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I have read a lot of threads about the joys and awesome points of unit testing. Is there have a good argument against unit testing?
In the places I have previously worked, unit testing is usually used as a reason to run with a smaller testing department; the logic is "we have UNIT TESTS!! Our code can't possibly fail!! Because we have unit tests, we don't need real testers!!"
Of course that logic is flawed. I have seen many cases where you cannot trust the tests. I have also seen many cases where the tests become out of date due to tight time schedules - when you have a week to do a big job, most developers would spend the week doing the real code and shipping the product, rather than refactoring the unit tests for that first week, then pleading for at least another week to do the real code, and then spending a final week bringing the unit tests up to date with what they actually wrote.
I have also seen cases where the business logic involved in the unit test was more monstrous and hard to understand than the logic buried in the application. When these tests fail, you have to spend twice as long trying to work out the problem - is the test flawed, or the real code?
Now the zealots are not going to like this bit: the place where I work has largely escaped using unit tests because the developers are of a high enough calibre that it is hard to justify the time and resource to write unit tests (not to mention we use REAL testers). For real. Writing unit tests would have only given us minimal value, and the return on investment is just not there. Sure it would give people a nice warm fuzzy feeling - "I can sleep at night because my code is PROTECTED by unit tests and consequently the universe is at a nice equilibrium", but the reality is we are in the business of writing software, not giving managers warm fuzzy feelings.
Sure, there absolutely are good reasons for having unit tests. The trouble with unit testing and TDD is:
Too many people bet the family farm on it.
Too many people use it as a religion rather than just a tool or another methodology.
Too many people have tried to make money out of it, which has skewed how it should be used.
In reality, it should be used as one of the tools or methodologies that you use on a day to day basis, and it should never become the single methodology.
It's important to understand that it's not free. Tests require effort to write - and, more importantly, maintain.
Project managers and development teams need to be aware of this.
Virtually none of my bugs would have been found by unit testing. My bugs are mostly integration or unexpected-use-case bugs, which in order to have found them earlier, more extensive (and ideally automated) system tests would have been the best bet.
I'm waiting for more evidence-based and less religion-based arguments for unit testing, as dummymo said. And I don't mean some experiment in some academic setting; I mean an argument that for my development scenario and programming ability, cost-benefit would be positive.
So, to agree with other answers to the OP: because they cost time and cost-benefit is not shown.
You have a data access layer that isn't easy adapted for mocking.
The simple truth is, when you write some code, you have to make sure it works before you say it's done. Which means you exercise it - build some scaffolding to call the function, passing some arguments, checking to make sure it returns what you expect. Is it so much extra work, to keep the scaffolding around, so you can run the tests again?
Well yes, actually, it can be. More often than not the tests will fail, even when the code is right, because the data you were using is no longer consistent, etc.
But if you have a unit testing framework in place, the cost of keeping the test code around can be only marginally more work than throwing it away. And while yes, you'll find that many of your test cases will fail because of problems with the data you are using, instead of problems with the code, that will happen less as you learn how to structure your tests so as to minimize the problem.
True, passing your unit tests does not guarantee that your system works. But it does provide some assurance that certain subsystems are working, which isn't nothing. And the test cases provide useful examples of how the functions were meant to be called.
It's not a panacea, but it's a useful practice.
Formal verification.
If you can formally prove the correctness of code, there is no reason to unit test it unless the test condition brings in new variables, in which case, you'd still only have a small amount of unit tests (or prove for the new variables).
Unit tests will tell you whether one specific class method sets a variable correctly (or some variation on that). That does not, in any way, shape, or form, indicate that your application will behave properly or that it will handle the circumstances it will need to handle.
Any problem you can think to write a test for, you are going to handle in your code, and that problem is never going to show up. So then you have 300 tests passing but real-world scenarios you just didn't think to test for. The effort required to create and maintain the tests, then, isn't necessarily worth it.
It's the usual cost/benefit analysis.
Cost: You need to spend time developing and maintaining the tests, and put resources into actually running them.
Benefits are well known (mostly cheaper maintenance/refactoring with less bugs).
So, you balance one against the other in the context of the project.
If it's a throwaway quick hack you know will never be re-used, unit tests might not make sense. Although to be honest, if I had a dollar for every throwaway quick hack that I saw running years later or worse, had to maintaing/refactor years later, I'd probably be able to be one of venture capitalists investing into SO :)
Non-deterministic outcomes.
In simple cases you can seed the random generator(s) (or mock them somehow) to get reproducible results but when the algorithm is complex this becomes impossible as code changes will alter the demand for random numbers and thus alter the results.
This would rarely be encountered in a business situation but it's quite possible in games.
Testing is like insurance.
You don't put all your money in to it.
But you don't avoid your life insurance. (People form US should still be remembering the Health Insurance Bill).
Insurance is ESSENTIAL evil.
BUT BUT BUT...
You don't get insured expecting a Fatal accident to recover all the money you put into your insurance plan.
In summary,
There is SOME reason to write Tests.
Unit tests are sometimes One of the many ways to go forward
BUT There is NO REASON to just to focus entirely on writing (Unit) Tests.
It can discourage experimenting with several variations, especially in early stages of a project. (But it can also encourage experimenting in later stages!)
It can't replace system testing, because it doesn't cover the relationship between components. So if you have to split up the available testing time between system testing and unit testing, then too much unit testing can have a negative impact on the amount of system tests.
I want to add, that I usually encourage unit testing!
It is impossible to generalize where unit tests are going to provide cost-benefit and where they are not. I see a lot of people arguing strongly in favor of unit testing and blaming people who don't for not using TDD enough, while completely ignoring the fact that applications can differ as much as the real world does.
For instance, it is incredibly hard to get anything useful out of unit tests when you have a lot of integration points, either between systems, and/or between processes and threads of your own application.
If all you ever did were websites like Stackoverflow, where problem domain is well understood, and most solutions are fairly trivial, then yes, writing unit tests have a lot of benefits, but there are lots of applications out there that simply can't be unit tested properly, as they lack, well, "units".
Laziness; sometimes I'm lazy and just don't want to do it!
But seriously, unit testing is great, but if I'm just coding for my own enjoyment I generally don't do it, because the projects are short lived, I'm the only one working on it, and they're not that big.
There is never a reason to never write unit tests.
There are good reasons to not write specific unit tests. (Especially if you use code generation. Of course you could code generate the unit tests to make sure nobody has mucked with the generated code. But that is dependent upon trusting the team.)
*Edit
Oh. And from what I understand some things in functional programming either compile thus work or don't compile.
Would those things need unit tests?
I agree with the notion that there are no good arguments against unit testing in general. There are some specific situations, however, where unit testing may not be a viable option or is at least problematic and/or poses a difficult return-on-investment proposition for the level of effort involved to create and maintain tests.
Here are some examples:
Real-time-dependent behavior in response to external conditions. Some purists may argue that this is not unit testing but rather involves scenarios at an integration or system testing level. However, I've written code for simple, low-level functionality for quasi-embedded applications where it would be useful to at least partially test real-time response via a unit-testing framework for build/regression testing purposes.
Testing behaviorial and/or policy-level functionality that requires a complex data description of the environmental state to which the tested code module is responding. This is related to an earlier poster's comment regarding the difficulty of doing unit testing involving a data access layer that isn't easily adapted for mocking. Although the behavior/policy being tested may be relatively simple, it needs to be tested across a complex state description. The value of doing unit testing here is in assuring that rare yet key conditions are handled correctly for a mission-critical application. One wants to mock the latter and create a simulated environment/state, but the cost of doing so may be high.
There are at least two alternatives to unit testing for the above scenarios:
For real-time or quasi-real-time functionality testing, extensive system testing can be done to try to compensate for the lack of good unit testing. For some applications this may be the only option, e.g., embedded systems involving hardware and/or physical systems.
Create a test harness or system-level simulator that facilitates extensive testing across a range of randomly simulated conditions. This can be useful for testing the policy/behavior scenarios described earlier involving a complex environmental state. Although significant work may be involved in creating the test harness or simulator, the return-on-investment may be a much better value than for isolated unit tests since a much broader range of conditions can be tested.
Since the test environment involves random rather than specific conditions, this approach may not offer quite the level of assurance desired for some mission-critical scenarios. Conducting extensive tests may help make up for this. Alternatively, creating a test harness or system simulator for random conditions may also help with reducing the overall cost of testing specific complex state scenarios since the development cost is now shared across a broader range of testing needs.
