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04.

TDD - Test Driven Development

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All right. So one of the problems is that when Bob, our park ranger, sees the dinosaur size... he can't remember if these are in meters... or centimeters... which makes a big difference when you step into a cage.

A better way might be to just use words like small, medium, or large. So... let's do that!

What is TDD?

But, to add this feature, we're going to use a philosophy called Test Driven Development or TDD. TDD is basically a buzzword that describes a 4-step process for writing your tests first.

Step 1: Write a test for the feature. Step 2: Run your test and watch it fail... since we haven't created that feature yet! Step 3: Write as little code as possible to get our test to pass. And Step 4: Now that it's passing, refactor your code if needed to make it more awesome

So, to get the Small, Medium, or Large text, I think we should add a new getSizeDescription() method to our Dinosaur class. But, remember, we're going to do this the TDD way, where Step 1 is to write a test for that method... even though it doesn't exist yet. Yes, I know that's weird... but it's kinda awesome!

Step 1: Write a test for the Feature

Add public function and let's first test that a dinosaur that's over 10 meters or greater is large:

32 lines | tests/Unit/Entity/DinosaurTest.php
// ... lines 1 - 7
class DinosaurTest extends TestCase
{
// ... lines 10 - 24
public function testDino10MetersOrGreaterIsLarge(): void
{
// ... lines 27 - 29
}
}

Inside, say $dino = new Dinosaur(), give him a name, let's use Big Eaty again, since he's a cool dude, and set his length to 10.

Then, assertSame() that Large will be identical to $dino->getSizeDescription(). For our failure message, let's use This is supposed to be a Large Dinosaur.

32 lines | tests/Unit/Entity/DinosaurTest.php
// ... lines 1 - 7
class DinosaurTest extends TestCase
{
// ... lines 10 - 24
public function testDino10MetersOrGreaterIsLarge(): void
{
$dino = new Dinosaur(name: 'Big Eaty', length: 10);
self::assertSame('Large', $dino->getSizeDescription(), 'This is supposed to be a large Dinosaur');
}
}

Yes, we're literally testing a method that doesn't exist yet. That's TDD.

Step 2: Run the test and watch it fail

Ok, step 1 is done. Step 2 is to run our test and make sure it fails. Open up a terminal and then run ./vendor/bin/phpunit.

./vendor/bin/phpunit

And... great! 2 tests, 4 assertions, and 1 error. Our new test failed because, of course, we called an undefined method! We kind of knew this would happen. Hm... Did you notice that our "this is supposed to be at large dinosaur" message isn't showing up here? I'll explain why in just a minute.

Step 3: Write simple code to make it pass

Time for step 3 of TDD: write simple code to make this test pass. This part, taken literally, can get kinda funny. Watch: back in our Dinosaur class add a new public function getSizeDescription() which will return a string. Inside... return 'Large':

45 lines | src/Entity/Dinosaur.php
// ... lines 1 - 4
class Dinosaur
{
// ... lines 7 - 39
public function getSizeDescription(): string
{
return 'Large';
}
}

Yup, that's it! Move back to your terminal and re-run the tests.

./vendor/bin/phpunit --testdox

And... Awesome - They Pass! Well... of course the test passed - we hard coded the result we wanted! But, that's technically what TDD says: write the least amount of code possible to get your test to pass. If your method is too simple after doing this, it means you're missing more tests - like for small or medium dinosaurs - that would force you to improve the method. We'll see that in a minute.

But let's be a bit more realistic. Say: if ($this->length >= 10) {, then return 'Large':

47 lines | src/Entity/Dinosaur.php
// ... lines 1 - 4
class Dinosaur
{
// ... lines 7 - 39
public function getSizeDescription(): string
{
if ($this->length >= 10) {
return 'Large';
}
}
}

Run the tests one more time to make sure they're still passing:

./vendor/bin/phpunit --testdox

And... yes! We're still good to go!

Next, let's finish this method the TDD-way: by writing more tests for the missing features first. Then we'll move onto the final - and most fun step of TDD: Refactoring!