Agile projects, by nature, break down features in a release into manageable pieces of work, and allocate the features to iterations. With each iteration the product starts to grow significantly; therefore the amount of testing needed also increases. Along with testing the code changes made in the current iteration, testers also need to verify no regression has been introduced on features that were developed and verified in previous iterations.
The risk of introducing regression in agile development is very high due to extensive code churn (lines of code added, modified or deleted to a file from one version to another) required when developing new features in an iterative lifecycle. The text above is a sample from the upcoming Agile Tester Add-On that will be released in early 2014. Please note that Agile Tester Add-On is on alpha phase, which means that its content may change. Visit www.istqb.org to get latest information.