In the end, how to best approach testing any given application comes down to cost vs. value. Unit testing is one of the best options and should always be used where feasible, but it is not universally applicable to all scenarios. Like many things in software, sometimes it will just be a judgment call one has to make and then be prepared to make adjustments based on the outcome.
Unit testing is a trade-off. I see two problems:
It takes time. Not only to write the tests, but also (and this is the most annoying) if you want to make an important change, now you have two places you need to modify. In the worst case it could possibly discourage you to re-architect your codebase.
It only protects against problems that you think could arise, and you mostly cannot test against side-effects. This can lead to a false sense of security as mentioned before.
I agree unit testing is a valuable tool for increasing the reliability of enterprise software with a relatively stable codebase. But for personal projects or infant projects, I think a generous use of asserts in your code is a much better trade-off.
I wouldn't say it's an argument against it, but for us we have a legacy application with a TON of code, and written in COBOL. It is virtually impossible at this point to say we want to implement unit testing and do it with any degree of accuracy or within a reasonable time frame for business as pointed out by duffymo.
So I guess to add onto that, maybe one argument would be the inability (in some cases) of trying to implement unit tests after development has been completed (and maintained for years).
Instead of completely getting rid of them, we write unit tests only for core functionality such as payment authorization, user authentication, etc etc. It is very useful as there will always be some touch points that are very sensitive to code changes in a large code base and you would want some way to verify those touch points work without failing in QA.
For writing unit tests in general, learning curve is the biggest reason I know of to not bother. I have been trying to learn good unit testing for about 1.5 years now, and I feel like I'm just getting good at it (writing audit log spies, mocking, testing 1 constraint per test, etc.), although I feel it has sped up development for me for about 1 year of that time. So call it 6 months of struggling through it before it really started paying off. (I was still doing "real" work during that time, of course.)
Most of the pain experienced during that time was due to failure to follow the guidelines of good unit testing.
For a variety of specific cases, ability to unit test may be blocked; others have commented on some of those.
In Test Driven Development, the unit tests are actually more importantly a way to design your code to be testable to begin with. As it turns out your code tends to be more modular and writing the tests helps to flesh out APIs and so forth.
Too often though, you find yourself developing the code then writing the tests, commenting out the code you just wrote to ensure that the tests fail, then selectively removing the comment tokens to make the tests pass. Why? Well because it's much harder to write tests than it is to write code in some cases. It's also often much more difficult to write code that can be tested in a completely automated way. Think about user interfaces, code that generates images or pdfs, database transactions.
So unit tests do help a lot, but expect to write about 3 times as much code for the tests than you will write for the actual code. Plus all of this will need to be maintained. Significant changes to the application will invalidate huge chunks of tests - a good measure of the impact to the system but still... Are you prepared for that? Are you on a small team where you are doing the job of 5 developers? If so then automated TDD development just won't fly - you won't have time to get stuff done fast enough. So then you end up relying on you're own manual testing, QA testing stuff as well and just living with bugs slipping through and then fixing things up ASAP. It's unfortunate, high pressure and exasperating but it's reality in small companies that don't hire enough developers for the work that needs to be done.
No, really I don't. In my experience people who do are presenting a straw man's argument or just don't know how to unit test things that are not obvious how to unit test.
#Khorkak - If you change a feature in your production code, only a handfull of your unit tests should be affected. If you don't that means that you are not decoupling your production code and testing in isolation, but instead excecising large chunks of your production code in integration. That's just poor unit testing skills, and yes it's a BIG problem. Not only because your unit test code base will become hard to maintain, but also because your production code base will suck and have the same problem.
Unit tests make no sense for Disposable Code: If the code is a Q&D proof of concept, something created during a spike to investigate various approaches, or anything else you are SURE will almost always be thrown away, then doing unit tests won't bring much return on the investment. In fact they could hurt you as the time spent there is time spent not trying a different approach etc (alternative cost)
The key is being sure that's the case, or having enough of an understanding with teammates etc that if someone says 'that's great, use that one' that you then invest the time bring the code up to the standards for NON disposable code.
For those who asked for better proof I'd refer you to this page. http://biblio.gdinwiddie.com/biblio/StudiesOfTestDrivenDevelopment
note that many of these are studies by academic types, but done against groups doing real production software work, so personally it seems like they have a pretty good amount of validity.
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Closed 10 years ago.
I've been test-infected for a long time now, but it would seem the majority of developers I work with either have never tried it or dismiss it for one reason or another, with arguments typically being that it adds overhead to development or they don't need to bother.
What bothers me most about this is that when I come along to make changes to their code, I have a hard time getting it under test as I have to apply refactorings to make it testable and sometimes end up having to do a lot of work just so that I can test the code I'm about to write.
What I want to know is, what arguments would you use to persuade other developers to start writing unit tests? Most developers I've introduced to it take to it quite well, see the benefits and continue to use it. This always seems to be the good developers though, who are already interested in improving the quality of their code and hence can see how unit testing does this.
How do persuade the rest of the motley crew? I'm not looking for a list of testing benefits as I already know what these are, but what techniques you have used or would use to get other people on board. Tips on how to persuade management to take an active role are appreciated as well
There's more than one side to that question, I guess. I find that actually convincing developers to starting using tests is not that hard, because the list of advantages of using testing often speaks for itself. When that said, it is quite a barrier to actually get going and I find that the learning curve often is a bit steep – especially for novice coders. Throwing testing frameworks, TDD test-first mentality, and mocking framework at someone who's not yet comfortable with neither C#, .Net or programming in general, could be just too much to handle.
I work as a consultant and therefore I often have to address the problem of implementing TDD in an organization. Luckily enough, when companies hire me it is often because of my expertise in certain areas, and therefore I might have a little advantage when it comes to getting people’s attention. Or maybe it's just that it's a bit easier to for me as an outsider to come in to a new team and say "Hi! I've tried TDD on other projects and I know that it works!" Or maybe it's my persuasiveness/stubbornness? :) Either way, I often don't find it very hard to convince devs to start writing tests. What I find hard though, is to teach them how to write good unit tests. And as you point out in your question; to stay on the righteous path.
But I have found one method that I think works pretty well when it comes to teaching unit testing. I've blogged about it here, but the essence is to sit down and do some pair-programming. And doing the pair programming I start out writing the unit test first. This way I show them a bit how the testing framework work, how I structure the tests and often some use of mocking. Unit tests should be simple, so all in all the test should be fairly easy to understand even for junior devs. The worst part to explain is often the mocking, but using easy-to-read mocking frameworks like Moq helps a lot. Then when the test is written (and nothing compiles or passes) I hand over the keyboard to my fellow coder so that (s)he can implement the functionality. I simply tell her/him; "Make it go green!” Then we move on to the next test; I write the test, the 'soon-to-be-test-infected-dev' next to me writes the functionality.
Now, it's important to understand that at this point the dev(s) you are teaching are probably not yet convinced that this is the right way to code. The point where most devs seem to see the (green) light is when a test fails due to some code changes that they never thought would break any functionality. When the test that covers that functionality blows up, that's when you've got yourself a loyal TDD'er on your team. Or that's at least my experience, but as always; your mileage will vary :)
Quality speaks for itself. If you're more successful than everyone else, that's all you need to say.
Use a test-coverage tool. Make it very visible. That way everybody can easily see how much code in each area is passed, failed and untested.
Then you may be able to start a culture where "untested" is a sign of bad coding, "failed" is a sign of work in progress and "passed" is a sign of finished code.
This works best if you also do "test-first". Then "untested" becomes "you forgot step 1".
Of course you don't need 100% test coverage. But of one area has 1% coverage and another has 30%, you have a metric for which area is most likely to fail in production.
Lead by example. If you can get evidence that there are less regression on unit tested code that elsewhere.
Getting QA and management buy-in so that your process mandates unit testing.
Be ready to help others to get started with unit testing: provide assistance, supply a framework so that they can start easily, run an introductory presentation.
You just have to get used to the mantra "if it ain't tested, the work ain't done!"
Edit: To add some more meat to my facetious comment above, how can someone know if they're actually finished if they haven't tested their work?
Mind you, you will have a battle convincing others if time isn't allowed in the estimate for the testing of the devleoped code.
A one-to-one split for between effort for coding and that for testing seems to be a good number.
HTH
cheers,
Rob
Give compliments for one writes more test and produce good results and show the best one to others and ask them to produce the same or better result than this.
