9 ms·

An apology to readers of Test-Driven iOS Development

231 points by Morendil 14y ago

habitue 14y ago
It's great to see such intellectual honesty. It looks like the real perpetrator, however, is McConnell.
- Maxious 14y ago
  "The fact that no studies have produced findings that contradict the 10x claim provides even more confidence in the 10x claim. When I consider the number of studies that have been done, in aggregate I find the research to be not only suggestive, but conclusive—which is rare in software engineering research." Steve McConnell http://forums.construx.com/blogs/stevemcc/archive/2011/01/09/origins-of-10x-how-valid-is-the-underlying-research.aspx http://forums.construx.com/blogs/stevemcc/archive/2011/01/09... http://news.ycombinator.com/item?id=4117417 http://news.ycombinator.com/item?id=4117417
  - Morendil 14y ago
    The linked post isn't about the 10x claim, it's about the unrelated "defect cost increase" claim.
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  - nateberkopec 14y ago
    Yikes, that doesn't strike me as very intellectually sound. "The fact that no studies have produced findings that contradict the existence of a teapot orbiting Jupiter..."
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    - gruseom 14y ago
      I think if you read the article you'll find that that's unfair. His argument is that there are many studies that support it and none that contradict it, and that such consistency is unusual in the literature. That may be wrong but it's not trivially stupid as you make it sound.
  - gruseom 14y ago
    Someone needs to defend McConnell here. I'll do it. He's one of the most meticulous people to work with this material. That comes through pretty clearly in the post you linked to. The problem is not McConnell, it's – and this is the dirty secret of software engineering – that the research literature itself is so weak and spotty. Most studies consist of arbitrary metrics on small data sets with no replication, rarely (ever?) making the actual data available. Massive assumptions and confounding factors are typically obvious and ignored (things like: how familiar were the programmers with the tools they were using). The overwhelming factor is the interpretive preferences of the authors, who knit their conclusions out of this dodgy material. As science, it not only does not hold up, it's a joke. On the other hand, what they are trying to study is incredibly complex - not just people, not just software, but people working on software, and even social systems of people working on software. How do you even begin to reliably measure that? Psychology looks like physics by comparison. Yet the resources available to do these studies are a drop in the bucket. This is not something society values – it's not even something our own industry values. So it's unsurprising that what we have so far is at best a smattering. You can argue that these toy studies ought not to be dressed up in formal scientific wear, and I don't disagree – it gives an altogether misleading impression of how solid their conclusions are. But no doubt that's true of a lot of papers. (Oh and on top of all that, much of the literature is hard to track down. Didn't anyone notice that the OP wasn't able to even find half of the citations he was trying to check? Based on that alone he shouldn't be claiming that "the table is completely false", only that he was unable to rebuild it from data.) The real question is whether we should throw it all out as junk or try to make something of it. I think there's a good argument for junking. But it's also reasonable to say: hold on, for all their weaknesses these studies are all we have and they're not nothing. At least someone is trying to work with actual data. So let's consider them, but carefully. Like walking on a swamp. McConnell is one of the few people who have made serious efforts to walk the swamp and filter it somewhat and convey its findings to professional programmers. Of all these people (that I've read), he actually stands out as the most meticulous. To fire cowboy accusations of dishonesty at him personally is likely unfair and misses the point. I do think McConnell overestimates how solid the swamp is, but he's not ignorant about it (read that whole post) and the claim that he outright falsifies citations, or anything like that, demands a high burden of proof. I haven't read Bossavit's critique (should I?) but anyone taking that position had better first make sure he's not standing on a swamp too. That's harder than it sounds.
zwdr 14y ago
I wish more authors would check their references like that. Not that I am interested in iOS-development, but still.
sunraa 14y ago
Lots of props to the blog author for going through the hoops that I suppose we should all be going through. I've always placed the CC books up there in the pantheon of great software engineering books. This is a chink in the armor and I hope Mr McConnell takes the time to provide a response although I'm not holding my breath. Another object lesson in not accepting things at face value.
thebooktocome 14y ago
Previously on LessWrong: http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange_case_of_the/ http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange...
- cousin_it 14y ago
  Note that the author of that post is Laurent Bossavit, the author of the "Leprechauns" book that was referenced in the OP.
consultutah 14y ago
Hopefully this will end in a discussion in which the actual data underlying the table can be had and matched up. Anecdotally, it seems to make sense that it is more expensive to find and fix a defect later in the process. If a dev finds a defect while implementing a feature, only his costs are involved. However, if a defect is found later in the our process, at least 2 qa analysts are involved: one to find the defect and another to confirm it. After that a project manager schedules out time and assigns the defect out to a developer, possibly not the one that introduced the defect gets the assignment to fix it. The developer fixes the defect, a build is made by the build person. The original tester retests the defect and marks the fix as being verified. That seems complex, but there are possibly even more steps than that. Unit tests may need to be written, customer test cases may need to be updated. I don't know if the costs end up being exponentially greater, but they would seem to be greater. At any rate, it would be good to have someone independently validate that data.
- philwelch 14y ago
