As discussed in our earlier article What is software testing?, in verification, testers ensure that the system meets the organization's standards and processes, and answers the question "Did we build the right system?" System means one or more software applications that support a business function. Testers ensure that software, hardware, documentation, and personnel comply together through relying on review or non-executable methods.
In validation, testers physically ensure that the system has met all business and user requirements, and that the features and functionalities are working as designed. Regression testing can be termed as a subset of validation testing. Validation is done by executing system functions through a series of tests which can be observed and evaluated by testers. In software testing, regression testing provides a consistent and repeatable validation on every change on the software to check if the change caused a new error, bug, or defect. Its other purpose is to ensure that functionalities, previously working components, and features are still working properly. Regression testing tests the whole software up to where the repairs have been applied and check if the software still complies with the requirements.