Related
I've been reading about TDD lately, and it is advocated because it supposedly results in code that is more testable and less coupled (and a bunch of other reasons).
I haven't been able to find much in the way of practical examples, except for a Roman numeral conversion and a number-to-English converter.
Observing these two examples, I observed the typical red-green-refactor cycles typical of TDD, as well as the application of the rules of TDD. However, this seemed like a big waste of time when normally I would observe a pattern and implement it in code, and then write tests for it after. Or possibly write a stub for the code, write the unit tests, and then write the implementation - which might arguably be TDD - but not this continuous case-by-case refactoring.
TDD appears to incite developers to jump right into the code and build their implementation inductively rather than designing a proper architecture. My opinion so far is that the benefits of TDD can be achieved by a proper architectural design, although admittedly not everyone can do this reasonably well.
So here I have two questions:
Am I right in understanding that using TDD pretty much doesn't allow you to design first (see the rules of TDD)?
Is there anything that TDD gives you that you can't get from doing proper design before you start coding?
well, I was in your shoes some time ago and had the same questions. Since then I have done quite some reading about TDD and decided to mess with it a little.
I can summarize my experience about TDD in these points:
TDD is unit testing done right, ATDD/BDD is TDD done right.
Whether you design beforehand or not is totally up to you. Just make sure you don't do BDUF. Believe me you will end up changing most of it midways because you can never fully understand the requirements until your hands get dirty.
OTOH, you can do enough design to get you started. Class diagrams, sequence diagrams, domain models, actors and collaborators are perfectly fine as long as you don't get hung up in the design phase trying to figure everything out.
Some people don't do any design at all. They just let the code talk and concentrate on refactoring.
IMHO, balance your approach. Do some design till you get the hang of it then start testing. When you reach a dead end then go back to the white board.
One more thing, some things can't be solved by TDD like figuring out an algorithm. This is a very interesting post that shows that some things just need to be designed first.
Unit testing is hard when you have the code already. TDD forces you to think from your API users perspective. This way you can early on decide if the public interface from your API is usable or not. If you decide to do unit testing after implementing everything you will find it tedious and most probably it will be only for some cases and I know some people who will right only passing test cases just to get the feature done. I mean who wants to break his own code after all that work?
TDD breaks this mentality. Tests are first class citizens. You aren't allowed to skip tests. You aren't allowed to postpone some tests till the next release because we don't have enough time.
Finally to answer your question if there anything that TDD gives you that you can't get from doing proper design before you start coding, I would say commitment.
As long as your doing TDD you are committed to apply good OO principles, so that your code is testable.
To answer your questions:
"Test Driven Development" (TDD) is often referred to as "Test Driven Design", in that this practice will result in a good design of the code. When you have written a failing unit test, you are forced into a test driven design approach, so that you can implement just what is needed to make the test pass i.e. you have to consider the design of the code you are writing to make the test pass.
When using a TDD approach a developer will implement the minimum amount of code required to pass the test. Doing proper design beforehand usually results in waste if the requirements change once the project has started.
You say "TDD appears to incite developers to jump right into the code and build their implementation inductively rather than designing a proper architecture" - If you are following an Agile approach to your software development, then you do still need to do some up front architectural investigation (e.g. if you were using the Scrum methodology you would create a development "Spike" at the start of a project) to ascertain what the minimum amount of architecture needed to start the project. At this stage you make decisions based on what you know now e.g. if you had to work with a small dataset you'd choose to use a regular DB, if you have a huge DB you might to choose to use a NoSQL big data DB etc.
However, once you have a general idea of the architecture, you should let the design evolve as the project progresses leaving further architectural decisions as late in the process as possible; Invariably as a project progresses the architecture and requirements will change.
Further more this rather popular post on SO will give you even more reasons why TDD is definetly worth the effort.
Can TDD be successful as a defect-reduction strategy without incorporating guidance on test case construction and evaluation?
IMO, my answer would be no. For TDD to be effective, there has to be guidelines around what is a test and what it means to have something be reasonably tested. Without a guideline, there may be some developers that end up with tons of defects because their initial tests cover a very small set of inputs,e.g. only the valid ones, which can cause the idea of using TDD to become worthless.
Test driven development can reduce defects in a QA cycle simply because testing allows developers to find defects prior to releasing their code to the QA team.
But without guidance on how to test you really won't be able to create any kind of long-term benefit since haphazard testing will only prevent defects by blind luck. Good tests based on good guidance can go a long way towards reducing defects.
if you don't have tests to reproduce defects, how do you know that "defect reduction" has taken place?
of course you do have tests - they're just manual, and thus tedious and time-consuming to reproduce...
Here's a study (warning: link to PDF file) done by microsoft on some of their internal teams.
A quote from it:
The results of the case studies indicate that the pre-release defect density of the four products decreased between 40% and 90% relative to similar projects that did not use the TDD practice. Subjectively, the teams experienced a 15–35% increase in initial development time after adopting TDD
That's the only actual empirical study done on TDD/Unit testing that I'm aware of, but there are plenty of people (including myself) that will anecdotally tell you that TDD (and unit testing in general) will definitely provide an increase in the quality of your code.