  It's not written in stone that you need 2 QA analysts, a project manager, a developer, and a build master to fix a bug. That only proves that bureaucracy is expensive, not that fixing bugs "late" in the process is expensive! I'm not sure what exactly the second QA person adds to the process. As a developer, I need to be able to reproduce a bug myself in order to have any chance of fixing it, so there's your confirmation step right there. Project manager? No, just have your QA person file the ticket as a bug (with the correct priority) and have your developers pull tickets off your bug tracker themselves. At worst, a slight email/verbal nudge from the usual boss should do. Build person? No, have a continuous, automated build system. The job of the build person should be to maintain that system, not to run individual builds. Now you're down to one QA person to file the ticket, one developer to fix the bug, and the same QA person again to close the ticket. Add in a few minutes of another developer's time to code review the first developer (you don't even do that despite having all that process?) and it's still cheaper. Unit tests? Developers write their own unit tests. Have a failing unit test that reproduces the root cause of the bug before you fix the bug--that's a best practice anyway. For testing above and beyond that, it's not unreasonable to have SDETs maintain that stuff, though you already have the root cause of the bug captured in a unit test so your main concern should be whether any existing tests actually rely upon the broken behavior.
f4stjack 14y ago
So yeah, long story short from what I gather is: I couldn't find the referenced sources to the table I am referencing so it must be false! What a leap of logic, seriously...
- pilif 14y ago
  That's not at all what he way saying. In the conclusion at the end of the article he said that "I therefore no longer consider Table 1-1 in Test-Driven iOS Development to be representative of defect fixing in software engineering [...]". So while the data might still be true, the numbers are not necessarily accurate and thus you shouldn't base conclusions on that table. He doesn't say that the values are wrong - just that they might be incorrect. On a related note: I'd love to get real numbers for this. Fixing bugs happening in production certainly feels much more expensive and cumbersome, but is there real data aside of this table which now apparently is inaccurate.
  - f4stjack 14y ago
    Well, that was what I gathered from the part I'll about to quote. But considering English is not my native language I might have misunderstood his meaning: "As explained in the book, this table is reproduced from an earlier publication: Table 1.1, reproduced from Code Complete, 2nd Edition, by Steve McConnell (Microsoft Press, 2004), shows the results of a survey that evaluated the cost of fixing a bug as a function of the time it lay “dormant” in the product. The table shows that fixing bugs at the end of a project is the most expensive way to work, which makes sense… The first mistake I made was simply that I seem to have made up the bit about it being the result of a survey. I don’t know where I got that from. In McConnell, it’s titled “Average Cost of Fixing Defects Based on When They’re Introduced and Detected” (Table 3-1, at the top of page 30). It’s introduced in a paragraph marked “HARD DATA”, and is accompanied by an impressive list of references in the table footer. McConnell: The data in Table 3-1 shows that, for example, an architecture defect that costs $1000 to fix when the architecture is being created can cost $15,000 to fix during system test. As already covered, the first problem is that I misattributed the data in the table. The second problem, and the one that in my opinion I’ve let down my readers the most by not catching, is that the table is completely false."
grayprog 14y ago
I know Graham. And he's both a great guy and a serious developer. I've also read his book and though I've not yet finished it, I've seen this table, as it's in the beginning. Having read this blog post, I now respect him even more. Both for the intellectual honesty and for his efforts to try and reconcile the data in the table, with all its consequences. I wish more people (including me) were this dedicated and willing to admit mistakes. Maybe that's what makes him a specialist in software security, of all things.
smoyer 14y ago
I seem to remember first seeing a table like the one the author describes in "The Mythical Man Month" but my copy is currently at home. The data underlying that book was gathered from projects at IBM in the '60s and '70s and I don't really doubt that the underlying data was fairly represented. The bigger question is whether improvements in processes and tools have obsoleted this data. TDD and automated regression testing would be one place where inter-phase defects could become less costly. On the other hand, projects that have uncorrected architectural errors can be completely functional and yet their maintenance costs never decrease. If someone has a copy handy, please validate my memory otherwise I'll check when I get home this evening.
- alttag 14y ago
  I've just gone through it page-by-page, and didn't see a table like that. Using the 20th Anniversary Edition, I also looked through the summarized list of claims in each chapter, and the 20-year retrospective, and did not see the table or a section that might have been a textual version of the same data. Perhaps the closest bit I found was in the chapter "Plan One to Throw Away": "The total cost of maintaining a widely used program is typically 40 percent or more of the cost of developing it" (p 121). Similarly, another section quotes Capers Jones, "Focus on quality, and productivity will follow" (p 217, emphasis original). That, I think, is about as close as MMM gets to these claims.
  - smoyer 14y ago
    I couldn't find it either but in addition to "Code Complete" this data is also shown in a chart in "The Software Project Survival Guide", also by Steve McConnell (p29). The attribution is "Researchers have found" but Boehm and Papaccio are listed in the references.
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Shish2k 14y ago
> I therefore no longer consider Table 1-1 in Test-Driven iOS Development to be representative of defect fixing in software engineering Surely this makes it more representative, in a literal sense -- if he'd checked his data at the start, he wouldn't have to go back to check it + issue an apology + reprint the books now :P
- marshray 14y ago
  The general idea ("bugs found later tend to cost more to correct") is uncontroversial. It's also accepted that this is a very difficult thing to study. There are so many subjective factors involved that's it's really hard to quantify the data or the results. But it seems to me that if Software Engineering as a wants to make progress methodically, it needs to throw out the old unsubstantiated assumptions in order to make room for new conclusions with a solid basis.
