test: raft leader election
This patch introduces two tests:
-
couple.test_failover
reproduces heatbeat timeout on a follower that leads to a new election. -
threesome.test_leader_dispuption
simulates disconnected follower. It shouldn't disrupt the leader in this case.
Leader death is already tested in threesome.test_log_rollback
.
Close https://gitlab.com/picodata/picodata/picodata/-/issues/25