It's hocus where contrasted to developer-driven testing, because Test Driven Development - as a development methodology (as opposed to a tool) - espouses that you Write All Your Tests first.

Have I had experience (and much value) out of sometimes writing tests for certain problem classes before writing any code? Yes. Changes to existing functionality are often a good candidate.

Does TDD as a methodology suggest you should ALWAYS write your tests first? Everything I've read suggests so.

And "as any fule kno" [sic], this is idioicy during a design or hacking or greenfield phase of development. Allowing your tests to dictate your code (rather than influence the design of modular code) and to dictate your design because you wrote over-invasive test.

tl;dr: Writing tests before code works pretty well in some situations. Test Driven Development, as handed down to us mortals by Agile Testing Experts and other assorted shills, is hocus.

> Writing tests before code works pretty well in some situations. Test Driven Development, as handed down to us mortals by Agile Testing Experts and other assorted shills, is hocus.

What? So it works in some situations, but not all. Thus hocus?

I'm no 'Agile Testing Expert', but I have worked for the last 2-3 years doing TDD exclusively (as in ALWAYS writing tests first). It isn't hocus. It is effective. I can understand it doesn't suit all problems, and can potentially be a hinderance sometimes, but that is the same for ANY methodology/practice. I don't quite understand your hostility towards it.

What do you mean by 'developer driven testing'?

The hocus is not that you can use TDD, if, in your professional judgment, you believe that to be the best solution to the problem.

The hocus is that you must use it, because some guru said so.

> I can understand it doesn't suit all problems, and can potentially be a hinderance sometimes

Then why do it exclusively?

Testing is about helping developers, and recognizing that automated testing is about benefit to developers, rather than cargo-culting a workflow and decreeing that one size fits all.

Writing tests first as a tool to be deployed where it works is "Developer Driven Testing" - focussing on making the developer more productive by choosing the right tool for the job. Generalizing a bunch of testing rules and saying This Is The One True Way Even When It Isn't (I mean seriously, you continued to use it when it was a hindrance?!) - that's not right.

Primarily I do web development, with python and ruby, TDDing is VERY well supported, and thus has allowed me to do it exclusively. But I can imagine there are systems out there that are difficult to TDD, web apps are not among them though.

Sounds like you are interpreting TDD in a rather extreme way. If you haven't found it useful, then fine don't use it. But that doesn't mean it is universally bad, and thus doesn't deserve the "It's all hocus and you are a stupid zealot if you do it"

Excuse me for interrupting the budding flame war, but I have a question regarding the subject, which you seem qualified to answer? :-)

My experience is the same as (what I believe is) the usual criticism of tests-first.

I often need to rethink the API to my functions/methods, sometimes more than once. This goes for both external and internal APIs, so it doesn't help with detailed interface specifications between modules.

Test-first is a problem, since it needs a fixed interface before I'm ready to lock down the interface.

I tend to instead write inside-out; a few pages of code and then write tests for that code. That model isn't really kosher/halal/etc, according to TDD?

One benefit to TDD is that you become a user for your API much more quickly, and so your API doesn't need to change as much.

TDD suggests 3 steps: 1. Write one test 2. Write the minimal code to make it pass 3. Refactor the code you've got.

Try not to think of tests as immutable. You can throw away tests when they don't provide value.

Finally, make sure you're using an IDE with refactoring support. That helps immensely when you make an API change which will affect your tests.

OK, thanks to you and zumda.

Interesting TDD argument. I'll buy a book or something and try again when my present hobby project is done and I have time for experimenting.

(IDE refactoring needs a stricter language than I prefer. Also, without an IDE and using my old eyes I have 2 A4 of code + 1 A4 of bash on a 24" monitor...)

If you're looking for book suggestions, I'd recommend "Growing Object-Oriented Software, Guided By Tests" by Steve Freeman and Nat Pryce. It's pretty pragmatic, and the treatment of the subject is pretty thought-provoking (at least, I thought so when I read it).

The examples are all Java, but the accompanying website (http://www.growing-object-oriented-software.com/) has links to reimplementations in several other languages.

According to TDD writing inside-out is one of the points it tries to combat.

The point of using TDD to write interfaces is that you first write the code you wish you had, and then implement it. The other way around you could end up with code that is optimized for the code inside the module, and not optimized for using it.

Of course now you have to rewrite your tests and your code when changing an API, but at least you know that no other part of your application got broken by the new API.

I personally like the TDD approach to write interfaces, since then I won't take shortcuts just because it is easier to do in the specific module that I'm programming/extending. It will actually produce code that can be used easily from the outside and removes a lot of dependencies in the process.

I don't think I've ever seen a description of TDD that suggests you write all of your tests before writing any production code - rather you iteratively write some tests, have them fail then write the code to make them work and then see the tests pass, repeating that process until you have implemented everything you need.

You can work within TDD by just calling all code that comes before the tests a `prototype'.

Sure, but you write /some/ tests first. And that means, if you want to do it meaningfully, that you either need to zoom down in to tiny bits of functionality first in order to be able to write those tests (see the isPalindrome discussion in the article), or you write a test that requires most of the software to be finished, or you cheat and fudge it.

Making tests a central part of the process because they're useful to developers? Awesome. Dictating a workflow to developers that works in some cases as the One True Way: ridiculous.