aptwebapps 14y ago
I wonder if he tried asking McConnell just how he compiled the table. It does seem a bit odd to construct such a simple table from eight different sources.
- mcguire 14y ago
  ...none of which seem to have the actual data to support the table.
siddhartag 14y ago
While its great that Graham has said all this, and it shows a lot of professionalism, it was probably not really necessary. After all, its a book, not a research paper. The point is, it gets more expensive to fix a bug later on. We aren't going to shoot down the book because some numbers, only tangentially related to the subject (of learning TDD for iOS), were off. Still, kudos for blogging it when he came across new information.
diego_moita 14y ago
Call me cynical but I am getting very skeptical against a lot of well established "truths" in Software Engineering: the cone of uncertainty, the orders of magnitude difference in programmers productivity, the efficiency of TDD, ... Most of these well established claims simply don't have enough empirical data to sustain them. They're all bloggers' hand waving and empty claims.
- itmag 14y ago
  the orders of magnitude difference in programmers productivity I am skeptical of this too. It makes more sense to have huge swings in ability, not productivity. Ie a poor programmer won't take 10x as long to code a given feature, he will just hit a ceiling of ability and not be able to do it at all.
  - robomartin 14y ago
    >Ie a poor programmer won't take 10x as long to code a given feature, he will just a ceiling of ability and not be able to do it at all. 10x longer is not a poor programmer, that's an incompetent programmer. If someone needs ten days to code something that can be done in one day something is very seriously wrong.
    - sirclueless 14y ago
      Are you surprised by that? The 10x longer statement doesn't surprise me at all. If you ask someone, "Please implement a Java class that has the following methods and behaves like this" you might expect any competent programmer to finish within ~3x of each other. But given some more nebulous task, where architectural decisions must be made and serious research and testing needs to be done, it's not surprising at all. For example, if you asked someone, "Please write me a library so that I can send and receive XMPP messages," I would expect a large number of otherwise competent programmers to make a significant number of false starts and poor decisions, and generally take much more time than the guy who has experience writing libraries and interpreting text protocols. For example, consider the case of Ron Jeffries and Peter Norvig writing a sudoku solver[1] (this example is a perennial favorite of mine in all sorts of discussions). And I don't think anything is "very seriously wrong" with this situation. Different skillsets and competence levels result in drastically different results. I think this is true of any profession that is largely about creative problem-solving: some can do it efficiently, some cannot. Programming is just a unique case because there are so many people trying it and not being deterred due to poor performance because there is such a demand. [1] http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-solvers.html http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-s...
robomartin 14y ago
The time and cost to fix bugs can have a huge variance which is sometimes dependent on the nature and field of the software being written. There are bugs that take seconds to fix and others that take months. I have personally experienced hunting down a bug for six months nearly full time (10 to 12 hours per day) until it was finally found. This was a real-time hardware system and the code was that of an FPGA. The culprit was a coefficient in one of many polyphase finite impulse response filters. The calculations used to generate this coefficient were done in a huge Excel spreadsheet. At one point, in the hundreds of equations in the spreadsheet, the author had used the ROUND() function when the ROUNDUP() function should have been used. This was enough cause a buffer issue in the FIFO feeding the polyphase filter. These are tricky problems to track down when you are literally looking for events that take somewhere in the order of single-digit nanoseconds to occur. On the other hand, there are those bugs where you know exactly what is going on and where in the code it is happening the instant you see the behavior. We've all experienced that during the course of software development. Fixing bugs for a dating website has vastly different requirements than, say, fixing bugs in a flight control system. One argument is for more up-front planning in order to avoid some bugs. At one point this can quickly become counterproductive. Sometimes it's better to just start writing code and fix issues as they come up. Now, if we are talking about fixing bugs after the fact, that's a different matter. One example here might be if you inherit the code to a complex website or an engine control system and, without any familiarity with the code, are required to fix bugs. This can easily take cubic time as it requires to learn the code-base (and sometimes the subject matter) while also trying to hunt down bugs. This is why I tend to take such tables or studies with great skepticism. I haven't really paid much attention to these studies, but I remember looking at one or two of them and thinking that they tended to focus on narrow cases such as fixing bugs in-house, with a stable programmer team and great familiarity with the code base.
- lttlrck 14y ago
  Skepticism is deserved. It's a very fine balance, and bearing in mind not much software exist that is entirely bug-free. What is the cost of a bug that is never discovered? Is it negative? What is the cost of fixing a bug that would never have caused a problem (at each stage of development)? It's way more complex than bugs == bad
ludflu 14y ago
Much respect for the frankness and forthrightness with which he addressed this. I've always taken the exponential increase in the cost of bug fixes with time for granted. I won't do so in the future. We need more empirical studies of software development!
unreal37 14y ago