People (and processes) don't change without one or more pain points. So you need to finjd the significant pain points and demonstrate how unit testing might help deal with them.
If you can't find any significant pain points, then unit testing may not add a lot of value to your current process.
As Steve Lott implies, delivering better results than the other team members will also help. But without the pain points, my experience is that people won't change.
Two ways: convince the project manager that unit testing improves quality AND saves time overall, then have him make unit tests mandatory.
Or wait for a development crunch just before an important release date, where everyone has to work overtime and weekends to finish the last features and eliminate the last bugs, only to find they've just introduced more bugs. Then point out that with proper unit tests they wouldn't have to work like that.
Another situation where unit tests can be shown as indispensable is when a release was actually delivered and turns out to contain a serious bug due to last-minute changes.
If developers are seeing that the "successful" developers are writing unit tests, and they are still not doing it then I suggest unit tests should become part of the formal development life-cycle.
E.g. nothing can be checked in until a unit test is written and reviewed.
Probably reefnet_alex' answer helps you:
Is Unit Testing worth the effort?
I think it was Fowler who said:
"Imperfect tests, run frequently, are
much better than perfect tests that
are never written at all". I
interprate this as giving me
permission to write tests where I
think they'll be most useful even if
the rest of my code coverage is
woefully incomplete.
You mentioned that your manager is on board with unit tests. If that's the case, then why isn't he (she) enforcing it? It isn't your job to get everybody else to follow along or to teach them and in fact, other developers will often resent you if you try to push it on them. In order to get your fellow developers to write unit tests, the manager has to emphasize it strongly. It might end up that part of that emphasis is education on unit test implementation which you might end up being the educator and that's great, but management of it is everything.
If you're in an environment where the group decides the style of implementation, then you have more of a say in how the group dynamic should be. If you are in that sort of environment and the group doesn't want to emphasize unit tests while you do, then maybe you're in the wrong group/company.
I have found that "evangelizing" or preaching rarely works. As others have said, do it your way for your own code, make it known that you do it, but don't try to force others to do it. If people ask about it be supportive and helpful. Offer to do a few lunch-time seminars or informal dog and pony shows. That will do a lot more than just complaining to your manager or the other developers that you have a hard time writing tests for code they wrote.
Slow and steady - it is not going to change overnight.
Once I realized that at one place where I worked the acceptance for peer reviews improved tremendously. My group just did it and stopped trying to get others to do it. Eventually people started asking s about how we got some of the success we did. Then it was easier.
We have a test framework which includes automated running of the test suite whenever anyone commits a change. If someone commits code that fails the tests, the whole team gets emailed with the errors.
This leads to introduced bugs being fixed pretty quickly.
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Closed 10 years ago.
I have been involved in a lot of projects, both old and new, and one thing that they have in common is that almost none of them have been using unit testing. I prefer to use it, but often the customer isn´t ready to pay for that, and suppose that the code just works as it should.
So, do you use unit testing in your projects, or do you rely on your coding skills?
Using unit-testing is a coding skill.
I find it adds very little overhead to coding time. On top of that the code produced tends to be much easier to understand and to refactor, with an untold reduction in maintenance time.
A full discussion of the benefits here: Is Unit Testing worth the effort?
I'll be honest. I've only recently started writing unit tests, and when I go back to modify an old DLL that's from my bad old days, I'll hunker down and write unit tests to get it near 100% code coverage. I say "near" because the last few percent can be hard to get to due to the way that the code is structured, that it didn't have mocking or unit testing in mind (this happens a lot with the abstract classes or classes that P/Invoke into native code). And while I understand that 100% code coverage is not the same thing as 100% of all code execution paths, I've found that having the tests there is a good way to tell when I'm doing something that's going to break a lot of things.
To be honest, this is probably one reason why it has taken many developers (including myself) so long to get around to adopting unit testing (let's not get into TDD just yet).
I'm not saying that any of these are legitimate reasons, but they did more or less go through my head, and I bet they went through some of yours too:
First, there's a thought along the lines of "Oh, I've written mountains of code with zero tests, and seeing as I'm already crushed by that mountain, I don't possibly have the time to add several more mountains of test code on top of it."
Second, nobody likes to talk about the fact that the classic code-run-debug cycle actually works "good enough" when you're
writing new code that does not alter the behavior of old code
working on a relatively small software project or a throwaway utility
the sole developer on a project (you can keep most of it in your head, up to a point)
Third, unit tests are easier to appreciate when you're maintaining existing code, and if you're always writing new code, well, the benefits aren't immediately obvious. When your job is to churn out a utility and never touch it again, a developer can see little value in the unit test because they probably won't be working on that utility or at the company by the time a maintenance programmer (who wishes there was a unit test) comes around.
Fourth, unit testing is a fairly recent innovation. (Oh, hush ... I know the idea has been around forever, especially in mission-critical and DoD applications, but for the "Joe the Plumber Developer" types like me? Unit testing wasn't mentioned at all during my entire CS undergraduate career in the early part of this decade; in 2008, I hear it's a requirement for all projects from level 101 up. Visual Studio didn't even get a built-in testing framework until this year, and even then only in the professional edition.) Was it blissful ignorance on my part? Sure, and I think a lot of people who code because it's their day job (which is fine) simply aren't aware. If they are, then they know that they have to stay current, but when it comes to learning a new methodology (particularly one that involves writing more code and taking more up-front time when you needed that new feature done yesterday) means that it'll get pushed back. This is the long tail, and in a decade or so our talks about unit testing will seem as quaint as our mutterings about object-oriented programming enabling a new era of development during the 1990s. Heck, if I've started unit testing, the end must be near, because I'm usually an idiot.
Fifth, unit testing some areas of code is really difficult, and this scared me away for a while. Multi-threaded event queues, graphical rendering, and GUIs come to mind. Many developers realize this and think "well heck, unit testing would be great for library code but when was the last time I wrote just a class library." It takes a while to come around. To that end, no unit tests does not necessarily mean bad code lies ahead.
Finally, the level of evangelism that sometimes comes from unit testing advocates can be intimidating and off-putting. Seriously, I thought I was a moron because I just couldn't grasp how to mock a certain interface and why I would want to. Selfishly, I wanted to hate unit testing if just for the fact that everybody would not shut UP about it. No silver bullet.
So, apologies for the rambling post. In summary:
I did not unit test for a long time. Now I do. Unit tests are a great tool, especially during maintenance.
For existing projects, you can at least go in and write a test that documents a current input and its output. When you change that big mess of murky code in the future, you'll be able to see if you've altered that little snapshot. This is also an excellent way to change the development culture in your company.
Let the flames begin! =)
Unit testing can't be an afterthought, it is and has to be something which factors in to your design. I would go so far as to say that even if you never write or call a single unit test, the benefits it has in leading tight component driven software is worth the effort 95% of the time.
Writing and running unit-tests is part of a healthy coding process, it is not an addition the customer should have the choice to pay or not pay for.
Testing strategy is a coding issue just as any other: what datastructures to use, variable naming conventions, comment standards, etc.
I use unit testing, and tdd, whenever I can. However in my experience for every unit test advocate there are three or more developers who don't really believe writing unit tests is worth the effort, and that it slows down development. However these people tend to keep quiet, so you are unlikely to see many here.
I like Bob Martin's analogy: imagine you're a surgeon. What would you say to a patient who wanted to pay the surgery but told you to skip washing up ahead of time?
When a client hires me to code they are hiring me as a professional, as someone with the skills and discipline of a professional. My job is to give them "code just works as it should", and I know the best way for me to do that is to use TDD.
After coming onto a couple of projects that were in production but needed major new functionality, one of my bottom lines as a technical lead starting up a project is that unit-tests are a must.
It just costs too much to try and rewrite code that has been written without unit tests. The code is invariably poorly structured (A multi-thousand line web-service all in a single code behind anyone?) and making changes to it (even when it is well structured) without introducing bugs is a really painful process.
This becomes particularly true when a project enters fire-fighting mode (and not having unit tests contributes to projects getting into that state too) - customers are getting grumpy, they've lost faith in the project, few things worse than being the poor guy trying to get the next fix in without introducing a whole pile of regression bugs, and not even having unit tests.
Those situations can be so easily avoided or at least mitigated by explaining the value of tests up front. Of course there are situations where unit tests aren't so important but they are truly the exception.
So yes - I insist on unit tests and have spent a lot of time fixing the messes made by other developers who relied on their coding skills.
