What is the difference between Regression Testing vs Retest?

Posted on Dec 6 2012 - 11:02am by Raj

This is one of the mostly commonly asked question in any software testing interview. In this article I will explain what is the difference between regression testing and retesting.

Regression Testing is the execution of all or a select group of test cases that have passed on the earlier build or release of the application under test so that you can validate, the original functions and features are still working as they were in the past.
The test cases we use are derived from the functional specification, the user manuals, user tutorials, and defect reports in relation to corrected problems.

First regression test should be done using functional test cases to make sure no new defect has been introduced. In addition, we repeat some of the tests using a performance tool, to see how a new version handles, with regards to time and memory usage.

In most of the organization, the regression testing is incremental. So as we add new functionality, or correct a defect, we add test cases, which are included in subsequent rounds of regression testing.

In addition to new software releases at our end, we repeat the tests when MS introduces a new service pack, and to check ongoing compatibility for supported legacy operating systems.

As you can probably see from the above, automation is the key for regression testing. If you haven’t gone down the automation route yet, regression testing is a good time to consider it. Manual regression testing tends to get more expensive with each new release.

Some of the possible failure of a regression test could be due to new functionality, changes in other applications or hardware that interfaces to your app. or even changes in the environment, like updated browser, security updates, or maybe a change in the screen controls.

Retesting is the execution of one or a set of test cases, which previously failed due to a suspected defect in the software which now is documented as being remedied.
However, the fix may introduce fault elsewhere in the software. The way to detect these “unexpected side effects” of fixes is to do regression testing as mentioned above.

So on the conclusion, in retesting we need to check the defects that have been logged by the tester and fixed by the developer. We need to test if that particular bug has been fixed but in regression testing, we need to check if that has been fixed or not and also make sure that change in code by the developer to fix that particular bug has not left any impact on any other phase of application. So regression testing is a kind of testing the whole scenario after fixation of every bug.

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