Testing JavaScript

Testing is a major part of JavaScript programming. 0:00 Testing helps developers avoid introducing bugs and defects in their projects, which 0:03 if deployed to production could cost them or their company money in returning users. 0:07 As developers add new features to a website or 0:11 app, they test that a feature works and that nothing else broke in the process. 0:14 They might use a combination of testing methods for this. 0:18 For example, they'll code a small part of their program, refresh the app or site and 0:21 interact with it to test if everything works as expected. 0:25 And they'll check for runtime errors and warning messages in the console. 0:28 This manual testing process works but it can be slow and error prone. 0:32 And it doesn't always prove that your logic works. 0:36 There might be times when you're unsure of what went wrong or how to fix it. 0:38 So how can developers prove that each piece of their code does what they want? 0:42 In many cases, developers programmatically test the code and 0:46 features in their project to ensure expected behavior. 0:49 They write special functions called unit tests to check if each part of their 0:53 program works, even in edge cases or extreme operating parameters. 0:57 They first identify the expected outcomes of every part of their program, 1:01 individual functions for example, and 1:06 write tests against them to make sure those parts work as intended. 1:08 For instance, they'll write a test that checks if a function exists, and 1:12 a test that checks a function's behavior when given a certain set of inputs. 1:16 The tests make sure that each function gets called with the required arguments 1:20 and returns the correct result. 1:24 Writing JavaScript unit tests from scratch, especially on big projects, 1:26 tend to be limited, hard to implement, and time consuming. 1:30 So the wonderful JavaScript community once again has our backs. 1:34 They've created libraries and frameworks that let you quickly write automated 1:37 unit tests that detect problems in your code. 1:41 Mocha is one of the most used JavaScript testing frameworks. 1:44 It runs on Node and in the browser. 1:48 Mocha is a flexible and 1:50 extendable library that provides the base structure for setting up your tests. 1:52 It can be easily integrated with other testing libraries for 1:57 additional functionality, too. 2:00 And Jasmine is another popular JavaScript unit testing framework. 2:02 The good thing is that Jasmine does not depend on any other JavaScript framework. 2:05 It comes batteries included, 2:10 providing everything you need to test your code right out of the box. 2:12 It's also the popular choice for testing angular applications. 2:16 It makes testing much easier to set up and run. 2:20 And Jest is a feature-rich testing library created by Facebook. 2:23 Many React developers test with Jest 2:28 because it's already set up when you create a project with Create React App. 2:30 But you can test any JavaScript application with Jest. 2:34 It's built for unit and integration testing, which means that it can run tests 2:37 that check if all the units of your app work together correctly. 2:41 And Enzyme is a JavaScript testing utility for React, created and used by Airbnb. 2:45 It's also built to be compatible with other testing libraries. 2:51 Writing unit test can help you improve your code, 2:55 before you even start writing it, and can serve as valuable documentation for 2:57 how your application is supposed to work. 3:01 You'll have your bugs, spend less time debugging, and 3:04 a better understand the problems you do have. 3:06 As JavaScript developer Eric Elliott stated, tests are your first and 3:09 best line of defense against software defects. 3:12