Regression testing in Selenium involves retesting the previously tested functionalities of a web application to ensure that any recent changes or updates have not introduced new defects or caused existing features to break.

Here’s an overview of how you can perform regression testing in Selenium:

1. Identify Test Cases: Identify the test cases that cover the functionalities or features that are impacted by the recent changes or updates. These test cases should focus on the areas where the highest risks or impacts are expected.

2. Update Test Scripts: If there have been changes to the application’s user interface or the underlying structure, you may need to update your test scripts to reflect those changes. Update the locators, element identifiers, or any other relevant test data as necessary to ensure that the tests can still interact with the application correctly.

3. Re-Execute Test Cases: Execute the updated test cases using Selenium WebDriver. Run the tests against the new version of the application to verify that the existing functionalities still work as expected. Selenium WebDriver provides methods to interact with web elements, perform actions, and validate expected outcomes.

4. Compare Results: Compare the test results with the expected results from the previous test runs. If any discrepancies or failures are observed, investigate and analyze the root causes. Determine whether the failures are due to the recent changes or updates or if they are unrelated.

5. Bug Reporting: If you encounter any new defects or issues during regression testing, log them as bugs in your bug tracking system. Provide detailed information about the failures, including steps to reproduce, expected behavior, and actual behavior. This helps in documenting and tracking any regressions introduced by the recent changes.

6. Test Coverage: Consider the test coverage of your regression test suite. Ensure that the critical functionalities and areas of the application are covered adequately. You may need to expand your test suite or modify existing test cases to enhance coverage based on the scope and impact of the changes.

7. Automation Framework: If you have a test automation framework in place, utilize its features to manage and execute regression tests effectively. Frameworks like TestNG or JUnit can provide functionalities such as test parameterization, test data management, parallel test execution, and reporting, which can streamline your regression testing process.

8. Continuous Integration: Integrate regression tests into your continuous integration (CI) process. Configure your CI system to trigger regression tests automatically upon code changes or as part of the deployment pipeline. This ensures that regression tests are run consistently and promptly after updates are made to the application.

Regression testing with Selenium ensures that changes in the application do not cause unintended side effects or break existing functionalities. It helps maintain the stability and quality of the software throughout its development lifecycle.