lighthouse/consensus/fork_choice/tests/tests.rs

#![cfg(not(debug_assertions))]

use beacon_chain::test_utils::{
    AttestationStrategy, BeaconChainHarness, BlockStrategy, EphemeralHarnessType,
};
use beacon_chain::{
    BeaconChain, BeaconChainError, BeaconForkChoiceStore, ChainConfig, ForkChoiceError,
    StateSkipConfig, WhenSlotSkipped,
};
use fork_choice::{
    ForkChoiceStore, InvalidAttestation, InvalidBlock, PayloadVerificationStatus, QueuedAttestation,
};
use std::fmt;
use std::sync::Mutex;
use std::time::Duration;
use store::MemoryStore;
use types::{
    test_utils::generate_deterministic_keypair, BeaconBlockRef, BeaconState, ChainSpec, Checkpoint,
    Epoch, EthSpec, ForkName, Hash256, IndexedAttestation, MainnetEthSpec, ProgressiveBalancesMode,
    RelativeEpoch, SignedBeaconBlock, Slot, SubnetId,
};

pub type E = MainnetEthSpec;

pub const VALIDATOR_COUNT: usize = 64;

/// Defines some delay between when an attestation is created and when it is mutated.
pub enum MutationDelay {
    /// No delay between creation and mutation.
    NoDelay,
    /// Create `n` blocks before mutating the attestation.
    Blocks(usize),
}

/// A helper struct to make testing fork choice more ergonomic and less repetitive.
struct ForkChoiceTest {
    harness: BeaconChainHarness<EphemeralHarnessType<E>>,
}

/// Allows us to use `unwrap` in some cases.
impl fmt::Debug for ForkChoiceTest {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("ForkChoiceTest").finish()
    }
}

impl ForkChoiceTest {
    /// Creates a new tester.
    pub fn new() -> Self {
        let harness = BeaconChainHarness::builder(MainnetEthSpec)
            .default_spec()
            .deterministic_keypairs(VALIDATOR_COUNT)
            .fresh_ephemeral_store()
            .build();

        Self { harness }
    }

    /// Creates a new tester with a custom chain config.
    pub fn new_with_chain_config(chain_config: ChainConfig) -> Self {
        let harness = BeaconChainHarness::builder(MainnetEthSpec)
            .default_spec()
            .chain_config(chain_config)
            .deterministic_keypairs(VALIDATOR_COUNT)
            .fresh_ephemeral_store()
            .build();

        Self { harness }
    }

    /// Creates a new tester with the specified `ProgressiveBalancesMode` and genesis from latest fork.
    fn new_with_progressive_balances_mode(mode: ProgressiveBalancesMode) -> ForkChoiceTest {
        // genesis with latest fork (at least altair required to test the cache)
        let spec = ForkName::latest().make_genesis_spec(ChainSpec::default());
        let harness = BeaconChainHarness::builder(MainnetEthSpec)
            .spec(spec)
            .chain_config(ChainConfig {
                progressive_balances_mode: mode,
                ..ChainConfig::default()
            })
            .deterministic_keypairs(VALIDATOR_COUNT)
            .fresh_ephemeral_store()
            .mock_execution_layer()
            .build();

        Self { harness }
    }

    /// Get a value from the `ForkChoice` instantiation.
    fn get<T, U>(&self, func: T) -> U
    where
        T: Fn(&BeaconForkChoiceStore<E, MemoryStore<E>, MemoryStore<E>>) -> U,
    {
        func(
            self.harness
                .chain
                .canonical_head
                .fork_choice_read_lock()
                .fc_store(),
        )
    }

    /// Assert the epochs match.
    pub fn assert_finalized_epoch(self, epoch: u64) -> Self {
        assert_eq!(
            self.get(|fc_store| fc_store.finalized_checkpoint().epoch),
            Epoch::new(epoch),
            "finalized_epoch"
        );
        self
    }

    /// Assert the epochs match.
    pub fn assert_justified_epoch(self, epoch: u64) -> Self {
        assert_eq!(
            self.get(|fc_store| fc_store.justified_checkpoint().epoch),
            Epoch::new(epoch),
            "justified_epoch"
        );
        self
    }

    /// Assert the given slot is greater than the head slot.
    pub fn assert_finalized_epoch_is_less_than(self, epoch: Epoch) -> Self {
        assert!(self.harness.finalized_checkpoint().epoch < epoch);
        self
    }

    /// Assert there was a shutdown signal sent by the beacon chain.
    pub fn shutdown_signal_sent(&self) -> bool {
        let mutex = self.harness.shutdown_receiver.clone();
        let mut shutdown_receiver = mutex.lock();

        shutdown_receiver.close();
        let msg = shutdown_receiver.try_next().unwrap();
        msg.is_some()
    }

