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I'm a new programmer (only been learning for about a year) and in my goal to become better at it I have just recently learned about TDD. I wanted to get into the habit of using it since it seems very helpful. I wanted to check and make sure I'm using it correctly.

What I'm doing:

  1. Think of a new method I need.
  2. Create a test for that method.
  3. Fail test.
  4. Write method.
  5. Pass test.
  6. Refactor method.
  7. Repeat.

I'm doing this for EVERY method I write, are there some I shouldn't bother with? Later on I usually think of a way to test my already existing methods in a different way or situation. Should I make these new tests I think of, or since each method already has a test of their own should I not bother? Can I be OVER testing my code I guess is my main concern in asking this.

EDIT

Also, this was something I was just wondering. When doing something like making a GUI, would TDD be necessary in that situation? Personally, I can't think of how I would write tests for that.

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    You are already doing it a lot better than seasoned professionals who say they are testing everything (but don't). Commented May 18, 2012 at 17:57
  • What you describe isn't the Spirit of TDD. Commented May 18, 2012 at 18:22
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    You may want to look into ATDD or BDD. Commented May 20, 2012 at 3:54
  • Perhaps start higher - think of a new module you need. Commented May 22, 2012 at 10:40

9 Answers 9

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What you are describing as a workflow isn't in my opinion the Spirit of TDD.

The synopsis of Kent Becks book on Amazon says:

Quite simply, test-driven development is meant to eliminate fear in application development. While some fear is healthy (often viewed as a conscience that tells programmers to "be careful!"), the author believes that byproducts of fear include tentative, grumpy, and uncommunicative programmers who are unable to absorb constructive criticism. When programming teams buy into TDD, they immediately see positive results. They eliminate the fear involved in their jobs, and are better equipped to tackle the difficult challenges that face them. TDD eliminates tentative traits, it teaches programmers to communicate, and it encourages team members to seek out criticism However, even the author admits that grumpiness must be worked out individually! In short, the premise behind TDD is that code should be continually tested and refactored.

Practical TDD

Formal automated Testing, especially Unit Testing every method of every class is just as bad an anti-pattern and not testing anything. There is a balance to be had. Are you writing unit tests for every setXXX/getXXX method, they are methods as well!

Also Tests can help save time and money, but don't forget that they cost time and money to develop and they are code, so they cost time and money to maintain. If they atrophy from lack of maintenance then they become a liability more than a benefit.

Like everything like this, there is a balance which can't be defined by anyone but yourself. Any dogma either way is probably more wrong that correct.

A good metric is code that is critical to the business logic and subject to frequent modification based on changing requirements. Those things needs formal tests that are automated, that would be a big return on investment.

You are going to be very hard pressed to find many professional shops that work this way either. It just doesn't make business sense to spend money testing things that will for all practical purposes never change after a simple smoke test is preformed. Writing formal automated unit tests for .getXXX/.setXXX methods is a prime example of this, complete waste of time.

It is now two decades since it was pointed out that program testing may convincingly demonstrate the presence of bugs, but can never demonstrate their absence. After quoting this well-publicized remark devoutly, the software engineer returns to the order of the day and continues to refine his testing strategies, just like the alchemist of yore, who continued to refine his chrysocosmic purifications.

-- Edsger W. Djikstra. (Written in 1988, so it's now closer to 4.5 decades.)

See also this answer.

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    That pretty much addresses what I was concerned about. I was feeling that I shouldn't be testing every method like I was, but wasn't sure. Looks like I may still need to read some more about TDD. Commented May 18, 2012 at 18:33
  • @kevincline Most of the time setXXX/getXXX are not needed at all :) Commented May 18, 2012 at 20:20
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    When you memoise that trivial getXXX and get it wrong, or introduce lazy loading in your getXXX and get it wrong, then you will know that sometimes you really do want to test your getters. Commented May 19, 2012 at 11:04
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You're very close. Try thinking in this slightly different way.

  1. Think of a new behaviour I need.
  2. Create a test for that behaviour.
  3. Fail test.
  4. Write new or extend existing method.
  5. Pass test.
  6. Refactor code.
  7. Repeat.

Don't automatically create getters and setters for every property. Don't think of a whole method and write the test(s) to cover all functionality. Try to encapsulate the properties inside the class and write methods to provide the behaviour that you need. Let your methods evolve into a good design instead of trying to plan them up-front. Remember that TDD is a design process, not a testing process. The advantage it has over other design processes is leaving a stream of automated regression tests behind, rather than a piece of paper you throw in the bin.

Also, remember Uncle Bob's three rules of TDD.

