Retesting and Regression Testing. What is the Difference?

In the dynamic world of software development, where changes accompany a system throughout its growth, testing is a pivotal element.
Software testing includes quite a few types, some of which are retesting and regression testing. What is the difference between retesting and regression testing? This article clears away doubt, misunderstanding, and confusion by addressing this question. Before knowing their difference, let's elaborate on each type of testing.

What is regression testing?

Simply put, regression testing checks a system for regressions (or rather their absence). The point of it is to make sure that the latest updates implemented in the software have not impacted on the functionality of the existing modules. Everything operates as expected. That’s the goal.

As Dynamics 365 FSCM and similar large-scale systems expand and incorporate new features, regression testing becomes a fundamental component.

When is regression testing used?

1. Code changes

Any code modification requires further testing of the whole system. It allows you to make sure that the innovation has not affected other parts of the code. Code modification may include bug fixes, new functionality, code optimization, etc.

2. Regular development cycles

In agile development methodologies, code changes are not uncommon. Regression testing is integrated into the development process to continuously check that changes made in one iteration do not negatively affect previously tested components.

3. Release cycles

Before each software release, regression testing is performed to check the general stability of the application. Again, this ensures that the introduction of new features does not break existing ones.

4. Integration testing

When different modules or components are integrated into a system, regression testing is necessary to confirm that the modification has not caused new tech-related issues.

It all boils down to one thing: regression testing is performed to make sure that the change made to the system has not brought with it new problems in the form of regressions (bugs). If a bug is found, you should start the next iteration cycle to eliminate it. After the detected bug is fixed, it is time to retest the system.

What is retesting?

Retesting is a process aimed at verifying whether a specific defect or problem previously identified in a software application has been successfully fixed. It is an important quality assurance process to ensure that reported and corrected bugs have actually been eliminated.

Thus, this type of testing is only invoked when a bug is found and fixed. That’s why retesting usually involves using only those test cases related to the identified problem.

Hence, regression testing is aimed at checking the absence of bugs, while retesting is about checking the system after fixing the bugs (often identified during the regression testing stage). This is the key difference between retesting and regression testing.

How does retesting take place?

Imagine that you are testing an e-commerce site and during initial testing, you encounter a bug: a user cannot complete the checkout process when using a certain payment method.
You report the problem to a developer who logs it into the bug tracking system (or you do it yourself).
The development team investigates and finds a bug in the code that causes the problem with this payment method.
They fix the bug.
The new software build is provided for retesting.

If, following retesting, you can complete the transaction without encountering the prior issue, it indicates that the defect has been resolved. However, if the problem persists, you should report it again as a new defect.

The key point is that retesting is aimed at confirming that specific defects have been eliminated, not at performing comprehensive testing of the entire software.

What is the difference between Regression and Retesting?

Regression testing is about finding defects, while retesting is about fixing specific defects you've already found.

They can occur in the same testing process, which is what makes them confusing. However, they have different phases of enforcement.

A brief scheme of applying the two types of testing can look like this:

You update the software (add a new feature, change the code).
You test existing functionality (aka perform regression testing).

Now there are two scenarios:

You haven't found a bug in the existing functionality (congratulations. you won't need retesting)
You have discovered a bug (what to do?)

The bug is found:

Fix the bug.
Retest the same functionality.

Often after this stage, the iteration can be considered complete: the system has been tested after the bug fixing. If retesting leads to a negative result, the bug-fixing cycle is started again.

Retesting and regression testing: final comparison

The main difference is that with regression testing you don't know about a specific bug yet (you run a test case to make sure it doesn't occur), whereas with retesting you test a specific test case where a bug was found.

Comparison parameter	Regression testing	Retesting
Essence	With regression testing, you test functioning software in order to make sure that updates don't bring bugs.	With retesting, you ensure that the software is now functioning properly after troubleshooting bugs.
Purpose	Ensure that the latest software updates have not adversely affected existing components.	Ensure that the particular defect or problem previously reported has been successfully fixed.
Scope	Broader in scope: it includes testing not only of the areas where changes have been made but also of related or dependent parts of the software.	Limited in scope: it focuses specifically on the test cases that initially identified the defect.
Test cases	A complete set of test cases is required, often including both new and existing tests.	Reuse the same test cases that are related to the detected bug.
Test execution	Performed when new changes are made to the code, regardless of the presence of known defects.	Performed once the defect has been fixed.
Automation	It's worth automating since the test suite will be expanded with new cases as the software matures.	Not worth automating since the test case for validation changes each time.
Timing	Ongoing: part of each development cycle.	Ad hoc: performed after defect resolution.
Execution timing	A regular part of the testing process, often performed with every code change; is a “must-have” in case of continuous integration.	Right after the defect has been fixed.
Efforts required	It usually requires more effort and a comprehensive set of test cases.	It usually requires less effort since it focuses on a specific defect (test case).

Regression testing vs. Retesting – conclusion

In fact, the difference between retesting and regression testing is significant. Regression testing safeguards against unintended consequences with each software update, making it vital for agile development. Retesting, in contrast, focuses solely on verifying issue resolution. Both methods are crucial for delivering reliable software, maintaining quality and agility.