    /// Assert there was a shutdown signal sent by the beacon chain.
    pub fn assert_shutdown_signal_sent(self) -> Self {
        assert!(self.shutdown_signal_sent());
        self
    }

    /// Assert no shutdown was signal sent by the beacon chain.
    pub fn assert_shutdown_signal_not_sent(self) -> Self {
        assert!(!self.shutdown_signal_sent());
        self
    }

    /// Inspect the queued attestations in fork choice.
    pub fn inspect_queued_attestations<F>(self, mut func: F) -> Self
    where
        F: FnMut(&[QueuedAttestation]),
    {
        self.harness
            .chain
            .canonical_head
            .fork_choice_write_lock()
            .update_time(self.harness.chain.slot().unwrap())
            .unwrap();
        func(
            self.harness
                .chain
                .canonical_head
                .fork_choice_read_lock()
                .queued_attestations(),
        );
        self
    }

    /// Skip a slot, without producing a block.
    pub fn skip_slot(self) -> Self {
        self.harness.advance_slot();
        self
    }

    /// Skips `count` slots, without producing a block.
    pub fn skip_slots(self, count: usize) -> Self {
        for _ in 0..count {
            self.harness.advance_slot();
        }
        self
    }

    /// Build the chain whilst `predicate` returns `true` and `process_block_result` does not error.
    pub async fn apply_blocks_while<F>(self, mut predicate: F) -> Result<Self, Self>
    where
        F: FnMut(BeaconBlockRef<'_, E>, &BeaconState<E>) -> bool,
    {
        self.harness.advance_slot();
        let mut state = self.harness.get_current_state();
        let validators = self.harness.get_all_validators();
        loop {
            let slot = self.harness.get_current_slot();
            let (block_contents, state_) = self.harness.make_block(state, slot).await;
            state = state_;
            if !predicate(block_contents.0.message(), &state) {
                break;
            }
            let block = block_contents.0.clone();
            if let Ok(block_hash) = self.harness.process_block_result(block_contents).await {
                self.harness.attest_block(
                    &state,
                    block.state_root(),
                    block_hash,
                    &block,
                    &validators,
                );
                self.harness.advance_slot();
            } else {
                return Err(self);
            }
        }

        Ok(self)
    }

    /// Apply `count` blocks to the chain (with attestations).
    pub async fn apply_blocks(self, count: usize) -> Self {
        self.harness.advance_slot();
        self.harness
            .extend_chain(
                count,
                BlockStrategy::OnCanonicalHead,
                AttestationStrategy::AllValidators,
            )
            .await;

        self
    }

    /// Slash a validator from the previous epoch committee.
    pub async fn add_previous_epoch_attester_slashing(self) -> Self {
        let state = self.harness.get_current_state();
        let previous_epoch_shuffling = state.get_shuffling(RelativeEpoch::Previous).unwrap();
        let validator_indices = previous_epoch_shuffling
            .iter()
            .map(|idx| *idx as u64)
            .take(1)
            .collect();

        self.harness
            .add_attester_slashing(validator_indices)
            .unwrap();

        self
    }

    /// Slash the proposer of a block in the previous epoch.
    pub async fn add_previous_epoch_proposer_slashing(self, slots_per_epoch: u64) -> Self {
        let previous_epoch_slot = self.harness.get_current_slot() - slots_per_epoch;
        let previous_epoch_block = self
            .harness
            .chain
            .block_at_slot(previous_epoch_slot, WhenSlotSkipped::None)
            .unwrap()
            .unwrap();
        let proposer_index: u64 = previous_epoch_block.message().proposer_index();

        self.harness.add_proposer_slashing(proposer_index).unwrap();

        self
    }

    /// Apply `count` blocks to the chain (without attestations).
    pub async fn apply_blocks_without_new_attestations(self, count: usize) -> Self {
        self.harness.advance_slot();
        self.harness
            .extend_chain(
                count,
                BlockStrategy::OnCanonicalHead,
                AttestationStrategy::SomeValidators(vec![]),
            )
            .await;

        self
    }

    /// Moves to the next slot that is *outside* the `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` range.
    ///
    /// If the chain is presently in an unsafe period, transition through it and the following safe
    /// period.
    ///
    /// Note: the `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` variable has been removed
    /// from the fork choice spec in Q1 2023. We're still leaving references to
    /// it in our tests because (a) it's easier and (b) it allows us to easily
    /// test for the absence of that parameter.
    pub fn move_to_next_unsafe_period(self) -> Self {
        self.move_inside_safe_to_update()
            .move_outside_safe_to_update()
    }

    /// Moves to the next slot that is *outside* the `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` range.
    pub fn move_outside_safe_to_update(self) -> Self {
        while is_safe_to_update(self.harness.chain.slot().unwrap(), &self.harness.chain.spec) {
            self.harness.advance_slot()
        }
        self
    }