I've always thought of testing as simply a way to verify that your code does what is supposed to do.

I tend to agree with you that TDD as a development methodology is deeply flawed. I have never found that the act of writing a test case and making it pass has helped me with the actual creative process of solving a problem via code. In fact, I'll frequently dash out a method I'm writing quickly, and then go back and reconstruct it piece by piece via TDD.

The main benefit writing tests first gives you is that you know your test is actually working (i.e. because it first fails) and that the code you implement actually passes it. It also keeps you honest because it prevents you from writing "extraneous" code, i.e. code that exists but is not specified by a test.

So yeah, I totally agree with you that the cult of TDD kind of sucks. But I haven't stumbled upon a better way yet. I've often thought it would be cool if there was some way for e.g. your version control software to be tied to the code you write that passes certain test(s), such that you could somehow verify that without that code your test fails and with that code your test passes. For the present though, TDD tends to work pretty well for me.

I think you're narrowing in on the distinction I'm trying to make between a methodology and a tool there; writing tests before you implement a piece of functionality is a useful tool to have in your testing toolbox.

Labouring under the idea that Tests Must Come First (and everything I've seen, and everything I /do/ see now suggests that that is the central idea in TDD - you write a test, then you write the code to pass it) without pivoting to see that testing is a useful practice in so much as it helps developers is the wrong approach.

I think you've hit the nail on the head, @peteretep.

The problem is that ideologies like TDD try to come up with simple rules for how to develop (i.e. always write tests first). In reality, it's better to use your brain when you're deciding how to approach something (i.e. is this a good situation for writing tests first?)

Perhaps by permuting your code the system could determine if there was anything that wasn't required to make the test pass and exclude it from the check-in.

I often code three or four commits worth at once when on a roll and it's a pain doing multiple staged adds, stashes, tests, and commits to store each sub-change on its own. Having a tool to help with this would be great.

This is a common misconception. TDD does not 'espouse' in any way that you write all your tests first. Nothing I have read suggests so.

For me, TDD, in practice means switching back and forth between writing tests and production code. That is, write some test code, run, fail, fix the production code, write some more test code. It is incremental.

EDIT: Fixed a typo

> And "as any fule kno" [sic], this is idioicy during a design or hacking or greenfield phase of development.

When you write something you run it to make sure it works. Bottle that and call it a test. And then merely do this before you write the code. "What will I be done when I get this code to do?"

Don't plan, and spec, your whole API before you've written a line of code or anything, but do write a one-liner to check whatever it is you're going to do so you know when you're done.

Ideally you'll write a test (still just a one-liner) for every corner-case that you cover in code, because you need a failing test to know if your fix actually worked.

And face it, if you're doing "real" development work you've got business goals, and a spec with features intended to deliver on that, and you need to cover every tiny detail. If you don't have the spec ('fail on values over n') directly linked to the code that implements it, it will get lost, and if you aren't testing it you can't legitimately claim to be delivering it.

A spec, such as you'd get by performing useful TDD, is a requirement for modern software development. You could write it all up-front in the planning phase (waterfall style), or all after in the testing phase (waterfall style again), or you could interleave it with research and development, which if you think about it, sounds kind of agile by comparison...

The issue/argument here is not that writing tests is worthless but that in many cases the approach of "if we write enough tests then the code that solves the problem will eventually emerge" is doomed to failure or at least results in an extremely verbose approach to development.

But then I think the approach is the wrong one. In TDD you are not required to write a lot of test and hope that they magically work in the future. Instead a small test to do one thing should be written, and then write enough code to make it pass.

For example lets take a simple newsletter signup form with only a field to enter an email address.

Now you shouldn't write a test to see what happens when you enter an email, a wrong email, if the confirmation email is sent, etc. Start with the simplest case: "If I fill in my email, and I press klick, then it should show me a confirmation that I singed up." Not more. Now make that pass, and you have working code!

Now you can add tests that verify that a wrong or empty email is rejected, now make that pass. More working code!

With TDD you should never end up with a lot of tests and no code that solves the problem. In that case you are actually writing too many tests and not enough code.

Sure, if you need training wheels on your bike...

Which we demonstrably do as an industry. When neither NASA nor Knuth can write 100% correct code, the rest of us can't reasonably expect to pull it off. Human beings doing meticulous work make lots and lots of mistakes, and I welcome any feasible tactic that stops mine from being released. Sure, automating "I got a confirmation after pushing the button" seems hokey on day one (it's not as if you'd otherwise commit and go home before having seen it work) but somebody is eventually going to make a change that unexpectedly breaks it, and I want to know about it.

I'm not debating the importance of tests, but rather of the test-driven approach. I can write code and then write tests (or intermingled) and satisfy your point. I don't have to switch my brain into this wierd test-driven approach to do that. TDD zealots don't seem to understand that.

People just assume older code works. I'm regularly finding stuff we've had in production for months that never did what it was supposed to. You could go back and write all the same tests after the code is done, but I find it extremely unlikely that anyone will actually reach the same degree of test coverage (I know I for one never have). And even if you're one of the rare few who will pay down this technical debt eventually, it takes away quite a bit of the value of the tests to muddle through all the coding work without them.