It seems he wasn't able to see some of the sources. One cost money to see, one is out of print and not available... It may be true and noble that since he isn't able to verify the data himself, he shouldn't have used it. But if you can't see the sources, you also can't state that the data is incorrect. One of those books he couldn't find might contain the data that directly corroborates this. I suspect the cost of fixing defects has more to do with your internal process, and less to do with how much work it takes to find and fix the actual defect. I have a client I work for now for which I need about 10 days lead time to get code from development to production. So it might take 1 hour to fix a bug that is discovered, and 8 hours to do the paperwork and go through the formal process of moving code through testing, staging and finally to production.
Tashtego 14y ago
Anecdotally, I have certainly found that although the cost in time may not vary as much as this table would indicate, the cost in stress ramps up even faster. Fixing a bug in production is usually a highly stressful endeavor for all involved. I would love to see a similar table phrased in terms of stress comparing different development methodologies currently in vogue (test and throw it over the wall, CI, automated pushes vs. manual pushes, etc.)
jakejake 14y ago
Based on my own subjective experience I've found the numbers regarding testing to be suspicious simply because "bugs" are so varied that any specific number would be subjective. I'd always assumed that these numbers referred to an architectural type of bug where, once made, more code is built upon the bug and so a cascading effect occurs. The more code that relies on the bug, the worse it is to fix because you have to fix all of it's dependent code. In some cases you may need to repair data, or entirely refactor sections of an application. But there's other bugs that are more "typo" level bugs where obviously the time to fix is exactly the same no matter what phase of development. I had just always assumed those numbers were a worse-case average to encourage developers to better plan their architecture. In part because the context of code complete is more about planning and estimation. Though there may not be support for the exact figures, I think the point of them is to not let things pile up and to try to put thought into your design especially at the architectural levels.
- MattRogish 14y ago
  This seems to have been my experience and interpretation as well. A bug is not a mistake in coding, but a mistake in selecting core architecture, 3rd party libraries, etc. Making a mistake picking the wrong storage engine can cause major problems if you find it can't scale to your load after 12 months of development. That's a ton of code to change if you're switching from MySQL to Redis (for a crazy example). Make a mistake in copy or layout, and that's usually much easier to change.
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Morendil 14y ago
Amusing exchange over at Reddit: Redditor 1: "I bet not a single f$%k was given about that table among the readers of the book :)" Redditor 2: "That table, or something like it, features strongly in every software engineering textbook that I've ever seen. The numbers differ, but the increasing order of magnitude differences are roughly the same. It's the essential justification for nearly everything in software engineering. "A single f$%k" doesn't begin to describe the importance of that table." And yes, "the essential justification for nearly everything in software engineering" is broadly correct. Anytime you see an argument that "it's important to get the requirements right" for instance, it's based on studies that purport to show these numbers.
- ajross 14y ago
  Indeed, with the semantic cavet that "software engineering" is used in the sense of "software development management process nattering" and not (always) the actual engineering of working software. The basic falseness of that chart is pretty well known among the hacker set. Or maybe it's a failure of interpretation among the natterers: the "high cost" of mistakes in the past is made mostly of work already spent. The immediate cost of correcting a past mistake is often (of course not always!) vastly lower than people think. And the farther you are from the actual code involved (i.e. if your role is "architect"), the higher your overestimate of that value is going to be. So this is a feedback loop: the "high level" people at the start of the process have a built-in bias against iterative solutions (which they perceive as "expensive") and thus a built-in predilection to overdesign as they try to get everything right the first time.
  - mcguire 14y ago
    I'm glad someone else sees the difference between the engineering of working software and the "process nattering" that seems to make up official "software engineering" as far as I can tell. You do miss a couple of steps in the feedback loop: 1. "The 'high level' people at the start of the process have a built-in bias against iterative solutions." 2. "A built-in predilection to overdesign as they try to get everything right the first time." 3. The wild-ass guesses that make up the overdesign prove to be completely wrong. 4. The project fails miserably or succeeds, miserably. 5. The "high level" people perceive software as "very expensive", reinforcing their biases.
jamieb 14y ago
"The second problem, and the one that in my opinion I’ve let down my readers the most by not catching, is that the table is completely false." There is a big difference between "unsupported by hard data" and "completely false", especially when the author later admits to not being willing to pay to see the first paper cited in support. It also seems, (from this post: http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange_case_of_the/ http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange...) that in fact the first line is supported by data, if only in aggregate. The author of that blog posts makes much of the phrase "this study didn't accurately record" while glossing over the next part of the sentence that states "so we will use average rates summarized from several other studies." It is common practice to aggregate data, and provided it is done properly, the aggregation can reduce error, not increase it. The claim that "a bug introduced in Requirements, costs more to fix the later it is discovered" is claimed to be supported by data. Well done for demanding to see that data. But epic fail for creating controversy by claiming that the opposite is true.
emmapersky 14y ago
A google scholar search for the title of the paper behind the paywall reveals numerous copies freely available through university websites.
emmapersky 14y ago
A google scholar search for the title of the paper behind the paywall reveals numerous copies freely available through university websites.
MaxGabriel 14y ago
Would people who've read the book recommend it? It sounds interesting to read because I'm not experienced with TDD, and iOS tends to shy away from it.

