diff --git a/beacon_node/beacon_chain/src/attestation_aggregation.rs b/beacon_node/beacon_chain/src/attestation_aggregator.rs
similarity index 98%
rename from beacon_node/beacon_chain/src/attestation_aggregation.rs
rename to beacon_node/beacon_chain/src/attestation_aggregator.rs
index 4cac5056cb..4b83bbebcb 100644
--- a/beacon_node/beacon_chain/src/attestation_aggregation.rs
+++ b/beacon_node/beacon_chain/src/attestation_aggregator.rs
@@ -9,12 +9,14 @@ pub struct AttestationAggregator {
     store: HashMap<Vec<u8>, Attestation>,
 }
 
+#[derive(Debug, PartialEq)]
 pub enum ProcessOutcome {
     AggregationNotRequired,
     Aggregated,
     NewAttestationCreated,
 }
 
+#[derive(Debug, PartialEq)]
 pub enum ProcessError {
     BadValidatorIndex,
     BadSignature,
diff --git a/beacon_node/beacon_chain/src/attestation_processing.rs b/beacon_node/beacon_chain/src/attestation_processing.rs
new file mode 100644
index 0000000000..90107dd97b
--- /dev/null
+++ b/beacon_node/beacon_chain/src/attestation_processing.rs
@@ -0,0 +1,47 @@
+use super::{BeaconChain, ClientDB, SlotClock};
+pub use crate::attestation_aggregator::{ProcessError as AggregatorError, ProcessOutcome};
+use crate::canonical_head::Error as HeadError;
+use types::{AttestationData, Signature};
+
+#[derive(Debug, PartialEq)]
+pub enum Error {
+    PresentSlotUnknown,
+    AggregatorError(AggregatorError),
+    HeadError(HeadError),
+}
+
+impl<T, U> BeaconChain<T, U>
+where
+    T: ClientDB,
+    U: SlotClock,
+{
+    pub fn process_free_attestation(
+        &self,
+        attestation_data: &AttestationData,
+        signature: &Signature,
+        validator_index: u64,
+    ) -> Result<ProcessOutcome, Error> {
+        let present_slot = self
+            .present_slot()
+            .ok_or_else(|| Error::PresentSlotUnknown)?;
+        let state = self.state(present_slot)?;
+
+        self.attestation_aggregator
+            .write()
+            .expect("Aggregator unlock failed.")
+            .process_free_attestation(&state, attestation_data, signature, validator_index)
+            .map_err(|e| e.into())
+    }
+}
+
+impl From<AggregatorError> for Error {
+    fn from(e: AggregatorError) -> Error {
+        Error::AggregatorError(e)
+    }
+}
+
+impl From<HeadError> for Error {
+    fn from(e: HeadError) -> Error {
+        Error::HeadError(e)
+    }
+}
diff --git a/beacon_node/beacon_chain/src/attestation_production.rs b/beacon_node/beacon_chain/src/attestation_production.rs
index 33d220b7f7..5adf70a4ac 100644
--- a/beacon_node/beacon_chain/src/attestation_production.rs
+++ b/beacon_node/beacon_chain/src/attestation_production.rs
@@ -3,11 +3,6 @@ use types::{AttestationData, Hash256};
 
 #[derive(Debug, PartialEq)]
 pub enum Error {
-    /*
-    DBError(String),
-    StateTransitionError(TransitionError),
-    PresentSlotIsNone,
-    */
     SlotTooOld,
     PresentSlotUnknown,
     StateError,
diff --git a/beacon_node/beacon_chain/src/canonical_head.rs b/beacon_node/beacon_chain/src/canonical_head.rs
index 121ded7676..04bbe57ed7 100644
--- a/beacon_node/beacon_chain/src/canonical_head.rs
+++ b/beacon_node/beacon_chain/src/canonical_head.rs
@@ -2,6 +2,7 @@ use crate::{BeaconChain, CheckPoint, ClientDB, SlotClock};
 use std::sync::RwLockReadGuard;
 use types::{beacon_state::SlotProcessingError, BeaconBlock, BeaconState, Hash256};
 
