Regression Testing Tutorial: Comprehensive Guide With Best Practices

Regression testing is a software testing process executed after making modifications or upgrades to a software application and re-tests the application areas that may have been affected by the fix. It can be performed manually and automatically by running a specific set of test cases.

When a software product undergoes alterations in the existing features, bug fixes, and the addition of new features, regression testing aims to ensure that after these alterations, the product works as expected.

The term ‘regression’ implies re-testing the unaltered sections of the product. Software testers are responsible for determining whether the new modifications have resulted in potential bugs or defects.

What Is Regression Testing?

When developers fix a bug, add new functionality, or modify an existing one, they need to change the program code. Even a minor change will likely result in several bugs. In such cases, regression tests are used to reveal and pinpoint undesirable side effects. For this, they re-execute the test cases that worked perfectly in the previous version of the product with the latest version to ensure that the product's functionalities are working correctly.

When a new build is to be validated, the testers do the functional testing to verify the modifications in the existing and newly added functionality. After this testing gets completed, the testers proceed with regression testing. They find out whether the new improvements have caused any functionality defect in the working that was satisfactory before the latest alterations.

Why Perform Regression Testing?

Whenever you add a code that enables new functionality or fixes any bug, you initiate regression tests. This initiation is mandatory because the existing and newly added functionality can have many dependencies. This quality check cannot be avoided because the new code must comply with the existing code. You must ensure that the unmodified code does not suffer an impact. You may frequently be required to check the system modifications done at the last minute.

During the development cycle, if a continuous enhancement or alteration exists in the product, the new functionality may harm the existing code that has been tested and found OK. The alteration in code might give rise to bugs. If such a code is not tested, you may encounter critical issues in the live environment. Due to this, your customer might get into trouble.

Let us consider an online website. You report an issue that the cost of a product for sale is not getting displayed correctly; that is, a lesser price is replacing the actual cost of a product. You conclude that this issue must be fixed as soon as possible.

Now, a developer has fixed this issue. At this juncture, it is feasible that the price on the reported page has been changed, but the summary page still has the erroneous cost, and the email sent to the client also has the wrong cost. This proves that after the bug fix is completed, the page that displayed a lesser price must be checked, and the related pages must be checked. This shows why it is crucial to run regression tests.

The below graph shows the importance of running a regression test.

An Example of Regression Testing

Let us assume that there is a software product XYZ. One of the functions is to trigger the dispatched, acceptance, and confirmation emails when a user clicks the Dispatch, Accept, and Confirm buttons. During development, the confirmation email develops some issues.

To fix these issues, the Developers make some code changes. In this process, it is evident that the confirmation emails must be tested. Moreover, the dispatched and acceptance emails should also be tested to verify that the code alterations have not impacted them.

Pros and Cons of Regression Testing

Regression testing has the following advantages and disadvantages.

Advantages:

• The quality of the software product increases.
• It can be ensured that software modifications and bug fixes do not negatively affect the product's functionality.
• There can be the implementation of automation test tools.
• It can be verified that the resolved issues do not occur in the future.

Disadvantages:

• If you do not use test automation and decide to perform manual testing, regression tests become very cumbersome and time-consuming because they have to be implemented repeatedly.
• Even a minor modification in the code generates issues in the product functionality. Therefore, this minor modification necessitates the regression test process.

When To Perform Regression Testing

Every scenario that involves alterations in the production code necessitates regression tests. All the following scenarios have the requirement for this testing.

• Addition of new functionality to the application: A website having login functionality. Users can use this functionality only with email. A new feature is to perform login using Facebook credentials.
• Requirement for change: An example is removing the Remember Password functionality, which was previously applicable.
• Fixing a defect: A Login page on which the Login button is not functioning correctly. A tester provides a report that there is a bug, which is that the Login button is broken. Once developers fix this bug, a QA engineer performs a test, ensuring that the Login button is working as expected. At the same time, the tester tests other functionality that is pertinent to the Login button.
• Performance issue fix: An example is that the home page needs five seconds to load. Now, this duration is decreased to two seconds.
• Modification in the environment: An example is when the database is changed from MySQL to Oracle.

