diff --git a/eth2/state_processing/Cargo.toml b/eth2/state_processing/Cargo.toml
index b6b0ea57c..85ac8b42a 100644
--- a/eth2/state_processing/Cargo.toml
+++ b/eth2/state_processing/Cargo.toml
@@ -4,6 +4,15 @@ version = "0.1.0"
 authors = ["Paul Hauner <paul@paulhauner.com>"]
 edition = "2018"
 
+[[bench]]
+name = "benches"
+harness = false
+
+[dev-dependencies]
+criterion = "0.2"
+test_harness = { path = "../../beacon_node/beacon_chain/test_harness" }
+env_logger = "0.6.0"
+
 [dependencies]
 hashing = { path = "../utils/hashing" }
 int_to_bytes = { path = "../utils/int_to_bytes" }
diff --git a/eth2/state_processing/benches/benches.rs b/eth2/state_processing/benches/benches.rs
new file mode 100644
index 000000000..29f9a1e86
--- /dev/null
+++ b/eth2/state_processing/benches/benches.rs
@@ -0,0 +1,28 @@
+use criterion::Criterion;
+use criterion::{black_box, criterion_group, criterion_main};
+// use env_logger::{Builder, Env};
+use state_processing::SlotProcessable;
+use types::{beacon_state::BeaconStateBuilder, ChainSpec, Hash256};
+
+fn epoch_processing(c: &mut Criterion) {
+    // Builder::from_env(Env::default().default_filter_or("debug")).init();
+
+    let mut builder = BeaconStateBuilder::with_random_validators(8);
+    builder.spec = ChainSpec::few_validators();
+
+    builder.genesis().unwrap();
+    builder.teleport_to_end_of_epoch(builder.spec.genesis_epoch + 4);
+
+    let state = builder.build().unwrap();
+
+    c.bench_function("epoch processing", move |b| {
+        let spec = &builder.spec;
+        b.iter_with_setup(
+            || state.clone(),
+            |mut state| black_box(state.per_slot_processing(Hash256::zero(), spec).unwrap()),
+        )
+    });
+}
+
+criterion_group!(benches, epoch_processing,);
+criterion_main!(benches);
diff --git a/eth2/state_processing/src/epoch_processable.rs b/eth2/state_processing/src/epoch_processable.rs
index 9b6c98c86..2cee455a3 100644
--- a/eth2/state_processing/src/epoch_processable.rs
+++ b/eth2/state_processing/src/epoch_processable.rs
@@ -9,6 +9,8 @@ use types::{
     Crosslink, Epoch, Hash256, InclusionError, PendingAttestation, RelativeEpoch,
 };
 
+mod tests;
+
 macro_rules! safe_add_assign {
     ($a: expr, $b: expr) => {
         $a = $a.saturating_add($b);
@@ -725,11 +727,3 @@ impl From<BeaconStateError> for WinningRootError {
         WinningRootError::BeaconStateError(e)
     }
 }
-
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        assert_eq!(2 + 2, 4);
-    }
-}
diff --git a/eth2/state_processing/src/epoch_processable/tests.rs b/eth2/state_processing/src/epoch_processable/tests.rs
new file mode 100644
index 000000000..353672fd1
--- /dev/null
+++ b/eth2/state_processing/src/epoch_processable/tests.rs
@@ -0,0 +1,21 @@
+#![cfg(test)]
+use crate::EpochProcessable;
+use env_logger::{Builder, Env};
+use types::beacon_state::BeaconStateBuilder;
+use types::*;
+
+#[test]
+fn runs_without_error() {
+    Builder::from_env(Env::default().default_filter_or("error")).init();
+
+    let mut builder = BeaconStateBuilder::with_random_validators(8);
+    builder.spec = ChainSpec::few_validators();
+
+    builder.genesis().unwrap();
+    builder.teleport_to_end_of_epoch(builder.spec.genesis_epoch + 4);
+
+    let mut state = builder.build().unwrap();
+
+    let spec = &builder.spec;
+    state.per_epoch_processing(spec).unwrap();
+}
diff --git a/eth2/types/src/beacon_state.rs b/eth2/types/src/beacon_state.rs
index 85b49bf01..f7df3b0ab 100644
--- a/eth2/types/src/beacon_state.rs
+++ b/eth2/types/src/beacon_state.rs
@@ -7,13 +7,16 @@ use crate::{
 };
 use bls::verify_proof_of_possession;
 use honey_badger_split::SplitExt;
-use log::{debug, trace};
+use log::{debug, error, trace};
 use rand::RngCore;
 use serde_derive::Serialize;
 use ssz::{hash, Decodable, DecodeError, Encodable, SszStream, TreeHash};
 use std::collections::HashMap;
 use swap_or_not_shuffle::get_permutated_index;
 
