From 6d2cb8ba8e7093ea40aa55cad9f5242d82967eed Mon Sep 17 00:00:00 2001
From: William Banfield <4561443+williambanfield@users.noreply.github.com>
Date: Fri, 24 Sep 2021 11:19:57 -0400
Subject: [PATCH] consensus: remove logic to unlock block on 2/3 prevote for
 nil (#6954)

---
 internal/consensus/common_test.go   |  20 +-
 internal/consensus/state.go         |  72 +---
 internal/consensus/state_test.go    | 556 ++++++++++++++++++----------
 internal/eventbus/event_bus.go      |   4 -
 internal/eventbus/event_bus_test.go |   3 -
 internal/test/factory/block.go      |   2 +-
 types/block.go                      |   6 +-
 types/canonical.go                  |   2 +-
 types/events.go                     |   2 -
 types/vote.go                       |   4 +-
 types/vote_set_test.go              |  20 +-
 11 files changed, 409 insertions(+), 282 deletions(-)

diff --git a/internal/consensus/common_test.go b/internal/consensus/common_test.go
index 6630a9e24..aaa250b5d 100644
--- a/internal/consensus/common_test.go
+++ b/internal/consensus/common_test.go
@@ -547,14 +547,6 @@ func ensureNoNewRoundStep(t *testing.T, stepCh <-chan tmpubsub.Message) {
 		"We should be stuck waiting, not receiving NewRoundStep event")
 }
 
-func ensureNoNewUnlock(t *testing.T, unlockCh <-chan tmpubsub.Message) {
-	t.Helper()
-	ensureNoNewEvent(t,
-		unlockCh,
-		ensureTimeout,
-		"We should be stuck waiting, not receiving Unlock event")
-}
-
 func ensureNoNewTimeout(t *testing.T, stepCh <-chan tmpubsub.Message, timeout int64) {
 	t.Helper()
 	timeoutDuration := time.Duration(timeout*10) * time.Nanosecond
@@ -653,10 +645,16 @@ func ensureNewBlockHeader(t *testing.T, blockCh <-chan tmpubsub.Message, height
 	}
 }
 
-func ensureNewUnlock(t *testing.T, unlockCh <-chan tmpubsub.Message, height int64, round int32) {
+func ensureLock(t *testing.T, lockCh <-chan tmpubsub.Message, height int64, round int32) {
 	t.Helper()
-	ensureNewEvent(t, unlockCh, height, round, ensureTimeout,
-		"Timeout expired while waiting for NewUnlock event")
+	ensureNewEvent(t, lockCh, height, round, ensureTimeout,
+		"Timeout expired while waiting for LockValue event")
+}
+
+func ensureRelock(t *testing.T, relockCh <-chan tmpubsub.Message, height int64, round int32) {
+	t.Helper()
+	ensureNewEvent(t, relockCh, height, round, ensureTimeout,
+		"Timeout expired while waiting for RelockValue event")
 }
 
 func ensureProposal(t *testing.T, proposalCh <-chan tmpubsub.Message, height int64, round int32, propID types.BlockID) {
diff --git a/internal/consensus/state.go b/internal/consensus/state.go
index 49559f15d..00596e36c 100644
--- a/internal/consensus/state.go
+++ b/internal/consensus/state.go
@@ -1413,7 +1413,6 @@ func (cs *State) enterPrevoteWait(ctx context.Context, height int64, round int32
 // Enter: `timeoutPrecommit` after any +2/3 precommits.
 // Enter: +2/3 precomits for block or nil.
 // Lock & precommit the ProposalBlock if we have enough prevotes for it (a POL in this round)
-// else, unlock an existing lock and precommit nil if +2/3 of prevotes were nil,
 // else, precommit nil otherwise.
 func (cs *State) enterPrecommit(ctx context.Context, height int64, round int32) {
 	logger := cs.logger.With("height", height, "round", round)
@@ -1460,21 +1459,9 @@ func (cs *State) enterPrecommit(ctx context.Context, height int64, round int32)
 		panic(fmt.Sprintf("this POLRound should be %v but got %v", round, polRound))
 	}
 
-	// +2/3 prevoted nil. Unlock and precommit nil.
-	if len(blockID.Hash) == 0 {
-		if cs.LockedBlock == nil {
-			logger.Debug("precommit step; +2/3 prevoted for nil")
-		} else {
-			logger.Debug("precommit step; +2/3 prevoted for nil; unlocking")
-			cs.LockedRound = -1
-			cs.LockedBlock = nil
-			cs.LockedBlockParts = nil
-
-			if err := cs.eventBus.PublishEventUnlock(ctx, cs.RoundStateEvent()); err != nil {
-				logger.Error("failed publishing event unlock", "err", err)
-			}
-		}
-
+	// +2/3 prevoted nil. Precommit nil.
+	if blockID.IsNil() {
+		logger.Debug("precommit step; +2/3 prevoted for nil")
 		cs.signAddVote(ctx, tmproto.PrecommitType, nil, types.PartSetHeader{})
 		return
 	}
@@ -1494,7 +1481,9 @@ func (cs *State) enterPrecommit(ctx context.Context, height int64, round int32)
 		return
 	}
 
-	// If +2/3 prevoted for proposal block, stage and precommit it
+	// If greater than 2/3 of the voting power on the network prevoted for
+	// the proposed block, update our locked block to this block and issue a
+	// precommit vote for it.
 	if cs.ProposalBlock.HashesTo(blockID.Hash) {
 		logger.Debug("precommit step; +2/3 prevoted proposal block; locking", "hash", blockID.Hash)
 
@@ -1516,23 +1505,14 @@ func (cs *State) enterPrecommit(ctx context.Context, height int64, round int32)
 	}
 
 	// There was a polka in this round for a block we don't have.
-	// Fetch that block, unlock, and precommit nil.
-	// The +2/3 prevotes for this round is the POL for our unlock.
+	// Fetch that block, and precommit nil.
 	logger.Debug("precommit step; +2/3 prevotes for a block we do not have; voting nil", "block_id", blockID)
 
-	cs.LockedRound = -1
-	cs.LockedBlock = nil
-	cs.LockedBlockParts = nil
-
 	if !cs.ProposalBlockParts.HasHeader(blockID.PartSetHeader) {
 		cs.ProposalBlock = nil
 		cs.ProposalBlockParts = types.NewPartSetFromHeader(blockID.PartSetHeader)
 	}
 
-	if err := cs.eventBus.PublishEventUnlock(ctx, cs.RoundStateEvent()); err != nil {
-		logger.Error("failed publishing event unlock", "err", err)
-	}
-
 	cs.signAddVote(ctx, tmproto.PrecommitType, nil, types.PartSetHeader{})
 }
 
@@ -1640,7 +1620,7 @@ func (cs *State) tryFinalizeCommit(ctx context.Context, height int64) {
 	}
 
 	blockID, ok := cs.Votes.Precommits(cs.CommitRound).TwoThirdsMajority()
-	if !ok || len(blockID.Hash) == 0 {
+	if !ok || blockID.IsNil() {
 		logger.Error("failed attempt to finalize commit; there was no +2/3 majority or +2/3 was for nil")
 		return
 	}
@@ -1967,7 +1947,7 @@ func (cs *State) addProposalBlockPart(
 		// Update Valid* if we can.
 		prevotes := cs.Votes.Prevotes(cs.Round)
 		blockID, hasTwoThirds := prevotes.TwoThirdsMajority()
-		if hasTwoThirds && !blockID.IsZero() && (cs.ValidRound < cs.Round) {
+		if hasTwoThirds && !blockID.IsNil() && (cs.ValidRound < cs.Round) {
 			if cs.ProposalBlock.HashesTo(blockID.Hash) {
 				cs.logger.Debug(
 					"updating valid block to new proposal block",
@@ -2120,33 +2100,13 @@ func (cs *State) addVote(
 		prevotes := cs.Votes.Prevotes(vote.Round)
 		cs.logger.Debug("added vote to prevote", "vote", vote, "prevotes", prevotes.StringShort())
 