I often use unit testing for complex mathematical algorithms, for example for functions like LineIntersectsLine where you can define some important examples to test. After that, it is easier to control this function. You can simply rewrite/optimize it and test if it still works, or you can add new tests if you encounter bugs and then try to correct these.
I find newer developers benefit more from unit testing than older ones who had to learn from the school of hard knocks of the pitfalls that could make something fail. Unit testing does not lead to good design - it just leads to a design that is more testable. You need to test your code but the way unit testing is preached is dangerous. "It will force you to design your code better", "How can you test whether it is correct?".
I prefer to have well written structured code that when you read it automatically tells you simply what it is trying to accomplish and how it does it. Functions/classes should be small and concise. They should only have one responsibility. Unit tests don't protect against logical errors.
Unit tests give more false positives than anything else particularly when a project is first written. Good design trumps tests - tests should be the verification stage nothing more. I never bought into the testing comes before everything else concept. In my experience this line of thinking favours testability at the expense of extensible code (may be ok for throwaway projects or one off utilities but ironically unit testing isn't as important for these).
I agree with Ken that unit testing is part of software development.
About the cost question, it's true than writing the code plus the unit test is longer than writing just the code. However, when you write the code along with its tests - which is called TDD - Test-Driven Development, you end with "clean code that works". When you just write the code, then you have to make it work, which can be long and painful.
Another benefit is that you know where you are, as the code that has been written has already been unit-tested.
To answer your question, yes, I'm using unit testing on my projects when it's possible. I write unit tests for all the new code and I strive to for legacy code.
I'm a big fan of unit testing, mainly because it's completely addicitive - the "code-test-see horrible red bar-fix-test-see lovely green bar" cycle in JUnit seriously gets the endorphins pumping.
My company makes system components for various companies in the Aerospace Industry.
The FAA requires Modified Condition/Decision Coverage for Quality level A Safety Critical flight software (DO-178-B) So for verification we do (again from DO-178-B):
Analysis of all code and traceability from tests and results to all requirements is typically required (depending on software level).
This process typically also involves:
Requirements based test tools
Code coverage analyser tools
Other names for tests performed in this process can be:
Unit testing
Integration testing
Black box and acceptance testing
Unit testing reveals code errors all the time.
In regards to relying on my coding skills, I find that my coding skills actually improve when I use TDD and rely on my unit tests to correct me when I break a test. You learn how to use many language features because you can make a tweak to test out an assumption.
I know from experience that when I write code without unit tests, I'll get a few issues that come up to fix, but when I've written the unit tests I rarely hear of issues. Also, from time spent writing unit tests I write better code to begin with. I look at methods and think of the ways they could fail and build them from the start not to fail or at least to fail in a better way.
Unit tests ARE essential to writing better code, but it also will make you a better developer because you SEE areas where things could go wrong and fix them before you ever get to testing.
Unit testing is an essential part of development, and (I have found) will actually reduce the time to completion of a project while improving overall quality, especially when done in a TDD fasion.
I do Unit test. I am actully building currently a constraint validation engine and my customers want it bullet proof. Well, without unit test, I would die from stress...
So yes, I use it !
Most functions that I write have tests. Like many have said up there, unit testing is an essential part of software engineering. So, to answer your question, yes, I REALLY write and run tests.
Also, with continuous integration, regression tests will be automated and constantly reported.
Another very useful reminder of why you want to unit test wherever you can just showed up in this post: Top 12 Reasons to Write Unit Tests I need to have that engraved on my retinas.
I can testify personally to the value of thinking about how something will be tested from the beginning, with tests developed through each iteration. I need to be more systematic, myself. I am printing out that list right now.
Your customers would probably save money overall if unit testing was in place. Some of the errors prevented by unit testing are much more of a liability if found later in the development stage rather than during unit testing. It saves so much headache in the future, now that I use it I don't think I could ever go back.
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What do I lose by adopting test driven design?
List only negatives; do not list benefits written in a negative form.
If you want to do "real" TDD (read: test first with the red, green, refactor steps) then you also have to start using mocks/stubs, when you want to test integration points.
When you start using mocks, after a while, you will want to start using Dependency Injection (DI) and a Inversion of Control (IoC) container. To do that you need to use interfaces for everything (which have a lot of pitfalls themselves).
At the end of the day, you have to write a lot more code, than if you just do it the "plain old way". Instead of just a customer class, you also need to write an interface, a mock class, some IoC configuration and a few tests.
And remember that the test code should also be maintained and cared for. Tests should be as readable as everything else and it takes time to write good code.
Many developers don't quite understand how to do all these "the right way". But because everybody tells them that TDD is the only true way to develop software, they just try the best they can.
It is much harder than one might think. Often projects done with TDD end up with a lot of code that nobody really understands. The unit tests often test the wrong thing, the wrong way. And nobody agrees how a good test should look like, not even the so called gurus.
All those tests make it a lot harder to "change" (opposite to refactoring) the behavior of your system and simple changes just becomes too hard and time consuming.
If you read the TDD literature, there are always some very good examples, but often in real life applications, you must have a user interface and a database. This is where TDD gets really hard, and most sources don't offer good answers. And if they do, it always involves more abstractions: mock objects, programming to an interface, MVC/MVP patterns etc., which again require a lot of knowledge, and... you have to write even more code.
So be careful... if you don't have an enthusiastic team and at least one experienced developer who knows how to write good tests and also knows a few things about good architecture, you really have to think twice before going down the TDD road.
Several downsides (and I'm not claiming there are no benefits - especially when writing the foundation of a project - it'd save a lot of time at the end):
Big time investment. For the simple case you lose about 20% of the actual implementation, but for complicated cases you lose much more.
Additional Complexity. For complex cases your test cases are harder to calculate, I'd suggest in cases like that to try and use automatic reference code that will run in parallel in the debug version / test run, instead of the unit test of simplest cases.
Design Impacts. Sometimes the design is not clear at the start and evolves as you go along - this will force you to redo your test which will generate a big time lose. I would suggest postponing unit tests in this case until you have some grasp of the design in mind.
Continuous Tweaking. For data structures and black box algorithms unit tests would be perfect, but for algorithms that tend to be changed, tweaked or fine tuned, this can cause a big time investment that one might claim is not justified. So use it when you think it actually fits the system and don't force the design to fit to TDD.
When you get to the point where you have a large number of tests, changing the system might require re-writing some or all of your tests, depending on which ones got invalidated by the changes. This could turn a relatively quick modification into a very time-consuming one.
Also, you might start making design decisions based more on TDD than on actually good design prinicipals. Whereas you may have had a very simple, easy solution that is impossible to test the way TDD demands, you now have a much more complex system that is actually more prone to mistakes.
I think the biggest problem for me is the HUGE loss of time it takes "getting in to it". I am still very much at the beginning of my journey with TDD (See my blog for updates my testing adventures if you are interested) and I have literally spent hours getting started.
It takes a long time to get your brain into "testing mode" and writing "testable code" is a skill in itself.
TBH, I respectfully disagree with Jason Cohen's comments on making private methods public, that's not what it is about. I have made no more public methods in my new way of working than before. It does, however involve architectural changes and allowing for you to "hot plug" modules of code to make everything else easier to test. You should not be making the internals of your code more accessible to do this. Otherwise we are back to square one with everything being public, where is the encapsulation in that?
So, (IMO) in a nutshell:
The amount of time taken to think (i.e. actually grok'ing testing).
The new knowledge required of knowing how to write testable code.
Understanding the architectural changes required to make code testable.
Increasing your skill of "TDD-Coder" while trying to improve all the other skills required for our glorious programming craft :)
Organising your code base to include test code without screwing your production code.
PS: If you would like links to positives, I have asked and answered several questions on it, check out my profile.
In the few years that I've been practicing Test Driven Development, I'd have to say the biggest downsides are:
Selling it to management
TDD is best done in pairs. For one, it's tough to resist the urge to just write the implementation when you KNOW how to write an if/else statement. But a pair will keep you on task because you keep him on task. Sadly, many companies/managers don't think that this is a good use of resources. Why pay for two people to write one feature, when I have two features that need to be done at the same time?
Selling it to other developers
Some people just don't have the patience for writing unit tests. Some are very proud of their work. Or, some just like seeing convoluted methods/functions bleed off the end of the screen. TDD isn't for everyone, but I really wish it were. It would make maintaining stuff so much easier for those poor souls who inherit code.
