What type of maintenance testing may be required for a system targeted for decommissioning?

The correct answer is retirement testing. This type of testing is specifically focused on systems that are being decommissioned. Retirement testing ensures that all necessary aspects of the system have been addressed before it is taken out of service, such as verifying that data is correctly archived and that all components of the system are properly closed down.

Retirement testing typically involves ensuring that no residual dependencies or functions will affect other systems after the decommissioning process. It may also encompass verifying that the necessary documentation regarding the decommissioned system has been completed.

Other types of testing mentioned, like regression testing, data migration testing, and patch testing, are important in different contexts but do not specifically align with the requirements of decommissioning a system. Regression testing addresses whether changes made in software affect existing functionalities, data migration testing involves the transfer of data from one system to another, and patch testing focuses on new updates or fixes deployed to an existing system. However, in the context of a system being decommissioned, retirement testing is the more relevant focus.