Understanding why testing matters is crucial for anyone writing JavaScript code. Testing plays a key role in improving code quality by ensuring that your code works as intended. When you write tests, you are able to catch mistakes early in the development process, which means you can fix issues before they cause bigger problems. This not only helps prevent bugs from slipping into production but also makes maintaining your code much easier over time. With a solid suite of tests, you can confidently make changes or add new features, knowing that your tests will alert you if anything breaks unexpectedly. This increased confidence in code changes leads to faster development and fewer surprises down the road.

Without testing, codebases often become fragile and difficult to change. Imagine working on a large project where every update feels risky because you are unsure if something else will break. This uncertainty can slow down development and make it harder to deliver features or fixes quickly. Testing acts as a safety net, catching issues before they reach users and allowing you to move faster with fewer worries.