+#[derive(Debug, PartialEq)]
 pub enum Error {
     PastSlot,
     UnableToDetermineProducer,
diff --git a/beacon_node/beacon_chain/src/info.rs b/beacon_node/beacon_chain/src/info.rs
index 441d56b784..fd23c0906c 100644
--- a/beacon_node/beacon_chain/src/info.rs
+++ b/beacon_node/beacon_chain/src/info.rs
@@ -52,4 +52,11 @@ where
             .beacon_block
             .slot
     }
+
+    pub fn validator_attestion_slot_and_shard(&self, validator_index: usize) -> Option<(u64, u64)> {
+        let present_slot = self.present_slot()?;
+        let state = self.state(present_slot).ok()?;
+
+        Some(state.attestation_slot_and_shard_for_validator(validator_index, &self.spec))
+    }
 }
diff --git a/beacon_node/beacon_chain/src/lib.rs b/beacon_node/beacon_chain/src/lib.rs
index c4da9099f1..401479e5a8 100644
--- a/beacon_node/beacon_chain/src/lib.rs
+++ b/beacon_node/beacon_chain/src/lib.rs
@@ -1,4 +1,5 @@
-mod attestation_aggregation;
+mod attestation_aggregator;
+pub mod attestation_processing;
 mod attestation_production;
 mod attestation_targets;
 mod block_graph;
@@ -14,7 +15,7 @@ mod state_transition;
 
 use self::attestation_targets::AttestationTargets;
 use self::block_graph::BlockGraph;
-use attestation_aggregation::AttestationAggregator;
+use attestation_aggregator::AttestationAggregator;
 use db::{
     stores::{BeaconBlockStore, BeaconStateStore},
     ClientDB, DBError,
diff --git a/beacon_node/beacon_chain/test_harness/Cargo.toml b/beacon_node/beacon_chain/test_harness/Cargo.toml
index 72fdf7164d..5aa57b0b46 100644
--- a/beacon_node/beacon_chain/test_harness/Cargo.toml
+++ b/beacon_node/beacon_chain/test_harness/Cargo.toml
@@ -12,11 +12,13 @@ harness = false
 criterion = "0.2"
 