  1. You are not allowed to write any production code unless it is to make a failing unit test pass.
  2. You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.
  3. You are not allowed to write any more production code than is sufficient to pass the one failing unit test.
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    @Zexanima: You're doing way better than most of us were after a year. Just trying to point you to the next step. Commented May 18, 2012 at 18:53
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    I think these 3 rules you link to; as idyllic as they may sound, are exceptionally dogmatic and highly unrealistically rigid in 99% of all production shops that anyone will encounter. Commented May 18, 2012 at 21:19
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    @FrankShearar or it can be seen as the impractical blathering of a fundamentalist extremist and wholesale disregarded. I have worked in shops that had this dogmatic attitude, they took the dogma literally and missed the point; writing tests that didn't test any of their actual code in a practical fashion and ending up just testing Mocking and Dependency Injection frameworks ability to confuse what was important at best. Commented May 18, 2012 at 21:46
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    @pdr The Spirit of something is diametrically opposed to the dogmatic formalized canonization of that thing. It is one thing to have a philosophy and another to twist it into a religion. TDD is more times than not conversed about in black and white dogmatic religious terms. That 3 rules sound dogmatic and religious in presentation and what gets heard is the Test, Test, Test mantra, to someone like the OP, they take them literally and that causes more harm than good. I countered Frank that polarizing statements can do more harm to the cause than good. Commented May 18, 2012 at 22:13
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    My point was that dogmatism comes from blindly accepting something as gospel. Take the polarising statement, try it out, make it force you out of your comfort zone. You cannot evaluate the tradeoffs involved in TDD if you do not try the 3-point-all-or-nothing extreme approach, because you will have no data. Commented May 19, 2012 at 11:02
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Few things to add to other's responses:

  1. There is such a thing as over testing. You want to make sure your unit tests overlap as little as possible. There's no point of having multiple tests verify the same conditions in the same piece of code. On the other hand, when you refactor your production code and you have many tests that overlap that section, you will have to go back and fix all those tests. Whereas if they do not overlap, then one change will at most break only one test.

  2. Just because you thought of a better way of writing a test, I would not go back there and start rewriting it. This is going back to the individuals who keep writing and rewriting the same class/function because they try to make it perfect. It will never be perfect, so move on. When you discover a better method, keep it in the back of your mind (or add to comments of the test). Next time you are in there, and you see immediate benefit of switching to the new way, that's the time to refactor. Otherwise, if the feature is done and you moved on and everything works, leave it working.

  3. TDD focuses on delivering immediate value, not simply making sure every function is testable. When you add functionality, start by asking "what does the client need". Then define an interface to give the client what it needs. Then implement whatever it takes to make the test pass. TDD is almost like testing use case scenarios (including all the "what-ifs"), rather than simply coding up public functions and testing each one.

  4. You asked about testing GUI code. Look up "Humble Dialog" and "MVVM" patterns. The idea behind both of these is that you create a set of "view model" classes, that don't actually have UI-specific logic. However, these classes will have all the business logic that typically is part of your UI and these classes should be 100% testable. What's left is a very thin UI shell and yes, typically that shell is left without test coverage, but at that point it should have almost no logic.

  5. If you have a large portion of existing code, as few others suggested, you shouldn't start adding unit tests absolutely everywhere. It'll take you forever and you won't get benefit from adding unit tests to 80% of classes which are stable and will not change in the near (or not so near) future. However, for new work, I do find using TDD development with ALL code to be extremely beneficial. Not only do you end up with a suite with automated tests when you are done, but actual development has huge benefits:

    • By considering testability, you will write code which is less coupled and more modular
    • By considering your public contract before anything else, you will end up with public interfaces which are much cleaner
    • As you are writing code, verifying new functionality takes milliseconds compared to running your entire application and trying to force execution down the right path. My team still releases error handling code which has not been even executed ONCE just because they couldn't get the right set of conditions to happen. It is amazing how much time we waste when later on in QA those conditions do happen. And yeah, a lot of this code is what someone would've considered "not area for a lot of change in the future once smoke testing is done".
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There are some methods that aren't being tested, namely those tests. However, there is something to be said for some tests being added after the initial code has been written, such as boundary conditions and other values so that there may be multiple tests on a single method.

While you can over test your code, that usually comes where someone wants to test every possible permutation of inputs which doesn't quite sound like what you are doing. For example, if you have a method that takes in a character, do you write a test for every possible value that could be entered? That would be where you'd get to overtesting, IMO.

