public async Task when_a_candidate_recieves_a_vote_response_from_a_node_with_a_higher_term_number_then_that_candidate_steps_down()
{
var peerObservable = new Subject <IEnumerable <Peer> >();
var testScheduler = new VirtualScheduler();
var nodes = TestNode.CreateCluster(peerObservable: peerObservable, scheduler: testScheduler);
var leader = nodes.First();
testScheduler.AdvanceBy(TestNode.ElectionTimeout);
await leader.StartElection();
leader.StepDown(2, "none");
testScheduler.AdvanceBy(TestNode.ElectionTimeout);
nodes.LogStatus();
await leader.StartElection();
leader.State.Should().Be(State.Leader);
nodes.ForEach(n => n.Term.Should().Be(3));
var candidateThatsBehind = TestNode.CreateTestNode("candidateThatsBehind", peerObservable, testScheduler);
nodes.Add(candidateThatsBehind);
peerObservable.OnNext(nodes.Select(n => n.AsPeer()));
testScheduler.AdvanceBy(TestNode.ElectionTimeout.Ticks * 2);
await candidateThatsBehind.StartElection();
leader.State.Should().Be(State.Leader);
candidateThatsBehind.Term.Should().Be(3);
candidateThatsBehind.State.Should().Be(State.Follower, "the node should have immediatly stepped down because it attempted to start an election for term 2 but the cluster was on term 3");
}
public async Task when_a_cluster_already_has_a_leader_if_an_usurper_node_attempts_an_election_it_fails()
{
var peerObservable = new Subject <IEnumerable <Peer> >();
var nodes = TestNode.CreateCluster(peerObservable: peerObservable);
var leader = nodes.First();
await leader.StartElection();
var usurper = TestNode.CreateTestNode("usurper", peerObservable);
nodes.Add(usurper);
peerObservable.OnNext(nodes.Select(n => n.AsPeer()));
await usurper.StartElection();
leader.State.Should().Be(State.Leader);
usurper.State.Should().Be(State.Candidate, "the node should remain a candidate and continue trying elections until it is contacted by a leader");
}
public async Task when_a_candidate_recieves_an_AppendEntries_from_a_leader_that_candidate_becomes_a_follower()
{
var peerObservable = new Subject <IEnumerable <Peer> >();
var nodes = TestNode.CreateCluster(peerObservable: peerObservable);
var leader = nodes.First();
await leader.StartElection();
var usurper = TestNode.CreateTestNode("usurper", peerObservable);
nodes.Add(usurper);
peerObservable.OnNext(nodes.Select(n => n.AsPeer()));
await usurper.StartElection();
leader.State.Should().Be(State.Leader);
usurper.State.Should().Be(State.Candidate);
await leader.SendHeartBeat();
usurper.State.Should().Be(State.Follower);
}