Unit testing is a software testing method that involves testing individual units or components of a software system. A unit is the smallest piece of code that can be logically isolated in a system, such as a function, subroutine, method, or property. Unit tests are typically automated tests written and run by software developers to ensure that a section of an application (known as the "unit") meets its design and behaves as intended.

The main objective of unit testing is to isolate written code to test and determine if it works as intended. By testing individual components in isolation, developers can quickly identify and address issues, leading to faster iteration and release cycles. This approach helps ensure the stability and reliability of the code, allowing organizations to deliver timely updates and enhancements to users. Unit testing promotes a more structured and systematic development process, resulting in better assessment of product quality and a more agile development.

Unit testing is typically performed by the developer during the development phase of an application. However, quality assurance engineers may also perform unit testing if developers are reluctant to test or if there is a time crunch. Unit testing is an important step in the development process, as it can detect early flaws in code which may be more difficult to find in later testing stages.

Unit testing can be manual or automated. Automated unit tests are run each time the code is changed to ensure that new code does not break existing functionality. Unit testing allows the programmer to refactor code or upgrade system libraries at a later date, and make sure the module still works correctly (e.g., in regression testing) . The procedure is to write test cases for all functions and methods so that whenever a change causes a fault, it can be identified quickly.