-		// If +2/3 prevotes for a block or nil for *any* round:
-		if blockID, ok := prevotes.TwoThirdsMajority(); ok {
-			// There was a polka!
-			// If we're locked but this is a recent polka, unlock.
-			// If it matches our ProposalBlock, update the ValidBlock
-
-			// Unlock if `cs.LockedRound < vote.Round <= cs.Round`
-			// NOTE: If vote.Round > cs.Round, we'll deal with it when we get to vote.Round
-			if (cs.LockedBlock != nil) &&
-				(cs.LockedRound < vote.Round) &&
-				(vote.Round <= cs.Round) &&
-				!cs.LockedBlock.HashesTo(blockID.Hash) {
-
-				cs.logger.Debug("unlocking because of POL", "locked_round", cs.LockedRound, "pol_round", vote.Round)
-
-				cs.LockedRound = -1
-				cs.LockedBlock = nil
-				cs.LockedBlockParts = nil
-
-				if err := cs.eventBus.PublishEventUnlock(ctx, cs.RoundStateEvent()); err != nil {
-					return added, err
-				}
-			}
+		// Check to see if >2/3 of the voting power on the network voted for any non-nil block.
+		if blockID, ok := prevotes.TwoThirdsMajority(); ok && !blockID.IsNil() {
+			// Greater than 2/3 of the voting power on the network voted for some
+			// non-nil block
 
 			// Update Valid* if we can.
-			// NOTE: our proposal block may be nil or not what received a polka..
-			if len(blockID.Hash) != 0 && (cs.ValidRound < vote.Round) && (vote.Round == cs.Round) {
+			if cs.ValidRound < vote.Round && vote.Round == cs.Round {
 				if cs.ProposalBlock.HashesTo(blockID.Hash) {
 					cs.logger.Debug("updating valid block because of POL", "valid_round", cs.ValidRound, "pol_round", vote.Round)
 					cs.ValidRound = vote.Round
@@ -2182,7 +2142,7 @@ func (cs *State) addVote(
 
 		case cs.Round == vote.Round && cstypes.RoundStepPrevote <= cs.Step: // current round
 			blockID, ok := prevotes.TwoThirdsMajority()
-			if ok && (cs.isProposalComplete() || len(blockID.Hash) == 0) {
+			if ok && (cs.isProposalComplete() || blockID.IsNil()) {
 				cs.enterPrecommit(ctx, height, vote.Round)
 			} else if prevotes.HasTwoThirdsAny() {
 				cs.enterPrevoteWait(ctx, height, vote.Round)
@@ -2210,7 +2170,7 @@ func (cs *State) addVote(
 			cs.enterNewRound(ctx, height, vote.Round)
 			cs.enterPrecommit(ctx, height, vote.Round)
 
-			if len(blockID.Hash) != 0 {
+			if !blockID.IsNil() {
 				cs.enterCommit(ctx, height, vote.Round)
 				if cs.config.SkipTimeoutCommit && precommits.HasAll() {
 					cs.enterNewRound(ctx, cs.Height, 0)
diff --git a/internal/consensus/state_test.go b/internal/consensus/state_test.go
index 797f5b197..e1a072553 100644
--- a/internal/consensus/state_test.go
+++ b/internal/consensus/state_test.go
@@ -35,16 +35,22 @@ x * TestFullRound1 - 1 val, full successful round
 x * TestFullRoundNil - 1 val, full round of nil
 x * TestFullRound2 - 2 vals, both required for full round
 LockSuite
-x * TestLockNoPOL - 2 vals, 4 rounds. one val locked, precommits nil every round except first.
-x * TestLockPOLRelock - 4 vals, one precommits, other 3 polka at next round, so we unlock and precomit the polka
-x * TestLockPOLUnlock - 4 vals, one precommits, other 3 polka nil at next round, so we unlock and precomit nil
-x * TestLockPOLSafety1 - 4 vals. We shouldn't change lock based on polka at earlier round
-x * TestLockPOLSafety2 - 4 vals. After unlocking, we shouldn't relock based on polka at earlier round
+x * TestStateLock_NoPOL - 2 vals, 4 rounds. one val locked, precommits nil every round except first.
+x * TestStateLock_POLUpdateLock - 4 vals, one precommits,
+other 3 polka at next round, so we unlock and precomit the polka
+x * TestStateLock_POLRelock - 4 vals, polka in round 1 and polka in round 2.
+Ensure validator updates locked round.
+x_*_TestStateLock_POLDoesNotUnlock 4 vals, one precommits, other 3 polka nil at
+next round, so we precommit nil but maintain lock
+x * TestStateLock_MissingProposalWhenPOLSeenDoesNotUpdateLock - 4 vals, 1 misses proposal but sees POL.
+x * TestStateLock_MissingProposalWhenPOLSeenDoesNotUnlock - 4 vals, 1 misses proposal but sees POL.
+x * TestStateLock_POLSafety1 - 4 vals. We shouldn't change lock based on polka at earlier round
+x * TestStateLock_POLSafety2 - 4 vals. After unlocking, we shouldn't relock based on polka at earlier round
   * TestNetworkLock - once +1/3 precommits, network should be locked
   * TestNetworkLockPOL - once +1/3 precommits, the block with more recent polka is committed
 SlashingSuite
-x * TestSlashingPrevotes - a validator prevoting twice in a round gets slashed
-x * TestSlashingPrecommits - a validator precomitting twice in a round gets slashed
+x * TestStateSlashing_Prevotes - a validator prevoting twice in a round gets slashed
+x * TestStateSlashing_Precommits - a validator precomitting twice in a round gets slashed
 CatchupSuite
   * TestCatchup - if we might be behind and we've seen any 2/3 prevotes, round skip to new round, precommit, or prevote
 HaltSuite
@@ -139,8 +145,7 @@ func TestStateProposerSelection2(t *testing.T) {
 			int(i+2)%len(vss),
 			prop.Address)
 
-		rs := cs1.GetRoundState()
-		signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, rs.ProposalBlockParts.Header(), vss[1:]...)
+		signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vss[1:]...)
 		ensureNewRound(t, newRoundCh, height, i+round+1) // wait for the new round event each round
 		incrementRound(vss[1:]...)
 	}
@@ -462,7 +467,7 @@ func TestStateFullRound2(t *testing.T) {
 
 // two validators, 4 rounds.
 // two vals take turns proposing. val1 locks on first one, precommits nil on everything else
-func TestStateLockNoPOL(t *testing.T) {
+func TestStateLock_NoPOL(t *testing.T) {
 	config := configSetup(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -668,11 +673,12 @@ func TestStateLockNoPOL(t *testing.T) {
 	ensurePrecommit(t, voteCh, height, round)
 }
 
-// 4 vals in two rounds,
-// in round one: v1 precommits, other 3 only prevote so the block isn't committed
-// in round two: v1 prevotes the same block that the node is locked on
-// the others prevote a new block hence v1 changes lock and precommits the new block with the others
-func TestStateLockPOLRelock(t *testing.T) {
+// TestStateLock_POLUpdateLock tests that a validator maintains updates its locked
+// block if the following conditions are met within a round:
+// 1. The validator received a valid proposal for the block
+// 2. The validator received prevotes representing greater than 2/3 of the voting
+// power on the network for the block.
+func TestStateLock_POLUpdateLock(t *testing.T) {
 	config := configSetup(t)
 	logger := log.TestingLogger()
 
@@ -691,16 +697,18 @@ func TestStateLockPOLRelock(t *testing.T) {
 	require.NoError(t, err)
 	addr := pv1.Address()
 	voteCh := subscribeToVoter(ctx, t, cs1, addr)
+	lockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryLock)
 	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
-	newBlockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewBlockHeader)
-
-	// everything done from perspective of cs1
 
 	/*
-		Round1 (cs1, B) // B B B B// B nil B nil
+		Round 0:
+		cs1 creates a proposal for block B.
+		Send a prevote for B from each of the validators to cs1.
+		Send a precommit for nil from all of the validators to cs1.
 