+pub use builder::BeaconStateBuilder;
+
+mod builder;
 mod epoch_cache;
 mod tests;
 
@@ -384,12 +387,13 @@ impl BeaconState {
         seed: Hash256,
         epoch: Epoch,
         spec: &ChainSpec,
-    ) -> Option<Vec<Vec<usize>>> {
+    ) -> Result<Vec<Vec<usize>>, Error> {
         let active_validator_indices =
             get_active_validator_indices(&self.validator_registry, epoch);
 
         if active_validator_indices.is_empty() {
-            return None;
+            error!("get_shuffling: no validators.");
+            return Err(Error::InsufficientValidators);
         }
 
         let committees_per_epoch =
@@ -402,22 +406,21 @@ impl BeaconState {
         );
 
         let mut shuffled_active_validator_indices = vec![0; active_validator_indices.len()];
-        for &i in &active_validator_indices {
+        for (i, _) in active_validator_indices.iter().enumerate() {
             let shuffled_i = get_permutated_index(
                 i,
                 active_validator_indices.len(),
                 &seed[..],
                 spec.shuffle_round_count,
-            )?;
+            )
+            .ok_or_else(|| Error::UnableToShuffle)?;
             shuffled_active_validator_indices[i] = active_validator_indices[shuffled_i]
         }
 
-        Some(
-            shuffled_active_validator_indices
-                .honey_badger_split(committees_per_epoch as usize)
-                .map(|slice: &[usize]| slice.to_vec())
-                .collect(),
-        )
+        Ok(shuffled_active_validator_indices
+            .honey_badger_split(committees_per_epoch as usize)
+            .map(|slice: &[usize]| slice.to_vec())
+            .collect())
     }
 
     /// Return the number of committees in the previous epoch.
@@ -522,7 +525,6 @@ impl BeaconState {
             self.get_committee_params_at_slot(slot, registry_change, spec)?;
 
         self.get_shuffling(seed, shuffling_epoch, spec)
-            .ok_or_else(|| Error::UnableToShuffle)
     }
 
