nimbus-eth2/tests/test_blockchain_dag.nim

707 lines
23 KiB
Nim

# beacon_chain
# Copyright (c) 2018-2021 Status Research & Development GmbH
# Licensed and distributed under either of
# * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
# * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.
{.used.}
import
chronicles,
unittest2,
stew/assign2,
eth/keys, taskpools,
../beacon_chain/spec/datatypes/base,
../beacon_chain/spec/[beaconstate, forks, helpers, signatures, state_transition],
../beacon_chain/[beacon_chain_db],
../beacon_chain/consensus_object_pools/[
attestation_pool, blockchain_dag, block_quarantine, block_clearance],
./testutil, ./testdbutil, ./testblockutil
func `$`(x: BlockRef): string = shortLog(x)
const
nilPhase0Callback = OnPhase0BlockAdded(nil)
nilAltairCallback = OnAltairBlockAdded(nil)
proc pruneAtFinalization(dag: ChainDAGRef) =
if dag.needStateCachesAndForkChoicePruning():
dag.pruneStateCachesDAG()
suite "ChainDAG helpers":
test "epochAncestor sanity" & preset():
let
s0 = BlockRef(bid: BlockId(slot: Slot(0)))
var cur = s0
for i in 1..SLOTS_PER_EPOCH * 2:
cur = BlockRef(bid: BlockId(slot: Slot(i)), parent: cur)
let ancestor = cur.epochAncestor(cur.slot.epoch)
check:
ancestor.epoch == cur.slot.epoch
ancestor.blck != cur # should have selected a parent
ancestor.blck.epochAncestor(cur.slot.epoch) == ancestor
ancestor.blck.epochAncestor(ancestor.blck.slot.epoch) != ancestor
suite "Block pool processing" & preset():
setup:
var
db = makeTestDB(SLOTS_PER_EPOCH)
dag = init(ChainDAGRef, defaultRuntimeConfig, db, {})
verifier = BatchVerifier(rng: keys.newRng(), taskpool: Taskpool.new())
quarantine = Quarantine.init()
state = newClone(dag.headState.data)
cache = StateCache()
info = ForkedEpochInfo()
att0 = makeFullAttestations(state[], dag.tail.root, 0.Slot, cache)
b1 = addTestBlock(state[], cache, attestations = att0).phase0Data
b2 = addTestBlock(state[], cache).phase0Data
test "getRef returns nil for missing blocks":
check:
dag.getRef(default Eth2Digest) == nil
test "loading tail block works" & preset():
let
b0 = dag.get(dag.tail.root)
check:
b0.isSome()
test "Simple block add&get" & preset():
let
b1Add = dag.addHeadBlock(verifier, b1, nilPhase0Callback)
b1Get = dag.get(b1.root)
check:
b1Get.isSome()
b1Get.get().refs.root == b1.root
b1Add[].root == b1Get.get().refs.root
dag.heads.len == 1
dag.heads[0] == b1Add[]
let
b2Add = dag.addHeadBlock(verifier, b2, nilPhase0Callback)
b2Get = dag.get(b2.root)
er = dag.findEpochRef(b1Add[], b1Add[].slot.epoch)
validators = getStateField(dag.headState.data, validators).lenu64()
check:
b2Get.isSome()
b2Get.get().refs.root == b2.root
b2Add[].root == b2Get.get().refs.root
dag.heads.len == 1
dag.heads[0] == b2Add[]
not er.isNil
# Same epoch - same epochRef
er == dag.findEpochRef(b2Add[], b2Add[].slot.epoch)
# Different epoch that was never processed
dag.findEpochRef(b1Add[], b1Add[].slot.epoch + 1).isNil
er.validatorKey(0'u64).isSome()
er.validatorKey(validators - 1).isSome()
er.validatorKey(validators).isNone()
# Skip one slot to get a gap
check:
process_slots(
defaultRuntimeConfig, state[], getStateField(state[], slot) + 1, cache,
info, {})
let
b4 = addTestBlock(state[], cache).phase0Data
b4Add = dag.addHeadBlock(verifier, b4, nilPhase0Callback)
check:
b4Add[].parent == b2Add[]
dag.updateHead(b4Add[], quarantine)
dag.pruneAtFinalization()
var blocks: array[3, BlockId]
check:
dag.getBlockRange(Slot(0), 1, blocks.toOpenArray(0, 0)) == 0
blocks[0..<1] == [dag.tail.bid]
dag.getBlockRange(Slot(0), 1, blocks.toOpenArray(0, 1)) == 0
blocks[0..<2] == [dag.tail.bid, b1Add[].bid]
dag.getBlockRange(Slot(0), 2, blocks.toOpenArray(0, 1)) == 0
blocks[0..<2] == [dag.tail.bid, b2Add[].bid]
dag.getBlockRange(Slot(0), 3, blocks.toOpenArray(0, 1)) == 1
blocks[1..<2] == [dag.tail.bid] # block 3 is missing!