From my own experience, there is definitely a reduction in the number of defects, but the numbers feel like they would be far less than even the 40% from the Microsoft study; This is (again, based solely on what I've seen) primarily because most corporate developers have little to no experience with Unit Testing (let alone TDD), and will invariably do a bad job of it while they are learning. Actually learning how to do TDD well requires at least a solid year of experience, and I've never worked in (or even seen) a team which actually had a full complement of developers with that experience.
You may want to pickup a copy of Gerard Meszaros' xUnit Test Patterns. Specifically, Chapter 5 might apply most directly to your question where it covers the Principles of Test Automation. Some of those principles that I think apply to your scenario where there needs to be some sort of guidance, common interest, or some sort of implied do this or fear the wrath of :
Principle: Communicate Intent
Tests need to be easy to maintain, readily apparent what the test is doing.
Principle: Keep Tests Independent
Small tests that cover one small piece. Tests should not interfere with each other.
Principle: Minimize Test Overlap
Need to design tests that cover a specific piece, and do not create tests that exercise the same paths repeatedly.
Principle: Verify One Condition Per Test
This one seemed simple enough for me, but is one of the most challenging in my experiences for people to grasp. I may write tests that have some multiple asserts, but I try to keep all those together around the specific area. When it comes to hunting down failures and other test issues, it is MUCH easier to fiddle with a single test that is testing a specific path instead of several different paths all clumped into a single test method.
Further relating to my experiences, if we want to talk about the corporate developer, I have seen some folks that are interested and take the initiative to learn something new, but more often than not, you have folks that like to go with the flow, and like to have things laid out for them. Without some sort of direction, be it a mandate from a senior engineer-type, or some sort of joint-team discussions (see Practices of an Agile Developer for some ideas such as lunch time meetings once a week), I think your chance of success would be limited.
In a team situation, where your code is likely to be used by someone else, the tests have a fringe benefit that can reduce defects without necessarily even improving anyone's code.
Where documentation is poor (which during development is "often"), the tests act a crib for how you expect your code to be called. So, even in cases where the code is really very fragile, TDD can still reduce the number of defects raised against the end-product -- by ensuring your colleagues can see well-written tests before they can use your code, you've ensured they know how you intend your code to be used before they call it. They are thus less-likely to call your code in an unexpected sequence / without having configured something you expected (but forgot to write a check for) as a prerequisite. Thus they are less likely to trigger the failure condition, and you are less likely to see them or the (human) test team raising a defect because something crashed.
Of course, whether you see that "there's a hidden bug in there, it's just not being called yet" as a problem itself is another good question.
I'm "just" a hobbyist programmer, but I find that as my programs get longer and longer the bugs get more annoying--and harder to track. Just when everything seems to be running smoothly, some new problem will appear, seemingly spontaneously. It may take me a long time to figure out what caused the problem. Other times I'll add a line of code, and it'll break something in another unit. This can get kind of frustrating if I thought everything was working well.
Is this common to everyone, or is it more of a newbie kind of thing? I hear about "unit testing," "design frameworks," and various other concepts that sound like they would decrease bugginess, make my apps "robust," and everything easy to understand at a glance :)
So, how big a deal are bugs to people with professional training?
Thanks -- Al C.
The problem of "make a fix, cause a problem elsewhere" is very well known, and is indeed one of the primary motivations behind unit testing.
The idea is that if you write exhaustive tests for each small part of your system independently, and run them on the entire system every time you make a change anywhere, you will see the problem immediately. The main benefit, however, is that in the process of building these tests you'll also be improving your code to have less dependencies.
The typical solution to these sort of problems is to reduce coupling; make different parts less dependent on one another. More experienced developers sometimes have habits or design skills to build systems in this manner. For example, we use interfaces and implementations rather than classes; we use model-view-controller for user interfaces, etc. In addition, we can use tools that help further reduce dependencies, like "Dependency injection" and aspect oriented programming.
All programmers make mistakes. Good and experienced programmers build their programs so that it is easier to find the mistakes and restrict their effects.
And it is a big deal for everyone. Most companies spend more time on maintenance than on writing new code.
Are you automating your tests? If you do not, you're signing up creating bugs without finding them.
Are you adding tests for bugs as you fix them? If you do not, you are signing up for creating the same bugs over and over.
Are you writing unit tests? If not, you are signing up for long debugging sessions when a test fails.
Are you writing your unit tests first? If not, your unit tests will be hard to write when your units are tightly coupled.
Are you refactoring mercilessly? If not, every edit will become more difficult and more likely to introduce bugs. (But make sure you have good tests, first.)
When you fix a bug, are you fixing the entire class? Don't just fix the bug; don't just fix similar bugs throughout your code; change the game so you can never create that kind of bug again.
Bugs are a big deal to everyone. I've always found that the more I program, the more I learn about programming in general. I cringe at the code I wrote a few years back!! I started out as a hobbyist and liked it so much that I went to engineering college to get a Computer Science Engineering major (I am in my final semester). These are the things that I have learned :
I take time to actually design what I am going to write and document the design. It really eliminates a lot of problems down the line. Whether the design is as simple as writing down a few points on what I am going to write or full blown UML modeling (:( ) doesn't matter. Its the clarity of thought and purpose and having material to look back at when I come back to the code after a while that matter the most.
No matter what language I write in, keeping my code simple and readable is important. I think that it is extremely important not to over complicate the code and at the same time not to over simplify it. (Hard learned lesson!!)
