How to Do Regression Testing Properly and Fast

What is regression testing?

Regression testing is a test of a previously tested program to make sure that the changes made will not lead to the appearance of defects in the part of the program that has not changed. Regression testing is used to make sure that the program, after changes, continues to meet the established requirements and successfully interacts with other systems.

Following dynamically changing needs, users want quick and frequent improvements to IT systems and applications. Adding new functionality, reworking old ones, adjusting for an updated version of the browser or operating system, and fixing defects is often an ongoing process of the software life cycle. Any modification to the code or the software environment does not exclude the occurrence of errors. Moreover, when the system is being improved, it is likely that the changes will affect its performance in terms of the previously developed functionality.

How does regression testing differ from other types of testing?

Now, let’s compare regression testing to the other most popular types of testing. 

Regression testing vs unit testing

The main difference is that unit testing checks the functionality of individual modules, commonly using mocks or stubs in the place of interface/API calls. Regression testing, on the other hand, re-runs previously-passed tests for each modified module. You can read more about the difference between regression testing and unit testing in our recent article.

Regression testing vs integration testing

Integration tests simply verify that the different parts of your program, which you have tested individually via unit tests, work well when integrated together. While regression tests are needed to check if the program still works well after certain changes.

With integration testing, we can take the analogy of the human body. First, unit tests verify that a particular muscle works well and that a particular bone is strong enough. The integration tests will verify that with such a nervous impulse, we should see the arm rise.

It is essential to have at least one integration test for each junction point between the different parts of the program.

Regression testing vs retesting

Retesting is a process of verifying fixes to a specific module or item, while regression testing is a process of verifying the effect of functionality changes on the software system as a whole. 

Retesting basically means re-running previously failed test cases, and regression testing involves re-running tests that passed in previous versions of the software system.

Additionally, regression testing is performed after the retest process. Regression testing and retesting are usually concurrently performed.

How regression testing is performed

QA engineers develop the regression test suite the first time they perform the tests. After that, they use the same set of tests for future releases, sometimes with minor modifications. The main stages include:

  • Analysis of business and functional needs
  • Development of the test plan
  • Test case development
  • Setting up the environment for testing
  • Configuring test data
  • Deciding on exit criteria

Tests execution 

  • Executing test cases
  • Recording test results 
  • Reporting bugs in the bug report tool
  • Rechecking bug fixes

Ending the process

  • Preparing the test report
  • Assessment of exit criteria
  • Closing of the test phase

Regression testing types

There are three types of regression testing: unit regression, partial regression, and complete regression. Let’s discuss each of them.

Unit regression is performed during the Unit Testing phase and the code is tested in isolation, i.e. all dependencies of the unit under test are blocked so that the unit can be tested individually without any divergence.

Partial regression is performed to verify that the code works correctly even when the changes have been made in the code and the unit is integrated with the retained or already existing code.

Complete regression is performed when a change in the code is made on a number of modules and also if the impact of a change in another module is uncertain. The product as a whole is regressed to check for the impact of changes due to modified code.

How much of your regression testing should be automated?

By its nature, regression testing is both time-consuming and a repetitive activity, which often leads to minimizing or even ignoring it, especially in small QA and testing teams with limited capacity. Manual regression testing is used on almost every product, especially early in development. However, despite being the most natural solution in many development environments, it is hardly effective. This is where test automation comes in.

Automated regression testing can take over tedious repetitive tasks and free up time for in-depth exploratory testing, ensuring product increments are delivered on time.

The easiest approach to get started with automated regression testing without expensive investments and heavy implementation is to use test automation tools.

We recommend automating at least 70% of manual regression tests. Here is the visualization of the problem:


Best practices of regression testing

A few tips on how to perform regression testing. For example:

– Prioritize test cases that cause frequent defects

– Perform regression testing whenever a change is made to the code

– Define regression test scenarios beforehand

– Automate your regression tests

First of all, check if your organization has already developed guidelines on regression testing and any testing tools to be used. There might be some knowledge base or recommendations in this area. consult with it and adhere to it.

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