Which type of testing should be done after a release upgrade has been implemented?

The appropriate type of testing to conduct after a release upgrade has been implemented is regression testing. Regression testing is essential to ensure that the updated system continues to function as expected without introducing new issues. When an upgrade occurs, changes can inadvertently affect existing functionalities, and regression testing helps identify any such impacts.

In the context of software development and system implementation, regression tests verify that previously developed and tested software still performs after a change. This includes not only checking the upgraded functionalities but also ensuring that related components work seamlessly together. Performing regression testing post-upgrade is a best practice, as it helps maintain system stability and reliability.

User acceptance testing, while important, is typically conducted before a release goes live to confirm that the system meets the business requirements from an end-user perspective. Integration testing focuses on verifying that different system modules or external applications interact correctly, which might be done before or after upgrades but does not specifically target the regressions caused by the upgrades. String tests are not a common term in this context and are less relevant to the focus on release upgrades.