Whenever developers change or modify their software, even a small tweak can have unexpected consequences. Regression testing is testing
existing software applications to make sure that a change or addition hasn’t broken any existing functionality. The purpose is to catch bugs that may have been accidentally introduced into a new build or release candidate, and to ensure that previously eradicated bugs continue to stay dead.  By re-running testing scenarios that were originally scripted when known problems were first fixed, you can make sure that any new changes to an application haven’t resulted in a regression, or caused components that formerly worked to fail.  Such tests can be performed manually on small projects, but in most cases repeating a suite of tests each time an update is made is too time-consuming and complicated to consider, so an automated testing tool is typically required.

To reduce the stress levels of programming teams everywhere, various automated testing programs that specialize in regression tests now make it relatively easy, with a few clicks of a mouse, to establish sets of testing parameters and to check new iterations of code against previous software baselines, or control states, highlighting inconsistencies in testing logs and specifying exactly where an unexpected function broke and why.

The Future of Regression Testing

For regression testing to be effective, it needs to be seen as one part of a comprehensive testing methodology that is cost-effective and efficient while still incorporating enough variety—such as well-designed front end UI automated tests alongside targeted unit testing, based on smart risk prioritization—to prevent any aspects of your software applications from going unchecked. 
These days, many Agile work environments employing workflow practices such as XP (Extreme Programming), RUP (Rational Unified Process), or Scrum appreciate regression testing as an essential aspect of a dynamic, iterative development and deployment schedule. 

But no matter what software development and quality-assurance process your organization uses, if you take the time to put in enough careful planning up front, crafting a clear and diverse testing strategy with automated regression testing at its core, you can help prevent projects from going over budget, keep your team on track, and, most importantly, prevent unexpected bugs from damaging your products and your company’s bottom line.

Example regression testing tools are: