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TDD & Unit, Integration & Functional Tests

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Unit, Functional & Integration Tests

Before we get back to coding... we need to talk about just a little bit of theory! No, don't run away! Give me just 2-ish minutes!

So, there are actually three different types of tests, and we're going to try them all. The first is a unit test - that's what we've created. In a unit test, you test one specific function on a class. It's the purest way to test: you call a function with some input, and test the return value. We'll learn more about this later, but each unit test is done in isolation. If, for example, a class needs a database connection, we're actually going to fake that database connection so that we can focus on testing just the logic of the class itself.

The second type of test is an integration test... or at least, that's my name for it. An integration test is basically a unit test: you call functions and check their return values. But now, instead of faking the database connection, you'll use the real database connection. We'll talk about when and why this is useful later.

The third type of test is a functional test. In our world, this basically means that you're writing a test where you programmatically command a browser. Yep, you literally write PHP code that tells a browser to go to a page, click a link, fill out a form, click submit, and then assert that some text appears on the next page.

More on all of these things later.

How much to Test?

Another question is how much you should test. Does every function need a unit test? Does every page and every validation error of every form need a functional test? Absolutely not! That sounds worse than a raptor claw across a chalkboard!

Especially if you're new to testing, don't worry: a few tests is way better than none. And honestly, I think many people create too many tests. I follow a simple rule: if it scares me, I test it. Too many tests take extra time, add little value, and slow you down later when they fail after you've made a minor change.

In our app, we've tested the getLength() and setLength() methods. These do not scare me. In the real world, I would not test them.

Test-Driven Development

A few minutes ago, I mentioned the term "Test-Driven Development" or TDD. TDD breaks coding into three steps. First, create the test. Second, write the minimum amount of code to get that test to pass. And third, now that your tests are passing, you can safely refactor your code to make it fancier.

So, test, code, refactor: these are the steps we're going to follow. Do I always use TDD in my real projects? Um... yes!? No, not really: I'm not a purist. Heck, sometimes you don't even need a test! Gasp! But yea, usually, if I plan to write a test for a new feature I'm working on I'll follow TDD.

Oh, and TDD is about more than just making sure you have a lot of tests. As you'll see, it forces you to think about how you want to design your code.

Enough theory! Let's try it already!