Regression testing in Selenium refers to the practice of re-running automated test scripts to ensure that new code changes or updates to an application have not introduced any unintended side effects or defects in the existing functionality. Selenium is a popular tool for automating web application testing, and regression testing with Selenium involves using its capabilities to ensure that the application’s features continue to work as expected after each round of changes.

Here’s a general process for performing regression testing in Selenium:

1. Test Case Selection: Choose the test cases that cover the critical functionality and features of your application. These test cases will serve as your regression test suite.

2. Create and Maintain Test Scripts: Develop automated test scripts using Selenium WebDriver and a programming language like Java, Python, C#, etc. These scripts simulate user interactions with the application, such as clicking buttons, filling forms, and verifying results.

3. Execute Initial Tests: Run your initial set of regression tests on the baseline version of the application to establish a baseline of expected behavior.

4. Capture Baseline Results: Store the results of the initial test runs as a reference for future comparisons.

5. Implement Changes: Make code changes, bug fixes, or updates to the application.

6. Modify Test Scripts: Update your test scripts to reflect any changes in the application’s UI or functionality due to the updates.

7. Execute Regression Tests: Run your updated test scripts against the new version of the application.

8. Compare Results: Compare the results of the current test run with the baseline results. Any discrepancies or failures indicate potential regressions, i.e., unintended issues introduced by the recent changes.

9. Investigate Failures: If there are test failures, investigate the failures to determine whether they are due to actual regressions or other factors like environment changes, test script issues, or test data problems.

10. Fix Defects: If regressions are identified, address the defects introduced by the changes. Once the defects are fixed, re-run the relevant test cases to ensure the issues are resolved.

11. Update Regression Suite: If necessary, update your regression test suite by adding new test cases that cover the new functionality introduced in the application.

12. Repeat the Process: As you continue to make changes to the application, repeat the process of running regression tests, comparing results, and addressing any regressions that are found.

By regularly performing regression testing with Selenium, you can catch potential issues early in the development cycle, ensuring that the application remains stable and reliable as it evolves over time.