JavaScript developers
You’re building projects in JavaScript and want the confidence of automated tests, but you’re not sure how to start or how to structure tests that stay maintainable.
JavaScript Unit Testing - The Practical Guide
Learn how to write automated tests (unit & integration tests) for your JavaScript projects with Vitest & Jest.
Course Overview
About This Course
You can write JavaScript that works — but the moment you change something, you’re never 100% sure what you just broke. And when testing feels intimidating, it’s easy to keep shipping without the safety net you know you should have.
This course gives you a practical, step-by-step way into automated testing without drowning you in theory. You’ll work with real examples, see typical testing problems defined clearly, and then solve them with repeatable strategies you can bring into any codebase.
By the end, you’ll be able to add reliable unit and integration tests to your own projects, choose what’s worth testing (and what isn’t), and keep tests stable even when your code interacts with the outside world. Whether you’re working on NodeJS or frontend code, you’ll leave with a workflow you can apply immediately.
What You'll Learn
You’ll build a testing workflow around Vitest (with Jest-compatible patterns) that you can reuse across NodeJS and frontend JavaScript projects.
Structure unit tests
You’ll be able to write unit tests that are easy to read and maintain, using clear patterns for arranging test code and keeping each test focused on one behavior.
Add integration coverage
You’ll be able to move beyond isolated units and create integration tests that verify multiple pieces working together, so you can catch issues that only appear when code is combined.
Mock side effects
You’ll be able to remove side effects from tests by using mocks, so your test suite stays deterministic even when your code would normally touch external dependencies.
Use spies effectively
You’ll be able to work with spies to observe calls and interactions, letting you verify how your code behaves without rewriting the production logic just to make it testable.
Write strong assertions
You’ll be able to formulate precise expectations (assertions) that prove the right outcomes, instead of tests that pass for the wrong reasons or fail with unclear messages.
Test async and sync code
You’ll be able to test both synchronous and asynchronous JavaScript reliably, so promises, timers, and async flows don’t turn your test suite into a flaky guessing game.
Ready to get started?
See enrollment optionsPrerequisites
Basic JavaScript knowledge is required.
No prior testing knowledge is necessary.
Who Is This Course For?
Testing-avoidant developers
You’ve always found automated testing intimidating, so you’ve postponed it — this course gives you a clear, practical path that makes testing feel approachable.
Frontend or NodeJS builders
You work on frontend code or NodeJS code and want a testing foundation that isn’t tied to one framework, so you can apply it across different kinds of projects.
Curriculum Overview
Start NowPreview the structure and pacing of this course before you begin.
Getting Started24m
- 01Welcome To This Course!0:54 min
- 02What Is Testing?4:41 min
- 03Unit Testing: What & Why?4:33 min
- 04Unit vs Integration vs E2E Tests5:51 min
- 05A Quick Note About Test-Driven Development (TDD)1:35 min
- 06About This Course6:42 min
- 07Join Our Learning Community0:00 min
- 08Course Resources & Project Snapshots0:00 min
Setup & Testing Software24m
- 01Module Introduction1:09 min
- 02Which Tools Are Needed For Testing?6:27 min
- 03Jest & Vitest6:56 min
- 04Installing Vitest1:36 min
- 05Course Project Setup7:59 min
Testing Basics1h 19m
- 01Module Introduction1:20 min
- 02Basic Test File & Project Setup7:04 min
- 03Writing a First Test6:54 min
- 04Running Tests4:18 min
- 05Why Are We Testing?3:02 min
- 06The AAA Pattern - Arrange, Act, Assert4:36 min
- 07Keep Your Tests Simple!1:34 min
- 08Defining Behaviors & Fixing Errors In Your Code7:38 min
- 09Demo: Writing More Tests4:37 min
- 10Testing For Errors4:14 min
- 11Demo: Adding More Tests3:29 min
- 12Testing For Thrown Errors & Error Messages4:59 min
- 13Exercise: Problem1:44 min
- 14Exercise: Solution4:47 min
- 15Tests With Multiple Assertions (Multiple Expectations)5:18 min
- 16More Practice!2:55 min
- 17Introducing Test Suites4:39 min
- 18Adding Tests To Frontend & Backend Projects3:36 min
- 19Module Summary2:22 min
Writing Good Tests37m
- 01Module Introduction1:25 min
- 02What To Test & Not To Test6:04 min
- 03Writing Good Tests - An Overview & Summary4:36 min
- 04Only Test "One Thing"2:02 min
- 05Splitting Functions For Easier Testing & Better Code5:01 min
- 06Refactoring Code10:13 min
- 07Formulating Different Expectations6:07 min
- 08A Word About Code Coverage0:00 min
- 09Module Summary2:01 min
Integration Tests15m
- 01Module Introduction0:57 min
- 02Introducing Integration Tests2:23 min
- 03Writing an Integration Test & Reasoning5:51 min
- 04Testing For Errors2:28 min
- 05Integration vs Unit Tests: Finding the Right Balance3:25 min
Advanced Testing Concepts37m
- 01Module Introduction1:06 min
- 02toBe() vs toEqual()4:21 min
- 03The Problem With Asynchronous Code6:13 min
- 04Testing Asynchronous Code With Callbacks5:02 min
- 05Testing Asynchronous Code With Promises & async / await4:32 min
- 06Returning Promises In Tests0:00 min
- 07Getting Started with "Testing Hooks"1:42 min
- 08Why Hooks?4:39 min
- 09Using Testing Hooks (beforeEach, beforeAll, afterEach, afterAll)6:13 min
- 10Concurrent Tests2:14 min
- 11Concurrency & Default Behavior0:00 min
- 12Module Summary1:48 min
Mocking & Spies: Dealing with Side Effects44m
- 01Module Introduction1:03 min
- 02The Starting Project4:11 min
- 03The Problem With Side Effects & Tests6:24 min
- 04Introducing Spies & Mocks2:07 min
- 05Working with Spies5:13 min
- 06Getting Started with Mocks & Automocking5:18 min
- 07Note on Mocking2:18 min
- 08Notes on Spies1:30 min
- 09Custom Mocking Logic7:51 min
- 10Managing Custom Mock Implementations Globally (__mocks__ Folder)6:11 min
- 11More Mocking Functionalities1:34 min
- 12Module Summary1:00 min
More on Mocking & Diving Deeper46m
- 01Module Introduction1:04 min
- 02The Starting Project3:02 min
- 03Refresher: Practicing Basic Tests (1)6:25 min
- 04Refresher: Practicing Basic Tests (2)4:43 min
- 05Reasons to Mock2:11 min
- 06Mocking Global Values & Functions8:13 min
- 07Mocking Frontend Libraries0:00 min
- 08Test-specific Mocking Logic6:59 min
- 09Mocking In Selected Places5:21 min
- 10Using Local Mock Values7:01 min
- 11Module Summary1:16 min
And 2 more sections in the full course.
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