Unit Testing in JavaScript (Jest) — AAA, Mocking, Happy Paths & Real-World Instances

Most developers don’t avoid unit tests — they avoid confusing and brittle ones.

In this video, I walk through unit testing the right way in JavaScript using Jest — starting from setup and syntax, all the way to testing real service logic with mocking, error paths, and best practices companies expect.

What you’ll learn:

How to set up Jest correctly

Unit testing syntax and structure

Testing services and utility functions

AAA pattern (Arrange, Act, Assert)

Happy path vs error path testing

Mocking and spying repositories

Common assertions you should know

Testing lifecycle hooks (beforeEach, beforeAll, etc.)

Why companies take unit testing seriously

If you want cleaner tests, safer refactors, and production-ready code, this tutorial is for you.

🔗 GitHub Code Starter Pack:
https://github.com/tekhryse-oss/unit-...

▶️ Watch, learn, and level up your testing skills on Tekhryse.

Table of Content
00:01 – Introduction
01:00 – Installing NPM packages (Jest setup)
03:14 – Unit testing syntax & example
05:31 – Testing the findUserByEmail function
09:34 – Mocking, AAA pattern & happy path testing
14:01 – Error path testing
16:22 – Testing the createUser function
25:35 – Testing the validateUser utility function
34:05 – Why companies take unit testing seriously
38:07 – Testing lifecycle hooks (beforeEach, beforeAll)
42:54 – Common and important assertions

#unittesting #javascript #jest #softwaretesting
#javascripttutorial #cleancode