The Power of Test Driven Development (TDD)

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Hi, this is the software that every club, episode 22.

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I'm your host Richard bound.

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And this week, I'm talking all about the power of TDD, the

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power of test driven development.

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So what's so good about TDD.

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I think before I read the book by kent back,

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I was just thinking pesky tests, what are they good for

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apart from getting in the way?

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What are they good for?

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Perhaps for proving we have control of our software.

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Often we written it.

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That we have thought about it and decided that we can automatically

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prove works and is deployable.

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perhaps the image problem that I've had with the idea of tests in the past.

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And that there's something that you have to do after coding in order

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it was to prove that it works.

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this really isn't what test driven development is all about.

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Maybe this is a misnomer of TDD test-driven development does not

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describe what it's all about at all.

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Maybe instead it should be called design through testing.

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Because TDD is not about driving development through testing.

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It's about designing and architecting your application.

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Through writing tests.

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There are lots of pluses to this technique and not many

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drawbacks that I can think of.

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Because it improves your design helps you get unstuck when you need help.

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Plus, you've got your test passing and through refactored

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and your code is written.

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So you've done everything.

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Sounds good.

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Right?

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So, what does this look like?

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Sometimes when you're building an application, especially if it's on and

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off, you're not doing it full time or perhaps you're distracted by production

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support, or you have to do other things.

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Perhaps it's an open source project.

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It can get to a point where you can't see the way forward.

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Or perhaps it's a case that when you come back to the code, you've

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forgotten what it's supposed to do.

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So how can TDD help with this?

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If you've read the book, test driven

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development, by example, by Kent Beck.

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Then at first it might all seem a bit obvious or perhaps a bit daunting.

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It's written in a chatty style, which may not make it the most obvious or

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easiest to follow in the first instance.

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It does require some work.

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You should get invested in the story a little bit.

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Once you do that and take your time with the exercises, particularly in

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the first parts of the book, then it will pay you back for your persistence.

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I find myself going backwards and forwards, making sure I understood

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every single step and what it meant in that first section.

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After a while it clicked for me.

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What I saw that this was a really clever way of designing code.

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And not just a way of making sure we have good code coverage.

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The first part of the book will tell you everything you need to know

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about TDD and why it's so powerful.

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The second part extends this knowledge without other paradigms.

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And the third gives you plenty of great examples.

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So, what does TDD do that is so different?

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If you're a programmer already, then you'll already be familiar

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of being in a coding zone.

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Perhaps when you put on your favorite least distracting music and you climb into

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your editor and your code excitedly, and you write and you write and write, and

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perhaps you test manually as you go along.

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But you don't formalize any of those tests, at least not straight away.

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You might grudgingly add some tests afterwards, but perhaps they're

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quite high level and abstracted.

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Perhaps you're kind of trying to scam the testing gods.

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And you're not too close to the actual core business or the domain language

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at the heart of your application.

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Then perhaps you come back to it later.

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And you want to get that coding feeling again.

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So you jumped straight back in.

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So the coding you want that coding high.

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And the coding high comes from writing the code, not the test.

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And so you carry on writing some more code.

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And eventually the whole thing becomes a great big ball of string.

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Lots of code and no tests.

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And you're not even sure what the original intention was anymore.

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So we're coding happily.

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And perhaps we end up in a blind alley and have to unpick our work,

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or sometimes even start again.

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This can feel like we're making progress, but not all the time.

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For solo coding, this can definitely happen.

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coding as part of a team, then this is less likely to happen

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because you do need to justify your code and your design decisions to

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othersthat you're working with.

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So TDD is therefore perhaps only useful for solo coders you may think.

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No, because it's more than it's all for just not getting stuck with a design.

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It's more of a tool for a structured approach to design in the first place.

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By taking your time with testing and design as you go you make

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it clear for everyone who works with the code in the future.

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So how does TTD differ from the code first or even a design first approach?

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Well, you write the test first and then you were tray one minus the time.

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To get passing tests.

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So you need to keep passing your test.

