What Is Testing?

[MUSIC] 0:00 Spend any time learning about programming, and 0:04 you're gonna come across the acronym TDD, which stands for Test Driven Development. 0:06 In TDD, once you know what you're going to build, you write the test for 0:11 it before you write the code. 0:14 For some people, this works. 0:17 For others, it doesn't. 0:18 Don't feel bad if TDD doesn't make sense to you right now. 0:20 What's important is that you write tests, not whether you write the test before you 0:22 write the code, or whether you write tests for code that you've already written. 0:26 So what is a test? 0:30 In this course, when I talk about tests, I'm really talking about unit tests. 0:31 Well that brings up another question, huh? 0:35 What the heck is a unit? 0:37 A unit is a single feature or aspect of your code. 0:39 Say you have a class that represents a car. 0:43 It has a make, a model and a year. 0:44 It also has attributes like top speed and fuel capacity and maybe it has methods 0:47 that let you start and stop the car's engine or drive the car. 0:51 Each of those things, each attribute and each method, would be a unit and 0:55 each would need at least one test for it. 0:59 Since these tests correspond to a unit of code, we call them unit tests. 1:01 For example, our car might have a top speed attribute which 1:06 should always be set to a number. 1:08 We can write a test that sets it to a string like really fast, and 1:10 make sure our code raises an exception when that happens. 1:14 There are other types of tests too. 1:17 Regression tests make sure that previous mistakes don't happen again and 1:19 integration tests run your code through a battery of uses to make sure that 1:22 a certain process, one that uses multiple units, works from beginning to end. 1:26 For example, if you wanted to test the registration flow of a Flask app, 1:30 you'd have a test that loads the account creation page, fills out and 1:34 submits the form, follows the redirect, and 1:36 checks that the user model was created, and that you ended up on the sign in page. 1:38 We're gonna focus on unit tests in this course, but 1:43 you can use the tools we talk about to write all three kinds of tests. 1:45 Okay. Now that we know what a test is, 1:48 let's go look at how to write the simplest type of test, a dock test. 1:50