-		eg. vs2 and vs4 didn't see the 2/3 prevotes
+		This ensures that cs1 will lock on B in this round but not precommit it.
 	*/
+	t.Log("### Starting Round 0")
 
 	// start round and wait for propose and prevote
 	startTestRound(ctx, cs1, height, round)
@@ -711,99 +719,211 @@ func TestStateLockPOLRelock(t *testing.T) {
 	theBlockHash := rs.ProposalBlock.Hash()
 	theBlockParts := rs.ProposalBlockParts.Header()
 
-	ensurePrevote(t, voteCh, height, round) // prevote
+	ensurePrevote(t, voteCh, height, round)
 
 	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, theBlockHash, theBlockParts, vs2, vs3, vs4)
 
-	ensurePrecommit(t, voteCh, height, round) // our precommit
-	// the proposed block should now be locked and our precommit added
+	// check that the validator generates a Lock event.
+	ensureLock(t, lockCh, height, round)
+
+	// the proposed block should now be locked and our precommit added.
+	ensurePrecommit(t, voteCh, height, round)
 	validatePrecommit(ctx, t, cs1, round, round, vss[0], theBlockHash, theBlockHash)
 
-	// add precommits from the rest
+	// add precommits from the rest of the validators.
 	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
-	// before we timeout to the new round set the new proposal
-	cs2 := newState(ctx, t, logger, cs1.state, vs2, kvstore.NewApplication())
-
-	prop, propBlock := decideProposal(ctx, t, cs2, vs2, vs2.Height, vs2.Round+1)
-	if prop == nil || propBlock == nil {
-		t.Fatal("Failed to create proposal block with vs2")
-	}
-	propBlockParts, err := propBlock.MakePartSet(partSize)
-	require.NoError(t, err)
-
-	propBlockHash := propBlock.Hash()
-	require.NotEqual(t, propBlockHash, theBlockHash)
-
-	incrementRound(vs2, vs3, vs4)
-
-	// timeout to new round
+	// timeout to new round.
 	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
 
-	round++ // moving to the next round
-	//XXX: this isnt guaranteed to get there before the timeoutPropose ...
-	if err := cs1.SetProposalAndBlock(ctx, prop, propBlock, propBlockParts, "some peer"); err != nil {
+	/*
+		Round 1:
+		Create a block, D and send a proposal for it to cs1
+		Send a prevote for D from each of the validators to cs1.
+		Send a precommit for nil from all of the validtors to cs1.
+
+		Check that cs1 is now locked on the new block, D and no longer on the old block.
+	*/
+	t.Log("### Starting Round 1")
+	incrementRound(vs2, vs3, vs4)
+	round++
+
+	// Generate a new proposal block.
+	cs2 := newState(ctx, t, logger, cs1.state, vs2, kvstore.NewApplication())
+	require.NoError(t, err)
+	propR1, propBlockR1 := decideProposal(ctx, t, cs2, vs2, vs2.Height, vs2.Round)
+	propBlockR1Parts, err := propBlockR1.MakePartSet(partSize)
+	require.NoError(t, err)
+	propBlockR1Hash := propBlockR1.Hash()
+	require.NotEqual(t, propBlockR1Hash, theBlockHash)
+	if err := cs1.SetProposalAndBlock(ctx, propR1, propBlockR1, propBlockR1Parts, "some peer"); err != nil {
 		t.Fatal(err)
 	}
 
 	ensureNewRound(t, newRoundCh, height, round)
-	t.Log("### ONTO ROUND 1")
 
-	/*
-		Round2 (vs2, C) // B C C C // C C C _)
-
-		cs1 changes lock!
-	*/
-
-	// now we're on a new round and not the proposer
-	// but we should receive the proposal
+	// ensure that the validator receives the proposal.
 	ensureNewProposal(t, proposalCh, height, round)
 
-	// go to prevote, node should prevote for locked block (not the new proposal) - this is relocking
+	// Prevote our locked block.
+	// TODO: Ensure we prevote for the proposal if it is valid and from a round greater than
+	// the valid round: https://github.com/tendermint/tendermint/issues/6850.
 	ensurePrevote(t, voteCh, height, round)
 	validatePrevote(ctx, t, cs1, round, vss[0], theBlockHash)
 
-	// now lets add prevotes from everyone else for the new block
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, propBlockHash, propBlockParts.Header(), vs2, vs3, vs4)
+	// Add prevotes from the remainder of the validators for the new locked block.
+	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, propBlockR1Hash, propBlockR1Parts.Header(), vs2, vs3, vs4)
+
+	// Check that we lock on a new block.
+	ensureLock(t, lockCh, height, round)
 
 	ensurePrecommit(t, voteCh, height, round)
-	// we should have unlocked and locked on the new block, sending a precommit for this new block
-	validatePrecommit(ctx, t, cs1, round, round, vss[0], propBlockHash, propBlockHash)
 
-	// more prevote creating a majority on the new block and this is then committed
-	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, propBlockHash, propBlockParts.Header(), vs2, vs3)
-	ensureNewBlockHeader(t, newBlockCh, height, propBlockHash)
-
-	ensureNewRound(t, newRoundCh, height+1, 0)
+	// We should now be locked on the new block and prevote it since we saw a sufficient amount
+	// prevote for the block.
+	validatePrecommit(ctx, t, cs1, round, round, vss[0], propBlockR1Hash, propBlockR1Hash)
 }
 
-// 4 vals, one precommits, other 3 polka at next round, so we unlock and precomit the polka
-func TestStateLockPOLUnlock(t *testing.T) {
-	config := configSetup(t)
+// TestStateLock_POLRelock tests that a validator updates its locked round if
+// it receives votes representing over 2/3 of the voting power on the network
+// for a block that it is already locked in.
+func TestStateLock_POLRelock(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
+	config := configSetup(t)
 
 	cs1, vss := randState(ctx, t, config, log.TestingLogger(), 4)
 	vs2, vs3, vs4 := vss[1], vss[2], vss[3]
 	height, round := cs1.Height, cs1.Round
 
-	partSize := types.BlockPartSizeBytes
-
-	proposalCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryCompleteProposal)
 	timeoutWaitCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryTimeoutWait)
-	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
-	unlockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryUnlock)
+	proposalCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryCompleteProposal)
 	pv1, err := cs1.privValidator.GetPubKey(ctx)
 	require.NoError(t, err)
 	addr := pv1.Address()
 	voteCh := subscribeToVoter(ctx, t, cs1, addr)
-
-	// everything done from perspective of cs1
+	lockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryLock)
+	relockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryRelock)
+	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
 
