Unit testing is a software development process where the smallest testable parts of a system, called units, are individually tested for proper operation. This process is often automated but can also be done manually.
The primary purpose of unit testing is to ensure that each unit functions as designed. Unit testing is normally performed using the white box testing method. It is the first stage of software testing, which is performed by software developers themselves or their peers, and is done prior to integration testing. This testing mode is an important component of extreme programming (XP), which is a significant software development process aimed at enhancing the quality of a product through continual testing and revision. It makes it easy for developers to modify the source code without worrying about how such changes are likely to affect the efficiency of the program as a whole or the functioning of other units.
Unit testing is important because it helps developers to identify any potential failures in algorithms and improve the quality of an individual code that is a core component in a certain function. It also helps in changing and maintaining the codes by making them less interdependent to facilitate the process of unit testing. Unit testing helps reduce the cost of bug fixing because it detects bugs at the early stages of software development. It also simplifies the debugging process; for instance, if a test fails, only the last changes made in the code need to be debugged.