what". It however leaves tons of questions unanswered. Where does the data come from and in what format? Is it ASCII or Unicode? Do we control the source or is it from a third party? How do we want to emit the summaries? Printed to a text console? Saved to an Excel spreadsheet? What version of Excel? Serialized to XML or JSON? Do we have a spec for that serialized form? What precision do we need to calculate vs what we emit? So the real "what" is: take in transaction data encoded as UTF-8 from a third party provider which lives in log files on the file system without inline metadata then translate the weird date format with only minute precision and lacking an explicit time zone and summarize daily stats to four decimal places but round to two decimal places for reporting and emit the summaries as JSON with dates as ISO ordinal dates and values at two decimal places saved to an FTP server we don't control. While waiting for all that necessarily but often elided detail you can either start writing some code with unit test or wait and do no work until you get a fully fleshed out spec that can serve as the basis for writing tests. Most organizations want to start work even while the final specs of the work are being worked on.
    • randomdata 4y ago
      > Most organizations want to start work even while the final specs of the work are being worked on. Is that significant? Your tests can start to answer these unanswered questions before you ever get around to writing implementation. Suppose you thought you wanted to write data in ASCII format. But then you write some test cases and realize that you actually need Unicode symbols. Now you know what your implementation needs to do. Testing is the spec. The exact purpose of testing, which in fairness doesn't have the greatest name, is to provide documentation around what the program does. That it is self-verifying is merely a nice side effect. There is no need for all the questions to be answered while writing the spec (a.k.a. tests). You learn about the answers as you write the documentation. The implementation then naturally follows.
• vrotaru 4y ago
  Even for something which is well defined up-front this can of dubious value. Converting an positive integer less than 3000 is well-defined task. Now if you try to write such a program using TDD what do you think will end up with? Try it. Write a test for 1, and an implementation which passes that test then for 2, and so on. Bellow is something written without any TDD (in Java) private static String convert(int digit, String one, String half, String ten) { switch(digit) { case 0: return ""; case 1: return one; case 2: return one + one; case 3: return one + one + one; case 4: return one + half; case 5: return half; case 6: return half + one; case 7: return half + one + one; case 8: return half + one + one + one; case 9: return one + ten; default: throw new IllegalArgumentException("Digit out of range 0-9: " + digit); } } public static String convert(int n) { if (n > 3000) { throw new IllegalArgumentException("Number out of range 0-3000: " + n); } return convert(n / 1000, "M", "", "") + convert((n / 100) % 10, "C", "D", "M") + convert((n / 10) % 10, "X", "L", "C") + convert(n % 10, "I", "V", "X"); }
• theptip 4y ago
  I think part of what you are getting at here also points to differences in what people mean by “unit test”. It’s always possible to write a test case that covers a new high-level functional requirement as you understand it; part of the skill of test-first (disclaimer - I use this approach sometimes but not religiously and don’t consider myself a master at this) is identifying the best next test to write. But a lot of people cast “unit test” as “test for each method on a class” which is too low-level and coupled to the implementation; if you are writing those sort of UTs then in some sense you are doing gradient descent with a too-small step size. There is no appreciable gradient to move down; adding a new test for a small method doesn’t always get you closer to adding the next meaningful bit of functionality. When I have done best with TDD is when I start with what most would call “functional tests” and test the behaviors, which is isomorphic to the design process of working with stakeholders to think through all the ways the product should react to inputs. I think the early TDD guys like Kent Beck probably assumed you are sitting next to a stakeholder so that you can rapidly iterate on those business/product/domain questions as you proceed. There is no “upfront spec” in agile, the process of growing an implementation leads you to the next product question to ask.