231 points by Morendil 14y ago

habitue 14y ago

It's great to see such intellectual honesty. It looks like the real perpetrator, however, is McConnell.

Maxious 14y ago
"The fact that no studies have produced findings that contradict the 10x claim provides even more confidence in the 10x claim. When I consider the number of studies that have been done, in aggregate I find the research to be not only suggestive, but conclusive—which is rare in software engineering research." Steve McConnell http://forums.construx.com/blogs/stevemcc/archive/2011/01/09/origins-of-10x-how-valid-is-the-underlying-research.aspx http://forums.construx.com/blogs/stevemcc/archive/2011/01/09... http://news.ycombinator.com/item?id=4117417 http://news.ycombinator.com/item?id=4117417
- Morendil 14y ago
  The linked post isn't about the 10x claim, it's about the unrelated "defect cost increase" claim.
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- nateberkopec 14y ago
  Yikes, that doesn't strike me as very intellectually sound. "The fact that no studies have produced findings that contradict the existence of a teapot orbiting Jupiter..."
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  - gruseom 14y ago
    I think if you read the article you'll find that that's unfair. His argument is that there are many studies that support it and none that contradict it, and that such consistency is unusual in the literature. That may be wrong but it's not trivially stupid as you make it sound.
- gruseom 14y ago
  Someone needs to defend McConnell here. I'll do it. He's one of the most meticulous people to work with this material. That comes through pretty clearly in the post you linked to. The problem is not McConnell, it's – and this is the dirty secret of software engineering – that the research literature itself is so weak and spotty. Most studies consist of arbitrary metrics on small data sets with no replication, rarely (ever?) making the actual data available. Massive assumptions and confounding factors are typically obvious and ignored (things like: how familiar were the programmers with the tools they were using). The overwhelming factor is the interpretive preferences of the authors, who knit their conclusions out of this dodgy material. As science, it not only does not hold up, it's a joke. On the other hand, what they are trying to study is incredibly complex - not just people, not just software, but people working on software, and even social systems of people working on software. How do you even begin to reliably measure that? Psychology looks like physics by comparison. Yet the resources available to do these studies are a drop in the bucket. This is not something society values – it's not even something our own industry values. So it's unsurprising that what we have so far is at best a smattering. You can argue that these toy studies ought not to be dressed up in formal scientific wear, and I don't disagree – it gives an altogether misleading impression of how solid their conclusions are. But no doubt that's true of a lot of papers. (Oh and on top of all that, much of the literature is hard to track down. Didn't anyone notice that the OP wasn't able to even find half of the citations he was trying to check? Based on that alone he shouldn't be claiming that "the table is completely false", only that he was unable to rebuild it from data.) The real question is whether we should throw it all out as junk or try to make something of it. I think there's a good argument for junking. But it's also reasonable to say: hold on, for all their weaknesses these studies are all we have and they're not nothing. At least someone is trying to work with actual data. So let's consider them, but carefully. Like walking on a swamp. McConnell is one of the few people who have made serious efforts to walk the swamp and filter it somewhat and convey its findings to professional programmers. Of all these people (that I've read), he actually stands out as the most meticulous. To fire cowboy accusations of dishonesty at him personally is likely unfair and misses the point. I do think McConnell overestimates how solid the swamp is, but he's not ignorant about it (read that whole post) and the claim that he outright falsifies citations, or anything like that, demands a high burden of proof. I haven't read Bossavit's critique (should I?) but anyone taking that position had better first make sure he's not standing on a swamp too. That's harder than it sounds.

zwdr 14y ago

I wish more authors would check their references like that. Not that I am interested in iOS-development, but still.

sunraa 14y ago

Lots of props to the blog author for going through the hoops that I suppose we should all be going through. I've always placed the CC books up there in the pantheon of great software engineering books. This is a chink in the armor and I hope Mr McConnell takes the time to provide a response although I'm not holding my breath. Another object lesson in not accepting things at face value.

thebooktocome 14y ago

Previously on LessWrong: http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange_case_of_the/ http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange...

cousin_it 14y ago
Note that the author of that post is Laurent Bossavit, the author of the "Leprechauns" book that was referenced in the OP.

consultutah 14y ago

Hopefully this will end in a discussion in which the actual data underlying the table can be had and matched up. Anecdotally, it seems to make sense that it is more expensive to find and fix a defect later in the process. If a dev finds a defect while implementing a feature, only his costs are involved. However, if a defect is found later in the our process, at least 2 qa analysts are involved: one to find the defect and another to confirm it. After that a project manager schedules out time and assigns the defect out to a developer, possibly not the one that introduced the defect gets the assignment to fix it. The developer fixes the defect, a build is made by the build person. The original tester retests the defect and marks the fix as being verified. That seems complex, but there are possibly even more steps than that. Unit tests may need to be written, customer test cases may need to be updated. I don't know if the costs end up being exponentially greater, but they would seem to be greater. At any rate, it would be good to have someone independently validate that data.