 	/*
-		Round1 (cs1, B) // B B B B // B nil B nil
-		eg. didn't see the 2/3 prevotes
+		Round 0:
+		cs1 creates a proposal for block B.
+		Send a prevote for B from each of the validators to cs1.
+		Send a precommit for nil from all of the validators to cs1.
+		This ensures that cs1 will lock on B in this round but not precommit it.
 	*/
+	t.Log("### Starting Round 0")
+
+	startTestRound(ctx, cs1, height, round)
+
+	ensureNewRound(t, newRoundCh, height, round)
+	ensureNewProposal(t, proposalCh, height, round)
+	rs := cs1.GetRoundState()
+	theBlock := rs.ProposalBlock
+	theBlockHash := rs.ProposalBlock.Hash()
+	theBlockParts := rs.ProposalBlockParts
+
+	ensurePrevote(t, voteCh, height, round)
+
+	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, theBlockHash, theBlockParts.Header(), vs2, vs3, vs4)
+
+	// check that the validator generates a Lock event.
+	ensureLock(t, lockCh, height, round)
+
+	// the proposed block should now be locked and our precommit added.
+	ensurePrecommit(t, voteCh, height, round)
+	validatePrecommit(ctx, t, cs1, round, round, vss[0], theBlockHash, theBlockHash)
+
+	// add precommits from the rest of the validators.
+	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
+
+	// timeout to new round.
+	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
+
+	/*
+		Round 1:
+		Create a proposal for block B, the same block from round 1.
+		Send a prevote for B from each of the validators to cs1.
+		Send a precommit for nil from all of the validtors to cs1.
+
+		Check that cs1 updates its 'locked round' value to the current round.
+	*/
+	t.Log("### Starting Round 1")
+	incrementRound(vs2, vs3, vs4)
+	round++
+	propBlockID := types.BlockID{Hash: theBlockHash, PartSetHeader: theBlockParts.Header()}
+	propR1 := types.NewProposal(height, round, cs1.ValidRound, propBlockID)
+	p := propR1.ToProto()
+	if err := vs2.SignProposal(context.Background(), cs1.state.ChainID, p); err != nil {
+		t.Fatalf("error signing proposal: %s", err)
+	}
+	propR1.Signature = p.Signature
+	if err := cs1.SetProposalAndBlock(ctx, propR1, theBlock, theBlockParts, ""); err != nil {
+		t.Fatal(err)
+	}
+
+	ensureNewRound(t, newRoundCh, height, round)
+
+	// ensure that the validator receives the proposal.
+	ensureNewProposal(t, proposalCh, height, round)
+
+	// Prevote our locked block.
+	// TODO: Ensure we prevote for the proposal if it is valid and from a round greater than
+	// the valid round: https://github.com/tendermint/tendermint/issues/6850.
+	ensurePrevote(t, voteCh, height, round)
+	validatePrevote(ctx, t, cs1, round, vss[0], theBlockHash)
+
+	// Add prevotes from the remainder of the validators for the locked block.
+	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, theBlockHash, theBlockParts.Header(), vs2, vs3, vs4)
+
+	// Check that we relock.
+	ensureRelock(t, relockCh, height, round)
+
+	ensurePrecommit(t, voteCh, height, round)
+
+	// We should now be locked on the same block but with an updated locked round.
+	validatePrecommit(ctx, t, cs1, round, round, vss[0], theBlockHash, theBlockHash)
+}
+
+// TestStateLock_POLDoesNotUnlock tests that a validator maintains its locked block
+// despite receiving +2/3 nil prevotes and nil precommits from other validators.
+// Tendermint used to 'unlock' its locked block when greater than 2/3 prevotes
+// for a nil block were seen. This behavior has been removed and this test ensures
+// that it has been completely removed.
+func TestStateLock_POLDoesNotUnlock(t *testing.T) {
+	config := configSetup(t)
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	/*
+		All of the assertions in this test occur on the `cs1` validator.
+		The test sends signed votes from the other validators to cs1 and
+		cs1's state is then examined to verify that it now matches the expected
+		state.
+	*/
+
+	cs1, vss := randState(ctx, t, config, log.TestingLogger(), 4)
+	vs2, vs3, vs4 := vss[1], vss[2], vss[3]
+	height, round := cs1.Height, cs1.Round
+
+	proposalCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryCompleteProposal)
+	timeoutWaitCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryTimeoutWait)
+	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
+	lockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryLock)
+	pv1, err := cs1.privValidator.GetPubKey(context.Background())
+	require.NoError(t, err)
+	addr := pv1.Address()
+	voteCh := subscribeToVoter(ctx, t, cs1, addr)
+
+	/*
+		Round 0:
+		Create a block, B
+		Send a prevote for B from each of the validators to `cs1`.
+		Send a precommit for B from one of the validtors to `cs1`.
+
+		This ensures that cs1 will lock on B in this round.
+	*/
+	t.Log("#### ONTO ROUND 0")
 
 	// start round and wait for propose and prevote
 	startTestRound(ctx, cs1, height, round)
@@ -819,63 +939,98 @@ func TestStateLockPOLUnlock(t *testing.T) {
 
 	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, theBlockHash, theBlockParts, vs2, vs3, vs4)
 
+	// the validator should have locked a block in this round.
+	ensureLock(t, lockCh, height, round)
+
 	ensurePrecommit(t, voteCh, height, round)
-	// the proposed block should now be locked and our precommit added
+	// the proposed block should now be locked and our should be for this locked block.
+
 	validatePrecommit(ctx, t, cs1, round, round, vss[0], theBlockHash, theBlockHash)
 
-	// add precommits from the rest
+	// Add precommits from the other validators.
+	// We only issue 1/2 Precommits for the block in this round.
+	// This ensures that the validator being tested does not commit the block.
+	// We do not want the validator to commit the block because we want the test
+	// test to proceeds to the next consensus round.
 	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs4)
 	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, theBlockHash, theBlockParts, vs3)
 
-	// before we time out into new round, set next proposal block
-	prop, propBlock := decideProposal(ctx, t, cs1, vs2, vs2.Height, vs2.Round+1)
-	propBlockParts, err := propBlock.MakePartSet(partSize)
-	require.NoError(t, err)
-
 	// timeout to new round
 	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
-	rs = cs1.GetRoundState()
-	lockedBlockHash := rs.LockedBlock.Hash()
 
-	incrementRound(vs2, vs3, vs4)
-	round++ // moving to the next round
-
-	ensureNewRound(t, newRoundCh, height, round)
-	t.Log("#### ONTO ROUND 1")
 	/*
-		Round2 (vs2, C) // B nil nil nil // nil nil nil _
-		cs1 unlocks!
+		Round 1:
+		Send a prevote for nil from >2/3 of the validators to `cs1`.
+		Check that cs1 maintains its lock on B but precommits nil.
+		Send a precommit for nil from >2/3 of the validators to `cs1`.
 	*/
-	//XXX: this isnt guaranteed to get there before the timeoutPropose ...
-	if err := cs1.SetProposalAndBlock(ctx, prop, propBlock, propBlockParts, "some peer"); err != nil {
+	t.Log("#### ONTO ROUND 1")
+	round++
+	incrementRound(vs2, vs3, vs4)
+	prop, propBlock := decideProposal(ctx, t, cs1, vs2, vs2.Height, vs2.Round)
+	propBlockParts, err := propBlock.MakePartSet(types.BlockPartSizeBytes)
+	require.NoError(t, err)
+	if err := cs1.SetProposalAndBlock(ctx, prop, propBlock, propBlockParts, ""); err != nil {
 		t.Fatal(err)
 	}
 
+	ensureNewRound(t, newRoundCh, height, round)
+
 	ensureNewProposal(t, proposalCh, height, round)
 
-	// go to prevote, prevote for locked block (not proposal)
+	// prevote for the locked block. We do not currently prevote for the
+	// proposal.
+	// TODO: do not prevote the locked block if it does not match the proposal.
+	// (https://github.com/tendermint/tendermint/issues/6850)
 	ensurePrevote(t, voteCh, height, round)
-	validatePrevote(ctx, t, cs1, round, vss[0], lockedBlockHash)
-	// now lets add prevotes from everyone else for nil (a polka!)
+	validatePrevote(ctx, t, cs1, round, vss[0], theBlockHash)
+	// add >2/3 prevotes for nil from all other validators
 	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
-	// the polka makes us unlock and precommit nil
-	ensureNewUnlock(t, unlockCh, height, round)
 	ensurePrecommit(t, voteCh, height, round)
 
