Regression testing: Complete Guide With Best Practices
Tags: testing, tutorial, webdev, programming
Published: 2022-12-26 11:59:43

The goal of software testing is to find and fix bugs. However, after a bug gets fixed, other bugs often ensue. This is when Regression testing comes into play. It ensures that additional problems do not arise after a bug fix or a code change. Hence, every software product company performs Regression tests.

Regression testing is executed after making changes to a software product and retests the product areas that may have been impacted by the fix. This can be automated or performed manually by executing a particular set of test cases (test scripts in case of Automation). No matter how the regression test is executed, this type of testing is critical for delivering a high-quality software product.

In this article, we look at what is Regression testing, its importance and types, and how to perform it.

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## What is Regression testing used for?

Before getting into the details of what it is, it’s important to understand why we need it.

When software developers fix a bug, add new functionality, or modify an existing feature or functionality, they must change the program code. Even a slight change will likely result in a plethora of new bugs. In such a scenario, a Test Engineer can reveal and pinpoint undesirable side effects through Regression tests. A properly executed regression test suite is vital. It is imperative that after a bug fix, the original product does not stop working.

The below graph depicts the importance of the Regression test:

![](https://cdn-images-1.medium.com/max/2000/0*T3BmOmtHaJ6CxA3r.png)

## When to perform Regression testing?

When new features or enhancements are deployed to an existing codebase or application, Regression testing is required. It ensures that any new functionality or update to an existing application works properly without any bugs or defects. Developers and testers often struggle to trace every code thread, with significant chances of code incompatibility issues. As a result, executing Regression tests of their codebase (or application) allows them to detect defects earlier and ship applications with fewer risks.

It can be used when a deployment takes longer than expected. In this case, the tester should run Regression tests daily. Also, it is better to run Regression tests after functional testing for weekly releases.

When some functionality is overhauled, Regression test becomes even more critical as it may risk the codebase’s present functionality. Furthermore, repairing one defect can sometimes lead to another. In this case, you can use a blend of debugging and Regression tests to ensure that everything works as intended.

## Types of Regression testing

Depending on your Software Development Life Cycle (SDLC) and the new feature or update you aim to deploy, you can implement various types of regression tests. However, it is essential to understand the several regression tests types to choose the right one.

Below are the different types of regression testing –

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## Corrective Regression Testing

Corrective Regression testing is one of the simpler forms of Regression tests requiring minimal effort. Corrective Regression testing involves no changes to the existing codebase and adding new functionality to the application. You simply need to test the existing functionality and the test cases that go with it rather than creating new ones.

## Unit Regression Testing

Unit Regression testing is an integral part of Regression tests in which the code is tested in isolation. All other interactions, integration, and dependencies are disabled while performing unit Regression testing, and the emphasis is on single unit code. Typically, this testing is done during low traffic and off-peak hours.

## Selective Regression Testing

Selective Regression testing analyzes the impact of existing code and the effect of both new and existing code. Common elements like variables and functions are incorporated into the application to identify quick results without affecting the process.

## Progressive Regression Testing

Test cases are created based on the requirements of a progressive regression test. When there are only minor product improvements, the new test cases are designed without affecting the existing code of a product.

## Complete Regression Testing

Some minor or significant changes might have a massive impact on the product. Complete Regression testing is used in this instance when there are significant modifications to the current code. It aids in the repair of any modifications made during the testing process.

## Partial Regression Testing

When new code is added to an existing codebase, partial Regression testing is conducted. This aids in the discovery of critical bugs in existing code and allows them to be tested without affecting the system.

## Retest-all Regression Testing

Re-test all Regression testing is the process of re-executing all the test cases to ensure that there are no bugs due to code changes in an application. This type of testing needs immense effort from the QA front.

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## Differences between Re-testing and Regression testing

In this section, we will explore how Re-testing is different from Regression testing.

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Re-testing is the continuous process of testing specific test cases to ensure that the bugs are fixed and the web product’s functionality works fine in the final execution. The same set of unit tests is repeated in re-testing to verify the code’s functionality. In other words, re-testing is executing the same manual or automated tests to validate that the new build is working flawlessly.

