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Third, you make a little change to your functional code

Next, you run the tests

In the optional fifth step, you refactor your code to remove any duplication.

two simple rules. First, you should write new business code only when an automated test has failed. Second, you should eliminate any duplication that you find.

Your designs must consist of highly cohesive

You write your own tests because you can’t wait

the running code providing feedback between decisions

Test-Driven Development (Addison-Wesley 2003)

a Smalltalk system with a completely test-driven approach that took four years and 40 person-years of effort

there’s far more to testing than unit tests, so you’ll still need other testing techniques such as functional testing, user acceptance testing, system integration testing and so on.

you have a clear measure of success

most programmers don’t read the written documentation for a system; instead, they prefer to dig right into the code.

Your acceptance tests define exactly what your stakeholders expect of your system; therefore, they truly do determine a good portion of your requirements.

Bob Martin says it best: “The act of writing a unit test is more an act of design than of verification. It’s also more an act of documentation than of verification.

Side by Side: Comparing TDD and AMDD TDD shortens the programming feedback loop; AMDD abridges the modeling feedback loop. TDD provides detailed specification (tests), while AMDD provides traditional specifications (agile documents). TDD promotes the development of high-quality code; AMDD encourages high-quality communication between your stakeholders and other developers. TDD provides concrete evidence that your software works, whereas AMDD supports your entire team, including stakeholders, in working toward a common understanding. TDD provides finely grained, concrete feedback in minutes. However, concrete feedback requires developers to follow the practice Prove It With Code, and they may become dependent on non-AM techniques; AMDD lets you get verbal feedback in minutes. TDD ensures that your design is clean by focusing on creation of callable and testable operations; AMDD lets you think through larger design and architectural issues before you code. TDD isn’t visually oriented; AMDD is. Both techniques are new and therefore may be threatening to traditional developers. Both techniques support evolutionary development. —S. W. Ambler

But to do that well, you absolutely must have enough test coverage that you just aren’t afraid to rip your code’s guts out

I always end up sketching in a few classes and then tearing them up and re-sketching, and after a few iterations I’m starting to have a feeling for X and Y.

once you’re into maintenance mode, there are really no excuses. Because you really know what all your X’s and Y’s are

I freely admit that this is not really truly TDD

Writing the tests points out all the mistakes you might make in signatures, prerequisites, etc. If the tests are too hard to make then you know that your API will be too hard to use, you're doing it completely wrong, and may as well pause for a rethink.

While the approach you advocate makes sense, it does require professionalism, not just from the developer but from management too.

the person left to maintain the code isn't the person who wrote it, leaving the maintainer with an unholy mess to untangle. Getting unit tests into such code is a monumental task.

he failure to address how unit tests can be introduced to an existing non unit-test codebase. (i.e. go from non-TDD to TDD)

I feel the TDD community only wants to focus on greenfield projects and has ignored maintenance/legacy issues. Which is strange when as you say code spends most of it's time in maintenance

The thing is that as long as the project is small you really don't see the benefits of TDD. I've done a couple of small projects and never had to go back to them ever again

Never use mocks unless you are mocking an interface that will almost never change

You are writing the client code (in the form of a test) so you are thinking how the worker code will be used. What is its public interface and what do you want it to do when it's called

From: Tathagata Chakraborty (Jun 24 2009, at 07:31)TDD is useful in another situation - in a commercial setting and when detailed specification documents have already been created by say a technical expert/architect. In this case you don't have to do a lot of designing while coding, so you can start off with the test cases.

writing the tests *first* is that it helps keep your code focused on exactly what it's meant to do, and no more

When work on production code begins, most of the code should fall into the categories of things that are not to be tested.

In theory, TDD is a great idea. The problem with TDD can be expressed in one word: money.

One approach to the unknown X and Y problem that I've been using recently has been to pretend that class X has been written already, and then write code that uses this pretend X object/API. I usually write this directly in the file that will become my unit test. Since X doesn't exist, I'm allowed to call whatever methods I want and pretend it all works. Once I'm satisfied with how it all looks, I cut and paste everything into a bunch of failing tests.

I get really bored adding tests to code that already runs

the seductive TDD trap

religious zealots

There is nothing wrong with building tests after you have built your product.

that goes a long way towards taking software development from a form of artisanal craftsmanship to a real engineering profession.

using tests to drive development cripples innovation, dramatically slows development

It always seem to me to be a codified form of reverse engineering, or at least a way to force the programmers into looking at their code from two separate angles at the same time.

If you're just adding tests at the end, then it's normal unit-testing, isn't it?

I do realize that this type of exercise might help younger coders in getting better structure, they do often rush in too quickly and focus more on the instructions than the abstractions.

TDD is test-driven *design*

He said he didn't write tests in cases where it would have taken him several hours to get a working test for a small piece of code.

In some applications, objects are self-contained, activities are sequential, and algorithms are tricky

I've seen cases where people have wrecked the architecture of systems in the name of making them testable... But have never written the tests.

Yes, it's possible to make peace with testability, and in the best situation, testability can improve the architecture of a program, but it can also lead people away from highly reliable and maintainable KISS approaches.

Like any infrastructure, it is always beneficial to provide unit testing. The most benefit is derived from installing it as early on in the project as possible.

The value of an untested feature, to a client, is ... zero. So, it doesn't matter how many of these you have rattled off in the past week, your net throughput is effectively... zero."

You can see in this thread the word "professionalism" (substitute "morality" with little gain/loss of substance) and even "sin" (used in jest, but not really!)

if I delay writing unit tests until after all the units are working together then because the system "already works" my subconscious enthusiasm for writing unit tests falls markedly, and so their quality and coverage fall

Experience teaches that if I generate that output by hand (1) it takes *much* longer (2) I almost always get it wrong. So I often write the code, get its output, carefully check it (really...) and then use it as the correct result.

My main objections to TDD are: 1) it promotes micro-design over macro-design and 2) it's hard to apply in practice (i.e. for any code that is not a bowling card calculator or a stack).

the tests are just a persistent artifact of the exploratory coding I've already done.