    /// Moves to the next slot that is *inside* the `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` range.
    pub fn move_inside_safe_to_update(self) -> Self {
        while !is_safe_to_update(self.harness.chain.slot().unwrap(), &self.harness.chain.spec) {
            self.harness.advance_slot()
        }
        self
    }

    /// Applies a block directly to fork choice, bypassing the beacon chain.
    ///
    /// Asserts the block was applied successfully.
    pub async fn apply_block_directly_to_fork_choice<F>(self, mut func: F) -> Self
    where
        F: FnMut(&mut SignedBeaconBlock<E>, &mut BeaconState<E>),
    {
        let state = self
            .harness
            .chain
            .state_at_slot(
                self.harness.get_current_slot() - 1,
                StateSkipConfig::WithStateRoots,
            )
            .unwrap();
        let slot = self.harness.get_current_slot();
        let (mut block_tuple, mut state) = self.harness.make_block(state, slot).await;
        func(&mut block_tuple.0, &mut state);
        let current_slot = self.harness.get_current_slot();
        self.harness
            .chain
            .canonical_head
            .fork_choice_write_lock()
            .on_block(
                current_slot,
                block_tuple.0.message(),
                block_tuple.0.canonical_root(),
                Duration::from_secs(0),
                &state,
                PayloadVerificationStatus::Verified,
                self.harness.chain.config.progressive_balances_mode,
                &self.harness.chain.spec,
                self.harness.logger(),
            )
            .unwrap();
        self
    }

    /// Applies a block directly to fork choice, bypassing the beacon chain.
    ///
    /// Asserts that an error occurred and allows inspecting it via `comparison_func`.
    pub async fn apply_invalid_block_directly_to_fork_choice<F, G>(
        self,
        mut mutation_func: F,
        mut comparison_func: G,
    ) -> Self
    where
        F: FnMut(&mut SignedBeaconBlock<E>, &mut BeaconState<E>),
        G: FnMut(ForkChoiceError),
    {
        let state = self
            .harness
            .chain
            .state_at_slot(
                self.harness.get_current_slot() - 1,
                StateSkipConfig::WithStateRoots,
            )
            .unwrap();
        let slot = self.harness.get_current_slot();
        let (mut block_tuple, mut state) = self.harness.make_block(state, slot).await;
        mutation_func(&mut block_tuple.0, &mut state);
        let current_slot = self.harness.get_current_slot();
        let err = self
            .harness
            .chain
            .canonical_head
            .fork_choice_write_lock()
            .on_block(
                current_slot,
                block_tuple.0.message(),
                block_tuple.0.canonical_root(),
                Duration::from_secs(0),
                &state,
                PayloadVerificationStatus::Verified,
                self.harness.chain.config.progressive_balances_mode,
                &self.harness.chain.spec,
                self.harness.logger(),
            )
            .expect_err("on_block did not return an error");
        comparison_func(err);
        self
    }

    /// Compares the justified balances in the `ForkChoiceStore` verses a direct lookup from the
    /// database.
    fn check_justified_balances(&self) {
        let harness = &self.harness;
        let fc = self.harness.chain.canonical_head.fork_choice_read_lock();

        let state_root = harness
            .chain
            .store
            .get_blinded_block(&fc.fc_store().justified_checkpoint().root)
            .unwrap()
            .unwrap()
            .message()
            .state_root();
        let state = harness
            .chain
            .store
            .get_state(&state_root, None)
            .unwrap()
            .unwrap();
        let balances = state
            .validators()
            .into_iter()
            .map(|v| {
                if v.is_active_at(state.current_epoch()) {
                    v.effective_balance
                } else {
                    0
                }
            })
            .collect::<Vec<_>>();

        assert_eq!(
            &balances[..],
            &fc.fc_store().justified_balances().effective_balances,
            "balances should match"
        );
        assert_eq!(
            balances.iter().sum::<u64>(),
            fc.fc_store().justified_balances().total_effective_balance
        );
    }

    /// Returns an attestation that is valid for some slot in the given `chain`.
    ///
    /// Also returns some info about who created it.
    async fn apply_attestation_to_chain<F, G>(
        self,
        delay: MutationDelay,
        mut mutation_func: F,
        mut comparison_func: G,
    ) -> Self
    where
        F: FnMut(&mut IndexedAttestation<E>, &BeaconChain<EphemeralHarnessType<E>>),
        G: FnMut(Result<(), BeaconChainError>),
    {
        let head = self.harness.chain.head_snapshot();
        let current_slot = self.harness.chain.slot().expect("should get slot");

        let mut attestation = self
            .harness
            .chain
            .produce_unaggregated_attestation(current_slot, 0)
            .expect("should not error while producing attestation");

        let validator_committee_index = 0;
        let validator_index = *head
            .beacon_state
            .get_beacon_committee(current_slot, attestation.data.index)
            .expect("should get committees")
            .committee
            .get(validator_committee_index)
            .expect("there should be an attesting validator");