Regression testing is a technique to verify the new build whenever any code commit takes place. In this process, a tester’s job is to verify that no new bugs are included in the code due to software modification and adjustments. Once the Regression test suite is developed, you can automate it using an [automation testing tool](https://www.lambdatest.com/automation-testing-tool?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog). However, this does not apply to re-testing.

Let’s look at the detailed comparison of Re-Testing vs. Regression testing

| RE-TESTING                                                                                                                  | REGRESSION TESTING                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------|
| It is a technique to ensure the test cases are bug-free and run flawlessly in the final execution after the bugs are fixed. | It is a technique to ensure that the code functionality remains unaffected after the application’s adjustment or modifications,  |
| It is performed for failed test cases.                                                                                      | It is performed for passed test cases.                                                                                           |
| It ensures the original bug in the build is fixed.                                                                          | It tests the code for unintended side effects.                                                                                   |
| Automated Re-testing of tests is not possible.                                                                              | Automated Regression testing is possible.                                                                                        |
| It is also known as planned testing.                                                                                        | It is also known as generic testing.                                                                                             |
| It can’t be performed in parallel with Regression tests due to its high priority.                                           | It can be performed in parallel with re-testing due to its lower priority in a few instances and resource availability.          |
| It doesn’t include bug verification as a part of testing.                                                                   | It includes bug verification as a part of testing.                                                                               |
| It is performed across all software releases.                                                                               | It is performed across a few latest versions of software.                                                                        


## Advantages of Regression testing

The software market growth relies heavily on the success of Regression tests. Besides functional tests, Regression tests must be performed at each stage to ensure application stability. DevOps teams can utilize Regression tests in their software development lifecycle and ensure their existing code isn’t affected by the newly added updates and features.

Below are a few advantages of Regression testing:

* It ensures smooth business operations by ensuring the new features are not affecting the existing codebase, dramatically improving the overall product quality.

* Regression tests may be used during the integration testing phase also. In this case, they will help detect bugs across different systems when putting two systems together.

* Manual test cases can be automated, and this automation principle can be applied to Regression checks. Automated Regression testing can help you cut down test execution time by multiple folds.

* A successfully executed Regression test suite ensures that the bugs are detected and fixed early and eventually helps achieve a high Customer Satisfaction Index (CSI).

* It thoroughly validates that the code modifications do not impact the correct functionality of already tested code — detect every side effect of any code change.

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## Developing Regression testing strategy

If you want to make the most of your Regression test suites, it is essential to plan a proper strategy by keeping certain factors in mind. This section, discusses some ways to help you create a winning Regression tests strategy:

* **Execute all existing tests once again**: After the product release, Test Engineers must check problem areas again. Many times this can be a challenge, especially when it comes to executing manual testing. Automated testing is recommended here.

* **Run high-priority tests first**: About 50% of time spent on Regression testing should be devoted to repeating tests that concern the application’s essential functionality.

* **Check the complicated features next**: Many applications have sophisticated and complicated parts, which can cause problems. Although the functionality is complicated to understand/comprehend, the quality of their functionality must be excellent.

* **Execute [Exploratory testing](https://www.lambdatest.com/blog/exploratory-testing-all-about-discovery/?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog)**: While learning the software version’s new features, design new tests for them and execute them. In the course of this testing, many new bugs will be found.

Boost productivity and reduce time/efforts spent on running tests with the help of automated testing. Using automation scripts, it is possible to perform tests much quicker and in a more effective way.

Finally, it is imperative to perform random testing. A software tester assumes the role of a user and tests randomly. Because there is always some problem or another, it is important to perform random testing.

## Selecting Test Cases for Regression testing

[End-to-end testing](https://www.lambdatest.com/blog/guide-to-end-to-end-testing-with-examples/?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog) is crucial for running your application smoothly across all browsers and operating systems. However, it has been observed that a substantial number of defects leak into an application during the deployment stage. This could be critical from the customer’s standpoint since it could increase turnover and create a terrible customer experience. Therefore, it’s vital to select the test cases wisely based on the customer requirements.

Below are the steps to select regression test cases –

 1. **Select test cases with frequent bugs**: A simple code commit can sometimes break an application’s complete functionality. As a result, testers should keep these factors in mind while selecting test cases that involve frequent defects. They can also choose the test cases depending on their prior knowledge and experience with the Regression test cycle.