philwelch 14y ago
It's not written in stone that you need 2 QA analysts, a project manager, a developer, and a build master to fix a bug. That only proves that bureaucracy is expensive, not that fixing bugs "late" in the process is expensive! I'm not sure what exactly the second QA person adds to the process. As a developer, I need to be able to reproduce a bug myself in order to have any chance of fixing it, so there's your confirmation step right there. Project manager? No, just have your QA person file the ticket as a bug (with the correct priority) and have your developers pull tickets off your bug tracker themselves. At worst, a slight email/verbal nudge from the usual boss should do. Build person? No, have a continuous, automated build system. The job of the build person should be to maintain that system, not to run individual builds. Now you're down to one QA person to file the ticket, one developer to fix the bug, and the same QA person again to close the ticket. Add in a few minutes of another developer's time to code review the first developer (you don't even do that despite having all that process?) and it's still cheaper. Unit tests? Developers write their own unit tests. Have a failing unit test that reproduces the root cause of the bug before you fix the bug--that's a best practice anyway. For testing above and beyond that, it's not unreasonable to have SDETs maintain that stuff, though you already have the root cause of the bug captured in a unit test so your main concern should be whether any existing tests actually rely upon the broken behavior.

f4stjack 14y ago

So yeah, long story short from what I gather is: I couldn't find the referenced sources to the table I am referencing so it must be false! What a leap of logic, seriously...

pilif 14y ago
That's not at all what he way saying. In the conclusion at the end of the article he said that "I therefore no longer consider Table 1-1 in Test-Driven iOS Development to be representative of defect fixing in software engineering [...]". So while the data might still be true, the numbers are not necessarily accurate and thus you shouldn't base conclusions on that table. He doesn't say that the values are wrong - just that they might be incorrect. On a related note: I'd love to get real numbers for this. Fixing bugs happening in production certainly feels much more expensive and cumbersome, but is there real data aside of this table which now apparently is inaccurate.
- f4stjack 14y ago
  Well, that was what I gathered from the part I'll about to quote. But considering English is not my native language I might have misunderstood his meaning: "As explained in the book, this table is reproduced from an earlier publication: Table 1.1, reproduced from Code Complete, 2nd Edition, by Steve McConnell (Microsoft Press, 2004), shows the results of a survey that evaluated the cost of fixing a bug as a function of the time it lay “dormant” in the product. The table shows that fixing bugs at the end of a project is the most expensive way to work, which makes sense… The first mistake I made was simply that I seem to have made up the bit about it being the result of a survey. I don’t know where I got that from. In McConnell, it’s titled “Average Cost of Fixing Defects Based on When They’re Introduced and Detected” (Table 3-1, at the top of page 30). It’s introduced in a paragraph marked “HARD DATA”, and is accompanied by an impressive list of references in the table footer. McConnell: The data in Table 3-1 shows that, for example, an architecture defect that costs $1000 to fix when the architecture is being created can cost $15,000 to fix during system test. As already covered, the first problem is that I misattributed the data in the table. The second problem, and the one that in my opinion I’ve let down my readers the most by not catching, is that the table is completely false."

grayprog 14y ago

I know Graham. And he's both a great guy and a serious developer. I've also read his book and though I've not yet finished it, I've seen this table, as it's in the beginning. Having read this blog post, I now respect him even more. Both for the intellectual honesty and for his efforts to try and reconcile the data in the table, with all its consequences. I wish more people (including me) were this dedicated and willing to admit mistakes. Maybe that's what makes him a specialist in software security, of all things.

smoyer 14y ago

I seem to remember first seeing a table like the one the author describes in "The Mythical Man Month" but my copy is currently at home. The data underlying that book was gathered from projects at IBM in the '60s and '70s and I don't really doubt that the underlying data was fairly represented. The bigger question is whether improvements in processes and tools have obsoleted this data. TDD and automated regression testing would be one place where inter-phase defects could become less costly. On the other hand, projects that have uncorrected architectural errors can be completely functional and yet their maintenance costs never decrease. If someone has a copy handy, please validate my memory otherwise I'll check when I get home this evening.

alttag 14y ago
I've just gone through it page-by-page, and didn't see a table like that. Using the 20th Anniversary Edition, I also looked through the summarized list of claims in each chapter, and the 20-year retrospective, and did not see the table or a section that might have been a textual version of the same data. Perhaps the closest bit I found was in the chapter "Plan One to Throw Away": "The total cost of maintaining a widely used program is typically 40 percent or more of the cost of developing it" (p 121). Similarly, another section quotes Capers Jones, "Focus on quality, and productivity will follow" (p 217, emphasis original). That, I think, is about as close as MMM gets to these claims.
- smoyer 14y ago
  I couldn't find it either but in addition to "Code Complete" this data is also shown in a chart in "The Software Project Survival Guide", also by Steve McConnell (p29). The attribution is "Researchers have found" but Boehm and Papaccio are listed in the references.