 [dependencies]
+attester = { path = "../../../eth2/attester" }
 beacon_chain = { path = "../../beacon_chain" }
 block_producer = { path = "../../../eth2/block_producer" }
 bls = { path = "../../../eth2/utils/bls" }
 boolean-bitfield = { path = "../../../eth2/utils/boolean-bitfield" }
 db = { path = "../../db" }
+parking_lot = "0.7"
 failure = "0.1"
 failure_derive = "0.1"
 genesis = { path = "../../../eth2/genesis" }
diff --git a/beacon_node/beacon_chain/test_harness/src/direct_beacon_node.rs b/beacon_node/beacon_chain/test_harness/src/direct_beacon_node.rs
deleted file mode 100644
index 9fcd7c2862..0000000000
--- a/beacon_node/beacon_chain/test_harness/src/direct_beacon_node.rs
+++ /dev/null
@@ -1,71 +0,0 @@
-use beacon_chain::block_processing::{Error as ProcessingError, Outcome as ProcessingOutcome};
-use beacon_chain::{block_production::Error as BlockProductionError, BeaconChain};
-use block_producer::{
-    BeaconNode as BeaconBlockNode, BeaconNodeError as BeaconBlockNodeError, PublishOutcome,
-};
-use db::ClientDB;
-use slot_clock::SlotClock;
-use std::sync::Arc;
-use types::{BeaconBlock, PublicKey, Signature};
-
-pub struct DirectBeaconNode<T: ClientDB, U: SlotClock> {
-    beacon_chain: Arc<BeaconChain<T, U>>,
-}
-
-impl<T: ClientDB, U: SlotClock> DirectBeaconNode<T, U> {
-    pub fn new(beacon_chain: Arc<BeaconChain<T, U>>) -> Self {
-        Self { beacon_chain }
-    }
-}
-
-impl<T: ClientDB, U: SlotClock> BeaconBlockNode for DirectBeaconNode<T, U>
-where
-    BlockProductionError: From<<U>::Error>,
-    ProcessingError: From<<U as SlotClock>::Error>,
-{
-    fn proposer_nonce(&self, pubkey: &PublicKey) -> Result<u64, BeaconBlockNodeError> {
-        let validator_index = self
-            .beacon_chain
-            .validator_index(pubkey)
-            .ok_or_else(|| BeaconBlockNodeError::RemoteFailure("pubkey unknown.".to_string()))?;
-
-        self.beacon_chain
-            .proposer_slots(validator_index)
-            .ok_or_else(|| {
-                BeaconBlockNodeError::RemoteFailure("validator_index unknown.".to_string())
-            })
-    }
-
-    fn produce_beacon_block(
-        &self,
-        slot: u64,
-        randao_reveal: &Signature,
-    ) -> Result<Option<BeaconBlock>, BeaconBlockNodeError>
-where {
-        let (block, _state) = self
-            .beacon_chain
-            .produce_block(randao_reveal.clone())
-            .map_err(|e| BeaconBlockNodeError::RemoteFailure(format!("{:?}", e)))?;
-
-        if block.slot == slot {
-            Ok(Some(block))
-        } else {
-            Err(BeaconBlockNodeError::RemoteFailure(
-                "Unable to produce at non-current slot.".to_string(),
-            ))
-        }
-    }
-
