What is Regression Testing? - An Overview

As we have discussed in The Types of Software Testing guide, regression testing is performed at any point when developers change or modify the code. This is done to ensure that the new modification or feature does not break the application’s functionality or introduce new bugs into the system. It may also be done when a new feature is added or when a functional defect has been fixed. 

This type of testing can be done manually, but, owing to its time-consuming nature, can be automated using a test automation tool for better results. Once the bugs have been identified and fixed, either all tests or a selection of tests may be re-executed as part of the regression testing process to ensure that existing functionalities have not been adversely impacted. Alternatively, test cases may be prioritized based on business impact, and only these tests are re-executed. 

While regression testing is required every time a small modification or change is introduced, it does help enhance the product’s overall quality and ensures that issues once fixed, do not reoccur. 

When is Regression Testing Performed?

Regression testing is essential to validate that new functionalities or changes in requirements do not adversely affect the application’s functionality and performance. These are some of the common scenarios where regression testing is performed–

1. Addition of new functionality: When a new feature or module is introduced into the application.
2. When there is a change in requirements: When there is a big change made to the system, all features have to be retested for accuracy. 
3. After bug fixes: Developers perform regression testing after fixing bugs or defects, to ensure that the bug fix has not impacted other related functionalities. 
4. After fixing performance issues: Regression testing is done in this scenario to ensure that no functionalities have been impacted as a direct result of fixing any performance issues. 
5. When integrating with a new environment: Regression testing is required in any scenario where the application is integrated with the external environment(s) or system(s). 

How to Perform Regression Testing?

Regression testing involves the following steps:

1. Identify source code changes 
2. Prioritize important changes and product requirements
3. Develop test scenarios
4. Categorize and prioritize these test cases
5. Perform regression testing with these selected test cases

Regression Testing Techniques

Regression testing can be performed using the following techniques: 

1. Re-Test All

With the re-test all approach to regression testing, all test cases are re-executed. Generally, the re-test is performed when a test fails and the cause of failure is due to a software error. This error is reported, following which the developer team fixes it. Now, the test is performed once again, to ensure that the software error has been corrected. 

2. Regression Test Selection

In this scenario, only a selected set of test cases are executed. These selected test cases could be reusable test cases that can be used in succeeding regression cycles or obsolete test cases that cannot be used in succeeding regression cycles. 

3. Prioritization of Test Cases

Here, the test cases are prioritized based on business impact, criticality, and the frequency at which the functionality is used. 

Advantages of Regression Testing

• Regression testing improves product quality and stability. 
• It ensures that issues once fixed, will not reoccur. 
• It provides certainty that bug fixes or other such changes do not impact product functionality. 
• Regression testing enables higher user satisfaction by facilitating efficient product development at critical stages. 

Disadvantages of Regression Testing

• Regression testing is required for any and all code changes, as even the slightest change can cause issues to existing functionalities.
• When performed manually, regression testing can be time-consuming and tedious. 
• As each test suite becomes larger and more complex with several regression runs, the entire regression test suite cannot be executed owing to time and budget constraints. 
• Regression testing requires continuous and rigorous maintenance to ensure that any new change or update does not affect existing regression tests. 
• It is challenging to determine the exact frequency of regression tests, whether it is to be done after every build update or bug fix, etc. 

Best Practices

• Regression testing should be an essential part of the entire testing methodology.
• It should be designed for cost-effectiveness and efficiency, while still providing optimal test coverage. 
• Build a regression framework at the very outset of the project, which delineates specific test case objectives, in order to avoid rework in the future. 
• Consistently update test cases based on evolving developer and user requirements. 
• Update the testing pack with new tests whenever a new functionality is added into the application. 
• Automate regression tests where applicable, in order to save time and foster accuracy. 

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