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What is Regression Testing? The Ultimate Guide with Examples-ACCELQ
Posted On: 29 June 2022

“Regression” is a term that means going back to a former state. While this might not be an ideal aspiration in other areas of our life and work, in the world of software testing, the term Regression holds mammoth importance. Regression testing has become critical in today’s software-driven world since users have no tolerance for fault-prone, slow, or bug-ridden applications. Research shows that 60% deleted an application or abandoned a website after a single attempt when performance was a problem. 80% of applications are deleted after one use.

The window to impress and hook users is getting increasingly small. This makes the practice of regression testing essential to software success.

What is regression testing?

As the name suggests, this testing catches regressions in software functionality that can occur due to bug fixes, adding new features to the code, or changing requirements in features and functionalities.

At times, an amendment or modification in the software introduces new bugs. Likewise, a functionality change sometimes re-introduces older bugs. In that light, regression testing works to ensure that the program, post the introduction of changes, retains its core functionality.

It confirms that new codes added to any program do not negatively impact the functions and existing features and that the new code works seamlessly without disrupting or eliminating the older codes.

Why is regression testing important?

Regression testing becomes vital since it ensures that a new code in one part of a system does not create unwanted side effects in other parts of the system. Furthermore, this helps ensure that new changes do not introduce new bugs in previously tested and bug-free software.

Updates, upgrades, changes in functionality, etc., have become a mainstay in the software development landscape. Much of that is attributed to constantly shifting customer demands. As software begins to touch multiple parts of the organization and becomes business-impacting, it becomes crucial to ensure that new changes do not bring about disruption. Let us understand this with an example.

Why is regression testing important-ACCELQ

An Example

Let us run through a scenario here –

  • An organization discovers a bug in the financial system and creates a task.
  • The developer creates the fix and runs a unit test. The test proves beyond doubt that the bug fix has worked.
  • They then release the fix into production, and everything seems to be in order.
  • Soon after, the organization finds itself unable to run the P&L statements. And the system times out every time they try to run an Aging report.
  • On deeper exploration of the task when it was first created and the subsequent steps taken, they discover quite a few things. While the unit test worked, this test ran against a small test database that was only sufficient to replicate the error for bug fixing and show a positive unit test result.
  • The code, however, was not tested using the production data.

The new code thereby created side effects in the system. This problem could have been easily avoided had the fix been incorporated into a system-wide regression test employing a copy of the production data.

Regression testing prevents degradation of the system quality with functionality growth and reduces the defects during release. It enhances software quality, anticipates errors before an update rollout or product deployment, and ensures happy end-users.

Regression v/s retesting - The difference

These are similar-sounding terms but not interchangeable. Retesting ascertains that a specific code fix works as expected.

Regression testing, on the contrary, ensures that the entire system works as designed after changes. Regression tests, as such, have a much wider scope of activity when compared to retesting.

Retesting usually takes place near the time of code development. Contrarily, regression testing is further along the development lifecycle. These tests need more time for execution as compared to retests. Complete regression testing demands testing for all aspects of the system and needs adequate, system-wide monitoring.

Types of regression testing

There are three primary types:

Unit regression testing

These tests are independent of aspects outside of the unit as they test only the specific unit. During the test, other system functionalities are blocked.

Partial regression testing

This tests the updated unit and the units that interact with it to evaluate if the changes applied to the updated unit affect the software functions and how. This test is applied when:

  • There are slight changes to the software
  • The developers are sure that new codes will not affect any other part of the system.

Complete regression testing

Tests and ensures that the system works as intended despite tweaks and updates. This testing comes to the fore when the updates affect the foundation of the code. That’s when the updates significantly affect the codebase and/or when multiple changes are added to the code.

This testing matters as software updates and upgrades become mainstays that ensure that the program is up secure, stable, and up to date in accordance with the latest technological developments.

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Regression testing techniques

It includes functional and non-functional tests and thoroughly investigates the software in search of flaws. Some of the techniques used include:

Retest All

This technique checks every test case to confirm if all software parts are working as intended. This is the most accurate and all-around method of regression testing. But it’s also the hardest and the most expensive technique.

Regression Test Selection

This technique does not run all the tests in the test suite. However, it divides all tests into three categories – reusable test cases, retestable test cases, and obsolete test cases. The tests have specific coverage criteria. Only relevant test cases of the software are tested. The testers can also use a minimization technique and select a minimum set of cases that they feel will do the job.

Test Case Prioritization

This technique assigns a priority to every test case, guaranteeing priority in their execution. General prioritization and Version Specific prioritization are two paths for Test Case Prioritization.

Hybrid Testing

This technique combines Regression Test Selection and Test Case Prioritization. It allows testers and QA teams to choose only the re-executed test cases based on their priority.

When to perform regression testing?

Given its importance, regression testing should become a regular process for developers and business owners to undertake. Here are the main instances for performing this type of testing:

  • The development phase and as early as the pre-deployment stages of software development
  • Before releasing new updates. Regression testing should become a part of the regular functionality tests if updates are very frequent and the time between two updates is short
  • After any bug or error, fix
  • When updating new features or adding new ones to the system
  • When making significant changes to the codebase or the system

The challenge with regression testing

Regression testing can begin to get complicated with every session with the introduction of software updates. It can also take up time and resources and is less than optimal when done manually.

Manual regression testing is effort-intensive and can be error-prone as checking the software’s overall functionality each time while conducting tests can lead testers to overlook other aspects of the system, especially during rapid testing.

Automating regression testing emerges as the perfect antidote to this challenge. Organizations can reduce the time and resources expended on this testing, expand test coverage and enable comprehensive, reliable, and faster testing.


As updates and upgrades and frequent changes become a norm, Regression testing becomes a way to ensure that the programs maintain functionality even after successive updates. This type of testing is extremely valuable now as the scope of fault-tolerance has reduced dramatically, and software touches multiple, business-impacting parts of an organization.

Delivering anything other than high-quality experiences is equivalent to testing fate. With soaring development costs, creating a clear and robust testing strategy and including regressing testing to the mix is the perfect way to produce excellent software.

Nidhi Achhaa author

Nidhi Achhaa | Content Specialist at ACCELQ

Nidhi specializes in technology-based content and strives to create a unique, customized, and compelling piece with a flavor of SEO. A writer with a love for words and a storyteller at heart.


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