Efficiency optimizations and fancy tricks should be applied at the end, only when necessary and only if they are needed. Another thing is that I apply them only If I really know what I am doing and I always test my code!
Learning language dependant details helps me keep my code bug free. For instance I learned that scanf() is evil in C!
Others have already commented on the zen of writing tests. I would like to add that you should always do regression tests. (i.e. Write new code, test all parts of your code to see if it breaks)
Keeping a mental picture of code is hard at times, so I always document my code.
I use methods to make sure that there is a bare minimum dependence between different parts of my code. Interfaces, class hierarchies etc. (Decoupled design)
Thinking before I code and being disciplined in whatever I write is another crucial skill. I know people who don't format their code so its readable (Shudder!).
Reading other peoples source to learn best practices is good. Making my own list is better!. When working in a team, there must be a common set of them.
Don't be paralyzed by analysis. Write tests, then code, then execute and test. Rinse wash repeat!
Learning to read over my own code and combing it for mistakes is important. Improving my arsenal of debugging skills was a great investment. I keep them sharp by helping my classmates fix bugs regularly.
When there is a bug in my code, I assume its my mistake, not the computers and work from there. That is a state of mind that really helps me.
A fresh pair of eyes aids in debugging. Programmers tend to miss even the most obvious errors in their own code when exhausted. Having someone to show your code to is great.
having someone to throw ideas at and not be judged is important. I talk to my mom (who is not a programmer) , throw ideas at her and find solutions. She helps me bounce my ideas back and forth and refine them. If she is unavailable, I talk to my pet cat.
I am not so be discouraged by bugs anymore. I've learned to love removing bugs almost as much as programming.
Using version control has really helped me manage different ideas I get while coding. That helps reduce errors. I recommend using git or any other version control system you might like.
As Jay Bazzuzi said - Refactor code. I just added this point after reading his answer, to keep my list complete. All credit goes to him.
Try to write reusable code. Reuse code, both yours and from libraries. Using libraries which are bug free to do some common tasks really reduces bugs (sometimes).
I think the following quote says it best - "If debugging is the art of removing bugs, programming must be the art of putting them in."
No offense to anyone who disagrees. I hope this answer helps.
Note
As others Peter has pointed out, use Object Oriented Programming if you are writing a large amount of code. There is a limit to code length after which it becomes harder and harder to manage if written procedurally. I like procedural for smaller stuff, like playing with algorithms.
There are two ways to write error-free programs; only the third one works. ~Alan J. Perlis
The only way for errors to occur in a program is by being put there by the author. No other mechanisms are known. Programs can't acquire bugs by sitting around with other buggy programs. ~Harlan Mills
Obviously, bugs are a big deal to any programmer. Just look through the list of questions on Stack Overflow to see this illustrated.
The difference between a hobbyist and an experienced professional is that the pro will be able to use his experience to code in a more "defensive" way, avoiding many types of bugs in the first place.
All the other answers are great. I'll add two things.
Source control is mandatory. I'm assuming you're on windows here. VisualSVN Server is free and maybe 4 clicks to install. TortoiseSVN is also free and it integrates into Windows Explorer, getting around the VS Express limitations of no add-ins. If you create too many bugs, you can revert your code and start over. Without source control, this is next to impossible. Plus you can sync your code if you have a laptop and a desktop.
People are going to recommend many techniques like unit testing, mocking, Inversion of Control, Test Driven Development, etc. These are great practices, but don't try to cram it all into your head too quickly. You have to write code to get better at writing code, so work these techniques slowly into your code writing. You have to crawl before you walk and walk before you can run.
Best of luck in your coding adventures!
This is a common newbie thing. As you get more experience, of course, you'll still have bugs, but they'll be easier to find and fix because you'll learn how to make your code more modular (so that changing one thing doesn't have ripple effects everywhere else), how to test it, and how to structure it to fail fast, close to the source of the problem, rather than in some arbitrary place. One very basic but useful thing that doesn't require complex infrastructure to implement is to check the inputs to all functions that have non-trivial precondtions with asserts. This has saved me several times in cases where I would have otherwise gotten weird segfaults and arbitrary behavior that would have been near impossible to debug.
If bugs weren't a problem then I'd be able to write a 100,000 line program in 10 minutes!
Your question is like, "As an amateur doctor, I worry about my patients' health: sometimes when I'm not careful enough, they sicken. Is patients' health a problem for you professional doctors too?"
Yes: it's the central problem, even the only problem (for any sufficiently all-inclusive definition of 'bug').
Bugs are common to everyone -- professional or not.
The larger and more distributed the project, the more careful one must be. One look at any open source bug database (ex: https://bugzilla.mozilla.org/ ) will confirm this for you.
The software industry has evolved various programming styles and standards, which when used right, make wrong code easier to spot or limited in its impact.
Therefore, training has a very positive on code quality... But at the end of the day, bugs still sneak through.
If you're just a hobbyist programmer, learning full bore TDD and OOP may involve more time than you're willing to put in. So, going on the assumption that you don't want to put in the time on them, a few easily digestible suggestions to cut down on bugs are:
Keep each function doing one thing. Be suspect of a function more than, say, 10 lines long. If you think you can break it into two functions, you probably should. Something that will help you control this is naming your functions according to exactly what they are doing. If you find that your names are long and unwieldy then you function is probably doing too many things.