-    fn publish_beacon_block(
-        &self,
-        block: BeaconBlock,
-    ) -> Result<PublishOutcome, BeaconBlockNodeError> {
-        match self.beacon_chain.process_block(block) {
-            Ok(ProcessingOutcome::ValidBlock(_)) => Ok(PublishOutcome::ValidBlock),
-            Ok(ProcessingOutcome::InvalidBlock(reason)) => {
-                Ok(PublishOutcome::InvalidBlock(format!("{:?}", reason)))
-            }
-            Err(error) => Err(BeaconBlockNodeError::RemoteFailure(format!("{:?}", error))),
-        }
-    }
-}
diff --git a/beacon_node/beacon_chain/test_harness/src/direct_duties.rs b/beacon_node/beacon_chain/test_harness/src/direct_duties.rs
deleted file mode 100644
index ff2cd7223f..0000000000
--- a/beacon_node/beacon_chain/test_harness/src/direct_duties.rs
+++ /dev/null
@@ -1,38 +0,0 @@
-use beacon_chain::{block_production::Error as BlockProductionError, BeaconChain};
-use block_producer::{DutiesReader, DutiesReaderError};
-use db::ClientDB;
-use slot_clock::SlotClock;
-use std::sync::Arc;
-use types::PublicKey;
-
-pub struct DirectDuties<T: ClientDB, U: SlotClock> {
-    beacon_chain: Arc<BeaconChain<T, U>>,
-    pubkey: PublicKey,
-}
-
-impl<T: ClientDB, U: SlotClock> DirectDuties<T, U> {
-    pub fn new(pubkey: PublicKey, beacon_chain: Arc<BeaconChain<T, U>>) -> Self {
-        Self {
-            beacon_chain,
-            pubkey,
-        }
-    }
-}
-
-impl<T: ClientDB, U: SlotClock> DutiesReader for DirectDuties<T, U>
-where
-    BlockProductionError: From<<U>::Error>,
-{
-    fn is_block_production_slot(&self, slot: u64) -> Result<bool, DutiesReaderError> {
-        let validator_index = self
-            .beacon_chain
-            .validator_index(&self.pubkey)
-            .ok_or_else(|| DutiesReaderError::UnknownValidator)?;
-
-        match self.beacon_chain.block_proposer(slot) {
-            Some(proposer) if proposer == validator_index => Ok(true),
-            Some(_) => Ok(false),
-            None => Err(DutiesReaderError::UnknownEpoch),
-        }
-    }
-}
diff --git a/beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs b/beacon_node/beacon_chain/test_harness/src/harness.rs
similarity index 100%
rename from beacon_node/beacon_chain/test_harness/src/beacon_chain_harness.rs
rename to beacon_node/beacon_chain/test_harness/src/harness.rs
diff --git a/beacon_node/beacon_chain/test_harness/src/lib.rs b/beacon_node/beacon_chain/test_harness/src/lib.rs
index efdc39e1e5..71f9a88558 100644
--- a/beacon_node/beacon_chain/test_harness/src/lib.rs
+++ b/beacon_node/beacon_chain/test_harness/src/lib.rs
@@ -1,11 +1,5 @@
-mod beacon_chain_harness;
-mod benching_beacon_node;
-mod direct_beacon_node;
-mod direct_duties;
+mod harness;
 mod validator;
 