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  • Ahh, okay. That's not what I'm doing. I just usually end up thinking of a different situation I could test my methods a ways down the line after I've already made their initial test. I was just making sure those 'extra' tests were worth making, or if it was over doing it. Commented May 18, 2012 at 18:03
  • If you work in small enough increments you can usually be reasonably sure your test actually works. In other words, having a test fail (for the right reason!) is in itself testing the test. But that level of "reasonably sure" won't be as high as the code under test. Commented May 20, 2012 at 9:28
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Generally you are doing it right.

Tests are code. So if you can improve the test, go ahead and refactor it. If you think that a test can be improved go ahead and change it. Do not be afraid to replace a test with a better one.

I recommend in testing your code, avoid specifying how the code is supposed to do what it is doing. Tests should look at the results of the methods. This will help with refactoring. Some methods do not need to be explicitly tested (i.e. simple getters and setters) because you will use those to verify the results of other tests.

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  • I was writing tests for getters and setters too so thanks for that tip. That'll save me some un-needed work. Commented May 18, 2012 at 18:10
  • "Some methods do not need to be explicitly tested (i.e. simple getters and setters)" - You've never copy/pasted a getter and setter and forgotten to change the field name behind it? The thing about simple code is that it requires simple tests -- how much time are you really saving? Commented May 18, 2012 at 18:13
  • I don't mean that the method isn't tested. It is just checked via confirming that other methods are set or during the actual setting up of a test. If the getter or setter doesn't work properly, the test will fail because the properties weren't set correctly. You get them tested for free, implicitly. Commented May 18, 2012 at 18:17
  • Getter and setter tests don't take long, so I probably will continue to do them. However, I never copy and paste any of my code so I don't run into that issue. Commented May 18, 2012 at 18:18
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My opinion on TDD is that the tooling has create a world of 'point and click' style developers. Just because the tools create a test stub for each method doesn't mean you should be writing tests for every method. Some people are 'renaming' TDD as BDD (behaviour driven development) where the tests are much larger-grained and intended to test the behaviour of the class, not each fiddly little method.

If you design your tests to test the class as its intended to be used, then you start to gain some benefits, especially as you start to write tests that exercise a bit more than each method, especially when you start to test the interaction of those methods. I suppose you could think of it as writing tests for a class, rather than methods. In any case, you must still write 'acceptance tests' that exercise the combination of methods to make sure there are no contradictions or conflicts in how they are used together.

Don't get TDD confused with testing - it's not. TDD is designed so that you write code to exercise your requirements, not to test the methods. Its a subtle but important point that's often lost on people who blindly write test code for every method. Its that you should be writing tests that make sure your code does what you want it to do, not that the code that you wrote works like its supposed to.

There's some good links to the right about BDD v TDD. Check them out.

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When you start learning TDD, yes, you should blindly follow the dogmatic approach of not writing a single line of code except to make a failing test pass, and writing only enough of a test to fail (and fail for the right/expected reason).

Once you have learned what TDD is about, THEN you can decide that certain kinds of things aren't worth testing. This is the same approach you should follow for everything, and the Japanese martial arts call this "shuhari". (The link also explains how one can progress through the stages of learning without a teacher which is, I suspect, how most people have to learn.)

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I believe that you are overtesting.

I have been practicing TDD for many years, and in my experience, when TDD is performed effectively, you get two main benefits:

  • Provide rapid feedback
  • Enable refactoring

Provide rapid feedback

Particularly with dynamic languages, I can execute the relevant tests on in less than a second. And I have file system watchers running these tests automatically when a source file is changed on disk. Thus I have virtually no waiting time for tests, and I immediately know if the code I write did as expected. Thus TDD leads to a very efficient way of working.

Enable refactoring

If you have a good test-suite, you can safely refactor, as you gain new insights into how the system should be designed.

A good test suite allows you to move responsibility around in your code, and still have confidence that the code works as expected after the move. And you should be able to do this with little changes to the test code.

If you write tests for every method in your system, then odds are that you cannot easily refactor your code, every refactor of you code will require massive changes to the test code. And can you even be sure that the test code still works as expected? Or did you accidentally introduce a bug in the test code, which consequently leads to a bug in the production code?

If you however, as also suggested in pdr's answer, focus on behavior instead of methods when writing tests, you will have tests that will require much less changes when refactoring the system.

Or as Ian Cooper says in this presentation (I quoted from memory, so might not be correctly quoted):

Your reason for writing a new test should be adding a new behavior, not adding a new class

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You should test every public method.

The catch here is that if your public methods are very small you are probably exposing too much information. The common practice of exposing every property as getXXX() actually breaks encapsulation.

If your public methods are actually behavior of the class, then you should test them. If not, they are not good public methods.

EDIT: pdr's answer is much more complete than mine.

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