        let committee_count = head
            .beacon_state
            .get_committee_count_at_slot(current_slot)
            .expect("should not error while getting committee count");

        let subnet_id = SubnetId::compute_subnet::<E>(
            current_slot,
            0,
            committee_count,
            &self.harness.chain.spec,
        )
        .expect("should compute subnet id");

        let validator_sk = generate_deterministic_keypair(validator_index).sk;

        attestation
            .sign(
                &validator_sk,
                validator_committee_index,
                &head.beacon_state.fork(),
                self.harness.chain.genesis_validators_root,
                &self.harness.chain.spec,
            )
            .expect("should sign attestation");

        let mut verified_attestation = self
            .harness
            .chain
            .verify_unaggregated_attestation_for_gossip(&attestation, Some(subnet_id))
            .expect("precondition: should gossip verify attestation");

        if let MutationDelay::Blocks(slots) = delay {
            self.harness.advance_slot();
            self.harness
                .extend_chain(
                    slots,
                    BlockStrategy::OnCanonicalHead,
                    AttestationStrategy::SomeValidators(vec![]),
                )
                .await;
        }

        mutation_func(
            verified_attestation.__indexed_attestation_mut(),
            &self.harness.chain,
        );

        let result = self
            .harness
            .chain
            .apply_attestation_to_fork_choice(&verified_attestation);

        comparison_func(result);

        self
    }

    /// Check to ensure that we can read the finalized block. This is a regression test.
    pub fn check_finalized_block_is_accessible(self) -> Self {
        self.harness
            .chain
            .canonical_head
            .fork_choice_read_lock()
            .get_block(&self.harness.finalized_checkpoint().root)
            .unwrap();

        self
    }
}

fn is_safe_to_update(slot: Slot, spec: &ChainSpec) -> bool {
    slot % E::slots_per_epoch() < spec.safe_slots_to_update_justified
}

#[test]
fn justified_and_finalized_blocks() {
    let tester = ForkChoiceTest::new();
    let fork_choice = tester.harness.chain.canonical_head.fork_choice_read_lock();

    let justified_checkpoint = fork_choice.justified_checkpoint();
    assert_eq!(justified_checkpoint.epoch, 0);
    assert!(justified_checkpoint.root != Hash256::zero());
    assert!(fork_choice.get_justified_block().is_ok());

    let finalized_checkpoint = fork_choice.finalized_checkpoint();
    assert_eq!(finalized_checkpoint.epoch, 0);
    assert!(finalized_checkpoint.root != Hash256::zero());
    assert!(fork_choice.get_finalized_block().is_ok());
}

/// - The new justified checkpoint descends from the current.
/// - Current slot is within `SAFE_SLOTS_TO_UPDATE_JUSTIFIED`
#[tokio::test]
async fn justified_checkpoint_updates_with_descendent_inside_safe_slots() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch == 0)
        .await
        .unwrap()
        .move_inside_safe_to_update()
        .assert_justified_epoch(0)
        .apply_blocks(1)
        .await
        .assert_justified_epoch(2);
}

/// - The new justified checkpoint descends from the current.
/// - Current slot is **not** within `SAFE_SLOTS_TO_UPDATE_JUSTIFIED`
/// - This is **not** the first justification since genesis
#[tokio::test]
async fn justified_checkpoint_updates_with_descendent_outside_safe_slots() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch <= 2)
        .await
        .unwrap()
        .move_outside_safe_to_update()
        .assert_justified_epoch(2)
        .apply_blocks(1)
        .await
        .assert_justified_epoch(3);
}

/// - The new justified checkpoint descends from the current.
/// - Current slot is **not** within `SAFE_SLOTS_TO_UPDATE_JUSTIFIED`
/// - This is the first justification since genesis
#[tokio::test]
async fn justified_checkpoint_updates_first_justification_outside_safe_to_update() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch == 0)
        .await
        .unwrap()
        .move_to_next_unsafe_period()
        .assert_justified_epoch(0)
        .apply_blocks(1)
        .await
        .assert_justified_epoch(2);
}

/// - The new justified checkpoint **does not** descend from the current.
/// - Current slot is within `SAFE_SLOTS_TO_UPDATE_JUSTIFIED`
/// - Finalized epoch has **not** increased.
#[tokio::test]
async fn justified_checkpoint_updates_with_non_descendent_inside_safe_slots_without_finality() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .move_inside_safe_to_update()
        .assert_justified_epoch(2)
        .apply_block_directly_to_fork_choice(|_, state| {
            // The finalized checkpoint should not change.
            state.finalized_checkpoint().epoch = Epoch::new(0);