 2. **Select test cases with critical core features**: To ensure that the application runs smoothly across multiple platforms, testers should first focus on choosing test cases that cover the essential key functionalities of an application. For example, an e-commerce application must include multiple payment methods, website navigation, extensive search functionality, etc.

 3. **Select test cases with recent code updates**: When new code or features are incorporated into an application, the probability of defects rises, and code must be modified multiple times. As a result, it is critical to prioritize test cases and choose those that involve frequent codebase adjustments and upgrades.

 4. **Select test cases based on the user interface**: Testers need to choose test cases based on the areas visible to users. The user interface’s visible elements are the brand logo, images, button text, and so on. However, these issues have low priority, yet they are crucial from the user’s perspective.

 5. **Select integration-based test cases**: End-to-end testing ensures an application runs smoothly across different platforms. There may be instances where one component’s functionality is dependent on another. For example, if the function of component C2 is dependent on C1 and C2 is modified, the behavior of C1 may be impacted. Therefore, running regression tests of such bugs is crucial to validate integration-based test scenarios.

 6. **Select complex test cases**: Complex test case execution can result in app crashes and poor performance. Testers must use various techniques to test complexity and ensure that all sophisticated test scenarios are addressed.

 7. **Incorporate risk-based testing**: In the risk-based testing method, testers prioritize the test cases based on the recent code changes, thereby reducing Regression time and efforts.

The priorities of regression test cases can be classified into three categories –

 1. **High priority**: It covers an application’s critical and core functionality, recent code modifications, and components with a significant chance of bugs.

 2. **Medium priority**: It involves aspects like field validations and other negative test scenarios.

 3. **Low priority**: It includes other functionality like user-interface areas like brand logos, button text, etc.

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## How much Regression is required?

In the previous section, we touched upon selecting the regression test cases. Now let’s look at how much regression is required.

The amount of regression required solely depends on the extent of an application’s new features or updates. If the fix or upgrade is major, extensive Regression tests of all application test cases is required. Since the update is significant, the test cases will also be huge; therefore, you can perform automated testing of all repetitive test cases. For the newly added functionality, the test suites require constant upgrades.

The next step is identifying appropriate Regression test cases in order to cover all of an application’s functionality. However, when the app’s changes are substantial, the most effective approach is to find relevant test cases based on the upgrades and the affected sections of the application. It will help you in cutting costs, time, and effort.

## How to perform Regression testing?

Regression testing can be executed both manually and in an automated manner. Test Engineers primarily use special techniques and methods to perform Regression tests.

![](https://cdn-images-1.medium.com/max/2000/0*DZtgmQ9H9E5Tco8Y.png)

Below are the phases involved in Regression testing –

 1. **Test Case Selection**: The selection of test cases is determined by the component, one with a massive number of code modifications. Testers can split the tests into two categories: reusable test cases and obsolete test cases. Reusable test cases will be used in future Regression test cycles, but obsolete test cases will not be considered in further Regression test cycles.

 2. **Time Estimation**: Following the selection of test cases, the next step is to estimate the test execution time. Test case generation, test case evaluation, and other factors impact test execution time.

 3. **Automate Test Cases**: Testers should select between manual and automated Regression testing based on the number of test cases after time estimation.

 4. **Test Case Prioritization**: In this step, testers prioritize test cases based on recent code changes, minimizing Regression time and effort. The test cases with high priority are executed first, followed by medium and low priority.

 5. **Test Execution**: Finally, all test cases are run in the order of priority to find flaws and ensure that the application is functioning correctly. Automated Regression testing tools like Selenium enable you to reduce test execution time and automate your Regression test suites more quickly.

## Regression testing example

Here is an example of Regression tests needed for the Tesla website. This company generates billions of dollars in annual revenues from its Website. Hence their websites must always be up and running — functionally, reliably, and with good performance.

**Example — Tesla**

On the front page of Tesla.com, you can see all Tesla’s products.

![](https://cdn-images-1.medium.com/max/2000/0*tjJOzkrSB6cTxbMT.png)

When Tesla releases their next product, i.e., the Cyber Truck, the developers at Tesla will add a new entry to the Website, most likely next to Model Y. But a lot of care needs to be taken to ensure that even though new UI flows are added to a new “Cyber Truck” entry on the main page, the rest of the product UI flows continue to work functionally as before. A Regression test suite is executed for this purpose. These Regression test cases can be manually executed or automated using a prevalent test automation framework called Selenium.