-	// we should have unlocked and committed nil
-	// NOTE: since we don't relock on nil, the lock round is -1
-	validatePrecommit(ctx, t, cs1, round, -1, vss[0], nil, nil)
+	// verify that we haven't update our locked block since the first round
+	validatePrecommit(ctx, t, cs1, round, 0, vss[0], nil, theBlockHash)
+
+	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
+	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
+
+	/*
+		Round 2:
+		The validator cs1 saw >2/3 precommits for nil in the previous round.
+		Send the validator >2/3 prevotes for nil and ensure that it did not
+		unlock its block at the end of the previous round.
+	*/
+	t.Log("#### ONTO ROUND 2")
+	round++
+	incrementRound(vs2, vs3, vs4)
+	prop, propBlock = decideProposal(ctx, t, cs1, vs3, vs3.Height, vs3.Round)
+	propBlockParts, err = propBlock.MakePartSet(types.BlockPartSizeBytes)
+	require.NoError(t, err)
+	if err := cs1.SetProposalAndBlock(ctx, prop, propBlock, propBlockParts, ""); err != nil {
+		t.Fatal(err)
+	}
+
+	ensureNewRound(t, newRoundCh, height, round)
+
+	ensureNewProposal(t, proposalCh, height, round)
+
+	ensurePrevote(t, voteCh, height, round)
+	validatePrevote(ctx, t, cs1, round, vss[0], theBlockHash)
+
+	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
+
+	ensurePrecommit(t, voteCh, height, round)
+
+	// verify that we haven't update our locked block since the first round
+	validatePrecommit(ctx, t, cs1, round, 0, vss[0], nil, theBlockHash)
 
-	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3)
-	ensureNewRound(t, newRoundCh, height, round+1)
 }
 
-// 4 vals, v1 locks on proposed block in the first round but the other validators only prevote
-// In the second round, v1 misses the proposal but sees a majority prevote an unknown block so
-// v1 should unlock and precommit nil. In the third round another block is proposed, all vals
-// prevote and now v1 can lock onto the third block and precommit that
-func TestStateLockPOLUnlockOnUnknownBlock(t *testing.T) {
+// TestStateLock_MissingProposalWhenPOLSeenDoesNotUnlock tests that observing
+// a two thirds majority for a block does not cause a validator to upate its lock on the
+// new block if a proposal was not seen for that block.
+func TestStateLock_MissingProposalWhenPOLSeenDoesNotUpdateLock(t *testing.T) {
 	config := configSetup(t)
 	logger := log.TestingLogger()
 	ctx, cancel := context.WithCancel(context.Background())
@@ -895,13 +1050,15 @@ func TestStateLockPOLUnlockOnUnknownBlock(t *testing.T) {
 	addr := pv1.Address()
 	voteCh := subscribeToVoter(ctx, t, cs1, addr)
 	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
-	// everything done from perspective of cs1
-
 	/*
-		Round0 (cs1, A) // A A A A// A nil nil nil
-	*/
+		Round 0:
+		cs1 creates a proposal for block B.
+		Send a prevote for B from each of the validators to cs1.
+		Send a precommit for nil from all of the validators to cs1.
 
-	// start round and wait for propose and prevote
+		This ensures that cs1 will lock on B in this round but not precommit it.
+	*/
+	t.Log("### Starting Round 0")
 	startTestRound(ctx, cs1, height, round)
 
 	ensureNewRound(t, newRoundCh, height, round)
@@ -921,9 +1078,22 @@ func TestStateLockPOLUnlockOnUnknownBlock(t *testing.T) {
 	// add precommits from the rest
 	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
-	// before we timeout to the new round set the new proposal
+	// timeout to new round
+	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
+
+	/*
+		Round 1:
+		Create a new block, D but do not send it to cs1.
+		Send a prevote for D from each of the validators to cs1.
+
+		Check that cs1 does not update its locked block to this missed block D.
+	*/
+	t.Log("### Starting Round 1")
+	incrementRound(vs2, vs3, vs4)
+	round++
 	cs2 := newState(ctx, t, logger, cs1.state, vs2, kvstore.NewApplication())
-	prop, propBlock := decideProposal(ctx, t, cs2, vs2, vs2.Height, vs2.Round+1)
+	require.NoError(t, err)
+	prop, propBlock := decideProposal(ctx, t, cs2, vs2, vs2.Height, vs2.Round)
 	if prop == nil || propBlock == nil {
 		t.Fatal("Failed to create proposal block with vs2")
 	}
@@ -933,21 +1103,7 @@ func TestStateLockPOLUnlockOnUnknownBlock(t *testing.T) {
 	secondBlockHash := propBlock.Hash()
 	require.NotEqual(t, secondBlockHash, firstBlockHash)
 
-	incrementRound(vs2, vs3, vs4)
-
-	// timeout to new round
-	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
-
-	round++ // moving to the next round
-
 	ensureNewRound(t, newRoundCh, height, round)
-	t.Log("### ONTO ROUND 1")
-
-	/*
-		Round1 (vs2, B) // A B B B // nil nil nil nil)
-	*/
-
-	// now we're on a new round but v1 misses the proposal
 
 	// go to prevote, node should prevote for locked block (not the new proposal) - this is relocking
 	ensurePrevote(t, voteCh, height, round)
@@ -957,61 +1113,89 @@ func TestStateLockPOLUnlockOnUnknownBlock(t *testing.T) {
 	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, secondBlockHash, secondBlockParts.Header(), vs2, vs3, vs4)
 
 	ensurePrecommit(t, voteCh, height, round)
-	// we should have unlocked and locked on the new block, sending a precommit for this new block
+	validatePrecommit(ctx, t, cs1, round, 0, vss[0], nil, firstBlockHash)
+}
+
+// TestStateLock_DoesNotLockOnOldProposal tests that observing
+// a two thirds majority for a block does not cause a validator to lock on the
+// block if a proposal was not seen for that block in the current round, but
+// was seen in a previous round.
+func TestStateLock_DoesNotLockOnOldProposal(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	config := configSetup(t)
+
+	cs1, vss := randState(ctx, t, config, log.TestingLogger(), 4)
+	vs2, vs3, vs4 := vss[1], vss[2], vss[3]
+	height, round := cs1.Height, cs1.Round
+
+	timeoutWaitCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryTimeoutWait)
+	proposalCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryCompleteProposal)
+	pv1, err := cs1.privValidator.GetPubKey(context.Background())
+	require.NoError(t, err)
+	addr := pv1.Address()
+	voteCh := subscribeToVoter(ctx, t, cs1, addr)
+	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
+	/*
+		Round 0:
+		cs1 creates a proposal for block B.
+		Send a prevote for nil from each of the validators to cs1.
+		Send a precommit for nil from all of the validators to cs1.
+
+		This ensures that cs1 will not lock on B.
+	*/
+	t.Log("### Starting Round 0")
+	startTestRound(ctx, cs1, height, round)
+
+	ensureNewRound(t, newRoundCh, height, round)
+	ensureNewProposal(t, proposalCh, height, round)
+	rs := cs1.GetRoundState()
+	firstBlockHash := rs.ProposalBlock.Hash()
+	firstBlockParts := rs.ProposalBlockParts.Header()
+
+	ensurePrevote(t, voteCh, height, round)
+
+	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
+
+	// The proposed block should not have been locked.
+	ensurePrecommit(t, voteCh, height, round)
 	validatePrecommit(ctx, t, cs1, round, -1, vss[0], nil, nil)
 