  • merlincorey 4y ago
    > But a lot of people cast “unit test” as “test for each method on a class” which is too low-level and coupled to the implementation; if you are writing those sort of UTs then in some sense you are doing gradient descent with a too-small step size. There is no appreciable gradient to move down; adding a new test for a small method doesn’t always get you closer to adding the next meaningful bit of functionality. In my experience, the best time to do "test for each method on a class" or "test for each function in a module" is when the component in question is a low level component in the system that must be relied upon for correctness by higher level parts of the system. Similarly, in my experience, it is often a waste of effort and time to do such thorough low level unit testing on higher level components composed of multiple lower level components. In those cases, I find it's much better to write unit tests at the highest level possible (i.e. checking `module.top_level_super_function()` inputs produce expected outputs or side effects)
    • 4y ago
• gregmac 4y ago
  > it's impossible to write adequate test coverage up front I'm not sure what you mean by this. Why are the tests you're writing not "adequate" for the code you're testing? If I read into this that you're using code coverage as a metric -- and perhaps even striving for as close to 100% as possible -- I'd argue that's not useful. Code coverage, as a goal, is perhaps even harmful. You can have 100% code coverage and still miss important scenarios -- this means the software can still be wrong, despite the huge effort put into getting 100% coverage and having all tests both correct and passing.
• yoden 4y ago
  > test coverage gets in the way of the iterative design process. In theory TDD should work as part of that iterative design, but in practice it means a growing collection of broken tests and tests for parts of the program that end up being completely irrelevant. So much of this is because TDD has become synonymous with unit testing, and specifically solitary unit testing of minimally sized units, even though that was often not the original intent of the ideators of unit testing. These tests are tightly coupled to your unit decomposition. Not the unit implementation (unless they're just bad UTs), but the decomposition of the software into which units/interfaces. Then the decomposition becomes very hard to change because the tests are exactly coupled to them. If you take a higher view of unit testing, such as what is suggested by Martin Fowler, a lot of these problems go away. Tests can be medium level and that's fine. You don't waste a bunch of time building mocks for abstractions you ultimately don't need. Decompositions are easier to change. Tests may be more flaky, but you can always improve that later once you've understood your requirements better. Tests are quicker to write, and they're more easily aligned with actual user requirements rather than made up unit boundaries. When those requirements change, it's obvious which tests are now useless. Since tests are decoupled from the lowest level implementation details, it's cheap to evolve those details to optimize implementation details when your performance needs change.
• twic 4y ago
  No, this is nonsense. You don't write the test coverage up front! You think of a small chunk of functionality you are comfident about, write the tests for that (some people say just one test, i am happy with up to three or so), then write the implementation that makes those tests pass. Then you refactor. Then you pick off another chunk and 20 GOTO 10. If at some point it turns out your belief about the functionality was wrong, fine. Delete the tests for that bit, delete the code for it, make sure no other tests are broken, refactor, and 20 GOTO 10 again. The process of TDD is precisely about writing code when you don't know how the program is going to work upfront! On the other hand, implementing a well-defined spec is when TDD is much less useful, because you have a rigid structure to work to in both implementation and testing. I think the biggest problem with TDD is that completely mistaken ideas about it are so widespread that comments like this get upvoted to the top even on HN.
  • switchbak 4y ago
    I feel like I'm in crazy town in this thread. Most of the replies seem to be misunderstanding the intent of TDD, and yours is one of the few that gets it right. Is general understanding of TDD really that far off the mark? I had no idea, and I've been doing this for essentially 2 decades now.
    • pjmlp 4y ago
      No we really understand that the whole religion of only writing code after a failing test only applies to niche cases of libraries for headless applications in monoliths. Lets say my designer came to me and now wants bump mapped textures on engine, well I cannot touch that compute shader without writing a test first, so suggestions for a TDD framework for GPU shaders.
      • pydry 4y ago
        Ive done a form of TDD where I have a test scenario set up that generates a picture and I tweak the code until the picture looks right and then "freeze" it. Once frozen the test compares the picture (or other artefact) against the generated picture (or artefact). Im not sure if it'd be useful in your situation though.
• Buttons840 4y ago
  When I've been serious about testing I'll usually: 1. Hack in what I want in some exploratory way 2. Write good tests 3. Delete my hacks from step 1, and ensure all my new tests now fail 4. Re-implement what I hacked together in step 1 5. Ensure all tests pass This allows you to explore while still retaining the benefits of TDD.
  • gleenn 4y ago
    There's a name for it, it's called a "spike". You write a bunch of exploratory stuff, get the idea right, throw it all away (without even writing tests) and then come back doing TDD.
