Explain the concept of regression testing in Software Quality Assurance.

Regression testing is a crucial aspect of software quality assurance that aims to ensure that any changes or modifications made to a software application do not introduce new defects or negatively impact the existing functionality. It involves retesting the previously tested functionalities to verify that they still perform as expected after any changes have been made.

The concept of regression testing is based on the assumption that any modification or addition to a software system can potentially introduce new bugs or cause existing functionalities to break. This can occur due to various reasons such as coding errors, integration issues, or unintended side effects of changes made in one part of the system affecting other interconnected components.

The primary objective of regression testing is to identify and fix any defects that may have been introduced during the development or modification process. By retesting the affected functionalities, software testers can ensure that the software application remains stable, reliable, and performs as intended.

Regression testing can be performed at different levels, including unit testing, integration testing, system testing, and acceptance testing. It involves creating and executing test cases that cover the affected functionalities and verifying that they still produce the expected results. This can be done manually or through the use of automated testing tools.

There are various techniques and approaches to regression testing, such as retesting all the test cases, selecting a subset of test cases based on risk analysis, prioritizing test cases based on the impact of changes, or using test case generation techniques to create new test cases specifically targeting the modified functionalities.

Regression testing is an iterative process that should be performed throughout the software development lifecycle. It is especially important when new features are added, defects are fixed, or changes are made to the software application. By conducting regression testing, software quality assurance teams can ensure that the software remains stable, reliable, and free from any unintended consequences of modifications or additions.