How is Regression testing different from Retesting?

Posted On: 6 April 2022

Errors, bugs, and fallacies are all a part of the software delivery process. It’s the presence of these inefficiencies that ultimately paves the way for an improved release. However, that’s only possible when a sound testing plan is in place, and understandably so.

The term “sound testing plan,” however, fuels a separate discussion around the best testing practices for a particular scenario and application – Should it be a test-driven approach? A load-driven scenario? And what about retesting?

In this blog, we will understand

What is regression testing?
What is retesting?
When is regression testing done?
When is retesting done?
Overview of differences between regression testing and retesting

What is Regression Testing?

Regression testing is the process of analyzing the program code and data files and executing its related tests to ensure that any changes made to the application or software do not break existing features or functionality. It’s an important practice in software testing.

The primary goal of regression testing is to maintain a bug-free environment for users and developers by blocking unwanted regressions when new features are introduced into an application. As such, regression testing should be done periodically even if no bugs were found during earlier stages of development, especially after supplementing any significant new functionality.

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.

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.

What is Retesting?

Contrary to regression testing, retesting is done to test whether a particular feature or functionality that has been developed, tested, and released is working as expected. It’s generally carried out after significant modifications to the code or software are made.

When running retests, your goal is to determine whether any known bugs have re-emerged or whether new bugs have appeared.

When Is Regression Testing Done?

A variety of cases entail the application of regression testing. This includes after installing a new feature, upgrading or patching, and releasing a new product.

The most common types of regression tests can be summarized as follows:

Implementation of a new feature – For example, when there has been a refactoring that may have removed some code, which was required but no longer exists – regression testing, in such case, would address the assumption that all the code needed for the new feature will still function properly.
Updates and patches application – Regression testing can be done before or after installation to ensure that the changes are compatible with the existing software. Likewise, a regression test can be run after deploying a new release to ensure no unintended consequences were associated with the same.

When is Retesting Done?

The most common types of retest cases are summarized as follows

Retesting is done when there are bugs in the software, problems with the reports, or re-emergence of other issues. A re-test ensures that these issues no longer appear.
Changes in the business logic – The numbers of a report may have changed, a new field has been added to a database table, or some other notable change has been made that would affect the overall functioning.

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.

Overview of the Differences

	Regression Testing	Retesting
Automation	Considering that the testing suite expands with the enhancements, the automated regression testing approach seems viable.	Because the motive is to fix the pre-existing areas, automating the methods seems unnecessary and implausible.
Involvement	Regression testing must be a perpetual monitoring process since updates, upgrades, and patches are constantly unearthed to keep up with the dynamic market.	Since retests depend on identifying the bugs in the first place, retesting may or may not be employed in each testing cycle.
Types	Corrective, selective, progressive, partial, unit, retest-all.	No types as such; however, the practice to re-test can differ according to the needs.
Nature	Since it’s perpetual, regression testing is often termed generic testing.	Since its implementation is specific to the identified defective area, it’s often termed planned testing.
Defect Verification	NA	A part of retesting process
Applicability	Fixated on passed test cases.	Fixated on failed test cases.
Priority	Low (exceptions surface during parallel testing)	High
Accuracy	To predetermine test cases, each methodology can’t be implemented with the same approach to ensure consistency.	Since the test strategies are often modified based on earlier findings, there is little chance of repetition.

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.

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.

Final Thoughts

Regression testing is more involved than retesting, and the benefits of proceeding with this type of testing are considerable. However, there’s no denying that a coalition of retesting and regression testing is helpful in the long run because the thoroughness of the process considerably extends.