For 8.3 and earlier: Testing your applications
Pega rigorously tests each patch release to ensure that it has no known compatibility issues between patch versions. Pega recommends that clients perform their own sanity or smoke testing after reviewing the list of "Resolved Issues" to re-validate appropriate features or functions in your Pega application that a patch can affect.
For details about testing and re-validation best practices, see Pega Infinity.