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Shish2k 14y ago

> I therefore no longer consider Table 1-1 in Test-Driven iOS Development to be representative of defect fixing in software engineering Surely this makes it more representative, in a literal sense -- if he'd checked his data at the start, he wouldn't have to go back to check it + issue an apology + reprint the books now :P

marshray 14y ago
The general idea ("bugs found later tend to cost more to correct") is uncontroversial. It's also accepted that this is a very difficult thing to study. There are so many subjective factors involved that's it's really hard to quantify the data or the results. But it seems to me that if Software Engineering as a wants to make progress methodically, it needs to throw out the old unsubstantiated assumptions in order to make room for new conclusions with a solid basis.

aptwebapps 14y ago

I wonder if he tried asking McConnell just how he compiled the table. It does seem a bit odd to construct such a simple table from eight different sources.

mcguire 14y ago
...none of which seem to have the actual data to support the table.

siddhartag 14y ago

While its great that Graham has said all this, and it shows a lot of professionalism, it was probably not really necessary. After all, its a book, not a research paper. The point is, it gets more expensive to fix a bug later on. We aren't going to shoot down the book because some numbers, only tangentially related to the subject (of learning TDD for iOS), were off. Still, kudos for blogging it when he came across new information.

diego_moita 14y ago

Call me cynical but I am getting very skeptical against a lot of well established "truths" in Software Engineering: the cone of uncertainty, the orders of magnitude difference in programmers productivity, the efficiency of TDD, ... Most of these well established claims simply don't have enough empirical data to sustain them. They're all bloggers' hand waving and empty claims.

itmag 14y ago
the orders of magnitude difference in programmers productivity I am skeptical of this too. It makes more sense to have huge swings in ability, not productivity. Ie a poor programmer won't take 10x as long to code a given feature, he will just hit a ceiling of ability and not be able to do it at all.
- robomartin 14y ago
  >Ie a poor programmer won't take 10x as long to code a given feature, he will just a ceiling of ability and not be able to do it at all. 10x longer is not a poor programmer, that's an incompetent programmer. If someone needs ten days to code something that can be done in one day something is very seriously wrong.
  - sirclueless 14y ago
    Are you surprised by that? The 10x longer statement doesn't surprise me at all. If you ask someone, "Please implement a Java class that has the following methods and behaves like this" you might expect any competent programmer to finish within ~3x of each other. But given some more nebulous task, where architectural decisions must be made and serious research and testing needs to be done, it's not surprising at all. For example, if you asked someone, "Please write me a library so that I can send and receive XMPP messages," I would expect a large number of otherwise competent programmers to make a significant number of false starts and poor decisions, and generally take much more time than the guy who has experience writing libraries and interpreting text protocols. For example, consider the case of Ron Jeffries and Peter Norvig writing a sudoku solver[1] (this example is a perennial favorite of mine in all sorts of discussions). And I don't think anything is "very seriously wrong" with this situation. Different skillsets and competence levels result in drastically different results. I think this is true of any profession that is largely about creative problem-solving: some can do it efficiently, some cannot. Programming is just a unique case because there are so many people trying it and not being deterred due to poor performance because there is such a demand. [1] http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-solvers.html http://ravimohan.blogspot.com/2007/04/learning-from-sudoku-s...

robomartin 14y ago

The time and cost to fix bugs can have a huge variance which is sometimes dependent on the nature and field of the software being written. There are bugs that take seconds to fix and others that take months. I have personally experienced hunting down a bug for six months nearly full time (10 to 12 hours per day) until it was finally found. This was a real-time hardware system and the code was that of an FPGA. The culprit was a coefficient in one of many polyphase finite impulse response filters. The calculations used to generate this coefficient were done in a huge Excel spreadsheet. At one point, in the hundreds of equations in the spreadsheet, the author had used the ROUND() function when the ROUNDUP() function should have been used. This was enough cause a buffer issue in the FIFO feeding the polyphase filter. These are tricky problems to track down when you are literally looking for events that take somewhere in the order of single-digit nanoseconds to occur. On the other hand, there are those bugs where you know exactly what is going on and where in the code it is happening the instant you see the behavior. We've all experienced that during the course of software development. Fixing bugs for a dating website has vastly different requirements than, say, fixing bugs in a flight control system. One argument is for more up-front planning in order to avoid some bugs. At one point this can quickly become counterproductive. Sometimes it's better to just start writing code and fix issues as they come up. Now, if we are talking about fixing bugs after the fact, that's a different matter. One example here might be if you inherit the code to a complex website or an engine control system and, without any familiarity with the code, are required to fix bugs. This can easily take cubic time as it requires to learn the code-base (and sometimes the subject matter) while also trying to hunt down bugs. This is why I tend to take such tables or studies with great skepticism. I haven't really paid much attention to these studies, but I remember looking at one or two of them and thinking that they tended to focus on narrow cases such as fixing bugs in-house, with a stable programmer team and great familiarity with the code base.

lttlrck 14y ago
Skepticism is deserved. It's a very fine balance, and bearing in mind not much software exist that is entirely bug-free. What is the cost of a bug that is never discovered? Is it negative? What is the cost of fixing a bug that would never have caused a problem (at each stage of development)? It's way more complex than bugs == bad

ludflu 14y ago

Much respect for the frankness and forthrightness with which he addressed this. I've always taken the exponential increase in the cost of bug fixes with time for granted. I won't do so in the future. We need more empirical studies of software development!

unreal37 14y ago

It seems he wasn't able to see some of the sources. One cost money to see, one is out of print and not available... It may be true and noble that since he isn't able to verify the data himself, he shouldn't have used it. But if you can't see the sources, you also can't state that the data is incorrect. One of those books he couldn't find might contain the data that directly corroborates this. I suspect the cost of fixing defects has more to do with your internal process, and less to do with how much work it takes to find and fix the actual defect. I have a client I work for now for which I need about 10 days lead time to get code from development to production. So it might take 1 hour to fix a bug that is discovered, and 8 hours to do the paperwork and go through the formal process of moving code through testing, staging and finally to production.