-pub use self::beacon_chain_harness::BeaconChainHarness;
-pub use self::benching_beacon_node::BenchingBeaconNode;
-pub use self::direct_beacon_node::DirectBeaconNode;
-pub use self::direct_duties::DirectDuties;
+pub use self::harness::BeaconChainHarness;
 pub use self::validator::TestValidator;
diff --git a/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/attester.rs b/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/attester.rs
new file mode 100644
index 0000000000..71c45dd314
--- /dev/null
+++ b/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/attester.rs
@@ -0,0 +1,40 @@
+use super::BenchingBeaconNode;
+use attester::{BeaconNode as AttesterBeaconNode, BeaconNodeError as NodeError, PublishOutcome};
+use beacon_chain::block_processing::Error as ProcessingError;
+use beacon_chain::block_production::Error as BlockProductionError;
+use db::ClientDB;
+use slot_clock::SlotClock;
+use types::{AttestationData, Signature};
+
+impl<T: ClientDB, U: SlotClock> AttesterBeaconNode for BenchingBeaconNode<T, U>
+where
+    BlockProductionError: From<<U>::Error>,
+    ProcessingError: From<<U as SlotClock>::Error>,
+{
+    fn produce_attestation_data(
+        &self,
+        slot: u64,
+        shard: u64,
+    ) -> Result<Option<AttestationData>, NodeError> {
+        match self.beacon_chain.produce_attestation_data(slot, shard) {
+            Ok(attestation_data) => Ok(Some(attestation_data)),
+            Err(e) => Err(NodeError::RemoteFailure(format!("{:?}", e))),
+        }
+    }
+
+    fn publish_attestation_data(
+        &self,
+        attestation_data: AttestationData,
+        signature: Signature,
+        validator_index: u64,
+    ) -> Result<PublishOutcome, NodeError> {
+        match self.beacon_chain.process_free_attestation(
+            &attestation_data,
+            &signature,
+            validator_index,
+        ) {
+            Ok(_) => Ok(PublishOutcome::ValidAttestation),
+            Err(e) => Err(NodeError::RemoteFailure(format!("{:?}", e))),
+        }
+    }
+}
diff --git a/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/mod.rs b/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/mod.rs
new file mode 100644
index 0000000000..60664468df
--- /dev/null
+++ b/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/mod.rs
@@ -0,0 +1,34 @@
+use beacon_chain::BeaconChain;
+use db::ClientDB;
+use parking_lot::RwLock;
+use slot_clock::SlotClock;
+use std::sync::Arc;
+use types::{AttestationData, BeaconBlock, Signature};
+
+mod attester;
+mod producer;
+
+/// An attestation that hasn't been aggregated into an `Attestation`.
+///
+/// (attestation_data, signature, validator_index)
+pub type FreeAttestation = (AttestationData, Signature, u64);
+
+pub struct BenchingBeaconNode<T: ClientDB, U: SlotClock> {
+    beacon_chain: Arc<BeaconChain<T, U>>,
+    published_blocks: RwLock<Vec<BeaconBlock>>,
+    published_attestations: RwLock<Vec<FreeAttestation>>,
+}
+
+impl<T: ClientDB, U: SlotClock> BenchingBeaconNode<T, U> {
+    pub fn new(beacon_chain: Arc<BeaconChain<T, U>>) -> Self {
+        Self {
+            beacon_chain,
+            published_blocks: RwLock::new(vec![]),
+            published_attestations: RwLock::new(vec![]),
+        }
+    }
+
+    pub fn last_published_block(&self) -> Option<BeaconBlock> {
+        Some(self.published_blocks.read().last()?.clone())
+    }
+}
diff --git a/beacon_node/beacon_chain/test_harness/src/benching_beacon_node.rs b/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/producer.rs
similarity index 67%
rename from beacon_node/beacon_chain/test_harness/src/benching_beacon_node.rs
rename to beacon_node/beacon_chain/test_harness/src/validator/beacon_node/producer.rs
index 551fbff99c..70ca4ff0cb 100644
--- a/beacon_node/beacon_chain/test_harness/src/benching_beacon_node.rs
+++ b/beacon_node/beacon_chain/test_harness/src/validator/beacon_node/producer.rs
@@ -1,37 +1,13 @@
+use super::BenchingBeaconNode;
 use beacon_chain::block_processing::Error as ProcessingError;
-use beacon_chain::{block_production::Error as BlockProductionError, BeaconChain};
+use beacon_chain::block_production::Error as BlockProductionError;
 use block_producer::{
     BeaconNode as BeaconBlockNode, BeaconNodeError as BeaconBlockNodeError, PublishOutcome,
 };
 use db::ClientDB;
 use slot_clock::SlotClock;
-use std::sync::{Arc, RwLock};
 use types::{BeaconBlock, PublicKey, Signature};
 