     /// Returns the following params for the given slot:
diff --git a/eth2/types/src/beacon_state/builder.rs b/eth2/types/src/beacon_state/builder.rs
new file mode 100644
index 000000000..7273f3658
--- /dev/null
+++ b/eth2/types/src/beacon_state/builder.rs
@@ -0,0 +1,215 @@
+use crate::*;
+use bls::create_proof_of_possession;
+
+/// Builds a `BeaconState` for use in testing or benchmarking.
+///
+/// Building the `BeaconState` is a three step processes:
+///
+/// 1. Create a new `BeaconStateBuilder`.
+/// 2. Run the `genesis` function to generate a new BeaconState.
+/// 3. (Optional) Use builder functions to modify the `BeaconState`.
+/// 4. Call `build()` to obtain a cloned `BeaconState`.
+///
+/// Step (2) is necessary because step (3) requires an existing `BeaconState` object. (2) is not
+/// included in (1) to allow for modifying params before generating the `BeaconState` (e.g., the
+/// spec).
+///
+/// Step (4) produces a clone of the BeaconState and doesn't consume the `BeaconStateBuilder` to
+/// allow access to the `keypairs` and `spec`.
+pub struct BeaconStateBuilder {
+    pub state: Option<BeaconState>,
+    pub genesis_time: u64,
+    pub initial_validator_deposits: Vec<Deposit>,
+    pub latest_eth1_data: Eth1Data,
+    pub spec: ChainSpec,
+    pub keypairs: Vec<Keypair>,
+}
+
+impl BeaconStateBuilder {
+    /// Create a new builder with the given number of validators.
+    pub fn with_random_validators(validator_count: usize) -> Self {
+        let genesis_time = 10_000_000;
+        let keypairs: Vec<Keypair> = (0..validator_count)
+            .collect::<Vec<usize>>()
+            .iter()
+            .map(|_| Keypair::random())
+            .collect();
+        let initial_validator_deposits = keypairs
+            .iter()
+            .map(|keypair| Deposit {
+                branch: vec![], // branch verification is not specified.
+                index: 0,       // index verification is not specified.
+                deposit_data: DepositData {
+                    amount: 32_000_000_000, // 32 ETH (in Gwei)
+                    timestamp: genesis_time - 1,
+                    deposit_input: DepositInput {
+                        pubkey: keypair.pk.clone(),
+                        withdrawal_credentials: Hash256::zero(), // Withdrawal not possible.
+                        proof_of_possession: create_proof_of_possession(&keypair),
+                    },
+                },
+            })
+            .collect();
+        let latest_eth1_data = Eth1Data {
+            deposit_root: Hash256::zero(),
+            block_hash: Hash256::zero(),
+        };
+        let spec = ChainSpec::foundation();
+
+        Self {
+            state: None,
+            genesis_time,
+            initial_validator_deposits,
+            latest_eth1_data,
+            spec,
+            keypairs,
+        }
+    }
+
+    /// Runs the `BeaconState::genesis` function and produces a `BeaconState`.
+    pub fn genesis(&mut self) -> Result<(), BeaconStateError> {
+        let state = BeaconState::genesis(
+            self.genesis_time,
+            self.initial_validator_deposits.clone(),
+            self.latest_eth1_data.clone(),
+            &self.spec,
+        )?;
+
+        self.state = Some(state);
+
+        Ok(())
+    }
+
+    /// Sets the `BeaconState` to be in the last slot of the given epoch.
+    ///
+    /// Sets all justification/finalization parameters to be be as "perfect" as possible (i.e.,
+    /// highest justified and finalized slots, full justification bitfield, etc).
+    pub fn teleport_to_end_of_epoch(&mut self, epoch: Epoch) {
+        let state = self.state.as_mut().expect("Genesis required");
+
+        let slot = epoch.end_slot(self.spec.epoch_length);
+
+        state.slot = slot;
+        state.validator_registry_update_epoch = epoch - 1;
+
+        state.previous_calculation_epoch = epoch - 1;
+        state.current_calculation_epoch = epoch;
+
+        state.previous_epoch_seed = Hash256::from(&b"previous_seed"[..]);
+        state.current_epoch_seed = Hash256::from(&b"current_seed"[..]);
+
+        state.previous_justified_epoch = epoch - 2;
+        state.justified_epoch = epoch - 1;
+        state.justification_bitfield = u64::max_value();
+        state.finalized_epoch = epoch - 1;
+    }
+
+    /// Creates a full set of attestations for the `BeaconState`. Each attestation has full
+    /// participation from its committee and references the expected beacon_block hashes.
+    ///
+    /// These attestations should be fully conducive to justification and finalization.
+    pub fn insert_attestations(&mut self) {
+        let state = self.state.as_mut().expect("Genesis required");
+
+        state
+            .build_epoch_cache(RelativeEpoch::Previous, &self.spec)
+            .unwrap();
+        state
+            .build_epoch_cache(RelativeEpoch::Current, &self.spec)
+            .unwrap();
+
+        let current_epoch = state.current_epoch(&self.spec);
+        let previous_epoch = state.previous_epoch(&self.spec);
+        let current_epoch_depth =
+            (state.slot - current_epoch.end_slot(self.spec.epoch_length)).as_usize();
+
+        let previous_epoch_slots = previous_epoch.slot_iter(self.spec.epoch_length);
+        let current_epoch_slots = current_epoch
+            .slot_iter(self.spec.epoch_length)
+            .take(current_epoch_depth);
+
+        for slot in previous_epoch_slots.chain(current_epoch_slots) {
+            let committees = state
+                .get_crosslink_committees_at_slot(slot, &self.spec)
+                .unwrap()
+                .clone();
+
+            for (committee, shard) in committees {
+                state
+                    .latest_attestations
+                    .push(committee_to_pending_attestation(
+                        state, &committee, shard, slot, &self.spec,
+                    ))
+            }
+        }
+    }
+
+    /// Returns a cloned `BeaconState`.
+    pub fn build(&self) -> Result<BeaconState, BeaconStateError> {
+        match &self.state {
+            Some(state) => Ok(state.clone()),
+            None => panic!("Genesis required"),
+        }
+    }
+}
+
+/// Builds a valid PendingAttestation with full participation for some committee.
+fn committee_to_pending_attestation(
+    state: &BeaconState,
+    committee: &[usize],
+    shard: u64,
+    slot: Slot,
+    spec: &ChainSpec,
+) -> PendingAttestation {
+    let current_epoch = state.current_epoch(spec);
+    let previous_epoch = state.previous_epoch(spec);
+
+    let mut aggregation_bitfield = Bitfield::new();
+    let mut custody_bitfield = Bitfield::new();
+
+    for (i, _) in committee.iter().enumerate() {
+        aggregation_bitfield.set(i, true);
+        custody_bitfield.set(i, true);
+    }
+
+    let is_previous_epoch = state.slot.epoch(spec.epoch_length) != slot.epoch(spec.epoch_length);
+
+    let justified_epoch = if is_previous_epoch {
+        state.previous_justified_epoch
+    } else {
+        state.justified_epoch
+    };
+
+    let epoch_boundary_root = if is_previous_epoch {
+        *state
+            .get_block_root(previous_epoch.start_slot(spec.epoch_length), spec)
+            .unwrap()
+    } else {
+        *state
+            .get_block_root(current_epoch.start_slot(spec.epoch_length), spec)
+            .unwrap()
+    };
+
+    let justified_block_root = *state
+        .get_block_root(justified_epoch.start_slot(spec.epoch_length), &spec)
+        .unwrap();
+
+    PendingAttestation {
+        aggregation_bitfield,
+        data: AttestationData {
+            slot,
+            shard,
+            beacon_block_root: *state.get_block_root(slot, spec).unwrap(),
+            epoch_boundary_root,
+            shard_block_root: Hash256::zero(),
+            latest_crosslink: Crosslink {
+                epoch: slot.epoch(spec.epoch_length),
+                shard_block_root: Hash256::zero(),
+            },
+            justified_epoch,
+            justified_block_root,
+        },
+        custody_bitfield,
+        inclusion_slot: slot,
+    }
+}
diff --git a/eth2/types/src/beacon_state/tests.rs b/eth2/types/src/beacon_state/tests.rs
index a4a43a8ed..01b4be803 100644
--- a/eth2/types/src/beacon_state/tests.rs
+++ b/eth2/types/src/beacon_state/tests.rs
@@ -2,73 +2,13 @@
 