Tashtego 14y ago

Anecdotally, I have certainly found that although the cost in time may not vary as much as this table would indicate, the cost in stress ramps up even faster. Fixing a bug in production is usually a highly stressful endeavor for all involved. I would love to see a similar table phrased in terms of stress comparing different development methodologies currently in vogue (test and throw it over the wall, CI, automated pushes vs. manual pushes, etc.)

jakejake 14y ago

Based on my own subjective experience I've found the numbers regarding testing to be suspicious simply because "bugs" are so varied that any specific number would be subjective. I'd always assumed that these numbers referred to an architectural type of bug where, once made, more code is built upon the bug and so a cascading effect occurs. The more code that relies on the bug, the worse it is to fix because you have to fix all of it's dependent code. In some cases you may need to repair data, or entirely refactor sections of an application. But there's other bugs that are more "typo" level bugs where obviously the time to fix is exactly the same no matter what phase of development. I had just always assumed those numbers were a worse-case average to encourage developers to better plan their architecture. In part because the context of code complete is more about planning and estimation. Though there may not be support for the exact figures, I think the point of them is to not let things pile up and to try to put thought into your design especially at the architectural levels.

MattRogish 14y ago
This seems to have been my experience and interpretation as well. A bug is not a mistake in coding, but a mistake in selecting core architecture, 3rd party libraries, etc. Making a mistake picking the wrong storage engine can cause major problems if you find it can't scale to your load after 12 months of development. That's a ton of code to change if you're switching from MySQL to Redis (for a crazy example). Make a mistake in copy or layout, and that's usually much easier to change.

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Morendil 14y ago

Amusing exchange over at Reddit: Redditor 1: "I bet not a single f$%k was given about that table among the readers of the book :)" Redditor 2: "That table, or something like it, features strongly in every software engineering textbook that I've ever seen. The numbers differ, but the increasing order of magnitude differences are roughly the same. It's the essential justification for nearly everything in software engineering. "A single f$%k" doesn't begin to describe the importance of that table." And yes, "the essential justification for nearly everything in software engineering" is broadly correct. Anytime you see an argument that "it's important to get the requirements right" for instance, it's based on studies that purport to show these numbers.

ajross 14y ago
Indeed, with the semantic cavet that "software engineering" is used in the sense of "software development management process nattering" and not (always) the actual engineering of working software. The basic falseness of that chart is pretty well known among the hacker set. Or maybe it's a failure of interpretation among the natterers: the "high cost" of mistakes in the past is made mostly of work already spent. The immediate cost of correcting a past mistake is often (of course not always!) vastly lower than people think. And the farther you are from the actual code involved (i.e. if your role is "architect"), the higher your overestimate of that value is going to be. So this is a feedback loop: the "high level" people at the start of the process have a built-in bias against iterative solutions (which they perceive as "expensive") and thus a built-in predilection to overdesign as they try to get everything right the first time.
- mcguire 14y ago
  I'm glad someone else sees the difference between the engineering of working software and the "process nattering" that seems to make up official "software engineering" as far as I can tell. You do miss a couple of steps in the feedback loop: 1. "The 'high level' people at the start of the process have a built-in bias against iterative solutions." 2. "A built-in predilection to overdesign as they try to get everything right the first time." 3. The wild-ass guesses that make up the overdesign prove to be completely wrong. 4. The project fails miserably or succeeds, miserably. 5. The "high level" people perceive software as "very expensive", reinforcing their biases.

jamieb 14y ago

"The second problem, and the one that in my opinion I’ve let down my readers the most by not catching, is that the table is completely false." There is a big difference between "unsupported by hard data" and "completely false", especially when the author later admits to not being willing to pay to see the first paper cited in support. It also seems, (from this post: http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange_case_of_the/ http://lesswrong.com/lw/9sv/diseased_disciplines_the_strange...) that in fact the first line is supported by data, if only in aggregate. The author of that blog posts makes much of the phrase "this study didn't accurately record" while glossing over the next part of the sentence that states "so we will use average rates summarized from several other studies." It is common practice to aggregate data, and provided it is done properly, the aggregation can reduce error, not increase it. The claim that "a bug introduced in Requirements, costs more to fix the later it is discovered" is claimed to be supported by data. Well done for demanding to see that data. But epic fail for creating controversy by claiming that the opposite is true.

emmapersky 14y ago

A google scholar search for the title of the paper behind the paywall reveals numerous copies freely available through university websites.

emmapersky 14y ago

A google scholar search for the title of the paper behind the paywall reveals numerous copies freely available through university websites.

MaxGabriel 14y ago

Would people who've read the book recommend it? It sounds interesting to read because I'm not experienced with TDD, and iOS tends to shy away from it.