-pub struct BenchingBeaconNode<T: ClientDB, U: SlotClock> {
-    beacon_chain: Arc<BeaconChain<T, U>>,
-    published_blocks: RwLock<Vec<BeaconBlock>>,
-}
-
-impl<T: ClientDB, U: SlotClock> BenchingBeaconNode<T, U> {
-    pub fn new(beacon_chain: Arc<BeaconChain<T, U>>) -> Self {
-        Self {
-            beacon_chain,
-            published_blocks: RwLock::new(vec![]),
-        }
-    }
-
-    pub fn last_published_block(&self) -> Option<BeaconBlock> {
-        Some(
-            self.published_blocks
-                .read()
-                .expect("Unable to unlock `published_blocks` for reading.")
-                .last()?
-                .clone(),
-        )
-    }
-}
-
 impl<T: ClientDB, U: SlotClock> BeaconBlockNode for BenchingBeaconNode<T, U>
 where
     BlockProductionError: From<<U>::Error>,
@@ -56,8 +32,7 @@ where
         &self,
         slot: u64,
         randao_reveal: &Signature,
-    ) -> Result<Option<BeaconBlock>, BeaconBlockNodeError>
-where {
+    ) -> Result<Option<BeaconBlock>, BeaconBlockNodeError> {
         let (block, _state) = self
             .beacon_chain
             .produce_block(randao_reveal.clone())
@@ -81,10 +56,7 @@ where {
         &self,
         block: BeaconBlock,
     ) -> Result<PublishOutcome, BeaconBlockNodeError> {
-        self.published_blocks
-            .write()
-            .expect("Unable to unlock `published_blocks` for writing.")
-            .push(block);
+        self.published_blocks.write().push(block);
         Ok(PublishOutcome::ValidBlock)
     }
 }
diff --git a/beacon_node/beacon_chain/test_harness/src/validator/direct_duties.rs b/beacon_node/beacon_chain/test_harness/src/validator/direct_duties.rs
new file mode 100644
index 0000000000..3259817ad1
--- /dev/null
+++ b/beacon_node/beacon_chain/test_harness/src/validator/direct_duties.rs
@@ -0,0 +1,70 @@
+use attester::{
+    DutiesReader as AttesterDutiesReader, DutiesReaderError as AttesterDutiesReaderError,
+};
+use beacon_chain::{block_production::Error as BlockProductionError, BeaconChain};
+use block_producer::{
+    DutiesReader as ProducerDutiesReader, DutiesReaderError as ProducerDutiesReaderError,
+};
+use db::ClientDB;
+use slot_clock::SlotClock;
+use std::sync::Arc;
+use types::PublicKey;
+
+pub struct DirectDuties<T: ClientDB, U: SlotClock> {
+    beacon_chain: Arc<BeaconChain<T, U>>,
+    pubkey: PublicKey,
+}
+
+impl<T: ClientDB, U: SlotClock> DirectDuties<T, U> {
+    pub fn new(pubkey: PublicKey, beacon_chain: Arc<BeaconChain<T, U>>) -> Self {
+        Self {
+            beacon_chain,
+            pubkey,
+        }
+    }
+}
+
+impl<T: ClientDB, U: SlotClock> ProducerDutiesReader for DirectDuties<T, U>
+where
+    BlockProductionError: From<<U>::Error>,
+{
+    fn is_block_production_slot(&self, slot: u64) -> Result<bool, ProducerDutiesReaderError> {
+        let validator_index = self
+            .beacon_chain
+            .validator_index(&self.pubkey)
+            .ok_or_else(|| ProducerDutiesReaderError::UnknownValidator)?;
+
+        match self.beacon_chain.block_proposer(slot) {
+            Some(proposer) if proposer == validator_index => Ok(true),
+            Some(_) => Ok(false),
+            None => Err(ProducerDutiesReaderError::UnknownEpoch),
+        }
+    }
+}
+
+impl<T: ClientDB, U: SlotClock> AttesterDutiesReader for DirectDuties<T, U>
+where
+    BlockProductionError: From<<U>::Error>,
+{
+    fn validator_index(&self) -> Option<u64> {
+        match self.beacon_chain.validator_index(&self.pubkey) {
+            Some(index) => Some(index as u64),
+            None => None,
+        }
+    }
+
+    fn attestation_shard(&self, slot: u64) -> Result<Option<u64>, AttesterDutiesReaderError> {
+        if let Some(validator_index) = self.validator_index() {
+            match self
+                .beacon_chain
+                .validator_attestion_slot_and_shard(validator_index as usize)
+            {
+                Some((attest_slot, attest_shard)) if attest_slot == slot => Ok(Some(attest_shard)),
+                Some(_) => Ok(None),
+                None => Err(AttesterDutiesReaderError::UnknownEpoch),
+            }
+        } else {
+            Err(AttesterDutiesReaderError::UnknownValidator)
+        }
+    }
+}
diff --git a/beacon_node/beacon_chain/test_harness/src/validator.rs b/beacon_node/beacon_chain/test_harness/src/validator/mod.rs
similarity index 79%
rename from beacon_node/beacon_chain/test_harness/src/validator.rs
rename to beacon_node/beacon_chain/test_harness/src/validator/mod.rs
index 1d7f7bd4a1..f2ac960755 100644
--- a/beacon_node/beacon_chain/test_harness/src/validator.rs
+++ b/beacon_node/beacon_chain/test_harness/src/validator/mod.rs
@@ -1,11 +1,18 @@
-use super::{BenchingBeaconNode, DirectDuties};
+use attester::Attester;
 use beacon_chain::BeaconChain;
-use block_producer::{test_utils::TestSigner, BlockProducer, Error as PollError};
+use block_producer::{BlockProducer, Error as PollError};
 use db::MemoryDB;
+use signer::TestSigner;
 use slot_clock::TestingSlotClock;
 use std::sync::Arc;
 use types::{BeaconBlock, ChainSpec, Keypair};
 