Maintaining the test code along with your production code
Ideally, your tests will only break when you make a bad code decision. That is, you thought the system worked one way, and it turns out it didn't. By breaking a test, or a (small) set of tests, this is actually good news. You know exactly how your new code will affect the system. However, if your tests are poorly written, tightly coupled or, worse yet, generated (cough VS Test), then maintaining your tests can become a choir quickly. And, after enough tests start to cause more work that the perceived value they are creating, then the tests will be the first thing to be deleted when schedules become compressed (eg. it gets to crunch time)
Writing tests so that you cover everything (100% code coverage)
Ideally, again, if you adhere to the methodology, your code will be 100% tested by default. Typically, thought, I end up with code coverage upwards of 90%. This usually happens when I have some template style architecture, and the base is tested, and I try to cut corners and not test the template customizations. Also, I have found that when I encounter a new barrier I hadn't previously encountered, I have a learning curve in testing it. I will admit to writing some lines of code the old skool way, but I really like to have that 100%. (I guess I was an over achiever in school, er skool).
However, with that I'd say that the benefits of TDD far outweigh the negatives for the simple idea that if you can achieve a good set of tests that cover your application but aren't so fragile that one change breaks them all, you will be able to keep adding new features on day 300 of your project as you did on day 1. This doesn't happen with all those who try TDD thinking it's a magic bullet to all their bug-ridden code, and so they think it can't work, period.
Personally I have found that with TDD, I write simpler code, I spend less time debating if a particular code solution will work or not, and that I have no fear to change any line of code that doesn't meet the criteria set forth by the team.
TDD is a tough discipline to master, and I've been at it for a few years, and I still learn new testing techniques all the time. It is a huge time investment up front, but, over the long term, your sustainability will be much greater than if you had no automated unit tests. Now, if only my bosses could figure this out.
On your first TDD project there are two big losses, time and personal freedom
You lose time because:
Creating a comprehensive, refactored, maintainable suite of unit and acceptance tests adds major time to the first iteration of the project. This may be time saved in the long run but equally it can be time you don't have to spare.
You need to choose and become expert in a core set of tools. A unit testing tool needs to be supplemented by some kind of mocking framework and both need to become part of your automated build system. You also want to pick and generate appropriate metrics.
You lose personal freedom because:
TDD is a very disciplined way of writing code that tends to rub raw against those at the top and bottom of the skills scale. Always writing production code in a certain way and subjecting your work to continual peer review may freak out your worst and best developers and even lead to loss of headcount.
Most Agile methods that embed TDD require that you talk to the client continually about what you propose to accomplish (in this story/day/whatever) and what the trade offs are. Once again this isn't everyone's cup of tea, both on the developers side of the fence and the clients.
Hope this helps
TDD requires you to plan out how your classes will operate before you write code to pass those tests. This is both a plus and a minus.
I find it hard to write tests in a "vacuum" --before any code has been written. In my experience I tend to trip over my tests whenever I inevitably think of something while writing my classes that I forgot while writing my initial tests. Then it's time to not only refactor my classes, but ALSO my tests. Repeat this three or four times and it can get frustrating.
I prefer to write a draft of my classes first then write (and maintain) a battery of unit tests. After I have a draft, TDD works fine for me. For example, if a bug is reported, I will write a test to exploit that bug and then fix the code so the test passes.
Prototyping can be very difficult with TDD - when you're not sure what road you're going to take to a solution, writing the tests up-front can be difficult (other than very broad ones). This can be a pain.
Honestly I don't think that for "core development" for the vast majority of projects there's any real downside, though; it's talked down a lot more than it should be, usually by people who believe their code is good enough that they don't need tests (it never is) and people who just plain can't be bothered to write them.
Well, and this stretching, you need to debug your tests. Also, there is a certain cost in time for writing the tests, though most people agree that it's an up-front investment that pays off over the lifetime of the application in both time saved debugging and in stability.
The biggest problem I've personally had with it, though, is getting up the discipline to actually write the tests. In a team, especially an established team, it can be hard to convince them that the time spent is worthwhile.
The downside to TDD is that it is usually tightly associated with 'Agile' methodology, which places no importance on documentation of a system, rather the understanding behind why a test 'should' return one specific value rather than any other resides only in the developer's head.
As soon as the developer leaves or forgets the reason that the test returns one specific value and not some other, you're screwed. TDD is fine IF it is adequately documented and surrounded by human-readable (ie. pointy-haired manager) documentation that can be referred to in 5 years when the world changes and your app needs to as well.
When I speak of documentation, this isn't a blurb in code, this is official writing that exists external to the application, such as use cases and background information that can be referred to by managers, lawyers and the poor sap who has to update your code in 2011.
I've encountered several situations where TDD makes me crazy. To name some:
Test case maintainability:
If you're in a big enterprise, many chances are that you don't have to write the test cases yourself or at least most of them are written by someone else when you enter the company. An application's features changes from time to time and if you don't have a system in place, such as HP Quality Center, to track them, you'll turn crazy in no time.
This also means that it'll take new team members a fair amount of time to grab what's going on with the test cases. In turn, this can be translated into more money needed.
Test automation complexity:
If you automate some or all of the test cases into machine-runnable test scripts, you will have to make sure these test scripts are in sync with their corresponding manual test cases and in line with the application changes.
Also, you'll spend time to debug the codes that help you catch bugs. In my opinion, most of these bugs come from the testing team's failure to reflect the application changes in the automation test script. Changes in business logic, GUI and other internal stuff can make your scripts stop running or running unreliably. Sometimes the changes are very subtle and difficult to detect. Once all of my scripts report failure because they based their calculation on information from table 1 while table 1 was now table 2 (because someone swapped the name of the table objects in the application code).
If your tests are not very thorough you might fall into a false sense of "everything works" just because you tests pass. Theoretically if your tests pass, the code is working; but if we could write code perfectly the first time we wouldn't need tests. The moral here is to make sure to do a sanity check on your own before calling something complete, don't just rely on the tests.
On that note, if your sanity check finds something that is not tested, make sure to go back and write a test for it.
The biggest problem are the people who don't know how to write proper unit tests. They write tests that depend on each other (and they work great running with Ant, but then all of sudden fail when I run them from Eclipse, just because they run in different order). They write tests that don't test anything in particular - they just debug the code, check the result, and change it into test, calling it "test1". They widen the scope of classes and methods, just because it will be easier to write unit tests for them. The code of unit tests is terrible, with all the classical programming problems (heavy coupling, methods that are 500 lines long, hard-coded values, code duplication) and is a hell to maintain. For some strange reason people treat unit tests as something inferior to the "real" code, and they don't care about their quality at all. :-(
You lose the ability to say you are "done" before testing all your code.
You lose the capability to write hundreds or thousands of lines of code before running it.
You lose the opportunity to learn through debugging.
You lose the flexibility to ship code that you aren't sure of.
You lose the freedom to tightly couple your modules.
You lose option to skip writing low level design documentation.
You lose the stability that comes with code that everyone is afraid to change.
You lose a lot of time spent writing tests. Of course, this might be saved by the end of the project by catching bugs faster.
Refocusing on difficult, unforeseen requirements is the constant bane of the programmer. Test-driven development forces you to focus on the already-known, mundane requirements, and limits your development to what has already been imagined.
Think about it, you are likely to end up designing to specific test cases, so you won't get creative and start thinking "it would be cool if the user could do X, Y, and Z". Therefore, when that user starts getting all excited about potential cool requirements X, Y, and Z, your design may be too rigidly focused on already specified test cases, and it will be difficult to adjust.
This, of course, is a double edged sword. If you spend all your time designing for every conceivable, imaginable, X, Y, and Z that a user could ever want, you will inevitably never complete anything. If you do complete something, it will be impossible for anyone (including yourself) to have any idea what you're doing in your code/design.
You will lose large classes with multiple responsibilities.
You will also likely lose large methods with multiple responsibilities.
You may lose some ability to refactor, but you will also lose some of the need to refactor.
Jason Cohen said something like:
TDD requires a certain organization for your code. This might be architecturally wrong; for example, since private methods cannot be called outside a class, you have to make methods non-private to make them testable.
I say this indicates a missed abstraction -- if the private code really needs to be tested, it should probably be in a separate class.
Dave Mann
The biggest downside is that if you really want to do TDD properly you will have to fail a lot before you succeed. Given how many software companies work (dollar per KLOC) you will eventually get fired. Even if your code is faster, cleaner, easier to maintain, and has less bugs.
