Which type of testing focuses on individual units of code?

Unit testing is a software testing method that focuses specifically on validating the smallest testable parts of an application, known as individual units of code. This kind of testing is typically performed by developers to ensure that each component of the software behaves as expected in isolation. The purpose is to verify that each unit functions correctly, identifying bugs at an early stage when they are typically easier and less costly to fix.

Unit tests are usually automated and executed frequently during development. By targeting individual units, this testing approach facilitates rapid feedback and encourages developers to refactor code with confidence, knowing that they have a safety net of tests ensuring that existing functionality is not broken by changes.

In contrast, integration testing combines multiple units and tests them together to evaluate how they interact when integrated. Functional testing evaluates the overall functionality of the application against the requirements and specifications. Smoke testing acts as a preliminary check to see if the build is stable enough for further testing. While important, these testing types do not focus exclusively on individual units of code as unit testing does.