Turn magic strings into constants. That is, instead of using:
people["mom"]
use instead
var mom = "mom";
people[mom]
Design your functions to either do something (command) or get something (query), but not both.
An extremely short and digestible take on OOP is here http://www.holub.com/publications/notes_and_slides/Everything.You.Know.is.Wrong.pdf. If you get this, you've got the gist of OOP and are quite frankly ahead of a lot of professional programmers.
The prevailing wisdom seems to be that the average programmer creates 12 bugs per 1000 lines of code - depends on who you ask for the exact number, but it's always per lines of code - so, the bigger the program, the more the bugs.
Subpar programmers tend to create way more bugs.
Newbies are often trapped by idiosyncrasies of the language, and lacking experience tends towards more bugs too. As you go on, you will get better, but never will you create bug-free code... well I still have bugs, even after 30 years, but that could be just me.
Nasty bugs happen to everyone from pros to hobbyists. Really good programmers get asked to track down really nasty bugs. It's part of the job. You'll know you've made it as a software developer when you stare at a nasty bug for two days and in frustration you shout, "Who wrote this crap!?!?" ... only to realize it was you. :-)
Part of the skill of a software developer is the ability to keep a large set of interrelated items straight in his/her head. It sounds like you're discovering what happens when your mental model of the system breaks down. With practice you will learn to design software that doesn't feel so brittle. There are tons of books, blogs, etc. out there on the subject of software design. And Stack Overflow of course for specific questions.
All that said, here's a couple of things you can do:
A good debugger is invaluable. Often you have to step through your code line by line to figure out what went wrong.
Use a garbage-collected language such as Python or Java if it makes sense for your project. GC will help you focus on making things work instead of getting bogged down by maddening memory errors.
If you write C++, learn to love RAII.
Write LOTS of code. Software is somewhat of an art form. Lots of practice will make you better at it.
Welcome to Stack Overflow!
What really changed my odds against code complexity and bugs was using a coding standart - how to place brackets an so on. It may seem like just boring and useless thing but it really unifies all the code and makes it much easier to read and maintain. So do you use a coding standart?
If you're not well organized, your codebase will become your very own Zebra Puzzle. Adding more code is like adding more people/animals/houses to your puzzle, and soon you have 150 various animals, people, houses and cigarette brands in your puzzle and you realize that it just took you a week to add 3 lines of code because everything is so inter-related that it takes forever to make sure the code still executes how you want it to.
The most popular organizational paradigm seems to be Object Oriented Programming, if you can break your logic down into small units which can be constructed and used independently of each other, then you will find bugs far less painful when they occur.
I have a project that I have been working on for a while, just one of those little pet projects that I would like to one day release to open source.
Now I started the project about 12 months ago but I was only working on it lightly, I have just started to concentrate a lot more of my time on it(almost every night).
Because it is a framework like application I sometimes struggle with a sense of direction due to the fact I don't have anything driving my design decisions and I sometimes end up making features that are hard to use or even find. I have been reading about how to do TDD and thought maybe this will help me with some of the problems that I am having.
So the question is do you think it's a good idea to start using TDD on a project that doesn't already use it.
EDIT: I have just added a bit to clarify what I mean by struggle with a "sense of direction", it properly wasn't the best thing to say without clarification.
In my opinion, it's never too late to adopt a better practice - or to drop a worse one - so I'd say "Yes, you should start".
However ... (there's always a "but") ...
... one of the biggest gains of TDD is that it impacts on your design, encouraging you to keep reponsibilties separate, interactions clean and so on.
At this point in your project, you may find it difficult to get tests written for some aspects of your framework. Don't give up though, even if you can't test some areas, your quality will be the better for the areas you can test, and your skills will improve for the experience.
Yes.
Basically, you can't do any harm by adding TDD for any new code you write, and any changes you make to existing code. Obviously it would be tricky to go back and retro-fit accurate tests to existing code, but it certainly couldn't hurt to cover the primary use-cases.
Maybe consider having a look at Brownfield Application Development in .NET? It is full of pragmatic and practical advice for exactly this scenario (one of the definitions offered for "Brownfield" is "without proper unit tests").
Yes, absolutely a good idea to start doing TDD.
You will pay a start-up cost for at least two reasons:
Learning a new skill TDD/unit testing.
Retrofitting your code to be testable.
You'll need to do some of both, but as you work if you find yourself struggling think of which of those two is the source of the effort.
But the end result is worth it. From what you describe this is a project you intend to live with for quite a while. Remember that when you lose an hour here or there. In a year you'll be very happy that you made this investment both in your skill set and the code base.
At worse, you can just do TDD on new stuff, while you slowly create tests for your existing code base.
Yes, it's never too late to start using TDD. I have introduced TDD to a commercial project that was already running for five years when I joined, and it was definitely a good decision.
While you are new to the technique, you should probably concentrate on using it for the code that you are writing from a clean slate - new classes, new methods etc. Once you got a hang on it, start writing tests for code that you change.
For some of the code, the latter might prove to be difficult, because the code you have written until now is unlikely to be written with testability in mind. There are some techniques to deal with that, but it's probably too early to care about them.
If you are missing a sense of direction, though, I doubt that TDD will help you a lot. You might want to look into Acceptance Testing instead, which is at least as important as unit testing, and will help you focus on the functionality of the system instead of single units of code. The TDD book by Lasse Koskela is a good introduction to both techniques.