 use super::*;
 use crate::test_utils::{SeedableRng, TestRandom, XorShiftRng};
-use crate::{
-    BeaconState, BeaconStateError, ChainSpec, Deposit, DepositData, DepositInput, Eth1Data,
-    Hash256, Keypair,
-};
-use bls::create_proof_of_possession;
+use crate::{BeaconState, ChainSpec};
 use ssz::{ssz_encode, Decodable};
 
-struct BeaconStateTestBuilder {
-    pub genesis_time: u64,
-    pub initial_validator_deposits: Vec<Deposit>,
-    pub latest_eth1_data: Eth1Data,
-    pub spec: ChainSpec,
-    pub keypairs: Vec<Keypair>,
-}
-
-impl BeaconStateTestBuilder {
-    pub fn with_random_validators(validator_count: usize) -> Self {
-        let genesis_time = 10_000_000;
-        let keypairs: Vec<Keypair> = (0..validator_count)
-            .collect::<Vec<usize>>()
-            .iter()
-            .map(|_| Keypair::random())
-            .collect();
-        let initial_validator_deposits = keypairs
-            .iter()
-            .map(|keypair| Deposit {
-                branch: vec![], // branch verification is not specified.
-                index: 0,       // index verification is not specified.
-                deposit_data: DepositData {
-                    amount: 32_000_000_000, // 32 ETH (in Gwei)
-                    timestamp: genesis_time - 1,
-                    deposit_input: DepositInput {
-                        pubkey: keypair.pk.clone(),
-                        withdrawal_credentials: Hash256::zero(), // Withdrawal not possible.
-                        proof_of_possession: create_proof_of_possession(&keypair),
-                    },
-                },
-            })
-            .collect();
-        let latest_eth1_data = Eth1Data {
-            deposit_root: Hash256::zero(),
-            block_hash: Hash256::zero(),
-        };
-        let spec = ChainSpec::foundation();
-
-        Self {
-            genesis_time,
-            initial_validator_deposits,
-            latest_eth1_data,
-            spec,
-            keypairs,
-        }
-    }
-
-    pub fn build(&self) -> Result<BeaconState, BeaconStateError> {
-        BeaconState::genesis(
-            self.genesis_time,
-            self.initial_validator_deposits.clone(),
-            self.latest_eth1_data.clone(),
-            &self.spec,
-        )
-    }
-}
-
 #[test]
 pub fn can_produce_genesis_block() {
-    let builder = BeaconStateTestBuilder::with_random_validators(2);
+    let mut builder = BeaconStateBuilder::with_random_validators(2);
+    builder.genesis().unwrap();
 
     builder.build().unwrap();
 }
@@ -79,9 +19,11 @@ pub fn can_produce_genesis_block() {
 pub fn get_attestation_participants_consistency() {
     let mut rng = XorShiftRng::from_seed([42; 16]);
 
-    let mut builder = BeaconStateTestBuilder::with_random_validators(8);
+    let mut builder = BeaconStateBuilder::with_random_validators(8);
     builder.spec = ChainSpec::few_validators();
 
+    builder.genesis().unwrap();
+
     let mut state = builder.build().unwrap();
     let spec = builder.spec.clone();