NiFi Mock Process Session Does Not Preserve Attributes when Using Write

The MockProcessSession behaves differently from the StandardProcessSession when it comes to altering the flowfile attributes. Some attribute modifications do not seem to take hold. This is because a couple of the write methods implemented in MockProcessSession return a modification of the flowfile passed in rather than the intended behaviour outlined in NIFI-3860 – a modification of the most recent version of the flowfile passed in. It also updates the currentVersions map with the modified version of the flowfile passed in which might not be current.