Another technique that might help you is the Extreme Programming planning game, where you put pieces of functionality on index cards and prioritize them. I typically notice that getting ideas out of my head and in prioritized order helps me a lot in understanding where I want to go next.
As others have said, TDD shouldn't hurt a project in progress, but think carefully if you're tempted to do large-scale refactoring just to allow testing. Make sure the benefits justify the cost.
I'm a little concerned that you "struggle with a sense of direction." I don't know that TDD will help you there. I find it's a great help for low-level design decisions, but not so great for architecture decisions. Adding TDD to a directionless project sounds a bit like having a baby to save a marriage - unwise. Hopefully I misread your intention.
Yes.
TDD makes it easier for other people to understand the code, as well as it gives the application a better design over time
In theory you were supposed to test first, but you didn't. In this scenario, contrary to others opinion, I wouldn't start with new features.
Take advantage of the 80:20 rule, run a profiler, and put the test cases to the most frequently called piece of code.
Put tests around the house jewel, gut, most-important code.
Put tests around the annoying, always-breaking, recurrent déjà vu buggy code.
Put tests around all bugs you come across before fixing the bug for failing test.
Warning: Putting test cases will require refactoring, which means you must fix something that's not breaking.
If you still love unit tests at this point, you'd be Red, Green, Refactoring on your own.
Absolutely.
Introduce TDD to new code and if time allows, introduce "Comment Driven Design" with your existing code if it's not already tested.
Comment out the block of existing code you need to test
Write your test
Uncomment your original code one statement at a time (if you have an if block, uncomment the entire block)
Determine if your original code ultimately passes your test and if not, re-write to pass your tests accordingly
Writing tests for existing, working code that you don't plan to change doesn't fit with the thrust of TDD, which is to write tests that teach you about the system you're building.
My approach to bringing in TDD mid-stream has been to:
write tests for all new features, and
when changing a piece of code, write a test that covers the existing functionality (to make sure I understand it), then change the test before changing the code.
It can also be beneficial to write tests for code related to code you're changing - e.g., if you're altering a parent class, you may want to build tests around child classes first to protect yourself from potential damage.
Yes, you should. I'm currently working on a project that until recently wasn't covered with unit tests, but we decided that we should start testing our code, so we started writing them now. Unfortunately, I'm the only developer that practices TDD, others just write tests after writing their code.
Still, I found that practicing TDD helps me write better code, and I write it faster than before. Now that I learned how to do TDD, I just don't want to go back to writing code the way I used to.
Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 3 years ago.
Improve this question
I'm a contract programmer with lots of experience. I'm used to being hired by a client to go in and do a software project of one form or another on my own, usually from nothing. That means a clean slate, almost every time. I can bring in libraries I've developed to get a quick start, but they're always optional. (and depend on getting the right IP clauses in the contract) Many times I can specify or even design the hardware platform... so we're talking serious freedom here.
I can see uses for constructing automated tests for certain code: Libraries with more than trivial functionality, core functionality with a high number of references, etc. Basically, as the value of a piece of code goes up through heavy use, I can see it would be more and more valuable to automatically test that code so that I know I don't break it.
However, in my situation, I find it hard to rationalize anything more than that. I'll adopt things as they prove useful, but I'm not about to blindly follow anything.
I find many of the things I do in 'maintenance' are actually small design changes. In this case, the tests would not have saved me anything and now they'd have to change too. A highly iterative, stub-first design approach works very well for me. I can't see actually saving myself that much time with more extensive tests.
Hobby projects are even harder to justify... they're usually anything from weekenders up to a say month long. Edge-case bugs rarely matter, it's all about playing with something.
Reading questions such as this one, The most voted on response seems to say that in that poster's experience/opinion TDD actually wastes time if you've got less than 5 people (even assuming a certain level of competence/experience with TDD). However, that appears to be covering initial development time, not maintenance. It's not clear how TDD stacks up over the entire life cycle of a project.
I think TDD could be a good step in the worthwhile goal of improving the quality of the products of our industry as a whole. Idealism on it's own is no longer all that effective at motivating me, though.
I do think TDD would be a good approach in large teams, or any size team containing at least one unreliable programmer. That's not my question.
Why would a sole developer with a good track record adopt TDD?
I'd love to hear of any kind of metrics done (formally or not) on TDD... focusing on solo developers or very small teams.
Failing that, anecdotes of your personal experiences would be nice, too. :)
Please avoid stating opinion without experience to back it. Let's not make this an ideology war. Also the skip greater employment options argument. This is simply an efficiency question.
I'm not about to blindly follow anything.
That's the right attitude. I use TDD all the time, but I don't adhere to it as strictly as some.
The best argument (in my mind) in favor of TDD is that you get a set of tests you can run when you finally get to the refactoring and maintenance phases of your project. If this is your only reason for using TDD, then you can write the tests any time you want, instead of blindly following the methodology.
The other reason I use TDD is that writing tests gets me thinking about my API up front. I'm forced to think about how I'm going to use a class before I write it. Getting my head into the project at this high level works for me. There are other ways to do this, and if you've found other methods (there are plenty) to do the same thing, then I'd say keep doing what works for you.
I find it even more useful when flying solo. With nobody around to bounce ideas off of and nobody around to perform peer reviews, you will need some assurance that you're code is solid. TDD/BDD will provide that assurance for you. TDD is a bit contraversial, though. Others may completely disagree with what I'm saying.
