Free online courseJavaScript Testing

Course Description

Reliable software is not just about writing code that works today, but about creating applications that keep working as they evolve. This free online course helps you build that confidence by introducing practical JavaScript testing with Jest, one of the most widely used testing tools in modern development. You will learn how to validate behavior early, reduce regressions, and collaborate more effectively by relying on clear, repeatable tests instead of manual checking.

Throughout the course, you will focus on the skills that make tests genuinely useful in real projects: writing clean unit tests, understanding what makes a test trustworthy, and using Jest features that speed up your workflow. You will explore why Jest is a popular choice for JavaScript applications, how its developer experience supports fast feedback, and how it fits naturally into everyday coding practices. This is especially valuable for anyone working in teams where quality, maintainability, and delivery speed matter.

A major part of testing is isolating code so you can verify outcomes without depending on fragile external factors. For that, you will practice creating mock functions and using Jest utilities designed for control and observability. You will understand when and why to use jest.fn(), how mock functions help verify interactions, and how to set expectations about calls, arguments, and returned values. These techniques are essential when testing modules that communicate with APIs, databases, or complex dependencies.

You will also strengthen your approach to asynchronous JavaScript, where timing can easily cause flaky tests. The course guides you through patterns to test async code properly, including how the done callback can be used to signal when asynchronous work has finished. By the end, you will be better prepared to write tests that stay stable, readable, and aligned with product behavior, turning testing into a practical skill you can apply immediately in professional software development.