Software testing is the process of evaluating and verifying that your code works as intended. The main purpose of software testing is to make sure that your programs behave correctly and reliably, catching mistakes or unexpected behavior before users encounter them. Testing is a critical part of the development process because it helps you find bugs early, improve code quality, and build confidence in your software.

In the typical development workflow, testing fits in after you have written some code, but before you release it to users or move it to production. By writing and running tests, you can check whether your code produces the right results, handles errors gracefully, and works well with other parts of your application.

There are several types of software tests, each serving a different purpose:

• Unit tests: Focus on testing individual functions or components in isolation;
• Integration tests: Check how different parts of your code work together;
• End-to-end (E2E) tests: Simulate real user scenarios to test the whole application from start to finish.

In this course, you will primarily focus on unit testing, because it is the foundation for building reliable and maintainable JavaScript code. Unit tests are fast, easy to write, and give you immediate feedback about the smallest pieces of your code.