EDIT: Might I add that if done right, you can actually generate specifications for your software at the same time you write tests. This is a great side effect of BDD. You can make yourself look like super developer if you're cranking out solid code along with specs, all on your own.
Ok my turn... I'd do TDD even on my own (for non-spike/experimental/prototype code) because
Think before you leap: forces me to think what I want to get done before i start cranking out code. What am I trying to accomplish here.. 'If I assume I already had this piece.. how would I expect it to work?' Encourages interface-in design of objects.
Easier to change: I can make modifications with confidence.. 'I didn't break anything in step1-10 when i changed step5.' Regression testing is instantaneous
Better designs emerge: I've found better designs emerging without me investing effort in a design activity. test-first + Refactoring lead to loosely coupled, minimal classes with minimal methods.. no overengineering.. no YAGNI code. The classes have better public interfaces, small methods and are more readable. This is kind of a zen thing.. you only notice you got it when you 'get it'.
The debugger is not my crutch anymore : I know what my program does.. without having to spend hours stepping thru my own code. Nowadays If I spend more than 10 mins with the debugger.. mental alarms start ringing.
Helps me go home on time I have noticed a marked decrease in the number of bugs in my code since TDD.. even if the assert is like a Console trace and not a xUnit type AT.
Productivity / Flow: it helps me to identify the next discrete baby-step that will take me towards done... keeps the snowball rolling. TDD helps me get into a rhythm (or what XPers call flow) quicker. I get a bigger chunk of quality work done per unit time than before. The red-green-refactor cycle turns into... a kind of perpetual motion machine.
I can prove that my code works at the touch of a button
Practice makes perfect I find myself learning & spotting dragons faster.. with more TDD time under my belt. Maybe dissonance.. but I feel that TDD has made me a better programmer even when I don't go test first. Spotting refactoring opportunities has become second nature...
I'll update if I think of any more.. this is what i came up with in the last 2 mins of reflection.
I'm also a contract programmer. Here are my 12 Reasons Why I Love Unit Tests.
My best experience with TDD is centered around the pyftpdlib project. Most of the development is done by the original author, and I've made a few small contributions, but it's essentially a solo project. The test suite for the project is very thorough, and tests all the major features of the FTPd library. Before checking in changes or releasing a version, all tests are checked, and when a new feature is added, the test suite is always updated as well.
As a result of this approach, this is the only project I've ever worked on that didn't have showstopper bugs appear after a new release, have changes checked in that broke a major feature, etc. The code is very solid and I've been consistently impressed with how few bug reports have been opened during the life of the project. I (and the original author) attribute much of this success to the comprehensive test suite and the ability to test every major code path at will.
From a logical perspective, any code you write has to be tested, and without TDD then you'll be testing it yourself manually. On the flip side to pyftpdlib, the worst code by number of bugs and frequency of major issues, is code that is/was solely being tested by the developers and QA trying out new features manually. Things don't get tested because of time crunch or falling through the cracks. Old code paths are forgotten and even the oldest stable features end up breaking, major releases end up with important features non-functional. etc. Manual testing is critically important for verification and some randomization of testing, but based on my experiences I'd say that it's essential to have both manual testing and a carefully constructed unit test framework. Between the two approaches the gaps in coverage are smaller, and your likelihood of problems can only be reduced.
It does not matter whether you are the sole developer or not. You have to think of it from the application point of view. All the applications needs to work properly, all the applications need to be maintained, all the applications needs to be less buggy. There are of course certain scenarios where a TDD approach might not suit you. This is when the deadline is approaching very fast and no time to perform unit testing.
Anyways, TDD does not depend on a solo or a team environment. It depends on the application as a whole.
I don't have an enormous amount of experience, but I have had the experience of seeing sharply-contrasted approaches to testing.
In one job, there was no automated testing. "Testing" consisted of poking around in the application, trying whatever popped in your head, to see if it broke. Needless to say, it was easy for flat-out-broken code to reach our production server.
In my current job, there is lots of automated testing, and a full CI-system. Now when code gets broken, it is immediately obvious. Not only that, but as I work, the tests really document what features are working in my code, and what haven't yet. It gives me great confidence to be able to add new features, knowing that if I break existing ones, it won't go unnoticed.
So, to me, it depends not so much on the size of the team, but the size of the application. Can you keep track of every part of the application? Every requirement? Every test you need to run to make sure the application is working? What does it even mean to say that the application is "working", if you don't have tests to prove it?
Just my $0.02.
Tests allow you to refactor with confidence that you are not breaking the system. Writing the tests first allows the tests to define what is working behavior for the system. Any behavior that isn't defined by the test is by definition a by-product and allowed to change when refactoring. Writing tests first also drive the design in good directions. To support testability you find that you need to decouple classes, use interfaces, and follow good pattern (Inversion of Control, for instance) to make your code easily testable. If you write tests afterwards, you can't be sure that you've covered all the behavior expected of your system in the tests. You also find that some things are hard to test because of the design -- since it was likely developed without testing in mind -- and are tempted to skimp on or omit tests.
I generally work solo and mostly do TDD -- the cases where I don't are simply where I fail to live up to my practices or haven't yet found a good way that works for me to do TDD, for example with web interfaces.