    • majikandy 4y ago
      Not sure why you got downvotes for this. It is a very effective technique. Since typing speed was never the bottleneck in software development. Throwing away the little bit of code you wrote, it not expensive. And writing it back in with TDD is incredibly efficient.
    • Double_a_92 4y ago
      Also not sure why you are getting downvoted. We call it "breakthrough", as in piercing though all the layers to connect one simple usecase from front to end. Once we established that that works properly, we think of a way to do it clean and tested for all other usecases. (In the book "the pragmatic programmer" it's called "tracer bullets / code".)
• agumonkey 4y ago
  I remember early uml courses (based on pre Java / OO languages). They were all about modules and coupling dependencies. Trying to keep them low, and the modules not too defined. It seems that the spirit behind this (at least the only one that make sense to me) is you don't know, so you just want to avoid coupling hard early, leave the room for low cost adaptation while you discover how things will be.
  • ThalesX 4y ago
    Whenever I start a greenfield frontend for someone they think I’m horrible in the first iteration. I tend to use style attributes and just shove CSS in there, and once I have enough things of a certain type I extract a class. They all love the result but distrust the first step.
• karmelapple 4y ago
  For the software you're thinking about, do you have specific use cases or users in mind? Or are you building, say, an app for the first time, perhaps for a very early stage startup that is nowhere close to market fit yet? We typically write acceptance tests, and they have been helpful either early on or later in our product development lifecycle. Even if software isn't defined upfront, the end goal is likely defined upfront, isn't it? "User X should be able to get data about a car," or "User Y should be able to add a star ratings to this review," etc. If you're building a product where you're regularly throwing out large parts of the UI / functionality, though, I suppose it could be bad. But as a small startup, we have almost never been in that situation over the many years we've been in business.
• jwarden 4y ago
  I wish I could remember who wrote the essay with the idea of tests as investment in protecting functionality. When after a bit of experimentation or iteration you think you have figured out more or less one part of how your software should behave, then you want to protect that result. It is worth investing in writing and maintaining a test to make sure you don't accidentally break this functionality. Functionality based on a set of initial specs and a hazy understanding of the actual problem you are trying to solve might on the other hand might not be worth investing in protecting.
• archibaldJ 4y ago
  Thus spake the Master Programmer: "When a program is being tested, it is too late to make design changes." - The Tao of Programming (1987)
• eitally 4y ago
  I still remember a project (I was the eng director and one of my team leads did this) where my team lead for a new dev project was given a group of near-shore SWEs + offshore SQA who were new to both the language & RDBMS of choice, and also didn't have any business domain experience. He decided that was exactly the time to implement TDD, and he took it upon himself to write 100% test coverage based on the approved specs, and literally just instructed the team to write code to pass the tests. They used daily stand-ups to answer questions, and weekly reviews to assess themes & progress. It was slow going, but it was a luxurious experience for the developers, many of whom were using pair programming at the time and now found themselves on a project where they had a committed & dedicated senior staffer to actively review their work and coach them through the project (and new tools learnings). I had never allowed a project to be run like that before, but it was one where we had a fairly flexible timeline as long as periodic deliverables were achieved, so I used it as a kind of science project to see how something that extreme would fare. The result was that 1) the devs were exceptionally happy, 2) the TL was mostly happy, except with some of the extra forced work he created for himself as the bottleneck, 3) the project took longer than expected, and 4) the code was SOOOOO readable but also very inefficient. We realized during the project that forcing unit tests for literally everything was also forcing a breaking up of methods & functions into much smaller discrete pieces than would have been optimal from both performance & extensibility perspectives. It wasn't the last TDD project we ran, but we were far more flexible after that. I had one other "science project" while managing that team, too. It was one where we decided to create an architect role (it was the hotness at that time), and let them design everything from the beginning, after which the dev team would run with it using their typical agile/sprint methodology. We ended up with the most spaghetti code of abstraction upon abstraction, factories for all sorts of things, and a codebase that became almost unsupportable from the time it was launched, necessitating v2.0 be a near complete rewrite of the business logic and a lot of the data interfaces. The lessons I learned from those projects was that it's important to have experienced folks on every dev team, and that creating a general standard that allows for flexibility in specific architectural/technical decisions will result in higher quality software, faster, than if one is too prescriptive (either in process or in architecture/design patterns). I also learned that there's no such thing as too much SQA, but that's for a different story.