The above points can be summarized into the following circumstances:

• The configuration undergoes modifications.
• There is an addition of patch fixes.
• There is an optimization of source code to enhance performance.
• There is a fixing of the codebase for defect resolution.
• There is an addition of new functionality or features.
• There is an addition of a new requirement to an existing feature.

Some software products require several months for completion. So for these products, regression tests are recommended daily. Some releases are done every week. In the case of such products, regression tests begin after the functional testing is over.

Let us consider the scenario when you are testing a specific feature, and the testing is not over by the end of the day. Now, you had to stop the process midway. On the next day, you come back and start the testing again from the start. This action is termed ‘Re-test.’ You are testing again for a particular reason. One reason can be that a specific test case has failed in the final execution, and hence, the test case must be rerun. The second reason can be that the source code has a defect that has been fixed.

Regression testing can be considered a slight change from the re-test. Regression testing is scheduled only when there is a change in the product or the code. This change can be design, code, or any other issue that brings about an alteration in the overall framework of the product. The most frequent reason for this alteration is that bugs were fixed or new versions of the product were created.

In a usual Software Testing Life Cycle (STLC), the earlier process is the re-test, which can be followed by regression tests. In, the concentration is only on failed test cases. In regression tests, the attention is on the test cases that have previously been passed, but there is a possibility of new and unexpected bugs.

What Should You Do in Regression Testing?

The Software Testing Life Cycle (STLC) is a continuous process that comprises many stages. After the smoke or sanity testing is over or in the last functional testing phase, you need to begin regression testing.

There are mainly two types of actions that you need to perform:

• The previously conducted tests are re-run.
• The current results of the test cases are compared with the previously executed test results.

The first step to efficient regression tests is to outline a regression test plan. This plan must detail your test strategy for regression and the exit criteria. You can also include performance testing in this plan. This inclusion aims to ensure that the alterations in the product components do not impact the product performance.

It is essential to adhere to the best practices in regression testing. You need to run automated test cases close to the end of the day. Further, if any regression side effects are detected, you can share them with developers to fix them in the next day's build. By this practice, you cover most of the regression defects in an early phase rather than toward the end of the release cycle. In this manner, the release risks are minimized.

Types of Regression Testing

You can implement various regression tests depending on the feature or update you aim to deploy. However, it is crucial to understand the several regression test types to choose the right one.

Regression testing is of the following types.

• Complete or Full Regression
• Partial Regression
• Unit Regression
• Corrective Regression
• Selective Regression
• Re-test Regression

Complete or Full Regression

You should opt for this type when there is an alteration of code on many modules, and the impact of this alteration on the other modules is unknown. So, the decision is to check the entire product to detect whether there are any other modifications originating due to the changed code.

For the second product release, the client suggests adding four or five new features, and some defects from the first release are to be fixed. The testing team implements an impact analysis and concludes that the entire product must be tested for these modifications. In a nutshell, this type implies testing all the altered and old features.

Let us consider a Java application with Java Virtual Machine (JVM) as the root file. The Java application must be tested if a change is essential for the JVM file.

Partial Regression

After developers make some code changes, the unit of this changed code is integrated with the existing (that is, unchanged) code. You have to verify whether the changed code works as per expectations.

Unit Regression

You have to do this while the unit testing phase is in progress. In this case, the code of a unit is tested in isolation. The goal of this type of testing is that the unit has to be tested at an individual level. So, there is blocking of all the dependencies on the unit being tested.

Corrective Regression

It is one of the simple regression tests requiring less effort. Corrective regression test involves zero changes to the existing codebase and adding new functionality to the software application. You need to test the existing functionality and the test cases that go with it rather than developing new ones.

Selective Regression

Selective Regression test determines the impact of the existing codebase and both new and existing code. Common elements like variables and functions are implemented into the application to identify results without affecting the entire process.

Re-Test Regression

Re-test regression involves re-executing all the test cases to ensure no defects due to code alterations in the software. This type of testing needs more manual effort from the QA side.

Classification of Regression Test Process

The regression test process can be classified by another criterion into two types: ‘across the release’ and ‘across the builds.’