TDD is not about testing it's about writing code. As such, it provides a lot of benefits to even a single developer. For many developers it is a mindshift to write more robust code. For example, how often do you think "Now how can this code fail?" after writing code without TDD? For many developers, the answer to that question is none. For TDD practioners it shifts the mindset to to doing things like checking if objects or strings are null before doing something with them because you are writing tests to specifically do that (break the code).
Another major reason is change. Anytime you deal with a customer, they can never seem to make up their minds. The only constant is change. TDD helps as a "safety net" to find all the other areas that could break.Even on small projects this can keep you from burning up precious time in the debugger.
I could go and on, but I think saying that TDD is more about writing code than anything should be enough to justify it's use as a sole developer.
I tend to agree with the validity of your point about the overhead of TDD for 'one developer' or 'hobby' projects not justifying the expenses.
You have to consider however that most best practices are relevant and useful if they are consistently applied for a long period of time.
For example TDD is saving you testing/bugfixing time in a long run, not within 5 minutes after you've created the first unit test.
You're a contract programmer which means that you will leave your current project when it will be finished and will switch to something else, most likely in another company. Your current client will have to maintain and support your application. If you do not leave the support team a good framework to work with they will be stuck. TDD will help the project to be sustainable. It will increase the stability of the code base so other people with less experience will not be able not do too much damage trying to change it.
The same applies for the hobby projects. You may be tired of it and will want to pass it to someone. You might become commercially successful (think Craiglist) and will have 5 more people working besides you.
Investment in proper process always pays-off, even if it is just gained experience. But most of the time you will be grateful that when you started a new project you decided to do it properly
You have to consider OTHER people when doing something. You you have to think ahead, plan for growth, plan for sustainability.
If you don't want to do that - stick to the cowboy coding, it's much simpler this way.
P.S. The same thing applies to other practices:
If you don't comment your code and you have ideal memory you'll be fine but someone else reading your code will not.
If you don't document your discussions with the customer somebody else will not know anything about a crucial decision you made
etc ad infinitum
I no longer refactor anything without a reasonable set of unit tests.
I don't do full-on TDD with unit tests first and code second. I do CALTAL -- Code A LIttle, Test A Little -- development. Generally, code goes first, but not always.
When I find that I've got to refactor, I make sure I've got enough tests and then I hack away at the structure with complete confidence that I don't have to keep the entire old-architecture-becomes-new-architecture plan in my head. I just have to get the tests to pass again.
I refactor the important bits. Get the existing suite of tests to pass.
Then I realize I forgot something, and I'm back to CALTAL development on the new stuff.
Then I see things I forgot to delete -- but are they really unused everywhere? Delete 'em and see what fails in the testing.
Just yesterday -- part way through a big refactoring -- I realized that I still didn't have the exact right design. But the tests still had to pass, so I was free to refactor my refactoring before I was even done with the first refactoring. (whew!) And it all worked nicely because I had a set of tests to validate the changes against.
For flying solo TDD is my copilot.
TDD lets me more clearly define the problem in my head. That helps me focus on implementing just the functionality that is required, and nothing more. It also helps me create a better API, because I'm writing a "client" before I write the code itself. I can also refactor without having to worry about breaking anything.
I'm going to answer this question quite quickly, and hopefully you will start to see some of the reasoning, even if you still disagree. :)
If you are lucky enough to be on a long-running project, then there will be times when you want to, for example, write your data tier first, then maybe the business tier, before moving on up the stack. If your client then makes a requirement change that requires re-work on your data layer, a set of unit tests on the data layer will ensure that your methods don't fail in undesirable ways (assuming you update the tests to reflect the new requirements). However, you are likely to be calling the data layer method from the business layer as well, and possibly in several places.
Let's assume you have 3 calls to a method in the business layer, but you only modify 2. In the third method, you may still be getting data back from your data layer that appears to be valid, but may break some of the assumptions you coded months before. Unit tests at this level (and above) should have been designed to spot broken assumptions, and in failing they should highlight to you that there is a section of code that needs to be revisited.
I'm hoping that this very simplistic example will be enough to get you thinking about TDD a little more, and that it might create a spark that makes you consider using it. Of course, if you still don't see the point, and you are confident in your own abilities to keep track of many thousands of lines of code, then I have no place to tell you you should start TDD.
The point about writing the tests first is that it enforces the requirements and design decisions you are making. When I mod the code, I want to make sure those are still enforced and it is easy enough to "break" something without getting a compiler or run-time error.
I have a test-first approach because I want to have a high degree of confidence in my code. Granted, the tests need to be good tests or they don't enforce anything.
I've got some pretty large code bases that I work on and there is a lot of non-trivial stuff going on. It is easy enough to make changes that ripple and suddenly X happens when X should never happen. My tests have saved me on several occasions from making a critical (but subtle) error that might have gone unnoticed by human testers.
When the tests do fail, they are opportunities to look at them and the production code and make sure that it is correct. Sometimes the design changes and the tests will need to be modified. Sometimes I'll write something that passes 99 out of 100 tests. That 1 test that didn't pass is like a co-worker reviewing my code (in a sense) to make sure I'm still building what I'm supposed to be building.
I feel that as a solo developer on a project, especially a larger one, you tend to be spread pretty thin.
You are in the middle of a large refactoring when all of a sudden a couple of critical bugs are detected that for some reason did not show up during pre-release testing. In this case you have to drop everything and fix them and after having spent two weeks tearing your hair out you can finally get back to whatever you were doing before.