            // The justified checkpoint has changed.
            state.current_justified_checkpoint_mut().epoch = Epoch::new(3);
            // The new block should **not** include the current justified block as an ancestor.
            state.current_justified_checkpoint_mut().root = *state
                .get_block_root(Epoch::new(1).start_slot(E::slots_per_epoch()))
                .unwrap();
        })
        .await
        .assert_justified_epoch(3);
}

/// - The new justified checkpoint **does not** descend from the current.
/// - Current slot is **not** within `SAFE_SLOTS_TO_UPDATE_JUSTIFIED`.
/// - Finalized epoch has **not** increased.
#[tokio::test]
async fn justified_checkpoint_updates_with_non_descendent_outside_safe_slots_without_finality() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .move_to_next_unsafe_period()
        .assert_justified_epoch(2)
        .apply_block_directly_to_fork_choice(|_, state| {
            // The finalized checkpoint should not change.
            state.finalized_checkpoint().epoch = Epoch::new(0);

            // The justified checkpoint has changed.
            state.current_justified_checkpoint_mut().epoch = Epoch::new(3);
            // The new block should **not** include the current justified block as an ancestor.
            state.current_justified_checkpoint_mut().root = *state
                .get_block_root(Epoch::new(1).start_slot(E::slots_per_epoch()))
                .unwrap();
        })
        .await
        // Now that `SAFE_SLOTS_TO_UPDATE_JUSTIFIED` has been removed, the new
        // block should have updated the justified checkpoint.
        .assert_justified_epoch(3);
}

/// - The new justified checkpoint **does not** descend from the current.
/// - Current slot is **not** within `SAFE_SLOTS_TO_UPDATE_JUSTIFIED`
/// - Finalized epoch has increased.
#[tokio::test]
async fn justified_checkpoint_updates_with_non_descendent_outside_safe_slots_with_finality() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .move_to_next_unsafe_period()
        .assert_justified_epoch(2)
        .apply_block_directly_to_fork_choice(|_, state| {
            // The finalized checkpoint should change.
            state.finalized_checkpoint_mut().epoch = Epoch::new(1);

            // The justified checkpoint has changed.
            state.current_justified_checkpoint_mut().epoch = Epoch::new(3);
            // The new block should **not** include the current justified block as an ancestor.
            state.current_justified_checkpoint_mut().root = *state
                .get_block_root(Epoch::new(1).start_slot(E::slots_per_epoch()))
                .unwrap();
        })
        .await
        .assert_justified_epoch(3);
}

/// Check that the balances are obtained correctly.
#[tokio::test]
async fn justified_balances() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.current_justified_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_justified_epoch(2)
        .check_justified_balances()
}

macro_rules! assert_invalid_block {
    ($err: tt, $($error: pat_param) |+ $( if $guard: expr )?) => {
        assert!(
            matches!(
                $err,
                $( ForkChoiceError::InvalidBlock($error) ) |+ $( if $guard )?
            ),
        )
    };
}

/// Specification v0.12.1
///
/// assert block.parent_root in store.block_states
#[tokio::test]
async fn invalid_block_unknown_parent() {
    let junk = Hash256::from_low_u64_be(42);

    ForkChoiceTest::new()
        .apply_blocks(2)
        .await
        .apply_invalid_block_directly_to_fork_choice(
            |block, _| {
                *block.message_mut().parent_root_mut() = junk;
            },
            |err| {
                assert_invalid_block!(
                    err,
                    InvalidBlock::UnknownParent(parent)
                    if parent == junk
                )
            },
        )
        .await;
}

/// Specification v0.12.1
///
/// assert get_current_slot(store) >= block.slot
#[tokio::test]
async fn invalid_block_future_slot() {
    ForkChoiceTest::new()
        .apply_blocks(2)
        .await
        .apply_invalid_block_directly_to_fork_choice(
            |block, _| {
                *block.message_mut().slot_mut() += 1;
            },
            |err| assert_invalid_block!(err, InvalidBlock::FutureSlot { .. }),
        )
        .await;
}

/// Specification v0.12.1
///
/// assert block.slot > finalized_slot
#[tokio::test]
async fn invalid_block_finalized_slot() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .apply_invalid_block_directly_to_fork_choice(
            |block, _| {
                *block.message_mut().slot_mut() =
                    Epoch::new(2).start_slot(E::slots_per_epoch()) - 1;
            },
            |err| {
                assert_invalid_block!(
                    err,
                    InvalidBlock::FinalizedSlot { finalized_slot, .. }
                    if finalized_slot == Epoch::new(2).start_slot(E::slots_per_epoch())
                )
            },
        )
        .await;
}

/// Specification v0.12.1
///
/// assert get_ancestor(store, hash_tree_root(block), finalized_slot) ==
/// store.finalized_checkpoint().root
///
/// Note: we technically don't do this exact check, but an equivalent check. Reference:
///
/// https://github.com/ethereum/eth2.0-specs/pull/1884
#[tokio::test]
async fn invalid_block_finalized_descendant() {
    let invalid_ancestor = Mutex::new(Hash256::zero());