+mod beacon_node;
+mod direct_duties;
+mod signer;
+
+pub use self::beacon_node::BenchingBeaconNode;
+pub use self::direct_duties::DirectDuties;
 pub use block_producer::PollOutcome;
 
 #[derive(Debug, PartialEq)]
@@ -21,6 +28,12 @@ pub struct TestValidator {
         DirectDuties<MemoryDB, TestingSlotClock>,
         TestSigner,
     >,
+    pub attester: Attester<
+        TestingSlotClock,
+        BenchingBeaconNode<MemoryDB, TestingSlotClock>,
+        DirectDuties<MemoryDB, TestingSlotClock>,
+        TestSigner,
+    >,
     pub spec: Arc<ChainSpec>,
     pub epoch_map: Arc<DirectDuties<MemoryDB, TestingSlotClock>>,
     pub keypair: Keypair,
@@ -49,8 +62,16 @@ impl TestValidator {
             signer.clone(),
         );
 
+        let attester = Attester::new(
+            epoch_map.clone(),
+            slot_clock.clone(),
+            beacon_node.clone(),
+            signer.clone(),
+        );
+
         Self {
             block_producer,
+            attester,
             spec,
             epoch_map,
             keypair,
diff --git a/beacon_node/beacon_chain/test_harness/src/validator/signer.rs b/beacon_node/beacon_chain/test_harness/src/validator/signer.rs
new file mode 100644
index 0000000000..572a870ffc
--- /dev/null
+++ b/beacon_node/beacon_chain/test_harness/src/validator/signer.rs
@@ -0,0 +1,46 @@
+use attester::Signer as AttesterSigner;
+use block_producer::Signer as BlockProposerSigner;
+use std::sync::RwLock;
+use types::{Keypair, Signature};
+
+/// A test-only struct used to simulate a Beacon Node.
+pub struct TestSigner {
+    keypair: Keypair,
+    should_sign: RwLock<bool>,
+}
+
+impl TestSigner {
+    /// Produce a new TestSigner with signing enabled by default.
+    pub fn new(keypair: Keypair) -> Self {
+        Self {
+            keypair,
+            should_sign: RwLock::new(true),
+        }
+    }
+
+    /// If set to `false`, the service will refuse to sign all messages. Otherwise, all messages
+    /// will be signed.
+    pub fn enable_signing(&self, enabled: bool) {
+        *self.should_sign.write().unwrap() = enabled;
+    }
+
+    fn bls_sign(&self, message: &[u8]) -> Option<Signature> {
+        Some(Signature::new(message, &self.keypair.sk))
+    }
+}
+
+impl BlockProposerSigner for TestSigner {
+    fn sign_block_proposal(&self, message: &[u8]) -> Option<Signature> {
+        self.bls_sign(message)
+    }
+
+    fn sign_randao_reveal(&self, message: &[u8]) -> Option<Signature> {
+        self.bls_sign(message)
+    }
+}
+
+impl AttesterSigner for TestSigner {
+    fn sign_attestation_message(&self, message: &[u8]) -> Option<Signature> {
+        self.bls_sign(message)
+    }
+}
diff --git a/eth2/attester/src/lib.rs b/eth2/attester/src/lib.rs
index 7e3f0eb6b8..6047626346 100644
--- a/eth2/attester/src/lib.rs
+++ b/eth2/attester/src/lib.rs
@@ -131,7 +131,7 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> Attester<T, U, V,
         self.store_produce(attestation_data);
 
         self.signer
-            .bls_sign(&attestation_data.signable_message(PHASE_0_CUSTODY_BIT)[..])
+            .sign_attestation_message(&attestation_data.signable_message(PHASE_0_CUSTODY_BIT)[..])
     }
 
     /// Returns `true` if signing some attestation_data is safe (non-slashable).
diff --git a/eth2/attester/src/test_utils/signer.rs b/eth2/attester/src/test_utils/signer.rs
index d43c0feb0c..185dec2787 100644
--- a/eth2/attester/src/test_utils/signer.rs
+++ b/eth2/attester/src/test_utils/signer.rs
@@ -25,7 +25,7 @@ impl TestSigner {
 }
 
 impl Signer for TestSigner {
-    fn bls_sign(&self, message: &[u8]) -> Option<Signature> {
+    fn sign_attestation_message(&self, message: &[u8]) -> Option<Signature> {
         Some(Signature::new(message, &self.keypair.sk))
     }
 }
diff --git a/eth2/attester/src/traits.rs b/eth2/attester/src/traits.rs
index bc3ccf63f1..ce6a635e71 100644
--- a/eth2/attester/src/traits.rs
+++ b/eth2/attester/src/traits.rs
@@ -47,5 +47,5 @@ pub trait DutiesReader: Send + Sync {
 