• jonstewart 4y ago
  It's funny, because I feel like TDD -- not just unit-testing, but TDD -- is most helpful when things aren't well-defined. I think back to "what's the simplest test that could fail?" and it helps me focus on getting some small piece done. From there, it snowballs and the code emerges. Obviously it's not always perfect, and something learned along the way spurs refactoring/redesign. That always strikes me as a natural process. In many ways I guess I lean maximalist in my practices, and find it helpful, but I'd readily concede that the maximalist advocates are annoying and off-putting. I once had the opportunity to program with Ward Cunningham for a weekend, and it was a completely easygoing and pragmatic experience.
• julianlam 4y ago
  I often come up with test cases (just the cases, not the actual logic) while writing the feature. However I am never in the mood to context switch to write the test, so I'll do the bare minimum. I'll flip over to the test file and write the `it()` boilerplate with the one-line test title and flip back to writing the feature. By the time I've reached a point where the feature can actually be tested, I end up with a pretty good skeleton of what tests should be written. There's a hidden benefit to doing this, actually. It frees up your brain from keeping that running tally of "the feature should do X" and "the feature should guard against Y", etc. (the very items that go poof when you get distracted, mind you)
  • majikandy 4y ago
    I seem to remember this being mentioned in the original TDD book. To brain dump that next test scenario title you think of so as to get it out of your head and get back to the current scenario you are trying to make pass. So by the same idea as above, to not context switch between the part of the feature you are trying to get to work.
• smrtinsert 4y ago
  I don't see how you can develop anything without at least technical clarity on what the components of your system should do.
• deleted 4y ago
  [deleted]
• no_wizard 4y ago
  thats kind of TDDs core point. you don't really know upfront, so you write tests to validate what you can define up front, and through that, you should find you discover other things that were not accounted for, and the cycle continues, until you have a working system that satisfies the requirements. Then all those tests serve as a basic form of documentation & reasonable validation of the software so when further modifications are desired, you don't break what you already know to be reasonably valid. Therefore, TDD's secret sauce is in concretely forcing developers to think through requirements, mental models etc. and quantify them in some way. When you hit a block, you need to ask yourself whats missing, then figure out, and continue onward, making adjustments along the way. This is quite malleable to unknown unknowns etc. I think the problem is most people just aren't chunking down the steps of creating a solution enough. I'd argue that the core way of approaching TDD fights most human behavioral traits. It forces a sort of abstract level of reasoning about something that lets you break things down into reasonable chunks.
  • pjmlp 4y ago
    I doubt ZFS authors would have succeeded designing it with TDD.
    • no_wizard 4y ago
      What's inherent about this problem that wouldn't benefit from chunking things into digestible, iterative parts that lend themselves nicely to the TDD approach as I described?
      • pjmlp 4y ago
        Don't write any code without tests doesn't provide a path to data structure design, or device drivers infrastructure.
        • no_wizard 4y ago
          What about behaviors and expectations? At the end of the day you’re verifying behaviors and expectations of software. I mean when designing a solution you need to think these things through. TDD compliments this just the same
• jiggawatts 4y ago
  This is precisely my experience also. I loved TDD when developing a parser for XLSX files to be used in a PowerShell pipeline. I created dozens of “edge case” sample spreadsheets with horrible things in them like Bad Strings in every property and field. Think control characters in the tab names, RTL Unicode in the file description, etc… I found several bugs… in Excel.
• quickthrower2 4y ago
  You can do TDD if you do something managers hate! And that is, write code, chuck it away, start again. Prototype your feature without TDD. Then chuck it away and build it again with TDD. My guess is by doing so code quality and reduced technical debt pay more than what is lost in time. Very few companies work like this I imagine: None that I have worked for. Since keyboard typing is a short part of software development it is probably a great use of time and could catch more bugs and design quirks early on when they cost $200/h instead of $2000/h.
