Create ns_tick_agent unit test

In this code review https://review.couchbase.org/c/ns_server/+/207726 it was suggested that a unit test be created. The issue that was fixed involved possibly losing a net leader notification. Via slack

Steve

I'm not sure how difficult a test it would be to write. I'd have to look into what other, if there are any, tests around subscribing to events exist.

Ben

I'm not sure you need to actually subscribe to events here. The fix and test should be for the ns_tick_agent module so you could just mock away the event subscription and send the message yourself.

I've opened this ticket to gather ideas of what should be tested in this case.