-	if err := cs1.SetProposalAndBlock(ctx, prop, propBlock, secondBlockParts, "some peer"); err != nil {
-		t.Fatal(err)
-	}
-
-	// more prevote creating a majority on the new block and this is then committed
 	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
-	// before we timeout to the new round set the new proposal
-	cs3 := newState(ctx, t, logger, cs1.state, vs3, kvstore.NewApplication())
-	require.NoError(t, err)
-	prop, propBlock = decideProposal(ctx, t, cs3, vs3, vs3.Height, vs3.Round+1)
-	if prop == nil || propBlock == nil {
-		t.Fatal("Failed to create proposal block with vs2")
-	}
-	thirdPropBlockParts, err := propBlock.MakePartSet(partSize)
-	require.NoError(t, err)
-	thirdPropBlockHash := propBlock.Hash()
-	require.NotEqual(t, secondBlockHash, thirdPropBlockHash)
-
 	incrementRound(vs2, vs3, vs4)
 
 	// timeout to new round
 	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
 
-	round++ // moving to the next round
-	ensureNewRound(t, newRoundCh, height, round)
-	t.Log("### ONTO ROUND 2")
-
 	/*
-		Round2 (vs3, C) // C C C C // C nil nil nil)
+		Round 1:
+		No proposal new proposal is created.
+		Send a prevote for B, the block from round 0, from each of the validators to cs1.
+		Send a precommit for nil from all of the validators to cs1.
+		cs1 saw a POL for the block it saw in round 0. We ensure that it does not
+		lock on this block, since it did not see a proposal for it in this round.
 	*/
-
-	if err := cs1.SetProposalAndBlock(ctx, prop, propBlock, thirdPropBlockParts, "some peer"); err != nil {
-		t.Fatal(err)
-	}
+	t.Log("### Starting Round 1")
+	round++
+	ensureNewRound(t, newRoundCh, height, round)
 
 	ensurePrevote(t, voteCh, height, round)
-	// we are no longer locked to the first block so we should be able to prevote
-	validatePrevote(ctx, t, cs1, round, vss[0], thirdPropBlockHash)
+	validatePrevote(ctx, t, cs1, round, vss[0], nil) // All validators prevote for the old block.
 
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, thirdPropBlockHash, thirdPropBlockParts.Header(), vs2, vs3, vs4)
+	// All validators prevote for the old block.
+	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, firstBlockHash, firstBlockParts, vs2, vs3, vs4)
 
+	// Make sure that cs1 did not lock on the block since it did not receive a proposal for it.
 	ensurePrecommit(t, voteCh, height, round)
-	// we have a majority, now vs1 can change lock to the third block
-	validatePrecommit(ctx, t, cs1, round, round, vss[0], thirdPropBlockHash, thirdPropBlockHash)
+	validatePrecommit(ctx, t, cs1, round, -1, vss[0], nil, nil)
 }
 
 // 4 vals
 // a polka at round 1 but we miss it
 // then a polka at round 2 that we lock on
 // then we see the polka from round 1 but shouldn't unlock
-func TestStateLockPOLSafety1(t *testing.T) {
+func TestStateLock_POLSafety1(t *testing.T) {
 	config := configSetup(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -1139,7 +1323,7 @@ func TestStateLockPOLSafety1(t *testing.T) {
 
 // What we want:
 // dont see P0, lock on P1 at R1, dont unlock using P0 at R2
-func TestStateLockPOLSafety2(t *testing.T) {
+func TestStateLock_POLSafety2(t *testing.T) {
 	config := configSetup(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -1153,7 +1337,6 @@ func TestStateLockPOLSafety2(t *testing.T) {
 	proposalCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryCompleteProposal)
 	timeoutWaitCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryTimeoutWait)
 	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
-	unlockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryUnlock)
 	pv1, err := cs1.privValidator.GetPubKey(ctx)
 	require.NoError(t, err)
 	addr := pv1.Address()
@@ -1231,23 +1414,22 @@ func TestStateLockPOLSafety2(t *testing.T) {
 	*/
 	ensureNewProposal(t, proposalCh, height, round)
 
-	ensureNoNewUnlock(t, unlockCh)
 	ensurePrevote(t, voteCh, height, round)
 	validatePrevote(ctx, t, cs1, round, vss[0], propBlockHash1)
 
 }
 
 // 4 vals.
-// polka P0 at R0 for B0. We lock B0 on P0 at R0. P0 unlocks value at R1.
+// polka P0 at R0 for B0. We lock B0 on P0 at R0.
 
 // What we want:
 // P0 proposes B0 at R3.
 func TestProposeValidBlock(t *testing.T) {
-	config := configSetup(t)
+	cfg := configSetup(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	cs1, vss := randState(ctx, t, config, log.TestingLogger(), 4)
+	cs1, vss := randState(ctx, t, cfg, log.TestingLogger(), 4)
 	vs2, vs3, vs4 := vss[1], vss[2], vss[3]
 	height, round := cs1.Height, cs1.Round
 
@@ -1257,7 +1439,6 @@ func TestProposeValidBlock(t *testing.T) {
 	timeoutWaitCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryTimeoutWait)
 	timeoutProposeCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryTimeoutPropose)
 	newRoundCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryNewRound)
-	unlockCh := subscribe(ctx, t, cs1.eventBus, types.EventQueryUnlock)
 	pv1, err := cs1.privValidator.GetPubKey(ctx)
 	require.NoError(t, err)
 	addr := pv1.Address()
@@ -1278,15 +1459,16 @@ func TestProposeValidBlock(t *testing.T) {
 	// the others sign a polka
 	bps, err := propBlock.MakePartSet(partSize)
 	require.NoError(t, err)
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType,
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrevoteType,
 		propBlockHash, bps.Header(), vs2,
 		vs3, vs4)
 
 	ensurePrecommit(t, voteCh, height, round)
-	// we should have precommitted
+	// we should have precommitted the proposed block in this round.
+
 	validatePrecommit(ctx, t, cs1, round, round, vss[0], propBlockHash, propBlockHash)
 
-	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
 	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Precommit(round).Nanoseconds())
 
@@ -1294,8 +1476,7 @@ func TestProposeValidBlock(t *testing.T) {
 	round++ // moving to the next round
 
 	ensureNewRound(t, newRoundCh, height, round)
-
-	t.Log("### ONTO ROUND 2")
+	t.Log("### ONTO ROUND 1")
 
 	// timeout of propose
 	ensureNewTimeout(t, timeoutProposeCh, height, round, cs1.config.Propose(round).Nanoseconds())
@@ -1303,20 +1484,19 @@ func TestProposeValidBlock(t *testing.T) {
 	ensurePrevote(t, voteCh, height, round)
 	validatePrevote(ctx, t, cs1, round, vss[0], propBlockHash)
 
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
-
-	ensureNewUnlock(t, unlockCh, height, round)
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
 	ensurePrecommit(t, voteCh, height, round)
-	// we should have precommitted
-	validatePrecommit(ctx, t, cs1, round, -1, vss[0], nil, nil)
+	// we should have precommitted nil during this round because we received
+	// >2/3 precommits for nil from the other validators.
+	validatePrecommit(ctx, t, cs1, round, 0, vss[0], nil, propBlockHash)
 
 	incrementRound(vs2, vs3, vs4)
 	incrementRound(vs2, vs3, vs4)
 
-	signAddVotes(ctx, t, config, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrecommitType, nil, types.PartSetHeader{}, vs2, vs3, vs4)
 
