Non-regression testing

Non-regression testing (NRT), or simply validation of a new issue, is an approach to software testing. The purpose of non-regression testing is to verify whether, after introducing or updating a given software application, the change has had the intended effect.

Contrast with regression testing (usually testing bug-correction of an old issue) which aims to show that the change has not had an unintended effect on the software.

The software development process can be divided in several steps, where each step culminates in a new software version, containing a number of new software features. This process continues until the final release when all the contents that satisfy the customer’s requirements have been included in the software. As the complexity of software architecture grows, the probability of introducing bugs increases. Bugs can occur after the software code has been modified for two main reasons:

Usually, the occurrence of software bugs can result in unexpected delays to the project. Due to time-to-market restrictions, the validation phase of software functionalities must be well organized and efficient. In this context, non-regression testing provides a systematic procedure for fast and efficient validation and discovery of bugs within the software architecture.

A non-regression test can be performed according the following steps:

Exploratory testing is performed following similar steps, but it differs from NRT in its analysis and conclusions. NRT aims to check if software modifications result in undesired behaviour. Here, the new behaviour of the application is previously known, making possible the identification of an eventual regression (bug). Exploratory testing, on the other hand, seeks to find out how the software actually works, consisting of simultaneous testing and learning, and stimulating testers to create new test cases.

The intent of regression testing is to assure that in the process of fixing a defect no existing functionality has been broken. Non-regression testing is performed to test that an intentional change has had the desired effect.

When a new software version is released without any new features relative to the previous version, i.e. the differences between the two versions are limited to bug fixes or software optimization, both the releases are expected to present the same functionalities. In this case, the tests applied to both versions are not expected to result in different behaviours, but only to assure that existing bugs have been fixed and no new bugs have been introduced. This testing methodology characterizes regression testing.

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