[jasonlotito]

You forgot a critical step. Refactoring. Refactoring is a critical part of TDD, one which many people seem to forget.

> It's needless context switching when I have a general idea of how I want the code structured before I start writing anyway.

That's good. You are allowed to have that. In fact, your first test is implementing initial parts of that code. What TDD is force you to document that in a formal manner. It also highlights where things become cumbersome. If it's hard to write a test, your code is probably far too complex for what it's trying to do.

Finally, knowing what you want is different then having what you need. TDD gives the opportunity to focus on getting a finalized code base faster by not having to implement things that are unnecessary.

But really, when you describe TDD as write failing test, then write code to pass the test, and leave it at that, you've left out an essential pieces of the steps that is just as important as writing the test and writing the code. It's akin to me describing TDD as writing code and then refactoring, and leaving out testing.

[dpark]

Unit tests are not formal documentation. Nor are they generally adequate documentation. At best they will explain what the code does, but never how or why.

[jasonlotito]

No, it isn't formal documentation. However, unlike other forms of documentation, it can be proven to be correct. If you want to know how the element being tested is to be used, unit tests are a great way of discovering that. It also tells you what it's supposed to do. Finally, it can tell you all this quickly and efficiently.

So, essentially, it gives you what the code does, as well as how to do it using the code. It doesn't tell you how it does this beneath the API, or why it does what it does, but it doesn't have to.

[dpark]

Your unit test beliefs are giving you a heavy bias.

Unit tests cannot be proven to be correct (not without some other actual formal proof). Running a suite of unit tests proves nothing except that the tests pass. The unit tests can be buggy. The code they test can also still be buggy. Indeed the code is buggy if it's nontrivial, unless you are asserting that unit tests end the very existence of bugs. Unit tests add more confidence about the state of the code, especially with respect to regressions, but they do not prove anything.

As for unit tests telling you how to use the code, I suppose they do to some extent. Your code should probably be clear enough without this, though. If I have to read your unit tests to know how to use your class, then you have failed at writing self-documenting code, and you've also failed at writing API documentation.

I would also say that the how and why are often extremely important. Anyone maintaining your code (i.e. Anyone who cares about your unit tests) needs to understand the how. Anyone using your code probably needs to understand the why. If your calendar unit tests indicate that certain days have 25 hours, but fail to explain that these are due to daylight savings time, that's a pretty important missing why.

[jasonlotito]

> Running a suite of unit tests proves nothing except that the tests pass.

Which, when compared to documentation, is light years ahead in terms or proof.

> Your code should probably be clear enough without this, though. If I have to read your unit tests to know how to use your class, then you have failed at writing self-documenting code, and you've also failed at writing API documentation.

sigh

Well, apparently, if my API is clean enough, then you shouldn't need API documentation. Right?

Regardless, a clean API can be self documenting, but having tests demonstrating all the forms and intents of the classes can help with precisely what to do. As for code being clear: What does code have to do with an API? The whole point is to avoid actually having to look at the implementation of the API.

> I would also say that the how and why are often extremely important. Anyone maintaining your code (i.e. Anyone who cares about your unit tests) needs to understand the how. Anyone using your code probably needs to understand the why. If your calendar unit tests indicate that certain days have 25 hours, but fail to explain that these are due to daylight savings time, that's a pretty important missing why.

These are two different issues entirely. One has nothing to do with the other. Regardless, documenting 25 hours doesn't change the fact that changing it requires testing. It's as simple as that.

You seem to be playing straw man with your first argument, you're just confused with your second, and targeting something that has nothing to do with what we are discussing.

It's like me bashing git because it doesn't compile your code.

[dpark]

> Which, when compared to documentation, is light years ahead in terms or proof.

In three replies you've gone from calling unit tests formal documentation to saying that they are not documentation at all. The fact that you don't see the problem with this is evidence of the bias I mentioned.

> Well, apparently, if my API is clean enough, then you shouldn't need API documentation. Right?

Sure. In an ideal world, the API would be so obvious that further documentation is redundant. That's often not realistic, though, so we have additional documentation to shore up the API. (In modern code, the bulk of this is actually in comments inside the API interface.)

> Regardless, a clean API can be self documenting, but having tests demonstrating all the forms and intents of the classes can help with precisely what to do. As for code being clear: What does code have to do with an API? The whole point is to avoid actually having to look at the implementation of the API.

So instead of looking at the API itself, it's more appropriate to look at unit tests? It's better to look at 'testWiggleWidgetThrowsOnNull()' than to just look at the API and see that 'wiggleWidget()' throws on null? Or better yet, look at the documentation that should state that null is not a valid argument?

Unit tests are not good documentation. Good documentation is intended for humans to read. Unit tests are intended to test code, not to convey information. They generally contain a ton of noise in the form of boilerplate and mock objects.

> These are two different issues entirely. One has nothing to do with the other. Regardless, documenting 25 hours doesn't change the fact that changing it requires testing. It's as simple as that.

Of course. I've not argued against testing. I don't believe unit tests are always appropriate, though, and I think the argument that they are documentation is really weak.

> You seem to be playing straw man with your first argument, you're just confused with your second, and targeting something that has nothing to do with what we are discussing.

I'm not sure exactly what you're referring to as my "first" and "second" argument. It's absolutely not a strawman to say that unit tests don't prove code correct. It's a fallacious claim on your part to say that they do. A unit test passing only proves that the code does what the unit test expects. It doesn't prove that the unit test expects the right thing, nor does it prove that the code is being tested where it actually matters.

If the second argument is about documentation, I stand by my assertion that unit tests are not good documentation. In fact, I would say that they are terrible documentation, for the reasons I outlined above.

> It's like me bashing git because it doesn't compile your code.

Which would be a pretty reasonable response to someone claiming that git is a great compiler.