Across the Release

This is about a new release for the same project. The old elements in the previous releases might be affected by the new features in the latest release. This type comprises the following steps:

• Release 1 is the first release. It does not have modifications. So, there is no regression test in this release.
• The client suggests some new requirements. Thus, from Release 2, regression testing begins.
• The new requirements are given to the developers and QA engineers. They understand the needs.
• The impact analysis is performed to prevent major risks. This is done by the customer using the business knowledge, the developer using the coding knowledge, and the QA engineer using the product knowledge. As all relevant persons are involved in the impact analysis, maximum test coverage of the impact analysis is done.
• The client, developer, and QA engineer share their impact area documents with the test lead.
• The developer and the QA engineer commence work on the new test cases.
• The test lead combines the three impact area documents and saves the consolidated document in the test case requirement repository for Release 1.
• The test lead refers to the Requirement Traceability Matrix (RTM), selects the pertinent regression test case from the test case requirement repository, and stores the test case files in the regression test suite.
• After the QA engineer completes work on the new test cases, the test lead allocates the regression test case to the QA engineer.
• All the regression test cases must pass, and all the new features must be stable to do the next step.
• Use the test cases to check the impact area until it is durable for the product's old and new features.
• Offer the product to the client.

Across the Builds

After a bug is fixed, the bug is re-tested, and regression testing is done if the bug has a dependent module. Let us consider an example where there are three builds (Build 1, Build 2, and Build 3), and all these have varying scenarios. This type comprises the following steps.

Build 1

• The customer shares the business requirements.
• The developers commence the development of the features.
• The testers start writing the test cases. Let us assume that for Build 1, they write 500 test cases.
• The testers begin the execution of the test cases.
• The product is released to the client.
• The client implements one round of acceptance testing.
• The product is saved on the production server.

Build 2

• The customer suggests four new features and shares the business requirement for these.
• The developers start developing the features.
• The testers begin writing the test cases for the four new features. Let us assume that for Build 2, they write 300 test cases. Thus, the total count of test cases is 800.
• The testers commence execution of the 300 test cases of the four new features.
• The testers commence execution of the 500 test cases for Build 1 to confirm that the four new features have not hampered the old ones.
• After the old and the new features are tested, the product is released to the customers.
• The customers perform the acceptance testing.
• The product is saved on the production server.

Build 3

• The customer decides to remove a feature, ‘Feature 1.’
• The tester deletes all the test cases pertinent to the module of Feature 1 (let us assume these are 150 cases).
• The testers test all the remaining features to confirm that after the removal of Feature 1, the rest of the features are working fine.

How To Determine the Quantum of Regression Testing

You can decide the quantum of regression tests based on the scope of the newly added features.

Let us consider that the scope of a feature or a fix is large. The product area getting affected is also large. You must get the developer's input regarding the change's amount, nature, and scope. Accordingly, you can decide the areas of the product that need regression.

In regression testing, the tests are repeated again and again. So, you can automate a set of test cases. Then, this set is executed on every new build. You have to select the test cases with care while keeping in mind the goal that a minimum count of test cases must cover the maximum functionality of the product.

Let us consider that the product scope is enormous, and continuous patches or increments are being added to the system. In this case, you can save the time and cost of testing by choosing selective tests. You need to consider the enhancements to the product and the parts where these enhancements can produce maximum impact to finalize the selective test cases.

Techniques of Regression Testing

The following are techniques used in regression tests: Test case prioritization, Regression test selection, Re-test all, and Hybrid.

Test Case Prioritization

Every test case is assigned a priority based on the criticality of the case, the impact on the product, and the frequency of the specific functionality of the product. The test cases of newly added functionalities and customer-facing aspects are in the high-priority category. Those with high priority are executed first. Those with medium priority follow these, and lastly, those with low priority are implemented.

Regression Test Selection

Based on the code modification in the module, you can choose some test cases from the test suite. Then, you re-execute these selected test cases. The entire test suite need not be re-executed. The test cases are categorized into two types: obsolete test cases and reusable test cases.

In the upcoming regression cycles, you should not execute the obsolete test cases but must execute the reusable ones. In this technique, you are implementing only the relevant test cases, which are limited in number. This decreases the time and effort of the regression test.

Re-Test All

You have to re-execute all the test cases in the test suite. This is to ensure that the alteration made in the code has not introduced any bugs. This type needs more time and resources than the other techniques. This is the most expensive technique.

