Bit confused about minion pact

My understanding of this support is that if there is a minion nearby, it will remove 100% of my life from them. Is there any visual indicator when this happens? I can't see any difference, and I can't see minions losing any life (only tested with srs and skeletons).

Is this currently not working? Or am I doing something wrong?

Edit: on further testing, it takes me like 12-13 casts to kill 2 lvl 9 skeletons. The tooltip says they have 1031 life, i have 618, so i should be killing them in basically 2 casts, shouldn't i?