 /// Signs message using an internally-maintained private key.
 pub trait Signer {
-    fn bls_sign(&self, message: &[u8]) -> Option<Signature>;
+    fn sign_attestation_message(&self, message: &[u8]) -> Option<Signature>;
 }
diff --git a/eth2/block_producer/src/lib.rs b/eth2/block_producer/src/lib.rs
index 4ea08647df..ed65622d4d 100644
--- a/eth2/block_producer/src/lib.rs
+++ b/eth2/block_producer/src/lib.rs
@@ -4,7 +4,7 @@ mod traits;
 use slot_clock::SlotClock;
 use ssz::ssz_encode;
 use std::sync::Arc;
-use types::{BeaconBlock, ChainSpec, Hash256, ProposalSignedData, PublicKey};
+use types::{BeaconBlock, ChainSpec, PublicKey};
 
 pub use self::traits::{
     BeaconNode, BeaconNodeError, DutiesReader, DutiesReaderError, PublishOutcome, Signer,
@@ -139,7 +139,7 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> BlockProducer<T, U
             // TODO: add domain, etc to this message.
             let message = ssz_encode(&producer_nonce);
 
-            match self.signer.bls_sign(&message) {
+            match self.signer.sign_randao_reveal(&message) {
                 None => return Ok(PollOutcome::SignerRejection(slot)),
                 Some(signature) => signature,
             }
@@ -171,7 +171,10 @@ impl<T: SlotClock, U: BeaconNode, V: DutiesReader, W: Signer> BlockProducer<T, U
     fn sign_block(&mut self, mut block: BeaconBlock) -> Option<BeaconBlock> {
         self.store_produce(&block);
 
-        match self.signer.bls_sign(&block.proposal_root(&self.spec)[..]) {
+        match self
+            .signer
+            .sign_block_proposal(&block.proposal_root(&self.spec)[..])
+        {
             None => None,
             Some(signature) => {
                 block.signature = signature;
diff --git a/eth2/block_producer/src/test_utils/signer.rs b/eth2/block_producer/src/test_utils/signer.rs
index d43c0feb0c..62163f5b21 100644
--- a/eth2/block_producer/src/test_utils/signer.rs
+++ b/eth2/block_producer/src/test_utils/signer.rs
@@ -25,7 +25,11 @@ impl TestSigner {
 }
 
 impl Signer for TestSigner {
-    fn bls_sign(&self, message: &[u8]) -> Option<Signature> {
+    fn sign_block_proposal(&self, message: &[u8]) -> Option<Signature> {
+        Some(Signature::new(message, &self.keypair.sk))
+    }
+
+    fn sign_randao_reveal(&self, message: &[u8]) -> Option<Signature> {
         Some(Signature::new(message, &self.keypair.sk))
     }
 }
diff --git a/eth2/block_producer/src/traits.rs b/eth2/block_producer/src/traits.rs
index 451ce6cc76..b09b81e672 100644
--- a/eth2/block_producer/src/traits.rs
+++ b/eth2/block_producer/src/traits.rs
@@ -47,5 +47,6 @@ pub trait DutiesReader: Send + Sync {
 
 /// Signs message using an internally-maintained private key.
 pub trait Signer {
-    fn bls_sign(&self, message: &[u8]) -> Option<Signature>;
+    fn sign_block_proposal(&self, message: &[u8]) -> Option<Signature>;
+    fn sign_randao_reveal(&self, message: &[u8]) -> Option<Signature>;
 }
diff --git a/eth2/types/src/beacon_state/slot_processing.rs b/eth2/types/src/beacon_state/slot_processing.rs
index e3be9cceeb..2070d57cb0 100644
--- a/eth2/types/src/beacon_state/slot_processing.rs
+++ b/eth2/types/src/beacon_state/slot_processing.rs
@@ -38,6 +38,20 @@ impl BeaconState {
         let validator_count = self.validator_registry.len();
         Some((slot as usize) % validator_count)
     }
+
+    pub fn attestation_slot_and_shard_for_validator(
+        &self,
+        validator_index: usize,
+        spec: &ChainSpec,
+    ) -> (u64, u64) {
+        // TODO: this is a stub; implement it properly.
+        let validator_index = validator_index as u64;
+
+        let slot = validator_index % spec.epoch_length;
+        let shard = validator_index % spec.shard_count;
+
+        (slot, shard)
+    }
 }
 
 fn merkle_root(_input: &[Hash256]) -> Hash256 {