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As your north star.

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And without that indication, you just don't move on.

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So immediately TDD imposes a discipline on your coding.

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You can't any more, just keep writing code and hope that it works.

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You need to prove it to yourself at every single step

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. How does this help with your design and

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It sounds like it might be boring.

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It sounds like you might miss something important.

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And you're worrying about tests so how can this help?

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This is in fact, one of the key benefits.

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Proving the what your building will do.

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The thing that you're intending.

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Writing a test helps show that it works.

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In fact, the word test is really wrong here.

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It's more of a proof than it is a test.

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It's proving that the thing you've created will do the thing that you say it well,

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And the cool thing about this.

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Is it the test or proof makes you think more deeply about what the code you're

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going to write is exactly going to do.

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You're creating a specification for your code to fit into.

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And that specification means two things.

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When you do write the code, it virtually writes itself.

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And when you've written the code, you can tell immediately if it's

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working by running the test.

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And this covers the first two important mantras of TDD, which are right a test.

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Then write the code.

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The third important mantra.

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And the discipline is refactor.

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Ensure that the code is not only doing the right thing.

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But doing it in the right way for the rest of your code for the rest of your

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design for the future of your application.

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Writing code in TDD can initially feel slow and labored but in only a short

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time, you'll start to notice the benefit.

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Not only because you have a lot of tests.

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But also because you'll have an emergent design.

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The design itself comes from creating tests and thinking about what your

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code would do before you write it.

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You're creating your expectations as specifications about what the code can do.

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By approaching this through constraints, we help our brain focus on what we intend.

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This is almost like the reverse Conway maneuver to Goldratt's

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theory of constraints.

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We add a constraint, then we solve that constraint by fixing the functionality.

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Step-by-step we constrain our domain.

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We constrain our functional model.

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And we constrain our application to be the thing that we intended to, but I've

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never actually described to this point.

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Okay, before I get too philosophical about this.

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How can we do TDD practically?

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Well, it's important that you have a project in source control.

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A build system and a way of running tests against your projects.

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So with a source control system.

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You can baseline all of your changes.

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If you don't have source control, then we can't be sure that we're

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doing the change we intend.

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Secondly, a build system is needed.

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Obviously, we need to be able to compile a code to validate

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that it's syntactically correct.

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And then finally we need to test framework.

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Sometimes it's built into the language or natively supported.

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Sometimes you need to find a framework that you can use with your build system.

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Once you have these three things.

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That it makes sense to invest also in some automation that your tests show, you can

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run your test manually, but after every change, do you really want to do this?

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Perhaps sets up your CI to run tests every time you push.

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Also I'm currently working in a rust and with vs code has got a nice feature

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where you can just click on the test in the code and run it from the editor.

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Whatever we do, there has to be a low barrier to entry for testing.

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You want to be writing tests and running tests continuously as you code.

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Therefore it needs to be simple and as automated as possible.

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So there is some upfront work here to set up your project with a testing framework

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but this will pay you dividends when it comes to creating something new.

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When it comes to you creating your design.

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So perhaps in your source repository, you can even create a template

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project that is ready to go.

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Again, the barrier to entry, it needs to be really low.

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ideally, so that when you have the idea, when you want to try something out new,

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you can immediately create your projects and start designing, start creating.

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And this is the true power of TDD.

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Rather than agonizing over design and architecture and advance.

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You can just see what flows from your mind whilst constraining yourself to

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focus on one piece of functionality at a time, one aspect at a time.

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Right a test.

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Write the code.

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Refactor.

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Red green refactor and then green again.

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Piece by piece.

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You will create something that not only more closely resembles

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what you intended to build.

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But also has a great code coverage already built in.

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For me, TDD is an absolute, no brainer.

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If you've not tried it yet.

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Then what are you waiting for?

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That's it for this week.

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Nice and short and sharp.

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I'm in the middle of writing something fun using TDD.

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So I need to get back to it.

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I wish you luck check out the book until next time.

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Goodbye.