Simple/best tool to verify PMTUD?

["Christopher J. Pilkington" <cjp () 0x1 net>]

I'm looking for a simple tool to verify PMTUD is usable along a
particular path. Ideally this tool would be cross-platform, or run on
Linux or Windows.

I've done some testing of my own by hand, but hoping a tool would help
the admin on the other side be able to test for themselves.