-	round += 2 // moving to the next round
+	round += 2 // increment by multiple rounds
 
 	ensureNewRound(t, newRoundCh, height, round)
 	t.Log("### ONTO ROUND 3")
@@ -1327,8 +1507,6 @@ func TestProposeValidBlock(t *testing.T) {
 
 	ensureNewRound(t, newRoundCh, height, round)
 
-	t.Log("### ONTO ROUND 4")
-
 	ensureNewProposal(t, proposalCh, height, round)
 
 	rs = cs1.GetRoundState()
@@ -1341,11 +1519,11 @@ func TestProposeValidBlock(t *testing.T) {
 // What we want:
 // P0 miss to lock B but set valid block to B after receiving delayed prevote.
 func TestSetValidBlockOnDelayedPrevote(t *testing.T) {
-	config := configSetup(t)
+	cfg := configSetup(t)
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 
-	cs1, vss := randState(ctx, t, config, log.TestingLogger(), 4)
+	cs1, vss := randState(ctx, t, cfg, log.TestingLogger(), 4)
 	vs2, vs3, vs4 := vss[1], vss[2], vss[3]
 	height, round := cs1.Height, cs1.Round
 
@@ -1375,10 +1553,10 @@ func TestSetValidBlockOnDelayedPrevote(t *testing.T) {
 	validatePrevote(ctx, t, cs1, round, vss[0], propBlockHash)
 
 	// vs2 send prevote for propBlock
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, propBlockHash, propBlockParts.Header(), vs2)
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrevoteType, propBlockHash, propBlockParts.Header(), vs2)
 
 	// vs3 send prevote nil
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs3)
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrevoteType, nil, types.PartSetHeader{}, vs3)
 
 	ensureNewTimeout(t, timeoutWaitCh, height, round, cs1.config.Prevote(round).Nanoseconds())
 
@@ -1393,7 +1571,7 @@ func TestSetValidBlockOnDelayedPrevote(t *testing.T) {
 	assert.True(t, rs.ValidRound == -1)
 
 	// vs2 send (delayed) prevote for propBlock
-	signAddVotes(ctx, t, config, cs1, tmproto.PrevoteType, propBlockHash, propBlockParts.Header(), vs4)
+	signAddVotes(ctx, t, cfg, cs1, tmproto.PrevoteType, propBlockHash, propBlockParts.Header(), vs4)
 
 	ensureNewValidBlock(t, validBlockCh, height, round)
 
@@ -1835,7 +2013,7 @@ func TestResetTimeoutPrecommitUponNewHeight(t *testing.T) {
 // TODO: Slashing
 
 /*
-func TestStateSlashingPrevotes(t *testing.T) {
+func TestStateSlashing_Prevotes(t *testing.T) {
 	cs1, vss := randState(2)
 	vs2 := vss[1]
 
@@ -1870,7 +2048,7 @@ func TestStateSlashingPrevotes(t *testing.T) {
 	// XXX: Check for existence of Dupeout info
 }
 
-func TestStateSlashingPrecommits(t *testing.T) {
+func TestStateSlashing_Precommits(t *testing.T) {
 	cs1, vss := randState(2)
 	vs2 := vss[1]
 
diff --git a/internal/eventbus/event_bus.go b/internal/eventbus/event_bus.go
index 58f357165..327330ba7 100644
--- a/internal/eventbus/event_bus.go
+++ b/internal/eventbus/event_bus.go
@@ -185,10 +185,6 @@ func (b *EventBus) PublishEventPolka(ctx context.Context, data types.EventDataRo
 	return b.Publish(ctx, types.EventPolkaValue, data)
 }
 
-func (b *EventBus) PublishEventUnlock(ctx context.Context, data types.EventDataRoundState) error {
-	return b.Publish(ctx, types.EventUnlockValue, data)
-}
-
 func (b *EventBus) PublishEventRelock(ctx context.Context, data types.EventDataRoundState) error {
 	return b.Publish(ctx, types.EventRelockValue, data)
 }
diff --git a/internal/eventbus/event_bus_test.go b/internal/eventbus/event_bus_test.go
index 6569d54fd..ffe14dd84 100644
--- a/internal/eventbus/event_bus_test.go
+++ b/internal/eventbus/event_bus_test.go
@@ -385,7 +385,6 @@ func TestEventBusPublish(t *testing.T) {
 	require.NoError(t, eventBus.PublishEventNewRound(ctx, types.EventDataNewRound{}))
 	require.NoError(t, eventBus.PublishEventCompleteProposal(ctx, types.EventDataCompleteProposal{}))
 	require.NoError(t, eventBus.PublishEventPolka(ctx, types.EventDataRoundState{}))
-	require.NoError(t, eventBus.PublishEventUnlock(ctx, types.EventDataRoundState{}))
 	require.NoError(t, eventBus.PublishEventRelock(ctx, types.EventDataRoundState{}))
 	require.NoError(t, eventBus.PublishEventLock(ctx, types.EventDataRoundState{}))
 	require.NoError(t, eventBus.PublishEventValidatorSetUpdates(ctx, types.EventDataValidatorSetUpdates{}))
@@ -487,7 +486,6 @@ var events = []string{
 	types.EventTimeoutProposeValue,
 	types.EventCompleteProposalValue,
 	types.EventPolkaValue,
-	types.EventUnlockValue,
 	types.EventLockValue,
 	types.EventRelockValue,
 	types.EventTimeoutWaitValue,
@@ -508,7 +506,6 @@ var queries = []tmpubsub.Query{
 	types.EventQueryTimeoutPropose,
 	types.EventQueryCompleteProposal,
 	types.EventQueryPolka,
-	types.EventQueryUnlock,
 	types.EventQueryLock,
 	types.EventQueryRelock,
 	types.EventQueryTimeoutWait,
diff --git a/internal/test/factory/block.go b/internal/test/factory/block.go
index 654572ddf..3fd34cdc5 100644
--- a/internal/test/factory/block.go
+++ b/internal/test/factory/block.go
@@ -51,7 +51,7 @@ func MakeHeader(t *testing.T, h *types.Header) *types.Header {
 	if h.Height == 0 {
 		h.Height = 1
 	}
-	if h.LastBlockID.IsZero() {
+	if h.LastBlockID.IsNil() {
 		h.LastBlockID = MakeBlockID()
 	}
 	if h.ChainID == "" {
diff --git a/types/block.go b/types/block.go
index e09d1830a..475f88953 100644
--- a/types/block.go
+++ b/types/block.go
@@ -883,7 +883,7 @@ func (commit *Commit) ValidateBasic() error {
 	}
 
 	if commit.Height >= 1 {
-		if commit.BlockID.IsZero() {
+		if commit.BlockID.IsNil() {
 			return errors.New("commit cannot be for nil block")
 		}
 
@@ -1204,8 +1204,8 @@ func (blockID BlockID) ValidateBasic() error {
 	return nil
 }
 