However, it is the most secure method because it ensures that all the bugs have been identified and fixed. This method is generally applicable when there is a major update in the operating system or the application is modified for a new language or platform.

Hybrid

This technique is a blend of test case prioritization and regression test selection. The complete test suite is not re-executed. Based on priority, you have to select test cases for re-execution.

Selection of a Regression Test Suite

In the production environment, the modifications to the code and the bugs addressed in the eleventh hour give rise to new bugs in the code.

This makes regression testing a critical task before the release of the product. The following test cases should be chosen for the regression test suite.

• The defects that are frequently failing.
• The recent testing defects.
• Priority 1 and Priority 2 test cases.
• The core feature or functionality of the product.
• Integration test cases related to all major components.
• Complex test cases.
• Test cases of the modules having modifications.
• Frequently used functionalities.

Steps Involved in Regression Testing

You can run regression tests manually and in an automated manner using special techniques and methods.

Below are the steps involved in running regression tests.

• Test Case Selection: The test case selection is determined by the component with many code alterations. Testers can divide the tests into reusable and obsolete test cases. Reusable test cases can be used later in regression test cycles, whereas obsolete test cases will not be included in further regression test cycles.
• Time Estimation: After selecting test cases, the next step is estimating the test execution time.
• Automate Test Cases: Testers should select between manual and automated testing based on the number of test cases once they are done with time estimation.
• Test Case Prioritization: In this step, testers prioritize test cases based on recent code commits, reducing regression time and effort. The test cases with high priority are run first, followed by medium and low priority.
• Test Execution: Finally, all test cases are executed in the order of priority to find defects and ensure that the application is working correctly.

Role of Configuration Management

In an Agile environment, when regression testing is being done, it is mandatory to do configuration management. In this environment, there are continuous alterations in the code. The following steps can ensure the validity of regression tests:

• During the regression test phase, the code must not be changed.
• The test case of regression tests must not be affected by alterations done by the developers.
• There must not be any changes to the database used for regression tests. To confirm this, it is essential to isolate the database.

The Agile Methodology for Regression Testing

The Agile methodology fosters an iterative and incremental way of working. The product development is executed in short iterations of two to four weeks named ‘sprint.’ The code modification and new functionality are performed in sprints. In the initial phase, you need to develop a regression test suite.

During every sprint, it is essential to update the test suite. Regression tests are categorized into two types.

• Sprint-level Regression
• End-to-End Regression

Sprint-Level Regression

In this type, the test suite is composed of test cases pertinent to the new functionality or code modification done in the previous sprint.

The short sprints in Agile make it mandatory to automate the test suite. The test cases are re-executed in a short time. If you automate the test cases, the time of execution and defect slippage is minimized.

End-To-End Regression

In this type, the test suite is composed of all the test cases for re-execution. The entire product is tested from the start to the end, encompassing all core functionalities of the product.

The short sprints in Agile make it mandatory to automate the test suite. The test cases are re-executed in a short time. If you automate the test cases, the time of execution and defect slippage is minimized.

Tools for Regression Testing

The testing where most of the testing efforts are automated is called automated regression testing. All the test cases previously executed are run on the new build. In this scenario, you have an available test case set, and manual testing of this test case set is time-consuming.

So, you automate this set, and the result is that the efficiency of the testing process is augmented. You have to navigate the Application Under Test (AUT) to observe whether the expected results exist. A large percentage of the regression test execution tools are categorized into the record and the playback types. Some of these tools are the following.

• Selenium: This is one of the top tools used for cross-platform and browser-based regression testing. It has a set of valuable features for the automation of web applications. It endorses automated test scripts that move in the cycle through data-driven tests and data sets. This tool is perfect if you have a large-scale testing team of advanced testers.
• TimeShiftX: The major advantages of this tool are a reduction in the necessary resources, adherence to timelines, and smaller test cycles. The combined effect is the release cycle becomes shorter while assuring high software reliability.
• Virtuoso: You can write the regression tests in plain English language by leveraging Natural Language Programming. This needs to be done like the authoring of a manual test script. This approach is a blend of the flexibility and power of the coded approach and the accessibility and speed of a codeless tool. Bots are launched by Virtuoso, which can dive into the DOM of the product and form a holistic model of the elements depending on the available attributes, IDs, and selectors.
• Katalon: If your user community for test automation is large, this is the preferred choice among the tools. It is an all-in-one platform. You need not have a complicated setup for this tool. It is a readymade framework that renders codeless and free solutions.

