01-fundamentals-of-testing-in-javascript

Fundamentals of Testing in Javascript

https://testingjavascript.com/courses/fundamentals-of-testing-in-javascript

Table of Contents

• 1. Throw an Error with a Simple Test in JavaScript
• 2. Abstract Test Assertions into a JavaScript Assertion Library
• 3. Encapsulate and Isolate Tests by building a JavaScript Testing Framework
• 4. Support Async Tests with JavaScripts Promises through async await
• 5. Provide Testing Helper Functions as Globals in JavaScript
• 6. Verify Custom JavaScript Tests with Jest

1. Throw an Error with a Simple Test in JavaScript

01-throw-an-error.js

$ node 01-throw-an-error.js

Throwing an error when a condition fails is the most fundamental aspect of a test.

2. Abstract Test Assertions into a JavaScript Assertion Library

02-abstract-assertions.js

$ node 02-abstract-assertions.js

An assertion library can be as simple as a function which takes a result and returns an object containing a number of different assertions which allows the user to determine how they want to evaluate that result against an expected value.

3. Encapsulate and Isolate Tests by building a JavaScript Testing Framework

03-encapsulate-and-isolate-tests.js

$ node 03-encapsulate-and-isolate-tests.js

Our naive implementation works, but prevents subsequent errors from being thrown. Additionally, the stack trace indicates the issue is at the location where the error was thrown. A better solution would be to allow tests to continue running beyond the failed ones, and indicates which test is revealing and issue.

This can be fixed by creating a function which takes a title, allowing us to name tests, and a callback function which will be responsible for running the actual tests, and making use of a try-catch block so as to prevent thrown errors from stopping further execution.

4. Support Async Tests with JavaScripts Promises through async await

04-support-async-tests.js

$ node 04-support-async-tests.js

In order to allow async tests to be run, we need our test function to be async, and we need to prepend the callack invocation with await.

5. Provide Testing Helper Functions as Globals in JavaScript

05-provide-testing-helpers-as-globals.js

$ node --require ./setup-globals.js 05-provide-testing-helpers-as-globals.js

Because of the usefulness of test utilities one could extract them into a module and import them everywhere.

Another strategy, because we're in a test environment and globals are pragmatic in this situation, is to make the helpers available globally.

The --require ./[file].js flag allows files to be required before executing scripts with the node command

6. Verify Custom JavaScript Tests with Jest

06-verify-custom-js-tests-with-jest.test.js

$ npx jest

We've implemented the Jest API in our tests, so we can instead run Jest.