@emcp Sorry for missing this – removed the link now. (The link was to an old doc that has since been archived. It has not been replaced with anything else because people are not supposed to interact with hook tools directly but rather through Ops (see the note at the top of the Hook tool doc). For how to handle leadership in Ops see Event leader-elected > Observing this event in ops.
@erik-lonroth pinging you too as I believe this might answer your question as well. For a bit more context: As @ppasotti just confirmed, in the typical case it is Juju who decides which unit is the leader (and then tells it to the unit via a leader-elected event). When you’re developing a charm, and testing that the charm will respond correctly, you can simulate this as mentioned in Event leader-elected > Observing this event in ops. PS This only tells you how to do it with Harness. There is also a way to do it with Scenario. Pietro will add info on that as well soon.