-// IsZero returns true if this is the BlockID of a nil block.
-func (blockID BlockID) IsZero() bool {
+// IsNil returns true if this is the BlockID of a nil block.
+func (blockID BlockID) IsNil() bool {
 	return len(blockID.Hash) == 0 &&
 		blockID.PartSetHeader.IsZero()
 }
diff --git a/types/canonical.go b/types/canonical.go
index 01c3d851d..fc07ab477 100644
--- a/types/canonical.go
+++ b/types/canonical.go
@@ -21,7 +21,7 @@ func CanonicalizeBlockID(bid tmproto.BlockID) *tmproto.CanonicalBlockID {
 		panic(err)
 	}
 	var cbid *tmproto.CanonicalBlockID
-	if rbid == nil || rbid.IsZero() {
+	if rbid == nil || rbid.IsNil() {
 		cbid = nil
 	} else {
 		cbid = &tmproto.CanonicalBlockID{
diff --git a/types/events.go b/types/events.go
index 00bed4b60..02e81ac71 100644
--- a/types/events.go
+++ b/types/events.go
@@ -39,7 +39,6 @@ const (
 	EventStateSyncStatusValue = "StateSyncStatus"
 	EventTimeoutProposeValue  = "TimeoutPropose"
 	EventTimeoutWaitValue     = "TimeoutWait"
-	EventUnlockValue          = "Unlock"
 	EventValidBlockValue      = "ValidBlock"
 	EventVoteValue            = "Vote"
 )
@@ -224,7 +223,6 @@ var (
 	EventQueryTimeoutPropose      = QueryForEvent(EventTimeoutProposeValue)
 	EventQueryTimeoutWait         = QueryForEvent(EventTimeoutWaitValue)
 	EventQueryTx                  = QueryForEvent(EventTxValue)
-	EventQueryUnlock              = QueryForEvent(EventUnlockValue)
 	EventQueryValidatorSetUpdates = QueryForEvent(EventValidatorSetUpdatesValue)
 	EventQueryValidBlock          = QueryForEvent(EventValidBlockValue)
 	EventQueryVote                = QueryForEvent(EventVoteValue)
diff --git a/types/vote.go b/types/vote.go
index 52fb73ec5..834af826b 100644
--- a/types/vote.go
+++ b/types/vote.go
@@ -68,7 +68,7 @@ func (vote *Vote) CommitSig() CommitSig {
 	switch {
 	case vote.BlockID.IsComplete():
 		blockIDFlag = BlockIDFlagCommit
-	case vote.BlockID.IsZero():
+	case vote.BlockID.IsNil():
 		blockIDFlag = BlockIDFlagNil
 	default:
 		panic(fmt.Sprintf("Invalid vote %v - expected BlockID to be either empty or complete", vote))
@@ -177,7 +177,7 @@ func (vote *Vote) ValidateBasic() error {
 
 	// BlockID.ValidateBasic would not err if we for instance have an empty hash but a
 	// non-empty PartsSetHeader:
-	if !vote.BlockID.IsZero() && !vote.BlockID.IsComplete() {
+	if !vote.BlockID.IsNil() && !vote.BlockID.IsComplete() {
 		return fmt.Errorf("blockID must be either empty or complete, got: %v", vote.BlockID)
 	}
 
diff --git a/types/vote_set_test.go b/types/vote_set_test.go
index a3ef9e802..8baa74172 100644
--- a/types/vote_set_test.go
+++ b/types/vote_set_test.go
@@ -31,7 +31,7 @@ func TestVoteSet_AddVote_Good(t *testing.T) {
 	assert.Nil(t, voteSet.GetByAddress(val0Addr))
 	assert.False(t, voteSet.BitArray().GetIndex(0))
 	blockID, ok := voteSet.TwoThirdsMajority()
-	assert.False(t, ok || !blockID.IsZero(), "there should be no 2/3 majority")
+	assert.False(t, ok || !blockID.IsNil(), "there should be no 2/3 majority")
 
 	vote := &Vote{
 		ValidatorAddress: val0Addr,
@@ -48,7 +48,7 @@ func TestVoteSet_AddVote_Good(t *testing.T) {
 	assert.NotNil(t, voteSet.GetByAddress(val0Addr))
 	assert.True(t, voteSet.BitArray().GetIndex(0))
 	blockID, ok = voteSet.TwoThirdsMajority()
-	assert.False(t, ok || !blockID.IsZero(), "there should be no 2/3 majority")
+	assert.False(t, ok || !blockID.IsNil(), "there should be no 2/3 majority")
 }
 
 func TestVoteSet_AddVote_Bad(t *testing.T) {
@@ -155,7 +155,7 @@ func TestVoteSet_2_3Majority(t *testing.T) {
 		require.NoError(t, err)
 	}
 	blockID, ok := voteSet.TwoThirdsMajority()
-	assert.False(t, ok || !blockID.IsZero(), "there should be no 2/3 majority")
+	assert.False(t, ok || !blockID.IsNil(), "there should be no 2/3 majority")
 
 	// 7th validator voted for some blockhash
 	{
@@ -166,7 +166,7 @@ func TestVoteSet_2_3Majority(t *testing.T) {
 		_, err = signAddVote(ctx, privValidators[6], withBlockHash(vote, tmrand.Bytes(32)), voteSet)
 		require.NoError(t, err)
 		blockID, ok = voteSet.TwoThirdsMajority()
-		assert.False(t, ok || !blockID.IsZero(), "there should be no 2/3 majority")
+		assert.False(t, ok || !blockID.IsNil(), "there should be no 2/3 majority")
 	}
 
 	// 8th validator voted for nil.
@@ -178,7 +178,7 @@ func TestVoteSet_2_3Majority(t *testing.T) {
 		_, err = signAddVote(ctx, privValidators[7], vote, voteSet)
 		require.NoError(t, err)
 		blockID, ok = voteSet.TwoThirdsMajority()
-		assert.True(t, ok || blockID.IsZero(), "there should be 2/3 majority for nil")
+		assert.True(t, ok || blockID.IsNil(), "there should be 2/3 majority for nil")
 	}
 }
 
@@ -213,7 +213,7 @@ func TestVoteSet_2_3MajorityRedux(t *testing.T) {
 		require.NoError(t, err)
 	}
 	blockID, ok := voteSet.TwoThirdsMajority()
-	assert.False(t, ok || !blockID.IsZero(),
+	assert.False(t, ok || !blockID.IsNil(),
 		"there should be no 2/3 majority")
 
 	// 67th validator voted for nil
@@ -225,7 +225,7 @@ func TestVoteSet_2_3MajorityRedux(t *testing.T) {
 		_, err = signAddVote(ctx, privValidators[66], withBlockHash(vote, nil), voteSet)
 		require.NoError(t, err)
 		blockID, ok = voteSet.TwoThirdsMajority()
-		assert.False(t, ok || !blockID.IsZero(),
+		assert.False(t, ok || !blockID.IsNil(),
 			"there should be no 2/3 majority: last vote added was nil")
 	}
 
@@ -239,7 +239,7 @@ func TestVoteSet_2_3MajorityRedux(t *testing.T) {
 		_, err = signAddVote(ctx, privValidators[67], withBlockPartSetHeader(vote, blockPartsHeader), voteSet)
 		require.NoError(t, err)
 		blockID, ok = voteSet.TwoThirdsMajority()
-		assert.False(t, ok || !blockID.IsZero(),
+		assert.False(t, ok || !blockID.IsNil(),
 			"there should be no 2/3 majority: last vote added had different PartSetHeader Hash")
 	}
 
@@ -253,7 +253,7 @@ func TestVoteSet_2_3MajorityRedux(t *testing.T) {
 		_, err = signAddVote(ctx, privValidators[68], withBlockPartSetHeader(vote, blockPartsHeader), voteSet)
 		require.NoError(t, err)
 		blockID, ok = voteSet.TwoThirdsMajority()
-		assert.False(t, ok || !blockID.IsZero(),
+		assert.False(t, ok || !blockID.IsNil(),
 			"there should be no 2/3 majority: last vote added had different PartSetHeader Total")
 	}
 
@@ -266,7 +266,7 @@ func TestVoteSet_2_3MajorityRedux(t *testing.T) {
 		_, err = signAddVote(ctx, privValidators[69], withBlockHash(vote, tmrand.Bytes(32)), voteSet)
 		require.NoError(t, err)
 		blockID, ok = voteSet.TwoThirdsMajority()
-		assert.False(t, ok || !blockID.IsZero(),
+		assert.False(t, ok || !blockID.IsNil(),
 			"there should be no 2/3 majority: last vote added had different BlockHash")
 	}