Write unit tests to verify that individual functions and components work correctly in isolation.
Unit testing is a software testing method where individual units or components of a software are tested. The purpose is to validate that each unit of the software code performs as expected. A 'unit' is the smallest testable part of any software. In procedural programming, a unit may be an individual function or procedure. In object-oriented programming, a unit is often an entire class, but it can be as small as a single method. The key principle of unit testing is isolation. When you test a unit, you should test it separately from other parts of the application. If a function depends on another module or an external service (like a database or an API), you should 'mock' that dependency. Mocking involves replacing the real dependency with a fake version that you can control for the test. For example, if you are testing a function that processes data fetched from an API, you would mock the API call so that it returns predictable data, allowing you to test your processing logic without making a real network request. Unit tests should be small and fast. A typical project might have hundreds or even thousands of unit tests. They are usually run automatically every time a developer makes a change to the code, providing a rapid feedback loop and acting as a safety net to prevent regressions (i.e., breaking existing functionality).