Regression testing & Retesting

Regression Testing

Regression Testing is defined as a type of software testing to confirm that a recent program or code change has not adversely affected existing features.

Regression Testing is nothing but full or partial selection of already executed test cases which are re-executed to ensure existing functionalities work fine.

This testing is done to make sure that new code changes should not have side effects on the existing functionalities. It ensures that old code still works once the new code changes are done. 

Retesting 

After a defect is detected and fixed, the software should be retested to confirm that the original defect has been successfully removed. This is called Confirmation Testing or Re-Testing.It is part of software defect life cycle

Regression vs Retesting

Regression Testing	Re-testing
Regression Testing is carried out to confirm whether a recent program or code change has not adversely affected existing features	Re-testing is carried out to confirm the test cases that failed in the final execution are passing after the defects are fixed
The purpose of Regression Testing is that new code changes should not have any side effects to existing functionalities	Re-testing is done on the basis of theDefect fixes
Defect verification is not the part of Regression Testing	Defect verification is the part of re-testing
Based on the project and availability of resources, Regression Testing can be carried out parallel with Re-testing	Priority of re-testing is higher than regression testing, so it is carried out before regression testing
You can do automation for regression testing, Manual Testing could be expensive and time consuming	You cannot automate the test cases for Retesting
Regression testing is known as a generic testing	Re-testing is a planned testing
Regression testing is done for passed test cases	Retesting is done only for failed test cases
Regression testing checks for un-expected side-effects	Re-testing makes sure that the original fault has been corrected
Regression testing is only done when there is any modification or changes become mandatory in existing project	Re-testing executes a defect with same data and the same environment with different inputs with new build
Test cases for regression testing can be obtained from the functional specification, user tutorials and manuals, and defect reports in regards to corrected problems	Test cases for retesting cannot be obtained before start testing.