[MUSIC] 0:00 When you start learning about testing, you very quickly start hearing about 0:04 a practice known as test-driven development, or TDD. 0:09 It's the practice of writing a test for 0:13 a small module or unit of code as if it worked already. 0:16 Then write the code until that test passes. 0:21 Repeat until you have tests for every unit of code that you've written. 0:25 What TDD does is force you to think about what your code looks like 0:30 at the unit level. 0:35 This doesn't mean that these modules will always be used in the exact 0:37 way that you planned. 0:41 It's like building with Lego. 0:42 Unit testing verifies that each piece is compatible so 0:44 that your application can use those pieces when needed. 0:48 Let's go build some units from a test driven approach. 0:52 We're going to write a simple English to Pig Latin translator. 0:57 Pig Latin is a game in which English words are altered 1:02 usually by moving the first consonant or 1:06 consonant cluster of a word to the end of the word and then adding a y. 1:09 So treehouse would become eehousetray. 1:15 Let's write the code for this translator in a test driven approach. 1:19 In test driven development, we write our test first and 1:23 then write the code until our test passes. 1:27 Let's add a new file in tests. 1:31 We'll name this PigLatinTest.php. 1:33 We're going to use PHP unit framework, 1:40 TestCase. 1:48 And then we'll add the class 1:50 PigLatinTest extends TestCase. 1:55 We'll add a .clock with the annotation test. 2:01 And then we're ready to add our first function. 2:07 The main functionality of our converter is to take a single starting 2:12 constant word and change it to pig Latin. 2:17 So convertSingleStartingConsonantWordToPigLa- 2:20 tin. 2:30 Now let's walk through how we expect to use our PigLatin converter. 2:34 We'll have an English word that we want to convert, and we'll use test. 2:40 Then we'll need our expected result. 2:46 And this will be esttay. 2:50 Next we create a new pigLatin object. 2:54 Then we're going to get the result of calling pigLatin->convert. 3:02 And passing the word. 3:12 Now we're ready for our assertion. 3:16 Instead of assertTrue, 3:19 we want to make sure that the result equals our expected result. 3:21 So we use $this->assertEquals 3:26 the $expectedResult and the actual result. 3:30 And the third parameter is optional, but allows us to add a custom message. 3:36 PigLatin conversion did not work correctly. 3:43 Now that we have our first test, we're ready to run our code. 3:51 Vendor/bin/phpunit tests/PigLatinTest.php. 3:55 Let's fix line 9. 4:04 First, it fails because there is not a Pig Latin class. 4:12 Let's add a PigLatin class to our source directory. 4:18 Class, PigLatin, now let's run our test again. 4:29 It's giving us the same error even though we have a class file. 4:37 That's because of the way we are autoloading. 4:42 If we look in vendor, composer, and our autoload_classmap, 4:45 we can see that our email is being included. 4:52 But nowhere in here is it adding our Pig Latin. 4:57 We need to run Composer update again to grab our Pig Latin file. 5:04 You only have to do this when you add files you need in your classmap. 5:16 If you're using proper name spacing for 5:22 your project, this is a different way of telling Composer where to look for 5:23 class files, and you don't need to update Composer each time. 5:27 We could also require the specific class we need directly in our test files. 5:31 We could require once, 5:45 Source, PigLatin. 5:52 But we already have our auto-load working, so let's comment this out. 5:57 Now let's run our test again. 6:02 This time, it tells us that we do not have a convert method. 6:05 So let's add that. 6:09 The function convert should accept a word, And 6:19 then for now we're just going to return the word. 6:24 Now let's run the test again. 6:31 This time we get a normal failure message, 6:34 we were expecting esttay, but instead, we just got test. 6:38