    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(2)
        .apply_invalid_block_directly_to_fork_choice(
            |block, state| {
                *block.message_mut().parent_root_mut() = *state
                    .get_block_root(Epoch::new(1).start_slot(E::slots_per_epoch()))
                    .unwrap();
                *invalid_ancestor.lock().unwrap() = block.parent_root();
            },
            |err| {
                assert_invalid_block!(
                    err,
                    InvalidBlock::NotFinalizedDescendant {  block_ancestor, .. }
                    if block_ancestor == Some(*invalid_ancestor.lock().unwrap())
                )
            },
        )
        .await;
}

macro_rules! assert_invalid_attestation {
    ($err: tt, $($error: pat_param) |+ $( if $guard: expr )?) => {
        assert!(
            matches!(
                $err,
                $( Err(BeaconChainError::ForkChoiceError(ForkChoiceError::InvalidAttestation($error))) ) |+ $( if $guard )?
            ),
            "{:?}",
            $err
        )
    };
}

/// Ensure we can process a valid attestation.
#[tokio::test]
async fn valid_attestation() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |_, _| {},
            |result| assert!(result.is_ok()),
        )
        .await;
}

/// This test is not in the specification, however we reject an attestation with an empty
/// aggregation bitfield since it has no purpose beyond wasting our time.
#[tokio::test]
async fn invalid_attestation_empty_bitfield() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _| {
                attestation.attesting_indices = vec![].into();
            },
            |result| {
                assert_invalid_attestation!(result, InvalidAttestation::EmptyAggregationBitfield)
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert target.epoch in [expected_current_epoch, previous_epoch]
///
/// (tests epoch after current epoch)
#[tokio::test]
async fn invalid_attestation_future_epoch() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _| {
                attestation.data.target.epoch = Epoch::new(2);
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::FutureEpoch { attestation_epoch, current_epoch }
                    if attestation_epoch == Epoch::new(2) && current_epoch == Epoch::new(0)
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert target.epoch in [expected_current_epoch, previous_epoch]
///
/// (tests epoch prior to previous epoch)
#[tokio::test]
async fn invalid_attestation_past_epoch() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(E::slots_per_epoch() as usize * 3 + 1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _| {
                attestation.data.target.epoch = Epoch::new(0);
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::PastEpoch { attestation_epoch, current_epoch }
                    if attestation_epoch == Epoch::new(0) && current_epoch == Epoch::new(3)
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert target.epoch == compute_epoch_at_slot(attestation.data.slot)
#[tokio::test]
async fn invalid_attestation_target_epoch() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(E::slots_per_epoch() as usize + 1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _| {
                attestation.data.slot = Slot::new(1);
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::BadTargetEpoch { target, slot }
                    if target == Epoch::new(1) && slot == Slot::new(1)
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert target.root in store.blocks
#[tokio::test]
async fn invalid_attestation_unknown_target_root() {
    let junk = Hash256::from_low_u64_be(42);

    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _| {
                attestation.data.target.root = junk;
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::UnknownTargetRoot(root)
                    if root == junk
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert attestation.data.beacon_block_root in store.blocks
#[tokio::test]
async fn invalid_attestation_unknown_beacon_block_root() {
    let junk = Hash256::from_low_u64_be(42);

    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _| {
                attestation.data.beacon_block_root = junk;
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::UnknownHeadBlock { beacon_block_root }
                    if beacon_block_root == junk
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert store.blocks[attestation.data.beacon_block_root].slot <= attestation.data.slot
#[tokio::test]
async fn invalid_attestation_future_block() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::Blocks(1),
            |attestation, chain| {
                attestation.data.beacon_block_root = chain
                    .block_at_slot(chain.slot().unwrap(), WhenSlotSkipped::Prev)
                    .unwrap()
                    .unwrap()
                    .canonical_root();
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::AttestsToFutureBlock { block, attestation }
                    if block == 2 && attestation == 1
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert target.root == get_ancestor(store, attestation.data.beacon_block_root, target_slot)
#[tokio::test]
async fn invalid_attestation_inconsistent_ffg_vote() {
    let local_opt = Mutex::new(None);
    let attestation_opt = Mutex::new(None);

    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, chain| {
                attestation.data.target.root = chain
                    .block_at_slot(Slot::new(1), WhenSlotSkipped::Prev)
                    .unwrap()
                    .unwrap()
                    .canonical_root();