dag.getBlockRange(Slot(2), 2, blocks.toOpenArray(0, 1)) == 0
blocks[0..<2] == [b2Add[].bid, b4Add[].bid] # block 3 is missing!
# large skip step
dag.getBlockRange(Slot(0), uint64.high, blocks.toOpenArray(0, 2)) == 2
blocks[2..2] == [dag.tail.bid]
# large skip step
dag.getBlockRange(Slot(2), uint64.high, blocks.toOpenArray(0, 1)) == 1
blocks[1..1] == [b2Add[].bid]
# empty length
dag.getBlockRange(Slot(2), 2, blocks.toOpenArray(0, -1)) == 0
# No blocks in sight
dag.getBlockRange(Slot(5), 1, blocks.toOpenArray(0, 1)) == 2
# No blocks in sight
dag.getBlockRange(Slot(uint64.high), 1, blocks.toOpenArray(0, 1)) == 2
# No blocks in sight either due to gaps
dag.getBlockRange(Slot(3), 2, blocks.toOpenArray(0, 1)) == 2
blocks[2..<2].len == 0
test "updateHead updates head and headState" & preset():
let
b1Add = dag.addHeadBlock(verifier, b1, nilPhase0Callback)
dag.updateHead(b1Add[], quarantine)
dag.pruneAtFinalization()
check:
dag.head == b1Add[]
getStateField(dag.headState.data, slot) == b1Add[].slot
test "updateStateData sanity" & preset():
let
b1Add = dag.addHeadBlock(verifier, b1, nilPhase0Callback)
b2Add = dag.addHeadBlock(verifier, b2, nilPhase0Callback)
bs1 = BlockSlot(blck: b1Add[], slot: b1.message.slot)
bs1_3 = b1Add[].atSlot(3.Slot)
bs2_3 = b2Add[].atSlot(3.Slot)
var tmpState = assignClone(dag.headState)
# move to specific block
var cache = StateCache()
dag.updateStateData(tmpState[], bs1, false, cache)
check:
tmpState.blck == b1Add[]
getStateField(tmpState.data, slot) == bs1.slot
# Skip slots
dag.updateStateData(tmpState[], bs1_3, false, cache) # skip slots
check:
tmpState.blck == b1Add[]
getStateField(tmpState.data, slot) == bs1_3.slot
# Move back slots, but not blocks
dag.updateStateData(tmpState[], bs1_3.parent(), false, cache)
check:
tmpState.blck == b1Add[]
getStateField(tmpState.data, slot) == bs1_3.parent().slot
# Move to different block and slot
dag.updateStateData(tmpState[], bs2_3, false, cache)
check:
tmpState.blck == b2Add[]
getStateField(tmpState.data, slot) == bs2_3.slot
# Move back slot and block
dag.updateStateData(tmpState[], bs1, false, cache)
check:
tmpState.blck == b1Add[]
getStateField(tmpState.data, slot) == bs1.slot
# Move back to genesis
dag.updateStateData(tmpState[], bs1.parent(), false, cache)
check:
tmpState.blck == b1Add[].parent
getStateField(tmpState.data, slot) == bs1.parent.slot
when declared(GC_fullCollect): # i386 test machines seem to run low..