• Software testers can leverage its advanced features, such as CI/CD integration, test reporting, cross-browser testing, self-healing, scripting mode, and inbuilt keywords. It is suitable for regression tests of mobile products, web services, and websites. It provides support for running scripts that are on multiple environments, browsers, and devices. The test reports are in PDF, CSV, HTML, and LOG formats.

• BugBug: This is the simplest tool to automate regression tests. It has an intuitive interface. Software testers have to only ‘record and replay’ their tests. This tool doesn’t need coding. It quickly creates production-ready regression tests. Being easy to learn, it is a very simple alternative to Selenium.
• Avo Assure: This is a heterogeneous test automation solution that doesn’t require any code. Software testers find regression tests very quick and simple with this tool. It has cross-platform compatibility. This tool can test across associated emulators, ERPs, mainframe, desktop, mobile, and web. You can do end-to-end regression tests even without a single line of code to finish with quick, superior-quality delivery.
• Watir: The complete name is web application testing in Ruby. The Ruby programming code is used to create this open-source library. Using this, you can write tests that can be easily read and maintained on a flexible, lightweight UI. Watir endorses disparate user interaction abilities for testing websites, such as validating texts, entering data in forms, and clicking links.
• IBM Rational Functional Tester: This is abbreviated as RFT. IBM has developed this tool for software test automation. It is used for different types of testing, such as data-driven, GUI, regression, and functional testing.
• Apache JMeter: This is open-source software for test automation. It can measure test performance and load functional test behaviors. It can render an entire Regression test suite for end users. It supports performance and load tests on disparate servers, applications, and protocols.
• Ranorex Studio: This has an inbuilt Selenium WebDriver. It can be used for automated regression testing of mobile, web, and desktop apps. The studio is inclusive of complete IDE plus tools to perform codeless automation.

Challenges of Regression Testing

Regression tests help unearth bugs while introducing new features or in an existing codebase and mitigate app failures and performance bottlenecks.

However, while running a regression test, the following are a few challenges testers face.

• Test suite cost and time: A regression test suite needs continuous improvement when deploying new features. Therefore, the number of test cases varies, and new tests must be re-tested with older tests, which require a lot of time to complete.

• Incorporating parallel testing can be a feasible solution to run test cases concurrently across multiple browsers and OS combinations.

• Complex test cases: As the software project becomes more intricate, the number of test cases and their complexity also rise, consuming a lot of time and resources.
• Maintenance: As the application size grows, the complexity of test cases in regression test suites increases. Therefore, proper maintenance is crucial to tackling the complexity and test execution time.

Best Practices for Regression Testing

In this section, let’s look at some of the best practices for running regression tests.

• With the introduction of newer features or upgrades, keep your test suites up to date. Also, add tests to check whether the old feature is working.
• Check for the features used by end-users, and test them to check if that specific functionality is working as intended.
• Incorporate regression testing frameworks to reduce additional maintenance.
• Update your test design specification as per the requirements of developers and testers.

However, the number of test cases will grow as your application becomes more complex. Hence, you need a cloud-based testing solution that scales with your testing requirements.

Continuous quality cloud testing platforms like LambdaTest offers a cloud-scalable infrastructure of 3000+ real browsers, devices, and OS combinations for your automation regression testing needs.

Conclusion

Regression testing enables the delivery of a high-quality product and user experience. The primary benefit of regression testing is that any code change does not impact the existing functionality.

You can automate the regression test cases by selecting an automation tool based on project requirements and its ability to update the test case suite because the frequent update of the test case suite cannot be avoided. After choosing the apt tool, you can leverage it to detect all surfaced bugs and get rid of them early in the pipeline.

When regression testing is coupled with the Agile methodology, the outcome is that there are many technical and business benefits. The more time and money invested in regression testing, the more control of the process, error handling, and budget.