If you are working in a company that pays you by the KLOCs (or requirements implemented -- even if not tested) stay away from TDD (or code reviews, or pair programming, or Continuous Integration, etc. etc. etc.).
I second the answer about initial development time. You also lose the ability to confortably work without the safety of tests. I've also been described as a TDD nutbar, so you could lose a few friends ;)
It's percieved as slower. Long term that's not true in terms of the grief it will save you down the road, but you'll end up writing more code so arguably you're spending time on "testing not coding". It's a flawed argument, but you did ask!
It can be hard and time consuming writing tests for "random" data like XML-feeds and databases (not that hard). I've spent some time lately working with weather data feeds. It's quite confusing writing tests for that, at least as i don't have too much experience with TDD.
You have to write applications in a different way: one which makes them testable. You'd be surprised how difficult this is at first.
Some people find the concept of thinking about what they're going to write before they write it too hard. Concepts such as mocking can be difficult for some too. TDD in legacy apps can be very difficult if they weren't designed for testing. TDD around frameworks that are not TDD friendly can also be a struggle.
TDD is a skill so junior devs may struggle at first (mainly because they haven't been taught to work this way).
Overall though the cons become solved as people become skilled and you end up abstracting away the 'smelly' code and have a more stable system.
unit test are more code to write, thus a higher upfront cost of development
it is more code to maintain
additional learning required
Good answers all. I would add a few ways to avoid the dark side of TDD:
I've written apps to do their own randomized self-test. The problem with writing specific tests is even if you write lots of them they only cover the cases you think of. Random-test generators find problems you didn't think of.
The whole concept of lots of unit tests implies that you have components that can get into invalid states, like complex data structures. If you stay away from complex data structures there's a lot less to test.
To the extent your application allows it, be shy of design that relies on the proper ordering of notifications, events and side-effects. Those can easily get dropped or scrambled so they need a lot of testing.
Let me add that if you apply BDD principles to a TDD project, you can alleviate a few of the major drawbacks listed here (confusion, misunderstandings, etc.). If you're not familiar with BDD, you should read Dan North's introduction. He came up the concept in answer to some of the issues that arose from applying TDD at the workplace. Dan's intro to BDD can be found here.
I only make this suggestion because BDD addresses some of these negatives and acts as a gap-stop. You'll want to consider this when collecting your feedback.
It takes some time to get into it and some time to start doing it in a project but... I always regret not doing a Test Driven approach when I find silly bugs that an automated test could have found very fast. In addition, TDD improves code quality.
You have to make sure your tests are always up to date, the moment you start ignoring red lights is the moment the tests become meaningless.
You also have to make sure the tests are comprehensive, or the moment a big bug appears, the stuffy management type you finally convinced to let you spend time writing more code will complain.
The person who taught my team agile development didn't believe in planning, you only wrote as much for the tiniest requirement.
His motto was refactor, refactor, refactor. I came to understand that refactor meant 'not planning ahead'.
Development time increases : Every method needs testing, and if you have a large application with dependencies you need to prepare and clean your data for tests.
TDD requires a certain organization for your code. This might be inefficient or difficult to read. Or even architecturally wrong; for example, since private methods cannot be called outside a class, you have to make methods non-private to make them testable, which is just wrong.
When code changes, you have to change the tests as well. With refactoring this can be a
lot of extra work.
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I am working to integrate unit testing into the development process on the team I work on and there are some sceptics. What are some good ways to convince the sceptical developers on the team of the value of Unit Testing? In my specific case we would be adding Unit Tests as we add functionality or fixed bugs. Unfortunately our code base does not lend itself to easy testing.
Every day in our office there is an exchange which goes something like this:
"Man, I just love unit tests, I've just been able to make a bunch of changes to the way something works, and then was able to confirm I hadn't broken anything by running the test over it again..."
The details change daily, but the sentiment doesn't. Unit tests and test-driven development (TDD) have so many hidden and personal benefits as well as the obvious ones that you just can't really explain to somebody until they're doing it themselves.
But, ignoring that, here's my attempt!
Unit Tests allows you to make big changes to code quickly. You know it works now because you've run the tests, when you make the changes you need to make, you need to get the tests working again. This saves hours.
TDD helps you to realise when to stop coding. Your tests give you confidence that you've done enough for now and can stop tweaking and move on to the next thing.
The tests and the code work together to achieve better code. Your code could be bad / buggy. Your TEST could be bad / buggy. In TDD you are banking on the chances of both being bad / buggy being low. Often it's the test that needs fixing but that's still a good outcome.
TDD helps with coding constipation. When faced with a large and daunting piece of work ahead writing the tests will get you moving quickly.
Unit Tests help you really understand the design of the code you are working on. Instead of writing code to do something, you are starting by outlining all the conditions you are subjecting the code to and what outputs you'd expect from that.
Unit Tests give you instant visual feedback, we all like the feeling of all those green lights when we've done. It's very satisfying. It's also much easier to pick up where you left off after an interruption because you can see where you got to - that next red light that needs fixing.
Contrary to popular belief unit testing does not mean writing twice as much code, or coding slower. It's faster and more robust than coding without tests once you've got the hang of it. Test code itself is usually relatively trivial and doesn't add a big overhead to what you're doing. This is one you'll only believe when you're doing it :)
I think it was Fowler who said: "Imperfect tests, run frequently, are much better than perfect tests that are never written at all". I interpret this as giving me permission to write tests where I think they'll be most useful even if the rest of my code coverage is woefully incomplete.
Good unit tests can help document and define what something is supposed to do
Unit tests help with code re-use. Migrate both your code and your tests to your new project. Tweak the code till the tests run again.
A lot of work I'm involved with doesn't Unit Test well (web application user interactions etc.), but even so we're all test infected in this shop, and happiest when we've got our tests tied down. I can't recommend the approach highly enough.
Unit testing is a lot like going to the gym. You know it is good for you, all the arguments make sense, so you start working out. There's an initial rush, which is great, but after a few days you start to wonder if it is worth the trouble. You're taking an hour out of your day to change your clothes and run on a hamster wheel and you're not sure you're really gaining anything other than sore legs and arms.
Then, after maybe one or two weeks, just as the soreness is going away, a Big Deadline begins approaching. You need to spend every waking hour trying to get "useful" work done, so you cut out extraneous stuff, like going to the gym. You fall out of the habit, and by the time Big Deadline is over, you're back to square one. If you manage to make it back to the gym at all, you feel just as sore as you were the first time you went.
You do some reading, to see if you're doing something wrong. You begin feel a little bit of irrational spite toward all the fit, happy people extolling the virtues of exercise. You realize that you don't have a lot in common. They don't have to drive 15 minutes out of the way to go to the gym; there is one in their building. They don't have to argue with anybody about the benefits of exercise; it is just something everybody does and accepts as important. When a Big Deadline approaches, they aren't told that exercise is unnecessary any more than your boss would ask you to stop eating.
So, to answer your question, Unit Testing is usually worth the effort, but the amount of effort required isn't going to be the same for everybody. Unit Testing may require an enormous amount of effort if you are dealing with spaghetti code base in a company that doesn't actually value code quality. (A lot of managers will sing Unit Testing's praises, but that doesn't mean they will stick up for it when it matters.)
If you are trying to introduce Unit Testing into your work and are not seeing all the sunshine and rainbows that you have been led to expect, don't blame yourself. You might need to find a new job to really make Unit Testing work for you.
Best way to convince... find a bug, write a unit test for it, fix the bug.
That particular bug is unlikely to ever appear again, and you can prove it with your test.
If you do this enough, others will catch on quickly.
thetalkingwalnut asks:
What are some good ways to convince the skeptical developers on the team of the value of Unit Testing?
Everyone here is going to pile on lots of reasons out of the blue why unit testing is good. However, I find that often the best way to convince someone of something is to listen to their argument and address it point by point. If you listen and help them verbalize their concerns, you can address each one and perhaps convert them to your point of view (or at the very least, leave them without a leg to stand on). Who knows? Perhaps they will convince you why unit tests aren't appropriate for your situation. Not likely, but possible. Perhaps if you post their arguments against unit tests, we can help identify the counterarguments.
It's important to listen to and understand both sides of the argument. If you try to adopt unit tests too zealously without regard to people's concerns, you'll end up with a religious war (and probably really worthless unit tests). If you adopt it slowly and start by applying it where you will see the most benefit for the least cost, you might be able to demonstrate the value of unit tests and have a better chance of convincing people. I realize this isn't as easy as it sounds - it usually requires some time and careful metrics to craft a convincing argument.