GC_fullCollect()
suite "Block pool altair processing" & preset():
setup:
var
cfg = defaultRuntimeConfig
cfg.ALTAIR_FORK_EPOCH = Epoch(1)
var
db = makeTestDB(SLOTS_PER_EPOCH)
dag = init(ChainDAGRef, cfg, db, {})
verifier = BatchVerifier(rng: keys.newRng(), taskpool: Taskpool.new())
quarantine = Quarantine.init()
state = newClone(dag.headState.data)
cache = StateCache()
info = ForkedEpochInfo()
# Advance to altair
check:
process_slots(
cfg, state[], cfg.ALTAIR_FORK_EPOCH.compute_start_slot_at_epoch(), cache,
info, {})
state[].kind == BeaconStateFork.Altair
var
b1 = addTestBlock(state[], cache).altairData
att1 = makeFullAttestations(state[], b1.root, b1.message.slot, cache)
b2 = addTestBlock(state[], cache, attestations = att1).altairData
test "Invalid signatures" & preset():
let badSignature = get_slot_signature(
Fork(), Eth2Digest(), 42.Slot,
MockPrivKeys[ValidatorIndex(0)]).toValidatorSig()
check:
dag.addHeadBlock(verifier, b1, nilAltairCallback).isOk()
block: # Main signature
var b = b2
b.signature = badSignature
let
bAdd = dag.addHeadBlock(verifier, b, nilAltairCallback)
check:
bAdd.error() == BlockError.Invalid
block: # Randao reveal
var b = b2
b.message.body.randao_reveal = badSignature
let
bAdd = dag.addHeadBlock(verifier, b, nilAltairCallback)
check:
bAdd.error() == BlockError.Invalid
block: # Attestations
var b = b2
b.message.body.attestations[0].signature = badSignature
let
bAdd = dag.addHeadBlock(verifier, b, nilAltairCallback)
check:
bAdd.error() == BlockError.Invalid
block: # SyncAggregate empty
var b = b2
b.message.body.sync_aggregate.sync_committee_signature = badSignature
let
bAdd = dag.addHeadBlock(verifier, b, nilAltairCallback)
check:
bAdd.error() == BlockError.Invalid
block: # SyncAggregate junk
var b = b2
b.message.body.sync_aggregate.sync_committee_signature = badSignature
b.message.body.sync_aggregate.sync_committee_bits[0] = true
let
bAdd = dag.addHeadBlock(verifier, b, nilAltairCallback)
check:
bAdd.error() == BlockError.Invalid
suite "chain DAG finalization tests" & preset():
setup:
var
db = makeTestDB(SLOTS_PER_EPOCH)
dag = init(ChainDAGRef, defaultRuntimeConfig, db, {})
verifier = BatchVerifier(rng: keys.newRng(), taskpool: Taskpool.new())
quarantine = Quarantine.init()
cache = StateCache()
info = ForkedEpochInfo()
test "prune heads on finalization" & preset():
# Create a fork that will not be taken
var
blck = makeTestBlock(dag.headState.data, cache).phase0Data
tmpState = assignClone(dag.headState.data)
check:
process_slots(
defaultRuntimeConfig, tmpState[],
getStateField(tmpState[], slot) + (5 * SLOTS_PER_EPOCH).uint64,
cache, info, {})
let lateBlock = addTestBlock(tmpState[], cache).phase0Data
block:
let status = dag.addHeadBlock(verifier, blck, nilPhase0Callback)
check: status.isOk()
assign(tmpState[], dag.headState.data)
for i in 0 ..< (SLOTS_PER_EPOCH * 6):
if i == 1:
# There are 2 heads now because of the fork at slot 1
check:
dag.heads.len == 2
blck = addTestBlock(
tmpState[], cache,
attestations = makeFullAttestations(
tmpState[], dag.head.root, getStateField(tmpState[], slot), cache, {})).phase0Data
let added = dag.addHeadBlock(verifier, blck, nilPhase0Callback)
check: added.isOk()
dag.updateHead(added[], quarantine)
dag.pruneAtFinalization()
check:
dag.heads.len() == 1
dag.getBlockBySlot(0.Slot) == BlockSlot(blck: dag.genesis, slot: 0.Slot)
dag.getBlockBySlot(dag.head.slot) == BlockSlot(
blck: dag.head, slot: dag.head.slot.Slot)
dag.getBlockBySlot(dag.head.slot + 1) == BlockSlot(
blck: dag.head, slot: dag.head.slot.Slot + 1)
check:
dag.db.immutableValidators.len() == getStateField(dag.headState.data, validators).len()
let
finalER = dag.findEpochRef(dag.finalizedHead.blck, dag.finalizedHead.slot.epoch)