A week later one of your largest customers realizes that they absolutely must have this cool new shiny feature or otherwise they won't place the order for those 1M units they should have already ordered a month ago.
Now, three months later you don't even remember why you started refactoring in the first place let alone what the code you are refactoring was supposed to do. Thank god you did a good job writing those unit tests because at least they tell you that your refactored code is still doing what it was supposed to do.
Lather, rinse, repeat.
..story of my life for the past 6 months. :-/
Sole developer should use TDD on his project (track record does not matter), since eventually this project could be passed to some other developer. Or more developers could be brought in.
New people will have extremely have hard time working with the code without the tests. They will break things.
Does your client own the source code when you deliver the product? If you can convince them that delivering the product with unit tests adds value, then you are up-selling your services and delivering a better product. From the client's perspective, test coverage not only ensures quality, it allows future maintainers to understand the code much more readily since the tests isolate functionality from the UI.
I think TDD as a methodology is not just about "having tests when making changes", thus it does not depend on team- nor on project size. It's about noting one's expectations about what a pice of code/an application does BEFORE one starts to really think about HOW the noted behaviour is implemented. The main focus of TDD is not only having test in place for written code but writing less code because you just do what make the test green (and refactor later).
If you're like me and find it quite hard to think about what a part/the whole application does WITHOUT thinking about how to implement it, I think its fine to write your test after your code and thus letting the code "drive" the tests.
If your question isn't so much about test-first (TDD) or test-after (good coding?) I think testing should be standard practise for any developer, wether alone or in a big team, who creates code which stays in production longer than three months. In my expirience that's the time-span after which even the original author has to think hard about what these twenty lines of complex, super-optimized, but sparsely documented code really code do. If you've got tests (which cover all paths throughth the code), there less to think - and less to ERR about, even years later...
Here are a few memes and my responses:
"TDD made me think about how it would fail, which made me a better programmer"
Given enough experience, being higly concerned with failure modes should naturally become part of your process anyway.
"Applications need to work properly"
This assumes you are able to test absolutely everything. You're not going to be any better at covering all possible tests correctly than you were at writing the functional code correctly in the first place. "Applications need to work better" is a much better argument. I agree with that, but it's idealistic and not quite tangible enough to motivate as much as I wish it would. Metrics/anecdotes would be great here.
"Worked great for my <library component X>"
I said in the question I saw value in these cases, but thanks for the anecdote.
"Think of the next developer"
This is probably one of the best arguments to me. However, it is quite likely that the next developer wouldn't practice TDD either, and it would therefore be a waste or possibly even a burden in that case. Back-door evangelism is what it amounts to there. I'm quite sure a TDD developer would really appeciate it, though.
How much are you going to appreciate projects done in deprecated must-do methodologies when you inherit one? RUP, anyone? Think of what TDD means to next developer if TDD isn't as great as everyone thinks it is.
"Refactoring is a lot easier"
Refactoring is a skill like any other, and iterative development certainly requires this skill. I tend to throw away considerable amounts of code if I think the new design will save time in the long run, and it feels like there would be an awful number of tests thrown away too. Which is more efficient? I don't know.
...
I would probably recommend some level of TDD to anyone new... but I'm still having trouble with the benefits for anyone who's been around the block a few times already. I will probably start adding automated tests to libraries. It's possible that after doing that, I'll see more value in doing it generally.
Motivated self interest.
In my case, sole developer translates to small business owner. I've written a reasonable amount of library code to (ostensibly) make my life easier. A lot of these routines and classes aren't rocket science, so I can be pretty sure they work properly (at least in most cases) by reviewing the code, some some spot testing and debugging into the methods to make sure they behave the way I think they do. Brute force, if you will. Life is good.
Over time, this library grows and gets used in more projects for different customers. Testing gets more time consuming. Especially cases where I'm (hopefully) fixing bugs and (even more hopefully) not breaking something else. And this isn't just for bugs in my code. I have to be careful adding functionality (customers keep asking for more "stuff") or making sure code still works when moved to a new version of my compiler (Delphi!), third party code, runtime environment or operating system.
Taken to the extreme, I could spend more time reviewing old code than working on new (read: billable) projects. Think of it as the angle of repose of software (how high can you stack untested software before it falls over :).
Techniques like TDD gives me methods and classes that are more thoughtfully designed, more thoroughly tested (before the customer gets them) and need less maintenance going forward.
Ultimately, it translates to less time doing maintenance and more time to spend doing things that are more profitable, more interesting (almost anything) and more important (like family).
We are all developers with a good track record. After all, we are all reading Stackoverflow. And many of us use TDD and perhaps those people have a great track record. I get hired because people want someone who writes great test automation and can teach that to others. When working alone, I do TDD on my coding projects at home because I found that if I don’t, I spent time doing manual testing or even debugging, and who needs that. (Perhaps those people have only good track records. I don’t know.)
When it comes to being a good automobile driver, everyone believes they are a “good driver.” This is a cognitive bias all drivers have. Programmers have their own biases. The reasons developers such as the OP don’t do TDD are covered in this Agile Thoughts podcast series. The podcast archive also has content on test automation concepts such as the test pyramid, and an intro about what is TDD and why write tests first starting with episode 9 in the podcast archive.