Unit tests are a tool, like any other, and should be applied in such a way that the benefits (catching bugs) outweigh the costs (the effort writing them). Don't use them if/where they don't make sense and remember that they are only part of your arsenal of tools (e.g. inspections, assertions, code analyzers, formal methods, etc). What I tell my developers is this:
They can skip writing a test for a method if they have a good argument why it isn't necessary (e.g. too simple to be worth it or too difficult to be worth it) and how the method will be otherwise verified (e.g. inspection, assertions, formal methods, interactive/integration tests). They need to consider that some verifications like inspections and formal proofs are done at a point in time and then need to be repeated every time the production code changes, whereas unit tests and assertions can be used as regression tests (written once and executed repeatedly thereafter). Sometimes I agree with them, but more often I will debate about whether a method is really too simple or too difficult to unit test.
If a developer argues that a method seems too simple to fail, isn't it worth taking the 60 seconds necessary to write up a simple 5-line unit test for it? These 5 lines of code will run every night (you do nightly builds, right?) for the next year or more and will be worth the effort if even just once it happens to catch a problem that may have taken 15 minutes or longer to identify and debug. Besides, writing the easy unit tests drives up the count of unit tests, which makes the developer look good.
On the other hand, if a developer argues that a method seems too difficult to unit test (not worth the significant effort required), perhaps that is a good indication that the method needs to be divided up or refactored to test the easy parts. Usually, these are methods that rely on unusual resources like singletons, the current time, or external resources like a database result set. These methods usually need to be refactored into a method that gets the resource (e.g. calls getTime()) and a method that takes the resource as a argument (e.g. takes the timestamp as a parameter). I let them skip testing the method that retrieves the resource and they instead write a unit test for the method that now takes the resource as a argument. Usually, this makes writing the unit test much simpler and therefore worthwhile to write.
The developer needs to draw a "line in the sand" in how comprehensive their unit tests should be. Later in development, whenever we find a bug, they should determine if more comprehensive unit tests would have caught the problem. If so and if such bugs crop up repeatedly, they need to move the "line" toward writing more comprehensive unit tests in the future (starting with adding or expanding the unit test for the current bug). They need to find the right balance.
Its important to realize the unit tests are not a silver bullet and there is such a thing as too much unit testing. At my workplace, whenever we do a lessons learned, I inevitably hear "we need to write more unit tests". Management nods in agreement because its been banged into their heads that "unit tests" == "good".
However, we need to understand the impact of "more unit tests". A developer can only write ~N lines of code a week and you need to figure out what percentage of that code should be unit test code vs production code. A lax workplace might have 10% of the code as unit tests and 90% of the code as production code, resulting in product with a lot of (albeit very buggy) features (think MS Word). On the other hand, a strict shop with 90% unit tests and 10% production code will have a rock solid product with very few features (think "vi"). You may never hear reports about the latter product crashing, but that likely has as much to do with the product not selling very well as much as it has to do with the quality of the code.
Worse yet, perhaps the only certainty in software development is that "change is inevitable". Assume the strict shop (90% unit tests/10% production code) creates a product that has exactly 2 features (assuming 5% of production code == 1 feature). If the customer comes along and changes 1 of the features, then that change trashes 50% of the code (45% of unit tests and 5% of the production code). The lax shop (10% unit tests/90% production code) has a product with 18 features, none of which work very well. Their customer completely revamps the requirements for 4 of their features. Even though the change is 4 times as large, only half as much of the code base gets trashed (~25% = ~4.4% unit tests + 20% of production code).
My point is that you have to communicate that you understand that balance between too little and too much unit testing - essentially that you've thought through both sides of the issue. If you can convince your peers and/or your management of that, you gain credibility and perhaps have a better chance of winning them over.
I have toyed with unit testing a number of times, and I am still to be convinced that it is worth the effort given my situation.
I develop websites, where much of the logic involves creating, retrieving or updating data in the database. When I have tried to "mock" the database for unit testing purposes, it has got very messy and seemed a bit pointless.
When I have written unit tests around business logic, it has never really helped me in the long run. Because I largely work on projects alone, I tend to know intuitively which areas of code may be affected by something I am working on, and I test these areas manually. I want to deliver a solution to my client as quickly as possible, and unit testing often seems a waste of time. I list manual tests and walk through them myself, ticking them off as I go.
I can see that it may be beneficial when a team of developers are working on a project and updating each other's code, but even then I think that if the developers are of a high quality, good communication and well-written code should often be enough.
One great thing about unit tests is that they serve as documentation for how your code is meant to behave. Good tests are kind of like a reference implementation, and teammates can look at them to see how to integrate their code with yours.
Unit-testing is well worth the initial investment. Since starting to use unit-testing a couple of years ago, I've found some real benefits:
regression testing removes the fear of
making changes to code (there's nothing
like the warm glow of seeing code
work or explode every time a change is
made)
executable code examples for
other team members (and yourself in
six months time..)
merciless refactoring - this is incredibly rewarding, try it!
Code snippets can be a great help in reducing the overhead of creating tests. It isn't difficult to create snippets that enable the creation of a class outline and an associated unit-test fixture in seconds.
You should test as little as possible!
meaning, you should write just enough unit tests to reveal intent. This often gets glossed over. Unit testing costs you. If you make changes and you have to change tests you will be less agile. Keep unit tests short and sweet. Then they have a lot of value.
Too often I see lots of tests that will never break, are big and clumsy and don't offer a lot of value, they just end up slowing you down.
I didn't see this in any of the other answers, but one thing I noticed is that I could debug so much faster. You don't need to drill down through your app with just the right sequence of steps to get to the code your fixing, only to find you've made a boolean error and need to do it all again. With a unit test, you can just step directly into the code you're debugging.
[I have a point to make that I cant see above]
"Everyone unit tests, they don't necessarily realise it - FACT"
Think about it, you write a function to maybe parse a string and remove new line characters. As a newbie developer you either run a few cases through it from the command line by implementing it in Main() or you whack together a visual front end with a button, tie up your function to a couple of text boxes and a button and see what happens.
That is unit testing - basic and badly put together but you test the piece of code for a few cases.
You write something more complex. It throws errors when you throw a few cases through (unit testing) and you debug into the code and trace though. You look at values as you go through and decide if they are right or wrong. This is unit testing to some degree.
Unit testing here is really taking that behaviour, formalising it into a structured pattern and saving it so that you can easily re-run those tests. If you write a "proper" unit test case rather than manually testing, it takes the same amount of time, or maybe less as you get experienced, and you have it available to repeat again and again
For years, I've tried to convince people that they needed to write unit test for their code. Whether they wrote the tests first (as in TDD) or after they coded the functionality, I always tried to explain them all the benefits of having unit tests for code. Hardly anyone disagreed with me. You cannot disagree with something that is obvious, and any smart person will see the benefits of unit test and TDD.
The problem with unit testing is that it requires a behavioral change, and it is very hard to change people's behavior. With words, you will get a lot of people to agree with you, but you won't see many changes in the way they do things.
You have to convince people by doing. Your personal success will atract more people than all the arguments you may have. If they see you are not just talking about unit test or TDD, but you are doing what you preach, and you are successful, people will try to imitate you.
You should also take on a lead role because no one writes unit test right the first time, so you may need to coach them on how to do it, show them the way, and the tools available to them. Help them while they write their first tests, review the tests they write on their own, and show them the tricks, idioms and patterns you've learned through your own experiences. After a while, they will start seeing the benefits on their own, and they will change their behavior to incorporate unit tests or TDD into their toolbox.
Changes won't happen over night, but with a little of patience, you may achieve your goal.
A major part of test-driven development that is often glossed over is the writing of testable code. It seems like some kind of a compromise at first, but you'll discover that testable code is also ultimately modular, maintainable and readable.
If you still need help convincing people this is a nice simple presentation about the advantages of unit testing.
If your existing code base doesn't lend itself to unit testing, and it's already in production, you might create more problems than you solve by trying to refactor all of your code so that it is unit-testable.
You may be better off putting efforts towards improving your integration testing instead. There's lots of code out there that's just simpler to write without a unit test, and if a QA can validate the functionality against a requirements document, then you're done. Ship it.
The classic example of this in my mind is a SqlDataReader embedded in an ASPX page linked to a GridView. The code is all in the ASPX file. The SQL is in a stored procedure. What do you unit test? If the page does what it's supposed to do, should you really redesign it into several layers so you have something to automate?