Let’s say one of the Regression tests fails; this means that an existing function of the Website broke while adding a new product flow. This bug needs to be immediately logged and fixed. This Regression test suite should be executed every time a minor or a significant UI flow addition/changes are made to the Website.

Similarly, the Regression test suite should also be enhanced to cover more UI flows with the help of newer test cases. This ensures that the Website is always up and running; any time there is a breakage, it is immediately detected and flagged with the help of a Regression test suite.

In the next section, we will talk about different Regression testing tools.

## Tools for performing successful Regression testing

Here are some tools that can be useful for creating and executing Regression tests. However, the requirements of each product should be thoroughly studied before deciding which ones to use.

## Selenium

Selenium is an open-source web automation testing tool to test websites and web apps. It is considered one of the top automated Regression tests tools for [web application testing](https://www.lambdatest.com/web-application-testing?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog). Selenium supports different browsers and platforms for [automated browser testing](https://www.lambdatest.com/automated-browser-testing?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog).

## Watir

Watir is a web application testing framework in Ruby. It is an open-source Ruby library for automating web browser tests. Watir is a testing tool that is used to automate Regression test suites.

## Serenity

Serenity BDD is an open-source framework that enables you to write higher-quality automated Regression and acceptance tests. Serenity allows for more flexible and easy-to-maintain tests. It also generates extensive test results and keeps you informed on how much application is being tested.

## Silk Test

Silk Test is an automated functional and Regression testing tool for enterprise software applications. It aids with regression, cross-platform, and [localization testing](https://www.lambdatest.com/blog/how-to-perform-localization-testing/?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog) of all mobile application types like web, native, and hybrid apps.

## QA Wizard

QA Wizard Pro is a tool that automates functional and Regression tests of web, Windows, and Java applications and performs [load testing](https://www.lambdatest.com/blog/how-to-get-started-with-load-testing/?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog) of web apps.

## Challenges of Regression testing

It helps uncover bugs while introducing new features or updates in an existing codebase and facilitates mitigation of app crashes and performance bottlenecks. However, while running a Regression test, a tester faces different challenges.

Shown below are a few of the challenges faced by testers –

* **Test suite cost and time**: A Regression test suite requires continuous improvement when new features are deployed. As a result, the number of test cases varies, and new tests must be re-run with older tests, which require a lot of time to complete. Incorporating [parallel testing](https://www.lambdatest.com/blog/what-is-parallel-testing-and-why-to-adopt-it/?utm_source=devto&utm_medium=organic&utm_campaign=dec26_pk&utm_term=pk&utm_content=blog) can be a viable solution as it allows you to run test cases concurrently across multiple browsers and OS combinations, reducing lead time by multiple folds.

* **Complex test cases**: As the project or application becomes more complex, the number of test cases and their complexity also rise. Thus, consuming a significant amount of time and resources.

* **Maintenance**: As the application grows in size, the complexity of test cases in Regression test suites increases. Therefore, proper maintenance is vital to handle the complexity and execution time.

## Best Practices of Regression testing

Some challenges were covered in the previous section. Now, let’s look at some of the best Regression testing practices.

* With the introduction of newer upgrades, it is best to keep your Regression test suites up to date. Include tests to see whether the old feature is still functional.

* Check for the features and capabilities of applications used by users, and then include a test case to check whether that specific functionality is working as expected.

* Use Regression testing frameworks in your project to save additional maintenance.

* Update your test designs based on devs and testers requirements.

* Automated Regression testing can help you save time, cost and deliver products faster.

It helps identify bugs ahead of the deployment deadline. However, as your application becomes more complicated, the number of test cases will expand. As a result, you need a cloud-based testing infrastructure that can scale as your testing requirements grow.

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## Conclusion

We hope you now have a good gist of what is Regression testing.

In short, Regression tests is to be executed when any change -big or small is made to code.

It can be done in many ways, including Corrective Regression testing, Progressive regression testing, Retest-All Strategy, and Selective Strategies. Some tips for strategies pertaining to Regression tests include Running High priority tests first, executing exploratory testing, etc.

Even though Regression tests consumes vast amounts of resources, it saves your effort and time. It eases the lives of devs and testers in their agile software development lifecycle and yields maximum output.

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