# The EpochRef for the finalized block is needed for eth1 voting, so we
# should never drop it!
check:
not finalER.isNil
block:
for er in dag.epochRefs:
check: er == nil or er.epoch >= dag.finalizedHead.slot.epoch
block:
let tmpStateData = assignClone(dag.headState)
# Check that cached data is available after updateStateData - since we
# just processed the head the relevant epochrefs should not have been
# evicted yet
cache = StateCache()
updateStateData(
dag, tmpStateData[], dag.head.atSlot(dag.head.slot), false, cache)
check:
dag.head.slot.epoch in cache.shuffled_active_validator_indices
(dag.head.slot.epoch - 1) in cache.shuffled_active_validator_indices
dag.head.slot in cache.beacon_proposer_indices
block:
# The late block is a block whose parent was finalized long ago and thus
# is no longer a viable head candidate
let status = dag.addHeadBlock(verifier, lateBlock, nilPhase0Callback)
check: status.error == BlockError.UnviableFork
block:
let
finalizedCheckpoint = dag.finalizedHead.stateCheckpoint
headCheckpoint = dag.head.atSlot(dag.head.slot).stateCheckpoint
check:
db.getStateRoot(headCheckpoint.blck.root, headCheckpoint.slot).isSome
db.getStateRoot(finalizedCheckpoint.blck.root, finalizedCheckpoint.slot).isSome
let
dag2 = init(ChainDAGRef, defaultRuntimeConfig, db, {})
# check that the state reloaded from database resembles what we had before
check:
dag2.tail.root == dag.tail.root
dag2.head.root == dag.head.root
dag2.finalizedHead.blck.root == dag.finalizedHead.blck.root
dag2.finalizedHead.slot == dag.finalizedHead.slot
getStateRoot(dag2.headState.data) == getStateRoot(dag.headState.data)
test "orphaned epoch block" & preset():
var prestate = (ref ForkedHashedBeaconState)(kind: BeaconStateFork.Phase0)
for i in 0 ..< SLOTS_PER_EPOCH:
if i == SLOTS_PER_EPOCH - 1:
assign(prestate[], dag.headState.data)
let blck = makeTestBlock(dag.headState.data, cache).phase0Data
let added = dag.addHeadBlock(verifier, blck, nilPhase0Callback)
check: added.isOk()
dag.updateHead(added[], quarantine)
dag.pruneAtFinalization()
check:
dag.heads.len() == 1
# The loop creates multiple branches, which StateCache isn't suitable for
cache = StateCache()
doAssert process_slots(
defaultRuntimeConfig, prestate[], getStateField(prestate[], slot) + 1,
cache, info, {})
# create another block, orphaning the head
let blck = makeTestBlock(prestate[], cache).phase0Data
# Add block, but don't update head
let added = dag.addHeadBlock(verifier, blck, nilPhase0Callback)
check: added.isOk()
var
dag2 = init(ChainDAGRef, defaultRuntimeConfig, db, {})
# check that we can apply the block after the orphaning
let added2 = dag2.addHeadBlock(verifier, blck, nilPhase0Callback)
check: added2.isOk()
test "init with gaps" & preset():
for blck in makeTestBlocks(
dag.headState.data, cache, int(SLOTS_PER_EPOCH * 6 - 2),
true):
let added = dag.addHeadBlock(verifier, blck.phase0Data, nilPhase0Callback)
check: added.isOk()
dag.updateHead(added[], quarantine)
dag.pruneAtFinalization()
# Advance past epoch so that the epoch transition is gapped
check:
process_slots(
defaultRuntimeConfig, dag.headState.data, Slot(SLOTS_PER_EPOCH * 6 + 2),
cache, info, {})
var blck = makeTestBlock(
dag.headState.data, cache,
attestations = makeFullAttestations(
dag.headState.data, dag.head.root, getStateField(dag.headState.data, slot),
cache, {})).phase0Data
let added = dag.addHeadBlock(verifier, blck, nilPhase0Callback)