One of the best things about unit testing is that your code will become easier to test as you do it. Preexisting code created without tests is always a challenge because since they weren't meant to be unit-tested, it's not rare to have a high level of coupling between classes, hard-to-configure objects inside your class - like an e-mail sending service reference - and so on. But don't let this bring you down! You'll see that your overall code design will become better as you start to write unit-tests, and the more you test, the more confident you'll become on making even more changes to it without fear of breaking you application or introducing bugs.
There are several reasons to unit-test your code, but as time progresses, you'll find out that the time you save on testing is one of the best reasons to do it. In a system I've just delivered, I insisted on doing automated unit-testing in spite of the claims that I'd spend way more time doing the tests than I would by testing the system manually. With all my unit tests done, I run more than 400 test cases in less than 10 minutes, and every time I had to do a small change in the code, all it took me to be sure the code was still working without bugs was ten minutes. Can you imagine the time one would spend to run those 400+ test cases by hand?
When it comes to automated testing - be it unit testing or acceptance testing - everyone thinks it's a wasted effort to code what you can do manually, and sometimes it's true - if you plan to run your tests only once. The best part of automated testing is that you can run them several times without effort, and after the second or third run, the time and effort you've wasted is already paid for.
One last piece of advice would be to not only unit test your code, but start doing test first (see TDD and BDD for more)
Unit tests are also especially useful when it comes to refactoring or re-writing a piece a code. If you have good unit tests coverage, you can refactor with confidence. Without unit tests, it is often hard to ensure the you didn't break anything.
In short - yes. They are worth every ounce of effort... to a point. Tests are, at the end of the day, still code, and much like typical code growth, your tests will eventually need to be refactored in order to be maintainable and sustainable. There's a tonne of GOTCHAS! when it comes to unit testing, but man oh man oh man, nothing, and I mean NOTHING empowers a developer to make changes more confidently than a rich set of unit tests.
I'm working on a project right now.... it's somewhat TDD, and we have the majority of our business rules encapuslated as tests... we have about 500 or so unit tests right now. This past iteration I had to revamp our datasource and how our desktop application interfaces with that datasource. Took me a couple days, the whole time I just kept running unit tests to see what I broke and fixed it. Make a change; Build and run your tests; fix what you broke. Wash, Rinse, Repeat as necessary. What would have traditionally taken days of QA and boat loads of stress was instead a short and enjoyable experience.
Prep up front, a little bit of extra effort, and it pays 10-fold later on when you have to start dicking around with core features/functionality.
I bought this book - it's a Bible of xUnit Testing knowledge - tis probably one of the most referenced books on my shelf, and I consult it daily: link text
Occasionally either myself or one of my co-workers will spend a couple of hours getting to the bottom of slightly obscure bug and once the cause of the bug is found 90% of the time that code isn't unit tested. The unit test doesn't exist because the dev is cutting corners to save time, but then looses this and more debugging.
Taking the small amount of time to write a unit test can save hours of future debugging.
I'm working as a maintenance-engineer of a poorly documented, awful and big code base. I wish the people who wrote the code had written the unit tests for it.
Each time I make a change and update the production code I'm scared that I might introduce a bug for not having considered some condition.
If they wrote the test making changes to the code base would be easier and faster.(at the same time the code base would be in a better state)..
I think unit tests prove a lot useful when writing api or frameworks that have to last for many years and to be used/modified/evolved by people other than the original coders.
Unit Testing is definitely worth the effort. Unfortunately you've chosen a difficult (but unfortunately common) scenario into which to implement it.
The best benefit from unit testing you'll get is when using it from the ground up - on a few, select, small projects I've been fortunate enough to write my unit tests before implementing my classes (the interface was already complete at this point). With proper unit tests, you will find and fix bugs in your classes while they're still in their infancy and not anywhere near the complex system that they'll undoubtedly become integrated in in the future.
If your software is solidly object oriented, you should be able to add unit testing at the class level without too much effort. If you aren't that fortunate, you should still try to incorporate unit testing wherever you can. Make sure when you add new functionality the new pieces are well defined with clear interfaces and you'll find unit testing makes your life much easier.
When you said, "our code base does not lend itself to easy testing" is the first sign of a code smell. Writing Unit Tests means you typically write code differently in order to make the code more testable. This is a good thing in my opinion as what I've seen over the years in writing code that I had to write tests for, it forced me to put forth a better design.
I do not know. A lot of places do not do unit test, but the quality of the code is good. Microsoft does unit test, but Bill Gates gave a blue screen at his presentation.
I wrote a very large blog post about the topic. I've found that unit testing alone isn't worth the work and usually gets cut when deadlines get closer.
Instead of talking about unit testing from the "test-after" verification point of view, we should look at the true value found when you set out to write a spec/test/idea before the implementation.
This simple idea has changed the way I write software and I wouldn't go back to the "old" way.
How test first development changed my life
Yes - Unit Testing is definitely worth the effort but you should know it's not a silver bullet. Unit Testing is work and you will have to work to keep the test updated and relevant as code changes but the value offered is worth the effort you have to put in. The ability to refactor with impunity is a huge benefit as you can always validate functionality by running your tests after any change code. The trick is to not get too hung up on exactly the unit-of-work you're testing or how you are scaffolding test requirements and when a unit-test is really a functional test, etc. People will argue about this stuff for hours on end and the reality is that any testing you do as your write code is better than not doing it. The other axiom is about quality and not quantity - I have seen code-bases with 1000's of test that are essentially meaningless as the rest don't really test anything useful or anything domain specific like business rules, etc of the particular domain. I've also seen codebases with 30% code coverage but the tests were relevant, meaningful and really awesome as they tested the core functionality of the code it was written for and expressed how the code should be used.
One of my favorite tricks when exploring new frameworks or codebases is to write unit-tests for 'it' to discover how things work. It's a great way to learn more about something new instead of reading a dry doc :)
I recently went through the exact same experience in my workplace and found most of them knew the theoretical benefits but had to be sold on the benefits to them specifically, so here were the points I used (successfully):
They save time when performing negative testing, where you handle unexpected inputs (null pointers, out of bounds values, etc), as you can do all these in a single process.
They provide immediate feedback at compile time regarding the standard of the changes.
They are useful for testing internal data representations that may not be exposed during normal runtime.
and the big one...
You might not need unit testing, but when someone else comes in and modifies the code without a full understanding it can catch a lot of the silly mistakes they might make.
I discovered TDD a couple of years ago, and have since written all my pet projects using it. I have estimated that it takes roughly the same time to TDD a project as it takes to cowboy it together, but I have such increased confidence in the end product that I can't help a feeling of accomplishment.
I also feel that it improves my design style (much more interface-oriented in case I need to mock things together) and, as the green post at the top writes, it helps with "coding constipation": when you don't know what to write next, or you have a daunting task in front of you, you can write small.
Finally, I find that by far the most useful application of TDD is in the debugging, if only because you've already developed an interrogatory framework with which you can prod the project into producing the bug in a repeatable fashion.
One thing no-one has mentioned yet is getting the commitment of all developers to actually run and update any existing automated test. Automated tests that you get back to and find broken because of new development looses a lot of the value and make automated testing really painful. Most of those tests will not be indicating bugs since the developer has tested the code manually, so the time spent updating them is just waste.
Convincing the skeptics to not destroy the work the others are doing on unit-tests is a lot more important for getting value from the testing and might be easier.
Spending hours updating tests that has broken because of new features each time you update from the repository is neither productive nor fun.
If you are using NUnit one simple but effective demo is to run NUnit's own test suite(s) in front of them. Seeing a real test suite giving a codebase a workout is worth a thousand words...
Unit testing helps a lot in projects that are larger than any one developer can hold in their head. They allow you to run the unit test suite before checkin and discover if you broke something. This cuts down a lot on instances of having to sit and twiddle your thumbs while waiting for someone else to fix a bug they checked in, or going to the hassle of reverting their change so you can get some work done. It's also immensely valuable in refactoring, so you can be sure that the refactored code passes all the tests that the original code did.
With unit test suite one can make changes to code while leaving rest of the features intact. Its a great advantage. Do you use Unit test sutie and regression test suite when ever you finish coding new feature.
I'm agree with the point of view opposite to the majority here:
It's OK Not to Write Unit Tests
Especially prototype-heavy programming (AI for example) is difficult to combine with unit testing.