Software testing is the process used to help identify the correctness, completeness, security, and quality of developed computer software. Testing is a process of executing a program or application with the intent of finding errors. With that in mind, testing can never completely establish the correctness of arbitrary computer software. In other words, testing is criticism or comparison that is comparing the actual value with an expected one. An important point is that software testing should be distinguished from the separate discipline of software quality assurance, which encompasses all business process areas, not just testing.

There are many approaches to software testing, but effective testing of complex products is essentially a process of investigation, not merely a matter of creating and following routine procedure. One definition of testing is "the process of questioning a product in order to evaluate it", where the "questions" are operations the tester attempts to execute with the product, and the product answers with its behavior in reaction to the probing of the tester.

Although most of the intellectual processes of testing are nearly identical to that of review or inspection, the word testing is connoted to mean the dynamic analysis of the product—putting the product through its paces.

The quality of the application can, and normally does, vary widely from system to system but some of the common quality attributes include capability, reliability, efficiency, portability, maintainability, compatibility and usability. A good test is sometimes described as one which reveals an error; however, more recent thinking suggests that a good test is one which reveals information of interest to someone who matters within the project community.