                *attestation_opt.lock().unwrap() = Some(attestation.data.target.root);
                *local_opt.lock().unwrap() = Some(
                    chain
                        .block_at_slot(Slot::new(0), WhenSlotSkipped::Prev)
                        .unwrap()
                        .unwrap()
                        .canonical_root(),
                );
            },
            |result| {
                assert_invalid_attestation!(
                    result,
                    InvalidAttestation::InvalidTarget { attestation, local }
                    if attestation == attestation_opt.lock().unwrap().unwrap()
                        && local == local_opt.lock().unwrap().unwrap()
                )
            },
        )
        .await;
}

/// Specification v0.12.1:
///
/// assert get_current_slot(store) >= attestation.data.slot + 1
#[tokio::test]
async fn invalid_attestation_delayed_slot() {
    ForkChoiceTest::new()
        .apply_blocks_without_new_attestations(1)
        .await
        .inspect_queued_attestations(|queue| assert_eq!(queue.len(), 0))
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |_, _| {},
            |result| assert!(result.is_ok()),
        )
        .await
        .inspect_queued_attestations(|queue| assert_eq!(queue.len(), 1))
        .skip_slot()
        .inspect_queued_attestations(|queue| assert_eq!(queue.len(), 0));
}

/// Tests that the correct target root is used when the attested-to block is in a prior epoch to
/// the attestation.
#[tokio::test]
async fn valid_attestation_skip_across_epoch() {
    ForkChoiceTest::new()
        .apply_blocks(E::slots_per_epoch() as usize - 1)
        .await
        .skip_slots(2)
        .apply_attestation_to_chain(
            MutationDelay::NoDelay,
            |attestation, _chain| {
                assert_eq!(
                    attestation.data.target.root,
                    attestation.data.beacon_block_root
                )
            },
            |result| result.unwrap(),
        )
        .await;
}

#[tokio::test]
async fn can_read_finalized_block() {
    ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .check_finalized_block_is_accessible();
}

#[test]
#[should_panic]
fn weak_subjectivity_fail_on_startup() {
    let epoch = Epoch::new(0);
    let root = Hash256::from_low_u64_le(1);

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(Checkpoint { epoch, root }),
        ..ChainConfig::default()
    };

    ForkChoiceTest::new_with_chain_config(chain_config);
}

#[tokio::test]
async fn weak_subjectivity_pass_on_startup() {
    let epoch = Epoch::new(0);
    let root = Hash256::zero();

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(Checkpoint { epoch, root }),
        ..ChainConfig::default()
    };

    ForkChoiceTest::new_with_chain_config(chain_config)
        .apply_blocks(E::slots_per_epoch() as usize)
        .await
        .assert_shutdown_signal_not_sent();
}

#[tokio::test]
async fn weak_subjectivity_check_passes() {
    let setup_harness = ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(2);

    let checkpoint = setup_harness.harness.finalized_checkpoint();

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(checkpoint),
        ..ChainConfig::default()
    };

    ForkChoiceTest::new_with_chain_config(chain_config.clone())
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(2)
        .assert_shutdown_signal_not_sent();
}

#[tokio::test]
async fn weak_subjectivity_check_fails_early_epoch() {
    let setup_harness = ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(2);

    let mut checkpoint = setup_harness.harness.finalized_checkpoint();

    checkpoint.epoch -= 1;

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(checkpoint),
        ..ChainConfig::default()
    };

    ForkChoiceTest::new_with_chain_config(chain_config.clone())
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 3)
        .await
        .unwrap_err()
        .assert_finalized_epoch_is_less_than(checkpoint.epoch)
        .assert_shutdown_signal_sent();
}

#[tokio::test]
async fn weak_subjectivity_check_fails_late_epoch() {
    let setup_harness = ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(2);

    let mut checkpoint = setup_harness.harness.finalized_checkpoint();

    checkpoint.epoch += 1;

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(checkpoint),
        ..ChainConfig::default()
    };

    ForkChoiceTest::new_with_chain_config(chain_config.clone())
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 4)
        .await
        .unwrap_err()
        .assert_finalized_epoch_is_less_than(checkpoint.epoch)
        .assert_shutdown_signal_sent();
}

#[tokio::test]
async fn weak_subjectivity_check_fails_incorrect_root() {
    let setup_harness = ForkChoiceTest::new()
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(2);

    let mut checkpoint = setup_harness.harness.finalized_checkpoint();

    checkpoint.root = Hash256::zero();

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(checkpoint),
        ..ChainConfig::default()
    };

    ForkChoiceTest::new_with_chain_config(chain_config.clone())
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 3)
        .await
        .unwrap_err()
        .assert_finalized_epoch_is_less_than(checkpoint.epoch)
        .assert_shutdown_signal_sent();
}

#[tokio::test]
async fn weak_subjectivity_check_epoch_boundary_is_skip_slot() {
    let setup_harness = ForkChoiceTest::new()
        // first two epochs
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap();