check: added.isOk()
dag.updateHead(added[], quarantine)
dag.pruneAtFinalization()
block:
# Check that we can rewind to every block from head to finalized
var
cur = dag.head
tmpStateData = assignClone(dag.headState)
while cur.slot >= dag.finalizedHead.slot:
assign(tmpStateData[], dag.headState)
dag.updateStateData(tmpStateData[], cur.atSlot(cur.slot), false, cache)
check:
dag.get(cur).data.phase0Data.message.state_root ==
getStateRoot(tmpStateData[].data)
getStateRoot(tmpStateData[].data) == hash_tree_root(
tmpStateData[].data.phase0Data.data)
cur = cur.parent
let
dag2 = init(ChainDAGRef, defaultRuntimeConfig, db, {})
# check that the state reloaded from database resembles what we had before
check:
dag2.tail.root == dag.tail.root
dag2.head.root == dag.head.root
dag2.finalizedHead.blck.root == dag.finalizedHead.blck.root
dag2.finalizedHead.slot == dag.finalizedHead.slot
getStateRoot(dag2.headState.data) == getStateRoot(dag.headState.data)
suite "Old database versions" & preset():
setup:
let
genState = newClone(initialize_hashed_beacon_state_from_eth1(
defaultRuntimeConfig,
Eth2Digest(),
0,
makeInitialDeposits(SLOTS_PER_EPOCH.uint64, flags = {skipBlsValidation}),
{skipBlsValidation}))
genBlock = get_initial_beacon_block(genState[])
var
verifier = BatchVerifier(rng: keys.newRng(), taskpool: Taskpool.new())
quarantine = Quarantine.init()
test "pre-1.1.0":
# only kvstore, no immutable validator keys
let db = BeaconChainDB.new("", inMemory = true)
# preInit a database to a v1.0.12 state
db.putStateRoot(
genState[].latest_block_root(), genState[].data.slot, genState[].root)
db.putStateV0(genState[].root, genState[].data)
db.putBlockV0(genBlock)
db.putTailBlock(genBlock.root)
db.putHeadBlock(genBlock.root)
db.putGenesisBlock(genBlock.root)
var
dag = init(ChainDAGRef, defaultRuntimeConfig, db, {})
state = newClone(dag.headState.data)
cache = StateCache()
att0 = makeFullAttestations(state[], dag.tail.root, 0.Slot, cache)
b1 = addTestBlock(state[], cache, attestations = att0).phase0Data
b1Add = dag.addHeadBlock(verifier, b1, nilPhase0Callback)
check:
b1Add.isOk()
suite "Diverging hardforks":
setup:
var
phase0RuntimeConfig = defaultRuntimeConfig
altairRuntimeConfig = defaultRuntimeConfig
phase0RuntimeConfig.ALTAIR_FORK_EPOCH = FAR_FUTURE_EPOCH
altairRuntimeConfig.ALTAIR_FORK_EPOCH = 2.Epoch
var
db = makeTestDB(SLOTS_PER_EPOCH)
dag = init(ChainDAGRef, phase0RuntimeConfig, db, {})
verifier = BatchVerifier(rng: keys.newRng(), taskpool: Taskpool.new())
quarantine = newClone(Quarantine.init())
cache = StateCache()
info = ForkedEpochInfo()
tmpState = assignClone(dag.headState.data)
test "Tail block only in common":
check:
process_slots(
phase0RuntimeConfig, tmpState[],
getStateField(tmpState[], slot) + (3 * SLOTS_PER_EPOCH).uint64,
cache, info, {})
# Because the first block is after the Altair transition, the only block in
# common is the tail block
var
b1 = addTestBlock(tmpState[], cache).phase0Data
b1Add = dag.addHeadBlock(verifier, b1, nilPhase0Callback)
check b1Add.isOk()
dag.updateHead(b1Add[], quarantine[])
var dagAltair = init(ChainDAGRef, altairRuntimeConfig, db, {})
discard AttestationPool.init(dagAltair, quarantine)
test "Non-tail block in common":
check:
process_slots(
phase0RuntimeConfig, tmpState[],
getStateField(tmpState[], slot) + SLOTS_PER_EPOCH.uint64,
cache, info, {})
# There's a block in the shared-correct phase0 hardfork, before epoch 2
var