• ParetoOptimal 4y ago
  >Unfortunately most software is just not well defined up front. Because for years people have practice with defining software iteratively, whether by choice or being forced by deadlines and agile. That doesn't inherently make one or the other harder, it's just another familiarity problem. TDD goes nicely with top-down design using something like Haskell's undefined to stub out functionality that typechecks and it's where clauses. myFunction = haveAParty . worldPeace . fixPoverty $ world where worldPeace = undefined haveAParty = undefined fixPoverty = undefined Iterative designs usually suck to maintain and use because they reflect the organizational structure of your company. That'll happen anyway to an extent, but better abstractions to make future you and future co-workers lives easier are totally worth it.
• silversmith 4y ago
  > The trouble with TDD is that quite often we don't really know how our programs are going to work Interesting - for me, that's the only time I truly practice TDD, when I don't know how the code is going to work. It allows me to start with describing the ideal use case - call the API / function I would like to have, describe the response I would expect. Then work on making those expectations a reality. Add more examples. When I run into a non-trivial function deeper down, repeat - write the ideal interface to call, describe the expected response, make it happen. For me, TDD is the software definition process itself. And if you start with the ideal interface, chances are you will end up with something above average, instead of whatever happened to fall in place while arranging code blocks.
• mirzap 4y ago
  > The trouble with TDD is that quite often we don't really know how our programs are going to work > The obvious exception to this, where I still use TDD, is when implementing a well defined spec. From my understanding (and experience), TDD is quite the opposite. It's most useful when you don't have the spec, don't have clue how software will work in the end. TDD creates the spec, iteratively.
  • pjmlp 4y ago
    Unless we are talking about any kind of GUI.
• majikandy 4y ago
  It sounds a little like you are trying to write all the tests to the spec up front? With TDD you are still allowed to change design choices as you go and as you realise how you want it to behave. That’s why the tests are one by one. In my experience, TDD carries the most value when you really don’t know where you are going, you write the first test and you start rolling, and somehow you end up at your destination and people think you were good at writing code but actually the code was writing itself in a way as it evolved its was to completeness.
  • Double_a_92 4y ago
    But often you don't know at all how to best solve a problem, since the solution will probably need to touch many existing code units somehow. It might work if you are starting on some new, relatively self-contained feature...
    • majikandy 4y ago
      Since you don’t know how to solve it, you first write a test that goes vaguely in the direction. If you can’t do that yet, you spike, mess around with it, get your bearings and some insight into where you want to go, try a few things out. Then, trash that and then write the first test as above. It almost always works, and excels somewhat in legacy code vs just changing things. It isn’t about ‘might work’. The TDD paradigm isn’t about finding shiny places where you can use. It is just a nice way of writing clean maintainable software in almost all areas. Places where TDD won’t work are usually by exception rather than the norm. Often those exceptions are where something already exists and wasn’t put in by TDD because by the definition of TDD you wouldn’t have been able to write that in the first place.
• hgomersall 4y ago
  Since I've moved to full time rust I'm finding it much harder to precede the code with tests (ignoring for a moment the maximalist/minimalist discussion). I think it's the because the abstractions can be so powerful that the development process is iterating over high level abstractions. The bit I worry about testing is the business logic, but that in my experience is not something you can test with a trivial unit test, and that test tends to iterate with the design to some extent. Essentially I end up with a series of behavioural tests and an implementation that as far as possible can't take inputs that can be mishandled (through e.g. the newtype pattern, static constraints etc). I'm not quite sure what is right or wrong about my approach, but I do find the code tends to work and work reliably once it compiles and the tests pass.
• gjadi 4y ago
  Isn't the issue because we are reluctant to remove stuff? In the same vein as other said we should throw away one or two version of a program before shipping it. Maybe we need to learn how to delete stuff that doesn't make sense. Get rid of broken test. Get rid of incorrect documentation. Don't be afraid to delete stuff to improve the overall program.
• mrjin 4y ago
  TDD is not really about making designs right but preventing known good logic from being broken unexpectedly and repeatedly.