    // get the head, it will become the finalized root of epoch 4
    let checkpoint_root = setup_harness.harness.head_block_root();

    setup_harness
        // epoch 3 will be entirely skip slots
        .skip_slots(E::slots_per_epoch() as usize)
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 5)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(5);

    // the checkpoint at epoch 4 should become the root of last block of epoch 2
    let checkpoint = Checkpoint {
        epoch: Epoch::new(4),
        root: checkpoint_root,
    };

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(checkpoint),
        ..ChainConfig::default()
    };

    // recreate the chain exactly
    ForkChoiceTest::new_with_chain_config(chain_config.clone())
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .skip_slots(E::slots_per_epoch() as usize)
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 5)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(5)
        .assert_shutdown_signal_not_sent();
}

#[tokio::test]
async fn weak_subjectivity_check_epoch_boundary_is_skip_slot_failure() {
    let setup_harness = ForkChoiceTest::new()
        // first two epochs
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap();

    // get the head, it will become the finalized root of epoch 4
    let checkpoint_root = setup_harness.harness.head_block_root();

    setup_harness
        // epoch 3 will be entirely skip slots
        .skip_slots(E::slots_per_epoch() as usize)
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 5)
        .await
        .unwrap()
        .apply_blocks(1)
        .await
        .assert_finalized_epoch(5);

    // Invalid checkpoint (epoch too early)
    let checkpoint = Checkpoint {
        epoch: Epoch::new(1),
        root: checkpoint_root,
    };

    let chain_config = ChainConfig {
        weak_subjectivity_checkpoint: Some(checkpoint),
        ..ChainConfig::default()
    };

    // recreate the chain exactly
    ForkChoiceTest::new_with_chain_config(chain_config.clone())
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        .skip_slots(E::slots_per_epoch() as usize)
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch < 6)
        .await
        .unwrap_err()
        .assert_finalized_epoch_is_less_than(checkpoint.epoch)
        .assert_shutdown_signal_sent();
}

/// Checks that `ProgressiveBalancesCache` is updated correctly after an attester slashing event,
/// where the slashed validator is a target attester in previous / current epoch.
#[tokio::test]
async fn progressive_balances_cache_attester_slashing() {
    ForkChoiceTest::new_with_progressive_balances_mode(ProgressiveBalancesMode::Strict)
        // first two epochs
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        // Note: This test may fail if the shuffling used changes, right now it re-runs with
        // deterministic shuffling. A shuffling change my cause the slashed proposer to propose
        // again in the next epoch, which results in a block processing failure
        // (`HeaderInvalid::ProposerSlashed`). The harness should be re-worked to successfully skip
        // the slot in this scenario rather than panic-ing. The same applies to
        // `progressive_balances_cache_proposer_slashing`.
        .apply_blocks(1)
        .await
        .add_previous_epoch_attester_slashing()
        .await
        // expect fork choice to import blocks successfully after a previous epoch attester is
        // slashed, i.e. the slashed attester's balance is correctly excluded from
        // the previous epoch total balance in `ProgressiveBalancesCache`.
        .apply_blocks(1)
        .await
        // expect fork choice to import another epoch of blocks successfully - the slashed
        // attester's balance should be excluded from the current epoch total balance in
        // `ProgressiveBalancesCache` as well.
        .apply_blocks(MainnetEthSpec::slots_per_epoch() as usize)
        .await;
}

/// Checks that `ProgressiveBalancesCache` is updated correctly after a proposer slashing event,
/// where the slashed validator is a target attester in previous / current epoch.
#[tokio::test]
async fn progressive_balances_cache_proposer_slashing() {
    ForkChoiceTest::new_with_progressive_balances_mode(ProgressiveBalancesMode::Strict)
        // first two epochs
        .apply_blocks_while(|_, state| state.finalized_checkpoint().epoch == 0)
        .await
        .unwrap()
        // Note: This test may fail if the shuffling used changes, right now it re-runs with
        // deterministic shuffling. A shuffling change my cause the slashed proposer to propose
        // again in the next epoch, which results in a block processing failure
        // (`HeaderInvalid::ProposerSlashed`). The harness should be re-worked to successfully skip
        // the slot in this scenario rather than panic-ing. The same applies to
        // `progressive_balances_cache_attester_slashing`.
        .apply_blocks(1)
        .await
        .add_previous_epoch_proposer_slashing(MainnetEthSpec::slots_per_epoch())
        .await
        // expect fork choice to import blocks successfully after a previous epoch proposer is
        // slashed, i.e. the slashed proposer's balance is correctly excluded from
        // the previous epoch total balance in `ProgressiveBalancesCache`.
        .apply_blocks(1)
        .await
        // expect fork choice to import another epoch of blocks successfully - the slashed
        // proposer's balance should be excluded from the current epoch total balance in
        // `ProgressiveBalancesCache` as well.
        .apply_blocks(MainnetEthSpec::slots_per_epoch() as usize)
        .await;
}