b1 = addTestBlock(tmpState[], cache).phase0Data
b1Add = dag.addHeadBlock(verifier, b1, nilPhase0Callback)
check:
b1Add.isOk()
process_slots(
phase0RuntimeConfig, tmpState[],
getStateField(tmpState[], slot) + (3 * SLOTS_PER_EPOCH).uint64,
cache, info, {})
var
b2 = addTestBlock(tmpState[], cache).phase0Data
b2Add = dag.addHeadBlock(verifier, b2, nilPhase0Callback)
check b2Add.isOk()
dag.updateHead(b2Add[], quarantine[])
var dagAltair = init(ChainDAGRef, altairRuntimeConfig, db, {})
discard AttestationPool.init(dagAltair, quarantine)
suite "Backfill":
setup:
let
genState = (ref ForkedHashedBeaconState)(
kind: BeaconStateFork.Phase0,
phase0Data: initialize_hashed_beacon_state_from_eth1(
defaultRuntimeConfig,
Eth2Digest(),
0,
makeInitialDeposits(SLOTS_PER_EPOCH.uint64, flags = {skipBlsValidation}),
{skipBlsValidation}))
genBlock = get_initial_beacon_block(genState[])
tailState = assignClone(genState[])
blocks = block:
var blocks: seq[ForkedSignedBeaconBlock]
var cache: StateCache
for i in 0..<SLOTS_PER_EPOCH:
blocks.add addTestBlock(tailState[], cache)
blocks
let
db = BeaconChainDB.new("", inMemory = true)
test "backfill to genesis":
let
tailBlock = blocks[^1]
ChainDAGRef.preInit(
db, genState[], tailState[], tailBlock.asTrusted())
let dag = init(ChainDAGRef, defaultRuntimeConfig, db, {})
check:
dag.getRef(tailBlock.root) == dag.tail
dag.getRef(blocks[^2].root) == nil
dag.getBlockBySlot(dag.tail.slot).blck == dag.tail
dag.getBlockBySlot(dag.tail.slot - 1).blck == nil
dag.getBlockBySlot(Slot(0)).blck == dag.genesis
dag.getBlockSlotIdBySlot(Slot(0)) == dag.genesis.bid.atSlot(Slot(0))
dag.getBlockSlotIdBySlot(Slot(1)) == BlockSlotId()
var
badBlock = blocks[^2].phase0Data
badBlock.signature = blocks[^3].phase0Data.signature
check:
dag.addBackfillBlock(badBlock).error == BlockError.Invalid
check:
dag.addBackfillBlock(blocks[^3].phase0Data).error == BlockError.MissingParent
dag.addBackfillBlock(tailBlock.phase0Data).error == BlockError.Duplicate
dag.addBackfillBlock(genBlock.phase0Data.asSigned()).error == BlockError.Duplicate
check:
dag.addBackfillBlock(blocks[^2].phase0Data).isOk()
dag.getRef(tailBlock.root) == dag.tail
dag.getRef(blocks[^2].root) == nil
dag.getBlockBySlot(dag.tail.slot).blck == dag.tail
dag.getBlockBySlot(dag.tail.slot - 1).blck == nil
dag.getBlockSlotIdBySlot(dag.tail.slot - 1) ==
blocks[^2].toBlockId().atSlot()
dag.getBlockSlotIdBySlot(dag.tail.slot - 2) == BlockSlotId()
check:
dag.addBackfillBlock(blocks[^3].phase0Data).isOk()
dag.getBlockSlotIdBySlot(dag.tail.slot - 2) ==
blocks[^3].toBlockId().atSlot()
dag.getBlockSlotIdBySlot(dag.tail.slot - 3) == BlockSlotId()
for i in 3..<blocks.len:
check: dag.addBackfillBlock(blocks[blocks.len - i - 1].phase0Data).isOk()
test "reload backfill position":
let
tailBlock = blocks[^1]
ChainDAGRef.preInit(
db, genState[], tailState[], tailBlock.asTrusted())
let dag = init(ChainDAGRef, defaultRuntimeConfig, db, {})
check:
dag.addBackfillBlock(blocks[^2].phase0Data).isOk()
let dag2 = init(ChainDAGRef, defaultRuntimeConfig, db, {})
check:
dag.getRef(tailBlock.root) == dag.tail
dag.getRef(blocks[^2].root) == nil
dag.getBlockBySlot(dag.tail.slot).blck == dag.tail
dag.getBlockBySlot(dag.tail.slot - 1).blck == nil
dag.getBlockSlotIdBySlot(dag.tail.slot - 1) ==
blocks[^2].toBlockId().atSlot()
dag.getBlockSlotIdBySlot(dag.tail.slot - 2) == BlockSlotId()